1 This is tar.info, produced by makeinfo version 4.13 from tar.texi.
3 This manual is for GNU `tar' (version 1.27, 24 September 2013), which
4 creates and extracts files from archives.
6 Copyright (C) 1992, 1994-1997, 1999-2001, 2003-2013 Free Software
9 Permission is granted to copy, distribute and/or modify this
10 document under the terms of the GNU Free Documentation License,
11 Version 1.3 or any later version published by the Free Software
12 Foundation; with the Invariant Sections being "GNU General Public
13 License", with the Front-Cover Texts being "A GNU Manual", and
14 with the Back-Cover Texts as in (a) below. A copy of the license
15 is included in the section entitled "GNU Free Documentation
18 (a) The FSF's Back-Cover Text is: "You have the freedom to copy
19 and modify this GNU manual."
21 INFO-DIR-SECTION Archiving
23 * Tar: (tar). Making tape (or disk) archives.
26 INFO-DIR-SECTION Individual utilities
28 * tar: (tar)tar invocation. Invoking GNU `tar'.
32 File: tar.info, Node: Top, Next: Introduction, Up: (dir)
34 GNU tar: an archiver tool
35 *************************
37 This manual is for GNU `tar' (version 1.27, 24 September 2013), which
38 creates and extracts files from archives.
40 Copyright (C) 1992, 1994-1997, 1999-2001, 2003-2013 Free Software
43 Permission is granted to copy, distribute and/or modify this
44 document under the terms of the GNU Free Documentation License,
45 Version 1.3 or any later version published by the Free Software
46 Foundation; with the Invariant Sections being "GNU General Public
47 License", with the Front-Cover Texts being "A GNU Manual", and
48 with the Back-Cover Texts as in (a) below. A copy of the license
49 is included in the section entitled "GNU Free Documentation
52 (a) The FSF's Back-Cover Text is: "You have the freedom to copy
53 and modify this GNU manual."
55 The first part of this master menu lists the major nodes in this Info
56 document. The rest of the menu lists all the lower level nodes.
66 * Date input formats::
69 * Reliability and security::
74 * Configuring Help Summary::
75 * Fixing Snapshot Files::
78 * Free Software Needs Free Documentation::
79 * GNU Free Documentation License::
80 * Index of Command Line Options::
83 --- The Detailed Node Listing ---
87 * Book Contents:: What this Book Contains
88 * Definitions:: Some Definitions
89 * What tar Does:: What `tar' Does
90 * Naming tar Archives:: How `tar' Archives are Named
91 * Authors:: GNU `tar' Authors
92 * Reports:: Reporting bugs or suggestions
94 Tutorial Introduction to `tar'
97 * stylistic conventions::
98 * basic tar options:: Basic `tar' Operations and Options
99 * frequent operations::
100 * Two Frequent Options::
101 * create:: How to Create Archives
102 * list:: How to List Archives
103 * extract:: How to Extract Members from an Archive
106 Two Frequently Used Options
112 How to Create Archives
114 * prepare for examples::
115 * Creating the archive::
124 How to Extract Members from an Archive
126 * extracting archives::
129 * extracting untrusted archives::
135 * using tar options::
145 The Three Option Styles
147 * Long Options:: Long Option Style
148 * Short Options:: Short Option Style
149 * Old Options:: Old Option Style
150 * Mixing:: Mixing Option Styles
154 * Operation Summary::
156 * Short Option Summary::
168 Advanced GNU `tar' Operations
177 How to Add Files to Existing Archives: `--append'
179 * appending files:: Appending Files to an Archive
186 Options Used by `--create'
188 * override:: Overriding File Metadata.
189 * Ignore Failed Read::
191 Options Used by `--extract'
193 * Reading:: Options to Help Read Archives
194 * Writing:: Changing How `tar' Writes Files
195 * Scarce:: Coping with Scarce Resources
197 Options to Help Read Archives
199 * read full records::
202 Changing How `tar' Writes Files
204 * Dealing with Old Files::
205 * Overwrite Old Files::
210 * Data Modification Times::
211 * Setting Access Permissions::
212 * Directory Modification Times and Permissions::
213 * Writing to Standard Output::
214 * Writing to an External Program::
217 Coping with Scarce Resources
222 Performing Backups and Restoring Files
224 * Full Dumps:: Using `tar' to Perform Full Dumps
225 * Incremental Dumps:: Using `tar' to Perform Incremental Dumps
226 * Backup Levels:: Levels of Backups
227 * Backup Parameters:: Setting Parameters for Backups and Restoration
228 * Scripted Backups:: Using the Backup Scripts
229 * Scripted Restoration:: Using the Restore Script
231 Setting Parameters for Backups and Restoration
233 * General-Purpose Variables::
234 * Magnetic Tape Control::
236 * backup-specs example:: An Example Text of `Backup-specs'
238 Choosing Files and Names for `tar'
240 * file:: Choosing the Archive's Name
241 * Selecting Archive Members::
242 * files:: Reading Names from a File
243 * exclude:: Excluding Some Files
244 * wildcards:: Wildcards Patterns and Matching
245 * quoting styles:: Ways of Quoting Special Characters in Names
246 * transform:: Modifying File and Member Names
247 * after:: Operating Only on New Files
248 * recurse:: Descending into Directories
249 * one:: Crossing File System Boundaries
251 Reading Names from a File
257 * problems with exclude::
259 Wildcards Patterns and Matching
261 * controlling pattern-matching::
263 Crossing File System Boundaries
265 * directory:: Changing Directory
266 * absolute:: Absolute File Names
270 * General date syntax:: Common rules.
271 * Calendar date items:: 19 Dec 1994.
272 * Time of day items:: 9:20pm.
273 * Time zone items:: EST, PDT, GMT.
274 * Day of week items:: Monday and others.
275 * Relative items in date strings:: next tuesday, 2 years ago.
276 * Pure numbers in date strings:: 19931219, 1440.
277 * Seconds since the Epoch:: @1078100502.
278 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
279 * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al.
281 Controlling the Archive Format
283 * Compression:: Using Less Space through Compression
284 * Attributes:: Handling File Attributes
285 * Portability:: Making `tar' Archives More Portable
286 * cpio:: Comparison of `tar' and `cpio'
288 Using Less Space through Compression
290 * gzip:: Creating and Reading Compressed Archives
291 * sparse:: Archiving Sparse Files
293 Creating and Reading Compressed Archives
295 * lbzip2:: Using lbzip2 with GNU `tar'.
297 Making `tar' Archives More Portable
299 * Portable Names:: Portable Names
300 * dereference:: Symbolic Links
301 * hard links:: Hard Links
302 * old:: Old V7 Archives
303 * ustar:: Ustar Archives
304 * gnu:: GNU and old GNU format archives.
305 * posix:: POSIX archives
306 * Checksumming:: Checksumming Problems
307 * Large or Negative Values:: Large files, negative time stamps, etc.
308 * Other Tars:: How to Extract GNU-Specific Data Using
309 Other `tar' Implementations
311 GNU `tar' and POSIX `tar'
313 * PAX keywords:: Controlling Extended Header Keywords.
315 How to Extract GNU-Specific Data Using Other `tar' Implementations
317 * Split Recovery:: Members Split Between Volumes
318 * Sparse Recovery:: Sparse Members
320 Tapes and Other Archive Media
322 * Device:: Device selection and switching
323 * Remote Tape Server::
324 * Common Problems and Solutions::
325 * Blocking:: Blocking
326 * Many:: Many archives on one tape
327 * Using Multiple Tapes:: Using Multiple Tapes
328 * label:: Including a Label in the Archive
334 * Format Variations:: Format Variations
335 * Blocking Factor:: The Blocking Factor of an Archive
337 Many Archives on One Tape
339 * Tape Positioning:: Tape Positions and Tape Marks
340 * mt:: The `mt' Utility
344 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
345 * Tape Files:: Tape Files
346 * Tarcat:: Concatenate Volumes into a Single Archive
351 * Standard:: Basic Tar Format
352 * Extensions:: GNU Extensions to the Archive Format
353 * Sparse Formats:: Storing Sparse Files
360 * PAX 0:: PAX Format, Versions 0.0 and 0.1
361 * PAX 1:: PAX Format, Version 1.0
365 * Generate Mode:: File Generation Mode.
366 * Status Mode:: File Status Mode.
367 * Exec Mode:: Synchronous Execution mode.
371 * GNU Free Documentation License:: License for copying this manual
374 File: tar.info, Node: Introduction, Next: Tutorial, Prev: Top, Up: Top
379 GNU `tar' creates and manipulates "archives" which are actually
380 collections of many other files; the program provides users with an
381 organized and systematic method for controlling a large amount of data.
382 The name "tar" originally came from the phrase "Tape ARchive", but
383 archives need not (and these days, typically do not) reside on tapes.
387 * Book Contents:: What this Book Contains
388 * Definitions:: Some Definitions
389 * What tar Does:: What `tar' Does
390 * Naming tar Archives:: How `tar' Archives are Named
391 * Authors:: GNU `tar' Authors
392 * Reports:: Reporting bugs or suggestions
395 File: tar.info, Node: Book Contents, Next: Definitions, Up: Introduction
397 1.1 What this Book Contains
398 ===========================
400 The first part of this chapter introduces you to various terms that will
401 recur throughout the book. It also tells you who has worked on GNU
402 `tar' and its documentation, and where you should send bug reports or
405 The second chapter is a tutorial (*note Tutorial::) which provides a
406 gentle introduction for people who are new to using `tar'. It is meant
407 to be self-contained, not requiring any reading from subsequent
408 chapters to make sense. It moves from topic to topic in a logical,
409 progressive order, building on information already explained.
411 Although the tutorial is paced and structured to allow beginners to
412 learn how to use `tar', it is not intended solely for beginners. The
413 tutorial explains how to use the three most frequently used operations
414 (`create', `list', and `extract') as well as two frequently used
415 options (`file' and `verbose'). The other chapters do not refer to the
416 tutorial frequently; however, if a section discusses something which is
417 a complex variant of a basic concept, there may be a cross-reference to
418 that basic concept. (The entire book, including the tutorial, assumes
419 that the reader understands some basic concepts of using a Unix-type
420 operating system; *note Tutorial::.)
422 The third chapter presents the remaining five operations, and
423 information about using `tar' options and option syntax.
425 The other chapters are meant to be used as a reference. Each chapter
426 presents everything that needs to be said about a specific topic.
428 One of the chapters (*note Date input formats::) exists in its
429 entirety in other GNU manuals, and is mostly self-contained. In
430 addition, one section of this manual (*note Standard::) contains a big
431 quote which is taken directly from `tar' sources.
433 In general, we give both long and short (abbreviated) option names
434 at least once in each section where the relevant option is covered, so
435 that novice readers will become familiar with both styles. (A few
436 options have no short versions, and the relevant sections will indicate
440 File: tar.info, Node: Definitions, Next: What tar Does, Prev: Book Contents, Up: Introduction
445 The `tar' program is used to create and manipulate `tar' archives. An
446 "archive" is a single file which contains the contents of many files,
447 while still identifying the names of the files, their owner(s), and so
448 forth. (In addition, archives record access permissions, user and
449 group, size in bytes, and data modification time. Some archives also
450 record the file names in each archived directory, as well as other file
451 and directory information.) You can use `tar' to "create" a new
452 archive in a specified directory.
454 The files inside an archive are called "members". Within this
455 manual, we use the term "file" to refer only to files accessible in the
456 normal ways (by `ls', `cat', and so forth), and the term "member" to
457 refer only to the members of an archive. Similarly, a "file name" is
458 the name of a file, as it resides in the file system, and a "member
459 name" is the name of an archive member within the archive.
461 The term "extraction" refers to the process of copying an archive
462 member (or multiple members) into a file in the file system. Extracting
463 all the members of an archive is often called "extracting the archive".
464 The term "unpack" can also be used to refer to the extraction of many
465 or all the members of an archive. Extracting an archive does not
466 destroy the archive's structure, just as creating an archive does not
467 destroy the copies of the files that exist outside of the archive. You
468 may also "list" the members in a given archive (this is often thought
469 of as "printing" them to the standard output, or the command line), or
470 "append" members to a pre-existing archive. All of these operations
471 can be performed using `tar'.
474 File: tar.info, Node: What tar Does, Next: Naming tar Archives, Prev: Definitions, Up: Introduction
479 The `tar' program provides the ability to create `tar' archives, as
480 well as various other kinds of manipulation. For example, you can use
481 `tar' on previously created archives to extract files, to store
482 additional files, or to update or list files which were already stored.
484 Initially, `tar' archives were used to store files conveniently on
485 magnetic tape. The name `tar' comes from this use; it stands for
486 `t'ape `ar'chiver. Despite the utility's name, `tar' can direct its
487 output to available devices, files, or other programs (using pipes).
488 `tar' may even access remote devices or files (as archives).
490 You can use `tar' archives in many ways. We want to stress a few of
491 them: storage, backup, and transportation.
494 Often, `tar' archives are used to store related files for
495 convenient file transfer over a network. For example, the GNU
496 Project distributes its software bundled into `tar' archives, so
497 that all the files relating to a particular program (or set of
498 related programs) can be transferred as a single unit.
500 A magnetic tape can store several files in sequence. However, the
501 tape has no names for these files; it only knows their relative
502 position on the tape. One way to store several files on one tape
503 and retain their names is by creating a `tar' archive. Even when
504 the basic transfer mechanism can keep track of names, as FTP can,
505 the nuisance of handling multiple files, directories, and multiple
506 links makes `tar' archives useful.
508 Archive files are also used for long-term storage. You can think
509 of this as transportation from the present into the future. (It
510 is a science-fiction idiom that you can move through time as well
511 as in space; the idea here is that `tar' can be used to move
512 archives in all dimensions, even time!)
515 Because the archive created by `tar' is capable of preserving file
516 information and directory structure, `tar' is commonly used for
517 performing full and incremental backups of disks. A backup puts a
518 collection of files (possibly pertaining to many users and
519 projects) together on a disk or a tape. This guards against
520 accidental destruction of the information in those files. GNU
521 `tar' has special features that allow it to be used to make
522 incremental and full dumps of all the files in a file system.
525 You can create an archive on one system, transfer it to another
526 system, and extract the contents there. This allows you to
527 transport a group of files from one system to another.
530 File: tar.info, Node: Naming tar Archives, Next: Authors, Prev: What tar Does, Up: Introduction
532 1.4 How `tar' Archives are Named
533 ================================
535 Conventionally, `tar' archives are given names ending with `.tar'.
536 This is not necessary for `tar' to operate properly, but this manual
537 follows that convention in order to accustom readers to it and to make
540 Often, people refer to `tar' archives as "`tar' files," and archive
541 members as "files" or "entries". For people familiar with the
542 operation of `tar', this causes no difficulty. However, in this
543 manual, we consistently refer to "archives" and "archive members" to
544 make learning to use `tar' easier for novice users.
547 File: tar.info, Node: Authors, Next: Reports, Prev: Naming tar Archives, Up: Introduction
549 1.5 GNU `tar' Authors
550 =====================
552 GNU `tar' was originally written by John Gilmore, and modified by many
553 people. The GNU enhancements were written by Jay Fenlason, then Joy
554 Kendall, and the whole package has been further maintained by Thomas
555 Bushnell, n/BSG, Franc,ois Pinard, Paul Eggert, and finally Sergey
556 Poznyakoff with the help of numerous and kind users.
558 We wish to stress that `tar' is a collective work, and owes much to
559 all those people who reported problems, offered solutions and other
560 insights, or shared their thoughts and suggestions. An impressive, yet
561 partial list of those contributors can be found in the `THANKS' file
562 from the GNU `tar' distribution.
564 Jay Fenlason put together a draft of a GNU `tar' manual, borrowing
565 notes from the original man page from John Gilmore. This was withdrawn
566 in version 1.11. Thomas Bushnell, n/BSG and Amy Gorin worked on a
567 tutorial and manual for GNU `tar'. Franc,ois Pinard put version 1.11.8
568 of the manual together by taking information from all these sources and
569 merging them. Melissa Weisshaus finally edited and redesigned the book
570 to create version 1.12. The book for versions from 1.14 up to 1.27
571 were edited by the current maintainer, Sergey Poznyakoff.
573 For version 1.12, Daniel Hagerty contributed a great deal of
574 technical consulting. In particular, he is the primary author of *note
577 In July, 2003 GNU `tar' was put on CVS at savannah.gnu.org (see
578 `http://savannah.gnu.org/projects/tar'), and active development and
579 maintenance work has started again. Currently GNU `tar' is being
580 maintained by Paul Eggert, Sergey Poznyakoff and Jeff Bailey.
582 Support for POSIX archives was added by Sergey Poznyakoff.
585 File: tar.info, Node: Reports, Prev: Authors, Up: Introduction
587 1.6 Reporting bugs or suggestions
588 =================================
590 If you find problems or have suggestions about this program or manual,
591 please report them to `bug-tar@gnu.org'.
593 When reporting a bug, please be sure to include as much detail as
594 possible, in order to reproduce it.
597 File: tar.info, Node: Tutorial, Next: tar invocation, Prev: Introduction, Up: Top
599 2 Tutorial Introduction to `tar'
600 ********************************
602 This chapter guides you through some basic examples of three `tar'
603 operations: `--create', `--list', and `--extract'. If you already know
604 how to use some other version of `tar', then you may not need to read
605 this chapter. This chapter omits most complicated details about how
611 * stylistic conventions::
612 * basic tar options:: Basic `tar' Operations and Options
613 * frequent operations::
614 * Two Frequent Options::
615 * create:: How to Create Archives
616 * list:: How to List Archives
617 * extract:: How to Extract Members from an Archive
621 File: tar.info, Node: assumptions, Next: stylistic conventions, Up: Tutorial
623 2.1 Assumptions this Tutorial Makes
624 ===================================
626 This chapter is paced to allow beginners to learn about `tar' slowly.
627 At the same time, we will try to cover all the basic aspects of these
628 three operations. In order to accomplish both of these tasks, we have
629 made certain assumptions about your knowledge before reading this
630 manual, and the hardware you will be using:
632 * Before you start to work through this tutorial, you should
633 understand what the terms "archive" and "archive member" mean
634 (*note Definitions::). In addition, you should understand
635 something about how Unix-type operating systems work, and you
636 should know how to use some basic utilities. For example, you
637 should know how to create, list, copy, rename, edit, and delete
638 files and directories; how to change between directories; and how
639 to figure out where you are in the file system. You should have
640 some basic understanding of directory structure and how files are
641 named according to which directory they are in. You should
642 understand concepts such as standard output and standard input,
643 what various definitions of the term `argument' mean, and the
644 differences between relative and absolute file names.
646 * This manual assumes that you are working from your own home
647 directory (unless we state otherwise). In this tutorial, you will
648 create a directory to practice `tar' commands in. When we show
649 file names, we will assume that those names are relative to your
650 home directory. For example, my home directory is
651 `/home/fsf/melissa'. All of my examples are in a subdirectory of
652 the directory named by that file name; the subdirectory is called
655 * In general, we show examples of archives which exist on (or can be
656 written to, or worked with from) a directory on a hard disk. In
657 most cases, you could write those archives to, or work with them
658 on any other device, such as a tape drive. However, some of the
659 later examples in the tutorial and next chapter will not work on
660 tape drives. Additionally, working with tapes is much more
661 complicated than working with hard disks. For these reasons, the
662 tutorial does not cover working with tape drives. *Note Media::,
663 for complete information on using `tar' archives with tape drives.
667 File: tar.info, Node: stylistic conventions, Next: basic tar options, Prev: assumptions, Up: Tutorial
669 2.2 Stylistic Conventions
670 =========================
672 In the examples, `$' represents a typical shell prompt. It precedes
673 lines you should type; to make this more clear, those lines are shown
674 in `this font', as opposed to lines which represent the computer's
675 response; those lines are shown in `this font', or sometimes `like
679 File: tar.info, Node: basic tar options, Next: frequent operations, Prev: stylistic conventions, Up: Tutorial
681 2.3 Basic `tar' Operations and Options
682 ======================================
684 `tar' can take a wide variety of arguments which specify and define the
685 actions it will have on the particular set of files or the archive.
686 The main types of arguments to `tar' fall into one of two classes:
687 operations, and options.
689 Some arguments fall into a class called "operations"; exactly one of
690 these is both allowed and required for any instance of using `tar'; you
691 may _not_ specify more than one. People sometimes speak of "operating
692 modes". You are in a particular operating mode when you have specified
693 the operation which specifies it; there are eight operations in total,
694 and thus there are eight operating modes.
696 The other arguments fall into the class known as "options". You are
697 not required to specify any options, and you are allowed to specify more
698 than one at a time (depending on the way you are using `tar' at that
699 time). Some options are used so frequently, and are so useful for
700 helping you type commands more carefully that they are effectively
701 "required". We will discuss them in this chapter.
703 You can write most of the `tar' operations and options in any of
704 three forms: long (mnemonic) form, short form, and old style. Some of
705 the operations and options have no short or "old" forms; however, the
706 operations and options which we will cover in this tutorial have
707 corresponding abbreviations. We will indicate those abbreviations
708 appropriately to get you used to seeing them. Note, that the "old
709 style" option forms exist in GNU `tar' for compatibility with Unix
710 `tar'. In this book we present a full discussion of this way of
711 writing options and operations (*note Old Options::), and we discuss
712 the other two styles of writing options (*Note Long Options::, and
713 *note Short Options::).
715 In the examples and in the text of this tutorial, we usually use the
716 long forms of operations and options; but the "short" forms produce the
717 same result and can make typing long `tar' commands easier. For
718 example, instead of typing
720 tar --create --verbose --file=afiles.tar apple angst aspic
723 tar -c -v -f afiles.tar apple angst aspic
726 tar -cvf afiles.tar apple angst aspic
728 For more information on option syntax, see *note Advanced tar::. In
729 discussions in the text, when we name an option by its long form, we
730 also give the corresponding short option in parentheses.
732 The term, "option", can be confusing at times, since "operations"
733 are often lumped in with the actual, _optional_ "options" in certain
734 general class statements. For example, we just talked about "short and
735 long forms of options and operations". However, experienced `tar'
736 users often refer to these by shorthand terms such as, "short and long
737 options". This term assumes that the "operations" are included, also.
738 Context will help you determine which definition of "options" to use.
740 Similarly, the term "command" can be confusing, as it is often used
741 in two different ways. People sometimes refer to `tar' "commands". A
742 `tar' "command" is the entire command line of user input which tells
743 `tar' what to do -- including the operation, options, and any arguments
744 (file names, pipes, other commands, etc.). However, you will also
745 sometimes hear the term "the `tar' command". When the word "command"
746 is used specifically like this, a person is usually referring to the
747 `tar' _operation_, not the whole line. Again, use context to figure
748 out which of the meanings the speaker intends.
751 File: tar.info, Node: frequent operations, Next: Two Frequent Options, Prev: basic tar options, Up: Tutorial
753 2.4 The Three Most Frequently Used Operations
754 =============================================
756 Here are the three most frequently used operations (both short and long
757 forms), as well as a brief description of their meanings. The rest of
758 this chapter will cover how to use these operations in detail. We will
759 present the rest of the operations in the next chapter.
763 Create a new `tar' archive.
767 List the contents of an archive.
771 Extract one or more members from an archive.
774 File: tar.info, Node: Two Frequent Options, Next: create, Prev: frequent operations, Up: Tutorial
776 2.5 Two Frequently Used Options
777 ===============================
779 To understand how to run `tar' in the three operating modes listed
780 previously, you also need to understand how to use two of the options to
781 `tar': `--file' (which takes an archive file as an argument) and
782 `--verbose'. (You are usually not _required_ to specify either of
783 these options when you run `tar', but they can be very useful in making
784 things more clear and helping you avoid errors.)
793 File: tar.info, Node: file tutorial, Next: verbose tutorial, Up: Two Frequent Options
798 `--file=ARCHIVE-NAME'
800 Specify the name of an archive file.
802 You can specify an argument for the `--file=ARCHIVE-NAME' (`-f
803 ARCHIVE-NAME') option whenever you use `tar'; this option determines
804 the name of the archive file that `tar' will work on.
806 If you don't specify this argument, then `tar' will examine the
807 environment variable `TAPE'. If it is set, its value will be used as
808 the archive name. Otherwise, `tar' will use the default archive,
809 determined at compile time. Usually it is standard output or some
810 physical tape drive attached to your machine (you can verify what the
811 default is by running `tar --show-defaults', *note defaults::). If
812 there is no tape drive attached, or the default is not meaningful, then
813 `tar' will print an error message. The error message might look
814 roughly like one of the following:
816 tar: can't open /dev/rmt8 : No such device or address
817 tar: can't open /dev/rsmt0 : I/O error
819 To avoid confusion, we recommend that you always specify an archive file
820 name by using `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') when writing
821 your `tar' commands. For more information on using the
822 `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option, see *note file::.
825 File: tar.info, Node: verbose tutorial, Next: help tutorial, Prev: file tutorial, Up: Two Frequent Options
827 The `--verbose' Option
828 ----------------------
832 Show the files being worked on as `tar' is running.
834 `--verbose' (`-v') shows details about the results of running `tar'.
835 This can be especially useful when the results might not be obvious.
836 For example, if you want to see the progress of `tar' as it writes
837 files into the archive, you can use the `--verbose' option. In the
838 beginning, you may find it useful to use `--verbose' at all times; when
839 you are more accustomed to `tar', you will likely want to use it at
840 certain times but not at others. We will use `--verbose' at times to
841 help make something clear, and we will give many examples both using
842 and not using `--verbose' to show the differences.
844 Each instance of `--verbose' on the command line increases the
845 verbosity level by one, so if you need more details on the output,
848 When reading archives (`--list', `--extract', `--diff'), `tar' by
849 default prints only the names of the members being extracted. Using
850 `--verbose' will show a full, `ls' style member listing.
852 In contrast, when writing archives (`--create', `--append',
853 `--update'), `tar' does not print file names by default. So, a single
854 `--verbose' option shows the file names being added to the archive,
855 while two `--verbose' options enable the full listing.
857 For example, to create an archive in verbose mode:
859 $ tar -cvf afiles.tar apple angst aspic
864 Creating the same archive with the verbosity level 2 could give:
866 $ tar -cvvf afiles.tar apple angst aspic
867 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
868 -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst
869 -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic
871 This works equally well using short or long forms of options. Using
872 long forms, you would simply write out the mnemonic form of the option
875 $ tar --create --verbose --verbose ...
877 Note that you must double the hyphens properly each time.
879 Later in the tutorial, we will give examples using
880 `--verbose --verbose'.
882 The full output consists of six fields:
884 * File type and permissions in symbolic form. These are displayed
885 in the same format as the first column of `ls -l' output (*note
886 format=verbose: (fileutils)What information is listed.).
888 * Owner name and group separated by a slash character. If these
889 data are not available (for example, when listing a `v7' format
890 archive), numeric ID values are printed instead.
892 * Size of the file, in bytes.
894 * File modification date in ISO 8601 format.
896 * File modification time.
898 * File name. If the name contains any special characters (white
899 space, newlines, etc.) these are displayed in an unambiguous form
900 using so called "quoting style". For the detailed discussion of
901 available styles and on how to use them, see *note quoting
904 Depending on the file type, the name can be followed by some
905 additional information, described in the following table:
908 The file or archive member is a "symbolic link" and LINK-NAME
909 is the name of file it links to.
912 The file or archive member is a "hard link" and LINK-NAME is
913 the name of file it links to.
916 The archive member is an old GNU format long link. You will
917 normally not encounter this.
920 The archive member is an old GNU format long name. You will
921 normally not encounter this.
924 The archive member is a GNU "volume header" (*note Tape
927 `--Continued at byte N--'
928 Encountered only at the beginning of a multi-volume archive
929 (*note Using Multiple Tapes::). This archive member is a
930 continuation from the previous volume. The number N gives the
931 offset where the original file was split.
933 `unknown file type C'
934 An archive member of unknown type. C is the type character
935 from the archive header. If you encounter such a message, it
936 means that either your archive contains proprietary member
937 types GNU `tar' is not able to handle, or the archive is
941 For example, here is an archive listing containing most of the
942 special suffixes explained above:
944 V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header--
945 -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at byte 32456--
946 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
947 lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple
948 -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues
949 hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues
953 File: tar.info, Node: help tutorial, Prev: verbose tutorial, Up: Two Frequent Options
955 Getting Help: Using the `--help' Option
956 ---------------------------------------
959 The `--help' option to `tar' prints out a very brief list of all
960 operations and option available for the current version of `tar'
961 available on your system.
964 File: tar.info, Node: create, Next: list, Prev: Two Frequent Options, Up: Tutorial
966 2.6 How to Create Archives
967 ==========================
969 _(This message will disappear, once this node revised.)_
971 One of the basic operations of `tar' is `--create' (`-c'), which you
972 use to create a `tar' archive. We will explain `--create' first
973 because, in order to learn about the other operations, you will find it
974 useful to have an archive available to practice on.
976 To make this easier, in this section you will first create a
977 directory containing three files. Then, we will show you how to create
978 an _archive_ (inside the new directory). Both the directory, and the
979 archive are specifically for you to practice on. The rest of this
980 chapter and the next chapter will show many examples using this
981 directory and the files you will create: some of those files may be
982 other directories and other archives.
984 The three files you will archive in this example are called `blues',
985 `folk', and `jazz'. The archive is called `collection.tar'.
987 This section will proceed slowly, detailing how to use `--create' in
988 `verbose' mode, and showing examples using both short and long forms.
989 In the rest of the tutorial, and in the examples in the next chapter,
990 we will proceed at a slightly quicker pace. This section moves more
991 slowly to allow beginning users to understand how `tar' works.
995 * prepare for examples::
996 * Creating the archive::
1002 File: tar.info, Node: prepare for examples, Next: Creating the archive, Up: create
1004 2.6.1 Preparing a Practice Directory for Examples
1005 -------------------------------------------------
1007 To follow along with this and future examples, create a new directory
1008 called `practice' containing files called `blues', `folk' and `jazz'.
1009 The files can contain any information you like: ideally, they should
1010 contain information which relates to their names, and be of different
1011 lengths. Our examples assume that `practice' is a subdirectory of your
1014 Now `cd' to the directory named `practice'; `practice' is now your
1015 "working directory". (_Please note_: Although the full file name of
1016 this directory is `/HOMEDIR/practice', in our examples we will refer to
1017 this directory as `practice'; the HOMEDIR is presumed.)
1019 In general, you should check that the files to be archived exist
1020 where you think they do (in the working directory) by running `ls'.
1021 Because you just created the directory and the files and have changed to
1022 that directory, you probably don't need to do that this time.
1024 It is very important to make sure there isn't already a file in the
1025 working directory with the archive name you intend to use (in this case,
1026 `collection.tar'), or that you don't care about its contents. Whenever
1027 you use `create', `tar' will erase the current contents of the file
1028 named by `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') if it exists. `tar'
1029 will not tell you if you are about to overwrite an archive unless you
1030 specify an option which does this (*note backup::, for the information
1031 on how to do so). To add files to an existing archive, you need to use
1032 a different option, such as `--append' (`-r'); see *note append:: for
1033 information on how to do this.
1036 File: tar.info, Node: Creating the archive, Next: create verbose, Prev: prepare for examples, Up: create
1038 2.6.2 Creating the Archive
1039 --------------------------
1041 To place the files `blues', `folk', and `jazz' into an archive named
1042 `collection.tar', use the following command:
1044 $ tar --create --file=collection.tar blues folk jazz
1046 The order of the arguments is not very important, _when using long
1047 option forms_. You could also say:
1049 $ tar blues --create folk --file=collection.tar jazz
1051 However, you can see that this order is harder to understand; this is
1052 why we will list the arguments in the order that makes the commands
1053 easiest to understand (and we encourage you to do the same when you use
1054 `tar', to avoid errors).
1056 Note that the sequence `--file=collection.tar' is considered to be
1057 _one_ argument. If you substituted any other string of characters for
1058 `collection.tar', then that string would become the name of the
1059 archive file you create.
1061 The order of the options becomes more important when you begin to use
1062 short forms. With short forms, if you type commands in the wrong order
1063 (even if you type them correctly in all other ways), you may end up with
1064 results you don't expect. For this reason, it is a good idea to get
1065 into the habit of typing options in the order that makes inherent sense.
1066 *Note short create::, for more information on this.
1068 In this example, you type the command as shown above: `--create' is
1069 the operation which creates the new archive (`collection.tar'), and
1070 `--file' is the option which lets you give it the name you chose. The
1071 files, `blues', `folk', and `jazz', are now members of the archive,
1072 `collection.tar' (they are "file name arguments" to the `--create'
1073 operation. *Note Choosing::, for the detailed discussion on these.)
1074 Now that they are in the archive, they are called _archive members_,
1075 not files. (*note members: Definitions.).
1077 When you create an archive, you _must_ specify which files you want
1078 placed in the archive. If you do not specify any archive members, GNU
1079 `tar' will complain.
1081 If you now list the contents of the working directory (`ls'), you
1082 will find the archive file listed as well as the files you saw
1085 blues folk jazz collection.tar
1087 Creating the archive `collection.tar' did not destroy the copies of the
1088 files in the directory.
1090 Keep in mind that if you don't indicate an operation, `tar' will not
1091 run and will prompt you for one. If you don't name any files, `tar'
1092 will complain. You must have write access to the working directory, or
1093 else you will not be able to create an archive in that directory.
1095 _Caution_: Do not attempt to use `--create' (`-c') to add files to
1096 an existing archive; it will delete the archive and write a new one.
1097 Use `--append' (`-r') instead. *Note append::.
1100 File: tar.info, Node: create verbose, Next: short create, Prev: Creating the archive, Up: create
1102 2.6.3 Running `--create' with `--verbose'
1103 -----------------------------------------
1105 If you include the `--verbose' (`-v') option on the command line, `tar'
1106 will list the files it is acting on as it is working. In verbose mode,
1107 the `create' example above would appear as:
1109 $ tar --create --verbose --file=collection.tar blues folk jazz
1114 This example is just like the example we showed which did not use
1115 `--verbose', except that `tar' generated the remaining lines.
1117 In the rest of the examples in this chapter, we will frequently use
1118 `verbose' mode so we can show actions or `tar' responses that you would
1119 otherwise not see, and which are important for you to understand.
1122 File: tar.info, Node: short create, Next: create dir, Prev: create verbose, Up: create
1124 2.6.4 Short Forms with `create'
1125 -------------------------------
1127 As we said before, the `--create' (`-c') operation is one of the most
1128 basic uses of `tar', and you will use it countless times. Eventually,
1129 you will probably want to use abbreviated (or "short") forms of
1130 options. A full discussion of the three different forms that options
1131 can take appears in *note Styles::; for now, here is what the previous
1132 example (including the `--verbose' (`-v') option) looks like using
1135 $ tar -cvf collection.tar blues folk jazz
1140 As you can see, the system responds the same no matter whether you use
1141 long or short option forms.
1143 One difference between using short and long option forms is that,
1144 although the exact placement of arguments following options is no more
1145 specific when using short forms, it is easier to become confused and
1146 make a mistake when using short forms. For example, suppose you
1147 attempted the above example in the following way:
1149 $ tar -cfv collection.tar blues folk jazz
1151 In this case, `tar' will make an archive file called `v', containing
1152 the files `blues', `folk', and `jazz', because the `v' is the closest
1153 "file name" to the `-f' option, and is thus taken to be the chosen
1154 archive file name. `tar' will try to add a file called
1155 `collection.tar' to the `v' archive file; if the file `collection.tar'
1156 did not already exist, `tar' will report an error indicating that this
1157 file does not exist. If the file `collection.tar' does already exist
1158 (e.g., from a previous command you may have run), then `tar' will add
1159 this file to the archive. Because the `-v' option did not get
1160 registered, `tar' will not run under `verbose' mode, and will not
1161 report its progress.
1163 The end result is that you may be quite confused about what happened,
1164 and possibly overwrite a file. To illustrate this further, we will show
1165 you how an example we showed previously would look using short forms.
1169 $ tar blues --create folk --file=collection.tar jazz
1171 is confusing as it is. When shown using short forms, however, it
1172 becomes much more so:
1174 $ tar blues -c folk -f collection.tar jazz
1176 It would be very easy to put the wrong string of characters immediately
1177 following the `-f', but doing that could sacrifice valuable data.
1179 For this reason, we recommend that you pay very careful attention to
1180 the order of options and placement of file and archive names,
1181 especially when using short option forms. Not having the option name
1182 written out mnemonically can affect how well you remember which option
1183 does what, and therefore where different names have to be placed.
1186 File: tar.info, Node: create dir, Prev: short create, Up: create
1188 2.6.5 Archiving Directories
1189 ---------------------------
1191 You can archive a directory by specifying its directory name as a file
1192 name argument to `tar'. The files in the directory will be archived
1193 relative to the working directory, and the directory will be re-created
1194 along with its contents when the archive is extracted.
1196 To archive a directory, first move to its superior directory. If you
1197 have followed the previous instructions in this tutorial, you should
1203 This will put you into the directory which contains `practice', i.e.,
1204 your home directory. Once in the superior directory, you can specify
1205 the subdirectory, `practice', as a file name argument. To store
1206 `practice' in the new archive file `music.tar', type:
1208 $ tar --create --verbose --file=music.tar practice
1210 `tar' should output:
1216 practice/collection.tar
1218 Note that the archive thus created is not in the subdirectory
1219 `practice', but rather in the current working directory--the directory
1220 from which `tar' was invoked. Before trying to archive a directory
1221 from its superior directory, you should make sure you have write access
1222 to the superior directory itself, not only the directory you are trying
1223 archive with `tar'. For example, you will probably not be able to
1224 store your home directory in an archive by invoking `tar' from the root
1225 directory; *Note absolute::. (Note also that `collection.tar', the
1226 original archive file, has itself been archived. `tar' will accept any
1227 file as a file to be archived, regardless of its content. When
1228 `music.tar' is extracted, the archive file `collection.tar' will be
1229 re-written into the file system).
1231 If you give `tar' a command such as
1233 $ tar --create --file=foo.tar .
1235 `tar' will report `tar: ./foo.tar is the archive; not dumped'. This
1236 happens because `tar' creates the archive `foo.tar' in the current
1237 directory before putting any files into it. Then, when `tar' attempts
1238 to add all the files in the directory `.' to the archive, it notices
1239 that the file `./foo.tar' is the same as the archive `foo.tar', and
1240 skips it. (It makes no sense to put an archive into itself.) GNU `tar'
1241 will continue in this case, and create the archive normally, except for
1242 the exclusion of that one file. (_Please note:_ Other implementations
1243 of `tar' may not be so clever; they will enter an infinite loop when
1244 this happens, so you should not depend on this behavior unless you are
1245 certain you are running GNU `tar'. In general, it is wise to always
1246 place the archive outside of the directory being dumped.)
1249 File: tar.info, Node: list, Next: extract, Prev: create, Up: Tutorial
1251 2.7 How to List Archives
1252 ========================
1254 Frequently, you will find yourself wanting to determine exactly what a
1255 particular archive contains. You can use the `--list' (`-t') operation
1256 to get the member names as they currently appear in the archive, as
1257 well as various attributes of the files at the time they were archived.
1258 For example, you can examine the archive `collection.tar' that you
1259 created in the last section with the command,
1261 $ tar --list --file=collection.tar
1263 The output of `tar' would then be:
1269 The archive `bfiles.tar' would list as follows:
1275 Be sure to use a `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option just
1276 as with `--create' (`-c') to specify the name of the archive.
1278 If you use the `--verbose' (`-v') option with `--list', then `tar'
1279 will print out a listing reminiscent of `ls -l', showing owner, file
1280 size, and so forth. This output is described in detail in *note
1281 verbose member listing::.
1283 If you had used `--verbose' (`-v') mode, the example above would
1286 $ tar --list --verbose --file=collection.tar folk
1287 -rw-r--r-- myself/user 62 1990-05-23 10:55 folk
1289 It is important to notice that the output of `tar --list --verbose'
1290 does not necessarily match that produced by `tar --create --verbose'
1291 while creating the archive. It is because GNU `tar', unless told
1292 explicitly not to do so, removes some directory prefixes from file
1293 names before storing them in the archive (*Note absolute::, for more
1294 information). In other words, in verbose mode GNU `tar' shows "file
1295 names" when creating an archive and "member names" when listing it.
1296 Consider this example:
1298 $ tar --create --verbose --file archive /etc/mail
1299 tar: Removing leading '/' from member names
1301 /etc/mail/sendmail.cf
1303 $ tar --test --file archive
1305 etc/mail/sendmail.cf
1308 This default behavior can sometimes be inconvenient. You can force
1309 GNU `tar' show member names when creating archive by supplying
1310 `--show-stored-names' option.
1312 `--show-stored-names'
1313 Print member (as opposed to _file_) names when creating the
1316 You can specify one or more individual member names as arguments when
1317 using `list'. In this case, `tar' will only list the names of members
1318 you identify. For example, `tar --list --file=afiles.tar apple' would
1321 Because `tar' preserves file names, these must be specified as they
1322 appear in the archive (i.e., relative to the directory from which the
1323 archive was created). Therefore, it is essential when specifying
1324 member names to `tar' that you give the exact member names. For
1325 example, `tar --list --file=bfiles.tar birds' would produce an error
1326 message something like `tar: birds: Not found in archive', because
1327 there is no member named `birds', only one named `./birds'. While the
1328 names `birds' and `./birds' name the same file, _member_ names by
1329 default are compared verbatim.
1331 However, `tar --list --file=bfiles.tar baboon' would respond with
1332 `baboon', because this exact member name is in the archive file
1333 `bfiles.tar'. If you are not sure of the exact file name, use
1334 "globbing patterns", for example:
1336 $ tar --list --file=bfiles.tar --wildcards '*b*'
1338 will list all members whose name contains `b'. *Note wildcards::, for
1339 a detailed discussion of globbing patterns and related `tar' command
1347 File: tar.info, Node: list dir, Up: list
1349 Listing the Contents of a Stored Directory
1350 ------------------------------------------
1352 To get information about the contents of an archived directory, use the
1353 directory name as a file name argument in conjunction with `--list'
1354 (`-t'). To find out file attributes, include the `--verbose' (`-v')
1357 For example, to find out about files in the directory `practice', in
1358 the archive file `music.tar', type:
1360 $ tar --list --verbose --file=music.tar practice
1364 drwxrwxrwx myself/user 0 1990-05-31 21:49 practice/
1365 -rw-r--r-- myself/user 42 1990-05-21 13:29 practice/blues
1366 -rw-r--r-- myself/user 62 1990-05-23 10:55 practice/folk
1367 -rw-r--r-- myself/user 40 1990-05-21 13:30 practice/jazz
1368 -rw-r--r-- myself/user 10240 1990-05-31 21:49 practice/collection.tar
1370 When you use a directory name as a file name argument, `tar' acts on
1371 all the files (including sub-directories) in that directory.
1374 File: tar.info, Node: extract, Next: going further, Prev: list, Up: Tutorial
1376 2.8 How to Extract Members from an Archive
1377 ==========================================
1379 Creating an archive is only half the job--there is no point in storing
1380 files in an archive if you can't retrieve them. The act of retrieving
1381 members from an archive so they can be used and manipulated as
1382 unarchived files again is called "extraction". To extract files from
1383 an archive, use the `--extract' (`--get' or `-x') operation. As with
1384 `--create', specify the name of the archive with `--file' (`-f')
1385 option. Extracting an archive does not modify the archive in any way;
1386 you can extract it multiple times if you want or need to.
1388 Using `--extract', you can extract an entire archive, or specific
1389 files. The files can be directories containing other files, or not. As
1390 with `--create' (`-c') and `--list' (`-t'), you may use the short or the
1391 long form of the operation without affecting the performance.
1395 * extracting archives::
1396 * extracting files::
1398 * extracting untrusted archives::
1399 * failing commands::
1402 File: tar.info, Node: extracting archives, Next: extracting files, Up: extract
1404 2.8.1 Extracting an Entire Archive
1405 ----------------------------------
1407 To extract an entire archive, specify the archive file name only, with
1408 no individual file names as arguments. For example,
1410 $ tar -xvf collection.tar
1414 -rw-r--r-- me/user 28 1996-10-18 16:31 jazz
1415 -rw-r--r-- me/user 21 1996-09-23 16:44 blues
1416 -rw-r--r-- me/user 20 1996-09-23 16:44 folk
1419 File: tar.info, Node: extracting files, Next: extract dir, Prev: extracting archives, Up: extract
1421 2.8.2 Extracting Specific Files
1422 -------------------------------
1424 To extract specific archive members, give their exact member names as
1425 arguments, as printed by `--list' (`-t'). If you had mistakenly
1426 deleted one of the files you had placed in the archive `collection.tar'
1427 earlier (say, `blues'), you can extract it from the archive without
1428 changing the archive's structure. Its contents will be identical to
1429 the original file `blues' that you deleted.
1431 First, make sure you are in the `practice' directory, and list the
1432 files in the directory. Now, delete the file, `blues', and list the
1433 files in the directory again.
1435 You can now extract the member `blues' from the archive file
1436 `collection.tar' like this:
1438 $ tar --extract --file=collection.tar blues
1440 If you list the files in the directory again, you will see that the file
1441 `blues' has been restored, with its original permissions, data
1442 modification times, and owner.(1) (These parameters will be identical
1443 to those which the file had when you originally placed it in the
1444 archive; any changes you may have made before deleting the file from
1445 the file system, however, will _not_ have been made to the archive
1446 member.) The archive file, `collection.tar', is the same as it was
1447 before you extracted `blues'. You can confirm this by running `tar'
1448 with `--list' (`-t').
1450 Remember that as with other operations, specifying the exact member
1451 name is important. `tar --extract --file=bfiles.tar birds' will fail,
1452 because there is no member named `birds'. To extract the member named
1453 `./birds', you must specify `tar --extract --file=bfiles.tar ./birds'.
1454 If you don't remember the exact member names, use `--list' (`-t') option
1455 (*note list::). You can also extract those members that match a
1456 specific "globbing pattern". For example, to extract from `bfiles.tar'
1457 all files that begin with `b', no matter their directory prefix, you
1460 $ tar -x -f bfiles.tar --wildcards --no-anchored 'b*'
1462 Here, `--wildcards' instructs `tar' to treat command line arguments as
1463 globbing patterns and `--no-anchored' informs it that the patterns
1464 apply to member names after any `/' delimiter. The use of globbing
1465 patterns is discussed in detail in *Note wildcards::.
1467 You can extract a file to standard output by combining the above
1468 options with the `--to-stdout' (`-O') option (*note Writing to Standard
1471 If you give the `--verbose' option, then `--extract' will print the
1472 names of the archive members as it extracts them.
1474 ---------- Footnotes ----------
1476 (1) This is only accidentally true, but not in general. Whereas
1477 modification times are always restored, in most cases, one has to be
1478 root for restoring the owner, and use a special option for restoring
1479 permissions. Here, it just happens that the restoring user is also the
1480 owner of the archived members, and that the current `umask' is
1481 compatible with original permissions.
1484 File: tar.info, Node: extract dir, Next: extracting untrusted archives, Prev: extracting files, Up: extract
1486 2.8.3 Extracting Files that are Directories
1487 -------------------------------------------
1489 Extracting directories which are members of an archive is similar to
1490 extracting other files. The main difference to be aware of is that if
1491 the extracted directory has the same name as any directory already in
1492 the working directory, then files in the extracted directory will be
1493 placed into the directory of the same name. Likewise, if there are
1494 files in the pre-existing directory with the same names as the members
1495 which you extract, the files from the extracted archive will replace
1496 the files already in the working directory (and possible
1497 subdirectories). This will happen regardless of whether or not the
1498 files in the working directory were more recent than those extracted
1499 (there exist, however, special options that alter this behavior *note
1502 However, if a file was stored with a directory name as part of its
1503 file name, and that directory does not exist under the working
1504 directory when the file is extracted, `tar' will create the directory.
1506 We can demonstrate how to use `--extract' to extract a directory
1507 file with an example. Change to the `practice' directory if you
1508 weren't there, and remove the files `folk' and `jazz'. Then, go back
1509 to the parent directory and extract the archive `music.tar'. You may
1510 either extract the entire archive, or you may extract only the files
1511 you just deleted. To extract the entire archive, don't give any file
1512 names as arguments after the archive name `music.tar'. To extract only
1513 the files you deleted, use the following command:
1515 $ tar -xvf music.tar practice/folk practice/jazz
1519 If you were to specify two `--verbose' (`-v') options, `tar' would have
1520 displayed more detail about the extracted files, as shown in the
1523 $ tar -xvvf music.tar practice/folk practice/jazz
1524 -rw-r--r-- me/user 28 1996-10-18 16:31 practice/jazz
1525 -rw-r--r-- me/user 20 1996-09-23 16:44 practice/folk
1527 Because you created the directory with `practice' as part of the file
1528 names of each of the files by archiving the `practice' directory as
1529 `practice', you must give `practice' as part of the file names when you
1530 extract those files from the archive.
1533 File: tar.info, Node: extracting untrusted archives, Next: failing commands, Prev: extract dir, Up: extract
1535 2.8.4 Extracting Archives from Untrusted Sources
1536 ------------------------------------------------
1538 Extracting files from archives can overwrite files that already exist.
1539 If you receive an archive from an untrusted source, you should make a
1540 new directory and extract into that directory, so that you don't have
1541 to worry about the extraction overwriting one of your existing files.
1542 For example, if `untrusted.tar' came from somewhere else on the
1543 Internet, and you don't necessarily trust its contents, you can extract
1548 $ tar -xvf ../untrusted.tar
1550 It is also a good practice to examine contents of the archive before
1551 extracting it, using `--list' (`-t') option, possibly combined with
1555 File: tar.info, Node: failing commands, Prev: extracting untrusted archives, Up: extract
1557 2.8.5 Commands That Will Fail
1558 -----------------------------
1560 Here are some sample commands you might try which will not work, and why
1563 If you try to use this command,
1565 $ tar -xvf music.tar folk jazz
1567 you will get the following response:
1569 tar: folk: Not found in archive
1570 tar: jazz: Not found in archive
1572 This is because these files were not originally _in_ the parent
1573 directory `..', where the archive is located; they were in the
1574 `practice' directory, and their file names reflect this:
1576 $ tar -tvf music.tar
1581 Likewise, if you try to use this command,
1583 $ tar -tvf music.tar folk jazz
1585 you would get a similar response. Members with those names are not in
1586 the archive. You must use the correct member names, or wildcards, in
1587 order to extract the files from the archive.
1589 If you have forgotten the correct names of the files in the archive,
1590 use `tar --list --verbose' to list them correctly.
1593 File: tar.info, Node: going further, Prev: extract, Up: Tutorial
1595 2.9 Going Further Ahead in this Manual
1596 ======================================
1598 _(This message will disappear, once this node revised.)_
1601 File: tar.info, Node: tar invocation, Next: operations, Prev: Tutorial, Up: Top
1603 3 Invoking GNU `tar'
1604 ********************
1606 This chapter is about how one invokes the GNU `tar' command, from the
1607 command synopsis (*note Synopsis::). There are numerous options, and
1608 many styles for writing them. One mandatory option specifies the
1609 operation `tar' should perform (*note Operation Summary::), other
1610 options are meant to detail how this operation should be performed
1611 (*note Option Summary::). Non-option arguments are not always
1612 interpreted the same way, depending on what the operation is.
1614 You will find in this chapter everything about option styles and
1615 rules for writing them (*note Styles::). On the other hand, operations
1616 and options are fully described elsewhere, in other chapters. Here,
1617 you will find only synthetic descriptions for operations and options,
1618 together with pointers to other parts of the `tar' manual.
1620 Some options are so special they are fully described right in this
1621 chapter. They have the effect of inhibiting the normal operation of
1622 `tar' or else, they globally alter the amount of feedback the user
1623 receives about what is going on. These are the `--help' and
1624 `--version' (*note help::), `--verbose' (*note verbose::) and
1625 `--interactive' options (*note interactive::).
1630 * using tar options::
1632 * All Options:: All `tar' Options.
1633 * help:: Where to Get Help.
1634 * defaults:: What are the Default Values.
1635 * verbose:: Checking `tar' progress.
1636 * checkpoints:: Checkpoints.
1637 * warnings:: Controlling Warning Messages.
1638 * interactive:: Asking for Confirmation During Operations.
1639 * external:: Running External Commands.
1642 File: tar.info, Node: Synopsis, Next: using tar options, Up: tar invocation
1644 3.1 General Synopsis of `tar'
1645 =============================
1647 The GNU `tar' program is invoked as either one of:
1649 tar OPTION... [NAME]...
1650 tar LETTER... [ARGUMENT]... [OPTION]... [NAME]...
1652 The second form is for when old options are being used.
1654 You can use `tar' to store files in an archive, to extract them from
1655 an archive, and to do other types of archive manipulation. The primary
1656 argument to `tar', which is called the "operation", specifies which
1657 action to take. The other arguments to `tar' are either "options",
1658 which change the way `tar' performs an operation, or file names or
1659 archive members, which specify the files or members `tar' is to act on.
1661 You can actually type in arguments in any order, even if in this
1662 manual the options always precede the other arguments, to make examples
1663 easier to understand. Further, the option stating the main operation
1664 mode (the `tar' main command) is usually given first.
1666 Each NAME in the synopsis above is interpreted as an archive member
1667 name when the main command is one of `--compare' (`--diff', `-d'),
1668 `--delete', `--extract' (`--get', `-x'), `--list' (`-t') or `--update'
1669 (`-u'). When naming archive members, you must give the exact name of
1670 the member in the archive, as it is printed by `--list'. For
1671 `--append' (`-r') and `--create' (`-c'), these NAME arguments specify
1672 the names of either files or directory hierarchies to place in the
1673 archive. These files or hierarchies should already exist in the file
1674 system, prior to the execution of the `tar' command.
1676 `tar' interprets relative file names as being relative to the
1677 working directory. `tar' will make all file names relative (by
1678 removing leading slashes when archiving or restoring files), unless you
1679 specify otherwise (using the `--absolute-names' option). *Note
1680 absolute::, for more information about `--absolute-names'.
1682 If you give the name of a directory as either a file name or a member
1683 name, then `tar' acts recursively on all the files and directories
1684 beneath that directory. For example, the name `/' identifies all the
1685 files in the file system to `tar'.
1687 The distinction between file names and archive member names is
1688 especially important when shell globbing is used, and sometimes a
1689 source of confusion for newcomers. *Note wildcards::, for more
1690 information about globbing. The problem is that shells may only glob
1691 using existing files in the file system. Only `tar' itself may glob on
1692 archive members, so when needed, you must ensure that wildcard
1693 characters reach `tar' without being interpreted by the shell first.
1694 Using a backslash before `*' or `?', or putting the whole argument
1695 between quotes, is usually sufficient for this.
1697 Even if NAMEs are often specified on the command line, they can also
1698 be read from a text file in the file system, using the
1699 `--files-from=FILE-OF-NAMES' (`-T FILE-OF-NAMES') option.
1701 If you don't use any file name arguments, `--append' (`-r'),
1702 `--delete' and `--concatenate' (`--catenate', `-A') will do nothing,
1703 while `--create' (`-c') will usually yield a diagnostic and inhibit
1704 `tar' execution. The other operations of `tar' (`--list', `--extract',
1705 `--compare', and `--update') will act on the entire contents of the
1708 Besides successful exits, GNU `tar' may fail for many reasons. Some
1709 reasons correspond to bad usage, that is, when the `tar' command line
1710 is improperly written. Errors may be encountered later, while
1711 processing the archive or the files. Some errors are recoverable, in
1712 which case the failure is delayed until `tar' has completed all its
1713 work. Some errors are such that it would be not meaningful, or at
1714 least risky, to continue processing: `tar' then aborts processing
1715 immediately. All abnormal exits, whether immediate or delayed, should
1716 always be clearly diagnosed on `stderr', after a line stating the
1717 nature of the error.
1719 Possible exit codes of GNU `tar' are summarized in the following
1723 `Successful termination'.
1726 `Some files differ'. If tar was invoked with `--compare'
1727 (`--diff', `-d') command line option, this means that some files
1728 in the archive differ from their disk counterparts (*note
1729 compare::). If tar was given `--create', `--append' or `--update'
1730 option, this exit code means that some files were changed while
1731 being archived and so the resulting archive does not contain the
1732 exact copy of the file set.
1735 `Fatal error'. This means that some fatal, unrecoverable error
1738 If `tar' has invoked a subprocess and that subprocess exited with a
1739 nonzero exit code, `tar' exits with that code as well. This can
1740 happen, for example, if `tar' was given some compression option (*note
1741 gzip::) and the external compressor program failed. Another example is
1742 `rmt' failure during backup to the remote device (*note Remote Tape
1746 File: tar.info, Node: using tar options, Next: Styles, Prev: Synopsis, Up: tar invocation
1748 3.2 Using `tar' Options
1749 =======================
1751 GNU `tar' has a total of eight operating modes which allow you to
1752 perform a variety of tasks. You are required to choose one operating
1753 mode each time you employ the `tar' program by specifying one, and only
1754 one operation as an argument to the `tar' command (the corresponding
1755 options may be found at *note frequent operations:: and *note
1756 Operations::). Depending on circumstances, you may also wish to
1757 customize how the chosen operating mode behaves. For example, you may
1758 wish to change the way the output looks, or the format of the files
1759 that you wish to archive may require you to do something special in
1760 order to make the archive look right.
1762 You can customize and control `tar''s performance by running `tar'
1763 with one or more options (such as `--verbose' (`-v'), which we used in
1764 the tutorial). As we said in the tutorial, "options" are arguments to
1765 `tar' which are (as their name suggests) optional. Depending on the
1766 operating mode, you may specify one or more options. Different options
1767 will have different effects, but in general they all change details of
1768 the operation, such as archive format, archive name, or level of user
1769 interaction. Some options make sense with all operating modes, while
1770 others are meaningful only with particular modes. You will likely use
1771 some options frequently, while you will only use others infrequently, or
1772 not at all. (A full list of options is available in *note All
1775 The `TAR_OPTIONS' environment variable specifies default options to
1776 be placed in front of any explicit options. For example, if
1777 `TAR_OPTIONS' is `-v --unlink-first', `tar' behaves as if the two
1778 options `-v' and `--unlink-first' had been specified before any
1779 explicit options. Option specifications are separated by whitespace.
1780 A backslash escapes the next character, so it can be used to specify an
1781 option containing whitespace or a backslash.
1783 Note that `tar' options are case sensitive. For example, the
1784 options `-T' and `-t' are different; the first requires an argument for
1785 stating the name of a file providing a list of NAMEs, while the second
1786 does not require an argument and is another way to write `--list'
1789 In addition to the eight operations, there are many options to
1790 `tar', and three different styles for writing both: long (mnemonic)
1791 form, short form, and old style. These styles are discussed below.
1792 Both the options and the operations can be written in any of these three
1796 File: tar.info, Node: Styles, Next: All Options, Prev: using tar options, Up: tar invocation
1798 3.3 The Three Option Styles
1799 ===========================
1801 There are three styles for writing operations and options to the command
1802 line invoking `tar'. The different styles were developed at different
1803 times during the history of `tar'. These styles will be presented
1804 below, from the most recent to the oldest.
1806 Some options must take an argument(1). Where you _place_ the
1807 arguments generally depends on which style of options you choose. We
1808 will detail specific information relevant to each option style in the
1809 sections on the different option styles, below. The differences are
1810 subtle, yet can often be very important; incorrect option placement can
1811 cause you to overwrite a number of important files. We urge you to
1812 note these differences, and only use the option style(s) which makes
1813 the most sense to you until you feel comfortable with the others.
1815 Some options _may_ take an argument. Such options may have at most
1816 long and short forms, they do not have old style equivalent. The rules
1817 for specifying an argument for such options are stricter than those for
1818 specifying mandatory arguments. Please, pay special attention to them.
1822 * Long Options:: Long Option Style
1823 * Short Options:: Short Option Style
1824 * Old Options:: Old Option Style
1825 * Mixing:: Mixing Option Styles
1827 ---------- Footnotes ----------
1829 (1) For example, `--file' (`-f') takes the name of an archive file
1830 as an argument. If you do not supply an archive file name, `tar' will
1831 use a default, but this can be confusing; thus, we recommend that you
1832 always supply a specific archive file name.
1835 File: tar.info, Node: Long Options, Next: Short Options, Up: Styles
1837 3.3.1 Long Option Style
1838 -----------------------
1840 Each option has at least one "long" (or "mnemonic") name starting with
1841 two dashes in a row, e.g., `--list'. The long names are more clear than
1842 their corresponding short or old names. It sometimes happens that a
1843 single long option has many different names which are synonymous, such
1844 as `--compare' and `--diff'. In addition, long option names can be
1845 given unique abbreviations. For example, `--cre' can be used in place
1846 of `--create' because there is no other long option which begins with
1847 `cre'. (One way to find this out is by trying it and seeing what
1848 happens; if a particular abbreviation could represent more than one
1849 option, `tar' will tell you that that abbreviation is ambiguous and
1850 you'll know that that abbreviation won't work. You may also choose to
1851 run `tar --help' to see a list of options. Be aware that if you run
1852 `tar' with a unique abbreviation for the long name of an option you
1853 didn't want to use, you are stuck; `tar' will perform the command as
1856 Long options are meant to be obvious and easy to remember, and their
1857 meanings are generally easier to discern than those of their
1858 corresponding short options (see below). For example:
1860 $ tar --create --verbose --blocking-factor=20 --file=/dev/rmt0
1862 gives a fairly good set of hints about what the command does, even for
1863 those not fully acquainted with `tar'.
1865 Long options which require arguments take those arguments
1866 immediately following the option name. There are two ways of
1867 specifying a mandatory argument. It can be separated from the option
1868 name either by an equal sign, or by any amount of white space
1869 characters. For example, the `--file' option (which tells the name of
1870 the `tar' archive) is given a file such as `archive.tar' as argument by
1871 using any of the following notations: `--file=archive.tar' or `--file
1874 In contrast, optional arguments must always be introduced using an
1875 equal sign. For example, the `--backup' option takes an optional
1876 argument specifying backup type. It must be used as
1877 `--backup=BACKUP-TYPE'.
1880 File: tar.info, Node: Short Options, Next: Old Options, Prev: Long Options, Up: Styles
1882 3.3.2 Short Option Style
1883 ------------------------
1885 Most options also have a "short option" name. Short options start with
1886 a single dash, and are followed by a single character, e.g., `-t'
1887 (which is equivalent to `--list'). The forms are absolutely identical
1888 in function; they are interchangeable.
1890 The short option names are faster to type than long option names.
1892 Short options which require arguments take their arguments
1893 immediately following the option, usually separated by white space. It
1894 is also possible to stick the argument right after the short option
1895 name, using no intervening space. For example, you might write
1896 `-f archive.tar' or `-farchive.tar' instead of using
1897 `--file=archive.tar'. Both `--file=ARCHIVE-NAME' and `-f ARCHIVE-NAME'
1898 denote the option which indicates a specific archive, here named
1901 Short options which take optional arguments take their arguments
1902 immediately following the option letter, _without any intervening white
1905 Short options' letters may be clumped together, but you are not
1906 required to do this (as compared to old options; see below). When
1907 short options are clumped as a set, use one (single) dash for them all,
1908 e.g., ``tar' -cvf'. Only the last option in such a set is allowed to
1909 have an argument(1).
1911 When the options are separated, the argument for each option which
1912 requires an argument directly follows that option, as is usual for Unix
1913 programs. For example:
1915 $ tar -c -v -b 20 -f /dev/rmt0
1917 If you reorder short options' locations, be sure to move any
1918 arguments that belong to them. If you do not move the arguments
1919 properly, you may end up overwriting files.
1921 ---------- Footnotes ----------
1923 (1) Clustering many options, the last of which has an argument, is a
1924 rather opaque way to write options. Some wonder if GNU `getopt' should
1925 not even be made helpful enough for considering such usages as invalid.
1928 File: tar.info, Node: Old Options, Next: Mixing, Prev: Short Options, Up: Styles
1930 3.3.3 Old Option Style
1931 ----------------------
1933 As far as we know, all `tar' programs, GNU and non-GNU, support "old
1934 options": that is, if the first argument does not start with `-', it is
1935 assumed to specify option letters. GNU `tar' supports old options not
1936 only for historical reasons, but also because many people are used to
1937 them. If the first argument does not start with a dash, you are
1938 announcing the old option style instead of the short option style; old
1939 options are decoded differently.
1941 Like short options, old options are single letters. However, old
1942 options must be written together as a single clumped set, without
1943 spaces separating them or dashes preceding them. This set of letters
1944 must be the first to appear on the command line, after the `tar'
1945 program name and some white space; old options cannot appear anywhere
1946 else. The letter of an old option is exactly the same letter as the
1947 corresponding short option. For example, the old option `t' is the
1948 same as the short option `-t', and consequently, the same as the long
1949 option `--list'. So for example, the command `tar cv' specifies the
1950 option `-v' in addition to the operation `-c'.
1952 When options that need arguments are given together with the command,
1953 all the associated arguments follow, in the same order as the options.
1954 Thus, the example given previously could also be written in the old
1957 $ tar cvbf 20 /dev/rmt0
1959 Here, `20' is the argument of `-b' and `/dev/rmt0' is the argument of
1962 The old style syntax can make it difficult to match option letters
1963 with their corresponding arguments, and is often confusing. In the
1964 command `tar cvbf 20 /dev/rmt0', for example, `20' is the argument for
1965 `-b', `/dev/rmt0' is the argument for `-f', and `-v' does not have a
1966 corresponding argument. Even using short options like in
1967 `tar -c -v -b 20 -f /dev/rmt0' is clearer, putting all arguments next
1968 to the option they pertain to.
1970 If you want to reorder the letters in the old option argument, be
1971 sure to reorder any corresponding argument appropriately.
1973 This old way of writing `tar' options can surprise even experienced
1974 users. For example, the two commands:
1976 tar cfz archive.tar.gz file
1977 tar -cfz archive.tar.gz file
1979 are quite different. The first example uses `archive.tar.gz' as the
1980 value for option `f' and recognizes the option `z'. The second
1981 example, however, uses `z' as the value for option `f' -- probably not
1984 This second example could be corrected in many ways, among which the
1985 following are equivalent:
1987 tar -czf archive.tar.gz file
1988 tar -cf archive.tar.gz -z file
1989 tar cf archive.tar.gz -z file
1992 File: tar.info, Node: Mixing, Prev: Old Options, Up: Styles
1994 3.3.4 Mixing Option Styles
1995 --------------------------
1997 All three styles may be intermixed in a single `tar' command, so long
1998 as the rules for each style are fully respected(1). Old style options
1999 and either of the modern styles of options may be mixed within a single
2000 `tar' command. However, old style options must be introduced as the
2001 first arguments only, following the rule for old options (old options
2002 must appear directly after the `tar' command and some white space).
2003 Modern options may be given only after all arguments to the old options
2004 have been collected. If this rule is not respected, a modern option
2005 might be falsely interpreted as the value of the argument to one of the
2008 For example, all the following commands are wholly equivalent, and
2009 illustrate the many combinations and orderings of option styles.
2011 tar --create --file=archive.tar
2012 tar --create -f archive.tar
2013 tar --create -farchive.tar
2014 tar --file=archive.tar --create
2015 tar --file=archive.tar -c
2016 tar -c --file=archive.tar
2017 tar -c -f archive.tar
2018 tar -c -farchive.tar
2021 tar -f archive.tar --create
2022 tar -f archive.tar -c
2023 tar -farchive.tar --create
2024 tar -farchive.tar -c
2025 tar c --file=archive.tar
2026 tar c -f archive.tar
2029 tar f archive.tar --create
2030 tar f archive.tar -c
2033 On the other hand, the following commands are _not_ equivalent to
2036 tar -f -c archive.tar
2042 These last examples mean something completely different from what the
2043 user intended (judging based on the example in the previous set which
2044 uses long options, whose intent is therefore very clear). The first
2045 four specify that the `tar' archive would be a file named `-c', `c',
2046 `carchive.tar' or `archive.tarc', respectively. The first two examples
2047 also specify a single non-option, NAME argument having the value
2048 `archive.tar'. The last example contains only old style option letters
2049 (repeating option `c' twice), not all of which are meaningful (eg., `.',
2050 `h', or `i'), with no argument value.
2052 ---------- Footnotes ----------
2054 (1) Before GNU `tar' version 1.11.6, a bug prevented intermixing old
2055 style options with long options in some cases.
2058 File: tar.info, Node: All Options, Next: help, Prev: Styles, Up: tar invocation
2060 3.4 All `tar' Options
2061 =====================
2063 The coming manual sections contain an alphabetical listing of all `tar'
2064 operations and options, with brief descriptions and cross-references to
2065 more in-depth explanations in the body of the manual. They also
2066 contain an alphabetically arranged table of the short option forms with
2067 their corresponding long option. You can use this table as a reference
2068 for deciphering `tar' commands in scripts.
2072 * Operation Summary::
2074 * Short Option Summary::
2077 File: tar.info, Node: Operation Summary, Next: Option Summary, Up: All Options
2084 Appends files to the end of the archive. *Note append::.
2088 Same as `--concatenate'. *Note concatenate::.
2092 Compares archive members with their counterparts in the file
2093 system, and reports differences in file size, mode, owner,
2094 modification date and contents. *Note compare::.
2098 Appends other `tar' archives to the end of the archive. *Note
2103 Creates a new `tar' archive. *Note create::.
2106 Deletes members from the archive. Don't try this on an archive on
2107 a tape! *Note delete::.
2111 Same `--compare'. *Note compare::.
2115 Extracts members from the archive into the file system. *Note
2120 Same as `--extract'. *Note extract::.
2124 Lists the members in an archive. *Note list::.
2128 Adds files to the end of the archive, but only if they are newer
2129 than their counterparts already in the archive, or if they do not
2130 already exist in the archive. *Note update::.
2134 File: tar.info, Node: Option Summary, Next: Short Option Summary, Prev: Operation Summary, Up: All Options
2141 Normally when creating an archive, `tar' strips an initial `/'
2142 from member names, and when extracting from an archive `tar'
2143 treats names specially if they have initial `/' or internal `..'.
2144 This option disables that behavior. *Note absolute::.
2147 (See `--newer', *note after::)
2150 A pattern must match an initial subsequence of the name's
2151 components. *Note controlling pattern-matching::.
2154 `--atime-preserve=replace'
2155 `--atime-preserve=system'
2156 Attempt to preserve the access time of files when reading them.
2157 This option currently is effective only on files that you own,
2158 unless you have superuser privileges.
2160 `--atime-preserve=replace' remembers the access time of a file
2161 before reading it, and then restores the access time afterwards.
2162 This may cause problems if other programs are reading the file at
2163 the same time, as the times of their accesses will be lost. On
2164 most platforms restoring the access time also requires `tar' to
2165 restore the data modification time too, so this option may also
2166 cause problems if other programs are writing the file at the same
2167 time (`tar' attempts to detect this situation, but cannot do so
2168 reliably due to race conditions). Worse, on most platforms
2169 restoring the access time also updates the status change time,
2170 which means that this option is incompatible with incremental
2173 `--atime-preserve=system' avoids changing time stamps on files,
2174 without interfering with time stamp updates caused by other
2175 programs, so it works better with incremental backups. However,
2176 it requires a special `O_NOATIME' option from the underlying
2177 operating and file system implementation, and it also requires
2178 that searching directories does not update their access times. As
2179 of this writing (November 2005) this works only with Linux, and
2180 only with Linux kernels 2.6.8 and later. Worse, there is
2181 currently no reliable way to know whether this feature actually
2182 works. Sometimes `tar' knows that it does not work, and if you use
2183 `--atime-preserve=system' then `tar' complains and exits right
2184 away. But other times `tar' might think that the option works
2185 when it actually does not.
2187 Currently `--atime-preserve' with no operand defaults to
2188 `--atime-preserve=replace', but this may change in the future as
2189 support for `--atime-preserve=system' improves.
2191 If your operating or file system does not support
2192 `--atime-preserve=system', you might be able to preserve access
2193 times reliably by using the `mount' command. For example, you can
2194 mount the file system read-only, or access the file system via a
2195 read-only loopback mount, or use the `noatime' mount option
2196 available on some systems. However, mounting typically requires
2197 superuser privileges and can be a pain to manage.
2201 During a `--create' operation, enables automatic compressed format
2202 recognition based on the archive suffix. The effect of this
2203 option is cancelled by `--no-auto-compress'. *Note gzip::.
2205 `--backup=BACKUP-TYPE'
2206 Rather than deleting files from the file system, `tar' will back
2207 them up using simple or numbered backups, depending upon
2208 BACKUP-TYPE. *Note backup::.
2212 With this option present, `tar' prints error messages for read
2213 errors with the block number in the archive file. *Note
2216 `--blocking-factor=BLOCKING'
2218 Sets the blocking factor `tar' uses to BLOCKING x 512 bytes per
2219 record. *Note Blocking Factor::.
2223 This option tells `tar' to read or write archives through `bzip2'.
2227 Check device numbers when creating a list of modified files for
2228 incremental archiving. This is the default. *Note device
2229 numbers::, for a detailed description.
2231 `--checkpoint[=NUMBER]'
2232 This option directs `tar' to print periodic checkpoint messages as
2233 it reads through the archive. It is intended for when you want a
2234 visual indication that `tar' is still running, but don't want to
2235 see `--verbose' output. You can also instruct `tar' to execute a
2236 list of actions on each checkpoint, see `--checkpoint-action'
2237 below. For a detailed description, see *note checkpoints::.
2239 `--checkpoint-action=ACTION'
2240 Instruct `tar' to execute an action upon hitting a breakpoint.
2241 Here we give only a brief outline. *Note checkpoints::, for a
2242 complete description.
2244 The ACTION argument can be one of the following:
2247 Produce an audible bell on the console.
2251 Print a single dot on the standard listing stream.
2254 Display a textual message on the standard error, with the
2255 status and number of the checkpoint. This is the default.
2258 Display STRING on the standard error. Before output, the
2259 string is subject to meta-character expansion.
2262 Execute the given COMMAND.
2265 Wait for TIME seconds.
2268 Output STRING on the current console (`/dev/tty').
2270 Several `--checkpoint-action' options can be specified. The
2271 supplied actions will be executed in order of their appearance in
2274 Using `--checkpoint-action' without `--checkpoint' assumes default
2275 checkpoint frequency of one checkpoint per 10 records.
2279 If this option was given, `tar' will check the number of links
2280 dumped for each processed file. If this number does not match the
2281 total number of hard links for the file, a warning message will be
2289 `tar' will use the `compress' program when reading or writing the
2290 archive. This allows you to directly act on archives while saving
2291 space. *Note gzip::.
2294 (See `--interactive'.) *Note interactive::.
2296 `--delay-directory-restore'
2297 Delay setting modification times and permissions of extracted
2298 directories until the end of extraction. *Note Directory
2299 Modification Times and Permissions::.
2303 When reading or writing a file to be archived, `tar' accesses the
2304 file that a symbolic link points to, rather than the symlink
2305 itself. *Note dereference::.
2309 When this option is specified, `tar' will change its current
2310 directory to DIR before performing any operations. When this
2311 option is used during archive creation, it is order sensitive.
2315 When performing operations, `tar' will skip files that match
2316 PATTERN. *Note exclude::.
2319 Exclude backup and lock files. *Note exclude-backups: exclude.
2321 `--exclude-from=FILE'
2323 Similar to `--exclude', except `tar' will use the list of patterns
2324 in the file FILE. *Note exclude::.
2327 Exclude from dump any directory containing a valid cache directory
2328 tag file, but still dump the directory node and the tag file
2331 *Note exclude-caches: exclude.
2333 `--exclude-caches-under'
2334 Exclude from dump any directory containing a valid cache directory
2335 tag file, but still dump the directory node itself.
2339 `--exclude-caches-all'
2340 Exclude from dump any directory containing a valid cache directory
2341 tag file. *Note exclude::.
2343 `--exclude-tag=FILE'
2344 Exclude from dump any directory containing file named FILE, but
2345 dump the directory node and FILE itself. *Note exclude-tag:
2348 `--exclude-tag-under=FILE'
2349 Exclude from dump the contents of any directory containing file
2350 named FILE, but dump the directory node itself. *Note
2351 exclude-tag-under: exclude.
2353 `--exclude-tag-all=FILE'
2354 Exclude from dump any directory containing file named FILE. *Note
2355 exclude-tag-all: exclude.
2358 Exclude from dump directories and files, that are internal for some
2359 widely used version control systems.
2361 *Note exclude-vcs: exclude.
2365 `tar' will use the file ARCHIVE as the `tar' archive it performs
2366 operations on, rather than `tar''s compilation dependent default.
2367 *Note file tutorial::.
2371 `tar' will use the contents of FILE as a list of archive members
2372 or files to operate on, in addition to those specified on the
2373 command-line. *Note files::.
2376 Forces `tar' to interpret the file name given to `--file' as a
2377 local file, even if it looks like a remote tape drive name. *Note
2378 local and remote archives::.
2382 Selects output archive format. FORMAT may be one of the following:
2385 Creates an archive that is compatible with Unix V7 `tar'.
2388 Creates an archive that is compatible with GNU `tar' version
2392 Creates archive in GNU tar 1.13 format. Basically it is the
2393 same as `oldgnu' with the only difference in the way it
2394 handles long numeric fields.
2397 Creates a POSIX.1-1988 compatible archive.
2400 Creates a POSIX.1-2001 archive.
2403 *Note Formats::, for a detailed discussion of these formats.
2406 This option instructs `tar' to print file times to their full
2407 resolution. Usually this means 1-second resolution, but that
2408 depends on the underlying file system. The `--full-time' option
2409 takes effect only when detailed output (verbosity level 2 or
2410 higher) has been requested using the `--verbose' option, e.g.,
2411 when listing or extracting archives:
2413 $ tar -t -v --full-time -f archive.tar
2415 or, when creating an archive:
2417 $ tar -c -vv --full-time -f archive.tar .
2419 Notice, thar when creating the archive you need to specify
2420 `--verbose' twice to get a detailed output (*note verbose
2424 Files added to the `tar' archive will have a group ID of GROUP,
2425 rather than the group from the source file. GROUP can specify a
2426 symbolic name, or a numeric ID, or both as NAME:ID. *Note
2429 Also see the comments for the `--owner=USER' option.
2435 This option tells `tar' to read or write archives through `gzip',
2436 allowing `tar' to directly operate on several kinds of compressed
2437 archives transparently. *Note gzip::.
2439 `--hard-dereference'
2440 When creating an archive, dereference hard links and store the
2441 files they refer to, instead of creating usual hard link members.
2447 `tar' will print out a short message summarizing the operations and
2448 options to `tar' and exit. *Note help::.
2451 Ignore case when matching member or file names with patterns.
2452 *Note controlling pattern-matching::.
2454 `--ignore-command-error'
2455 Ignore exit codes of subprocesses. *Note Writing to an External
2458 `--ignore-failed-read'
2459 Do not exit unsuccessfully merely because an unreadable file was
2460 encountered. *Note Ignore Failed Read::.
2464 With this option, `tar' will ignore zeroed blocks in the archive,
2465 which normally signals EOF. *Note Reading::.
2469 Informs `tar' that it is working with an old GNU-format
2470 incremental backup archive. It is intended primarily for
2471 backwards compatibility only. *Note Incremental Dumps::, for a
2472 detailed discussion of incremental archives.
2475 Send verbose output to FILE instead of to standard output.
2477 `--info-script=COMMAND'
2478 `--new-volume-script=COMMAND'
2480 When `tar' is performing multi-tape backups, COMMAND is run at the
2481 end of each tape. If it exits with nonzero status, `tar' fails
2482 immediately. *Note info-script::, for a detailed discussion of
2488 Specifies that `tar' should ask the user for confirmation before
2489 performing potentially destructive options, such as overwriting
2490 files. *Note interactive::.
2492 `--keep-directory-symlink'
2493 This option changes the behavior of tar when it encounters a
2494 symlink with the same name as the directory that it is about to
2495 extract. By default, in this case tar would first remove the
2496 symlink and then proceed extracting the directory.
2498 The `--keep-directory-symlink' option disables this behavior and
2499 instructs tar to follow symlinks to directories when extracting
2502 It is mainly intended to provide compatibility with the Slackware
2503 installation scripts.
2505 `--keep-newer-files'
2506 Do not replace existing files that are newer than their archive
2507 copies when extracting files from an archive.
2511 Do not overwrite existing files when extracting files from an
2512 archive. Return error if such files exist. See also *note
2515 *Note Keep Old Files::.
2519 When creating an archive, instructs `tar' to write NAME as a name
2520 record in the archive. When extracting or listing archives, `tar'
2521 will only operate on archives that have a label matching the
2522 pattern specified in NAME. *Note Tape Files::.
2525 Force incremental backup of level N. As of GNU `tar' version
2526 1.27, the option `--level=0' truncates the snapshot file, thereby
2527 forcing the level 0 dump. Other values of N are effectively
2528 ignored. *Note --level=0::, for details and examples.
2530 The use of this option is valid only in conjunction with the
2531 `--listed-incremental' option. *Note Incremental Dumps::, for a
2532 detailed description.
2534 `--listed-incremental=SNAPSHOT-FILE'
2536 During a `--create' operation, specifies that the archive that
2537 `tar' creates is a new GNU-format incremental backup, using
2538 SNAPSHOT-FILE to determine which files to backup. With other
2539 operations, informs `tar' that the archive is in incremental
2540 format. *Note Incremental Dumps::.
2543 This option tells `tar' to read or write archives through `lzip'.
2547 This option tells `tar' to read or write archives through `lzma'.
2551 This option tells `tar' to read or write archives through `lzop'.
2554 `--mode=PERMISSIONS'
2555 When adding files to an archive, `tar' will use PERMISSIONS for
2556 the archive members, rather than the permissions from the files.
2557 PERMISSIONS can be specified either as an octal number or as
2558 symbolic permissions, like with `chmod'. *Note override::.
2561 When adding files to an archive, `tar' will use DATE as the
2562 modification time of members when creating archives, instead of
2563 their actual modification times. The value of DATE can be either
2564 a textual date representation (*note Date input formats::) or a
2565 name of the existing file, starting with `/' or `.'. In the
2566 latter case, the modification time of that file is used. *Note
2571 Informs `tar' that it should create or otherwise operate on a
2572 multi-volume `tar' archive. *Note Using Multiple Tapes::.
2574 `--new-volume-script'
2575 (see `--info-script')
2580 When creating an archive, `tar' will only add files that have
2581 changed since DATE. If DATE begins with `/' or `.', it is taken
2582 to be the name of a file whose data modification time specifies
2583 the date. *Note after::.
2585 `--newer-mtime=DATE'
2586 Like `--newer', but add only files whose contents have changed (as
2587 opposed to just `--newer', which will also back up files for which
2588 any status information has changed). *Note after::.
2591 An exclude pattern can match any subsequence of the name's
2592 components. *Note controlling pattern-matching::.
2594 `--no-auto-compress'
2595 Disables automatic compressed format recognition based on the
2596 archive suffix. *Note --auto-compress::. *Note gzip::.
2599 Do not check device numbers when creating a list of modified files
2600 for incremental archiving. *Note device numbers::, for a detailed
2603 `--no-delay-directory-restore'
2604 Modification times and permissions of extracted directories are
2605 set when all files from this directory have been extracted. This
2606 is the default. *Note Directory Modification Times and
2610 Use case-sensitive matching. *Note controlling pattern-matching::.
2612 `--no-ignore-command-error'
2613 Print warnings about subprocesses that terminated with a nonzero
2614 exit code. *Note Writing to an External Program::.
2617 If the `--null' option was given previously, this option cancels
2618 its effect, so that any following `--files-from' options will
2619 expect their file lists to be newline-terminated.
2621 `--no-overwrite-dir'
2622 Preserve metadata of existing directories when extracting files
2623 from an archive. *Note Overwrite Old Files::.
2625 `--no-quote-chars=STRING'
2626 Remove characters listed in STRING from the list of quoted
2627 characters set by the previous `--quote-chars' option (*note
2631 With this option, `tar' will not recurse into directories. *Note
2636 When extracting an archive, do not attempt to preserve the owner
2637 specified in the `tar' archive. This the default behavior for
2640 `--no-same-permissions'
2641 When extracting an archive, subtract the user's umask from files
2642 from the permissions specified in the archive. This is the
2643 default behavior for ordinary users.
2646 The archive media does not support seeks to arbitrary locations.
2647 Usually `tar' determines automatically whether the archive can be
2648 seeked or not. Use this option to disable this mechanism.
2651 Treat all input file or member names literally, do not interpret
2652 escape sequences. *Note input name quoting::.
2655 Do not use wildcards. *Note controlling pattern-matching::.
2657 `--no-wildcards-match-slash'
2658 Wildcards do not match `/'. *Note controlling pattern-matching::.
2661 When `tar' is using the `--files-from' option, this option
2662 instructs `tar' to expect file names terminated with NUL, so `tar'
2663 can correctly work with file names that contain newlines. *Note
2667 This option will notify `tar' that it should use numeric user and
2668 group IDs when creating a `tar' file, rather than names. *Note
2672 The function of this option depends on the action `tar' is
2673 performing. When extracting files, `-o' is a synonym for
2674 `--no-same-owner', i.e., it prevents `tar' from restoring
2675 ownership of files being extracted.
2677 When creating an archive, it is a synonym for `--old-archive'.
2678 This behavior is for compatibility with previous versions of GNU
2679 `tar', and will be removed in future releases.
2681 *Note Changes::, for more information.
2683 `--occurrence[=NUMBER]'
2684 This option can be used in conjunction with one of the subcommands
2685 `--delete', `--diff', `--extract' or `--list' when a list of files
2686 is given either on the command line or via `-T' option.
2688 This option instructs `tar' to process only the NUMBERth
2689 occurrence of each named file. NUMBER defaults to 1, so
2691 tar -x -f archive.tar --occurrence filename
2693 will extract the first occurrence of the member `filename' from
2694 `archive.tar' and will terminate without scanning to the end of
2698 Synonym for `--format=v7'.
2701 Used when creating an archive. Prevents `tar' from recursing into
2702 directories that are on different file systems from the current
2706 Overwrite existing files and directory metadata when extracting
2707 files from an archive. *Note Overwrite Old Files::.
2710 Overwrite the metadata of existing directories when extracting
2711 files from an archive. *Note Overwrite Old Files::.
2714 Specifies that `tar' should use USER as the owner of members when
2715 creating archives, instead of the user associated with the source
2716 file. USER can specify a symbolic name, or a numeric ID, or both
2717 as NAME:ID. *Note override::.
2719 This option does not affect extraction from archives.
2721 `--pax-option=KEYWORD-LIST'
2722 This option enables creation of the archive in POSIX.1-2001 format
2723 (*note posix::) and modifies the way `tar' handles the extended
2724 header keywords. KEYWORD-LIST is a comma-separated list of
2725 keyword options. *Note PAX keywords::, for a detailed discussion.
2729 Synonym for `--format=v7'.
2732 Same as `--format=posix'.
2735 Synonymous with specifying both `--preserve-permissions' and
2736 `--same-order'. *Note Setting Access Permissions::.
2739 (See `--same-order'; *note Reading::.)
2741 `--preserve-permissions'
2742 `--same-permissions'
2744 When `tar' is extracting an archive, it normally subtracts the
2745 users' umask from the permissions specified in the archive and uses
2746 that number as the permissions to create the destination file.
2747 Specifying this option instructs `tar' that it should use the
2748 permissions directly from the archive. *Note Setting Access
2751 `--quote-chars=STRING'
2752 Always quote characters from STRING, even if the selected quoting
2753 style would not quote them (*note quoting styles::).
2755 `--quoting-style=STYLE'
2756 Set quoting style to use when printing member and file names
2757 (*note quoting styles::). Valid STYLE values are: `literal',
2758 `shell', `shell-always', `c', `escape', `locale', and `clocale'.
2759 Default quoting style is `escape', unless overridden while
2760 configuring the package.
2762 `--read-full-records'
2764 Specifies that `tar' should reblock its input, for reading from
2765 pipes on systems with buggy implementations. *Note Reading::.
2767 `--record-size=SIZE[SUF]'
2768 Instructs `tar' to use SIZE bytes per record when accessing the
2769 archive. The argument can be suffixed with a "size suffix", e.g.
2770 `--record-size=10K' for 10 Kilobytes. *Note size-suffixes::, for
2771 a list of valid suffixes. *Note Blocking Factor::, for a detailed
2772 description of this option.
2775 With this option, `tar' recurses into directories (default).
2778 `--recursive-unlink'
2779 Remove existing directory hierarchies before extracting
2780 directories of the same name from the archive. *Note Recursive
2784 Directs `tar' to remove the source file from the file system after
2785 appending it to an archive. *Note remove files::.
2788 Disable use of some potentially harmful `tar' options. Currently
2789 this option disables shell invocation from multi-volume menu
2790 (*note Using Multiple Tapes::).
2793 Notifies `tar' that it should use CMD instead of the default
2794 `/usr/libexec/rmt' (*note Remote Tape Server::).
2797 Notifies `tar' that is should use CMD to communicate with remote
2798 devices. *Note Device::.
2803 This option is an optimization for `tar' when running on machines
2804 with small amounts of memory. It informs `tar' that the list of
2805 file arguments has already been sorted to match the order of files
2806 in the archive. *Note Reading::.
2809 When extracting an archive, `tar' will attempt to preserve the
2810 owner specified in the `tar' archive with this option present.
2811 This is the default behavior for the superuser; this option has an
2812 effect only for ordinary users. *Note Attributes::.
2814 `--same-permissions'
2815 (See `--preserve-permissions'; *note Setting Access Permissions::.)
2819 Assume that the archive media supports seeks to arbitrary
2820 locations. Usually `tar' determines automatically whether the
2821 archive can be seeked or not. This option is intended for use in
2822 cases when such recognition fails. It takes effect only if the
2823 archive is open for reading (e.g. with `--list' or `--extract'
2827 Displays the default options used by `tar' and exits successfully.
2828 This option is intended for use in shell scripts. Here is an
2829 example of what you can see using this option:
2831 $ tar --show-defaults
2832 --format=gnu -f- -b20 --quoting-style=escape
2833 --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
2835 Notice, that this option outputs only one line. The example output
2836 above has been split to fit page boundaries. *Note defaults::.
2838 `--show-omitted-dirs'
2839 Instructs `tar' to mention the directories it is skipping when
2840 operating on a `tar' archive. *Note show-omitted-dirs::.
2842 `--show-snapshot-field-ranges'
2843 Displays the range of values allowed by this version of `tar' for
2844 each field in the snapshot file, then exits successfully. *Note
2847 `--show-transformed-names'
2848 `--show-stored-names'
2849 Display file or member names after applying any transformations
2850 (*note transform::). In particular, when used in conjunction with
2851 one of the archive creation operations it instructs `tar' to list
2852 the member names stored in the archive, as opposed to the actual
2853 file names. *Note listing member and file names::.
2856 Do not overwrite existing files when extracting files from an
2857 archive. *Note Keep Old Files::.
2859 This option differs from `--keep-old-files' in that it does not
2860 treat such files as an error, instead it just silently avoids
2863 The `--warning=existing-file' option can be used together with
2864 this option to produce warning messages about existing old files
2869 Invokes a GNU extension when adding files to an archive that
2870 handles sparse files efficiently. *Note sparse::.
2872 `--sparse-version=VERSION'
2873 Specifies the "format version" to use when archiving sparse files.
2874 Implies `--sparse'. *Note sparse::. For the description of the
2875 supported sparse formats, *Note Sparse Formats::.
2877 `--starting-file=NAME'
2879 This option affects extraction only; `tar' will skip extracting
2880 files in the archive until it finds one that matches NAME. *Note
2883 `--strip-components=NUMBER'
2884 Strip given NUMBER of leading components from file names before
2885 extraction. For example, if archive `archive.tar' contained
2886 `/some/file/name', then running
2888 tar --extract --file archive.tar --strip-components=2
2890 would extract this file to file `name'.
2893 Alters the suffix `tar' uses when backing up files from the default
2894 `~'. *Note backup::.
2896 `--tape-length=NUM[SUF]'
2898 Specifies the length of tapes that `tar' is writing as being
2899 NUM x 1024 bytes long. If optional SUF is given, it specifies a
2900 multiplicative factor to be used instead of 1024. For example,
2901 `-L2M' means 2 megabytes. *Note size-suffixes::, for a list of
2902 allowed suffixes. *Note Using Multiple Tapes::, for a detailed
2903 discussion of this option.
2906 Reads the volume label. If an argument is specified, test whether
2907 it matches the volume label. *Note --test-label option::.
2909 `--to-command=COMMAND'
2910 During extraction `tar' will pipe extracted files to the standard
2911 input of COMMAND. *Note Writing to an External Program::.
2915 During extraction, `tar' will extract files to stdout rather than
2916 to the file system. *Note Writing to Standard Output::.
2919 Displays the total number of bytes transferred when processing an
2920 archive. If an argument is given, these data are displayed on
2921 request, when signal SIGNO is delivered to `tar'. *Note totals::.
2925 Sets the data modification time of extracted files to the
2926 extraction time, rather than the data modification time stored in
2927 the archive. *Note Data Modification Times::.
2929 `--transform=SED-EXPR'
2931 Transform file or member names using `sed' replacement expression
2932 SED-EXPR. For example,
2934 $ tar cf archive.tar --transform 's,^\./,usr/,' .
2936 will add to `archive' files from the current working directory,
2937 replacing initial `./' prefix with `usr/'. For the detailed
2938 discussion, *Note transform::.
2940 To see transformed member names in verbose listings, use
2941 `--show-transformed-names' option (*note show-transformed-names::).
2944 (See `--compress', *note gzip::)
2947 (See `--gzip', *note gzip::)
2951 Directs `tar' to remove the corresponding file from the file
2952 system before extracting it from the archive. *Note Unlink
2956 Enable unquoting input file or member names (default). *Note
2957 input name quoting::.
2959 `--use-compress-program=PROG'
2961 Instructs `tar' to access the archive through PROG, which is
2962 presumed to be a compression program of some sort. *Note gzip::.
2965 Display file modification dates in UTC. This option implies
2970 Specifies that `tar' should be more verbose about the operations
2971 it is performing. This option can be specified multiple times for
2972 some operations to increase the amount of information displayed.
2977 Verifies that the archive was correctly written when creating an
2978 archive. *Note verify::.
2981 Print information about the program's name, version, origin and
2982 legal status, all on standard output, and then exit successfully.
2986 Used in conjunction with `--multi-volume'. `tar' will keep track
2987 of which volume of a multi-volume archive it is working in FILE.
2991 Enable or disable warning messages identified by KEYWORD. The
2992 messages are suppressed if KEYWORD is prefixed with `no-'. *Note
2996 Use wildcards when matching member names with patterns. *Note
2997 controlling pattern-matching::.
2999 `--wildcards-match-slash'
3000 Wildcards match `/'. *Note controlling pattern-matching::.
3004 Use `xz' for compressing or decompressing the archives. *Note
3008 ---------- Footnotes ----------
3010 (1) Earlier versions of GNU `tar' understood `-l' as a synonym for
3011 `--one-file-system'. The current semantics, which complies to UNIX98,
3012 was introduced with version 1.15.91. *Note Changes::, for more
3016 File: tar.info, Node: Short Option Summary, Prev: Option Summary, Up: All Options
3018 3.4.3 Short Options Cross Reference
3019 -----------------------------------
3021 Here is an alphabetized list of all of the short option forms, matching
3022 them with the equivalent long option.
3024 Short Option Reference
3025 --------------------------------------------------------------------------
3026 -A *note --concatenate::.
3027 -B *note --read-full-records::.
3028 -C *note --directory::.
3029 -F *note --info-script::.
3030 -G *note --incremental::.
3032 -K *note --starting-file::.
3033 -L *note --tape-length::.
3034 -M *note --multi-volume::.
3036 -O *note --to-stdout::.
3037 -P *note --absolute-names::.
3038 -R *note --block-number::.
3039 -S *note --sparse::.
3040 -T *note --files-from::.
3041 -U *note --unlink-first::.
3043 -W *note --verify::.
3044 -X *note --exclude-from::.
3045 -Z *note --compress::.
3046 -b *note --blocking-factor::.
3047 -c *note --create::.
3048 -d *note --compare::.
3050 -g *note --listed-incremental::.
3051 -h *note --dereference::.
3052 -i *note --ignore-zeros::.
3054 -k *note --keep-old-files::.
3055 -l *note --check-links::.
3057 -o When creating, *note --no-same-owner::, when extracting --
3058 *note --portability::.
3060 The latter usage is deprecated. It is retained for
3061 compatibility with the earlier versions of GNU `tar'. In
3062 future releases `-o' will be equivalent to
3063 `--no-same-owner' only.
3064 -p *note --preserve-permissions::.
3065 -r *note --append::.
3066 -s *note --same-order::.
3068 -u *note --update::.
3069 -v *note --verbose::.
3070 -w *note --interactive::.
3071 -x *note --extract::.
3075 File: tar.info, Node: help, Next: defaults, Prev: All Options, Up: tar invocation
3077 3.5 GNU `tar' documentation
3078 ===========================
3080 Being careful, the first thing is really checking that you are using
3081 GNU `tar', indeed. The `--version' option causes `tar' to print
3082 information about its name, version, origin and legal status, all on
3083 standard output, and then exit successfully. For example,
3084 `tar --version' might print:
3087 Copyright (C) 2013 Free Software Foundation, Inc.
3088 License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
3089 This is free software: you are free to change and redistribute it.
3090 There is NO WARRANTY, to the extent permitted by law.
3092 Written by John Gilmore and Jay Fenlason.
3094 The first occurrence of `tar' in the result above is the program name
3095 in the package (for example, `rmt' is another program), while the
3096 second occurrence of `tar' is the name of the package itself,
3097 containing possibly many programs. The package is currently named
3098 `tar', after the name of the main program it contains(1).
3100 Another thing you might want to do is checking the spelling or
3101 meaning of some particular `tar' option, without resorting to this
3102 manual, for once you have carefully read it. GNU `tar' has a short
3103 help feature, triggerable through the `--help' option. By using this
3104 option, `tar' will print a usage message listing all available options
3105 on standard output, then exit successfully, without doing anything else
3106 and ignoring all other options. Even if this is only a brief summary,
3107 it may be several screens long. So, if you are not using some kind of
3108 scrollable window, you might prefer to use something like:
3112 presuming, here, that you like using `less' for a pager. Other popular
3113 pagers are `more' and `pg'. If you know about some KEYWORD which
3114 interests you and do not want to read all the `--help' output, another
3115 common idiom is doing:
3117 tar --help | grep KEYWORD
3119 for getting only the pertinent lines. Notice, however, that some `tar'
3120 options have long description lines and the above command will list
3121 only the first of them.
3123 The exact look of the option summary displayed by `tar --help' is
3124 configurable. *Note Configuring Help Summary::, for a detailed
3127 If you only wish to check the spelling of an option, running `tar
3128 --usage' may be a better choice. This will display a terse list of
3129 `tar' options without accompanying explanations.
3131 The short help output is quite succinct, and you might have to get
3132 back to the full documentation for precise points. If you are reading
3133 this paragraph, you already have the `tar' manual in some form. This
3134 manual is available in a variety of forms from
3135 `http://www.gnu.org/software/tar/manual'. It may be printed out of the
3136 GNU `tar' distribution, provided you have TeX already installed
3137 somewhere, and a laser printer around. Just configure the
3138 distribution, execute the command `make dvi', then print `doc/tar.dvi'
3139 the usual way (contact your local guru to know how). If GNU `tar' has
3140 been conveniently installed at your place, this manual is also
3141 available in interactive, hypertextual form as an Info file. Just call
3142 `info tar' or, if you do not have the `info' program handy, use the
3143 Info reader provided within GNU Emacs, calling `tar' from the main Info
3146 There is currently no `man' page for GNU `tar'. If you observe such
3147 a `man' page on the system you are running, either it does not belong
3148 to GNU `tar', or it has not been produced by GNU. Some package
3149 maintainers convert `tar --help' output to a man page, using
3150 `help2man'. In any case, please bear in mind that the authoritative
3151 source of information about GNU `tar' is this Texinfo documentation.
3153 ---------- Footnotes ----------
3155 (1) There are plans to merge the `cpio' and `tar' packages into a
3156 single one which would be called `paxutils'. So, who knows if, one of
3157 this days, the `--version' would not output `tar (GNU paxutils) 3.2'.
3160 File: tar.info, Node: defaults, Next: verbose, Prev: help, Up: tar invocation
3162 3.6 Obtaining GNU `tar' default values
3163 ======================================
3165 GNU `tar' has some predefined defaults that are used when you do not
3166 explicitly specify another values. To obtain a list of such defaults,
3167 use `--show-defaults' option. This will output the values in the form
3168 of `tar' command line options:
3170 $ tar --show-defaults
3171 --format=gnu -f- -b20 --quoting-style=escape
3172 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
3174 Notice, that this option outputs only one line. The example output
3175 above has been split to fit page boundaries.
3177 The above output shows that this version of GNU `tar' defaults to using
3178 `gnu' archive format (*note Formats::), it uses standard output as the
3179 archive, if no `--file' option has been given (*note file tutorial::),
3180 the default blocking factor is 20 (*note Blocking Factor::). It also
3181 shows the default locations where `tar' will look for `rmt' and `rsh'
3185 File: tar.info, Node: verbose, Next: checkpoints, Prev: defaults, Up: tar invocation
3187 3.7 Checking `tar' progress
3188 ===========================
3190 Typically, `tar' performs most operations without reporting any
3191 information to the user except error messages. When using `tar' with
3192 many options, particularly ones with complicated or
3193 difficult-to-predict behavior, it is possible to make serious mistakes.
3194 `tar' provides several options that make observing `tar' easier. These
3195 options cause `tar' to print information as it progresses in its job,
3196 and you might want to use them just for being more careful about what
3197 is going on, or merely for entertaining yourself. If you have
3198 encountered a problem when operating on an archive, however, you may
3199 need more information than just an error message in order to solve the
3200 problem. The following options can be helpful diagnostic tools.
3202 Normally, the `--list' (`-t') command to list an archive prints just
3203 the file names (one per line) and the other commands are silent. When
3204 used with most operations, the `--verbose' (`-v') option causes `tar'
3205 to print the name of each file or archive member as it is processed.
3206 This and the other options which make `tar' print status information
3207 can be useful in monitoring `tar'.
3209 With `--create' or `--extract', `--verbose' used once just prints
3210 the names of the files or members as they are processed. Using it
3211 twice causes `tar' to print a longer listing (*Note verbose member
3212 listing::, for the description) for each member. Since `--list'
3213 already prints the names of the members, `--verbose' used once with
3214 `--list' causes `tar' to print an `ls -l' type listing of the files in
3215 the archive. The following examples both extract members with long
3218 $ tar --extract --file=archive.tar --verbose --verbose
3219 $ tar xvvf archive.tar
3221 Verbose output appears on the standard output except when an archive
3222 is being written to the standard output, as with `tar --create --file=-
3223 --verbose' (`tar cvf -', or even `tar cv'--if the installer let
3224 standard output be the default archive). In that case `tar' writes
3225 verbose output to the standard error stream.
3227 If `--index-file=FILE' is specified, `tar' sends verbose output to
3228 FILE rather than to standard output or standard error.
3230 The `--totals' option causes `tar' to print on the standard error
3231 the total amount of bytes transferred when processing an archive. When
3232 creating or appending to an archive, this option prints the number of
3233 bytes written to the archive and the average speed at which they have
3236 $ tar -c -f archive.tar --totals /home
3237 Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
3239 When reading an archive, this option displays the number of bytes
3242 $ tar -x -f archive.tar --totals
3243 Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
3245 Finally, when deleting from an archive, the `--totals' option
3246 displays both numbers plus number of bytes removed from the archive:
3248 $ tar --delete -f foo.tar --totals --wildcards '*~'
3249 Total bytes read: 9543680 (9.2MiB, 201MiB/s)
3250 Total bytes written: 3829760 (3.7MiB, 81MiB/s)
3251 Total bytes deleted: 1474048
3253 You can also obtain this information on request. When `--totals' is
3254 used with an argument, this argument is interpreted as a symbolic name
3255 of a signal, upon delivery of which the statistics is to be printed:
3258 Print statistics upon delivery of signal SIGNO. Valid arguments
3259 are: `SIGHUP', `SIGQUIT', `SIGINT', `SIGUSR1' and `SIGUSR2'.
3260 Shortened names without `SIG' prefix are also accepted.
3262 Both forms of `--totals' option can be used simultaneously. Thus,
3263 `tar -x --totals --totals=USR1' instructs `tar' to extract all members
3264 from its default archive and print statistics after finishing the
3265 extraction, as well as when receiving signal `SIGUSR1'.
3267 The `--checkpoint' option prints an occasional message as `tar'
3268 reads or writes the archive. It is designed for those who don't need
3269 the more detailed (and voluminous) output of `--block-number' (`-R'),
3270 but do want visual confirmation that `tar' is actually making forward
3271 progress. By default it prints a message each 10 records read or
3272 written. This can be changed by giving it a numeric argument after an
3275 $ tar -c --checkpoint=1000 /var
3276 tar: Write checkpoint 1000
3277 tar: Write checkpoint 2000
3278 tar: Write checkpoint 3000
3280 This example shows the default checkpoint message used by `tar'. If
3281 you place a dot immediately after the equal sign, it will print a `.'
3282 at each checkpoint(1). For example:
3284 $ tar -c --checkpoint=.1000 /var
3287 The `--checkpoint' option provides a flexible mechanism for
3288 executing arbitrary actions upon hitting checkpoints, see the next
3289 section (*note checkpoints::), for more information on it.
3291 The `--show-omitted-dirs' option, when reading an archive--with
3292 `--list' or `--extract', for example--causes a message to be printed
3293 for each directory in the archive which is skipped. This happens
3294 regardless of the reason for skipping: the directory might not have
3295 been named on the command line (implicitly or explicitly), it might be
3296 excluded by the use of the `--exclude=PATTERN' option, or some other
3299 If `--block-number' (`-R') is used, `tar' prints, along with every
3300 message it would normally produce, the block number within the archive
3301 where the message was triggered. Also, supplementary messages are
3302 triggered when reading blocks full of NULs, or when hitting end of file
3303 on the archive. As of now, if the archive is properly terminated with
3304 a NUL block, the reading of the file may stop before end of file is
3305 met, so the position of end of file will not usually show when
3306 `--block-number' (`-R') is used. Note that GNU `tar' drains the
3307 archive before exiting when reading the archive from a pipe.
3309 This option is especially useful when reading damaged archives, since
3310 it helps pinpoint the damaged sections. It can also be used with
3311 `--list' (`-t') when listing a file-system backup tape, allowing you to
3312 choose among several backup tapes when retrieving a file later, in
3313 favor of the tape where the file appears earliest (closest to the front
3314 of the tape). *Note backup::.
3316 ---------- Footnotes ----------
3318 (1) This is actually a shortcut for `--checkpoint=N
3319 --checkpoint-action=dot'. *Note dot: checkpoints.
3322 File: tar.info, Node: checkpoints, Next: warnings, Prev: verbose, Up: tar invocation
3327 A "checkpoint" is a moment of time before writing Nth record to the
3328 archive (a "write checkpoint"), or before reading Nth record from the
3329 archive (a "read checkpoint"). Checkpoints allow to periodically
3330 execute arbitrary actions.
3332 The checkpoint facility is enabled using the following option:
3335 Schedule checkpoints before writing or reading each Nth record.
3336 The default value for N is 10.
3338 A list of arbitrary "actions" can be executed at each checkpoint.
3339 These actions include: pausing, displaying textual messages, and
3340 executing arbitrary external programs. Actions are defined using the
3341 `--checkpoint-action' option.
3343 `--checkpoint-action=ACTION'
3344 Execute an ACTION at each checkpoint.
3346 The simplest value of ACTION is `echo'. It instructs `tar' to
3347 display the default message on the standard error stream upon arriving
3348 at each checkpoint. The default message is (in POSIX locale) `Write
3349 checkpoint N', for write checkpoints, and `Read checkpoint N', for read
3350 checkpoints. Here, N represents ordinal number of the checkpoint.
3352 In another locales, translated versions of this message are used.
3354 This is the default action, so running:
3356 $ tar -c --checkpoint=1000 --checkpoint-action=echo /var
3360 $ tar -c --checkpoint=1000 /var
3362 The `echo' action also allows to supply a customized message. You
3363 do so by placing an equals sign and the message right after it, e.g.:
3365 --checkpoint-action="echo=Hit %s checkpoint #%u"
3367 The `%s' and `%u' in the above example are "meta-characters". The
3368 `%s' meta-character is replaced with the "type" of the checkpoint:
3369 `write' or `read' (or a corresponding translated version in locales
3370 other than POSIX). The `%u' meta-character is replaced with the
3371 ordinal number of the checkpoint. Thus, the above example could
3372 produce the following output when used with the `--create' option:
3374 tar: Hit write checkpoint #10
3375 tar: Hit write checkpoint #20
3376 tar: Hit write checkpoint #30
3378 Aside from meta-character expansion, the message string is subject to
3379 "unquoting", during which the backslash "escape sequences" are replaced
3380 with their corresponding ASCII characters (*note escape sequences::).
3381 E.g. the following action will produce an audible bell and the message
3382 described above at each checkpoint:
3384 --checkpoint-action='echo=\aHit %s checkpoint #%u'
3386 There is also a special action which produces an audible signal:
3387 `bell'. It is not equivalent to `echo='\a'', because `bell' sends the
3388 bell directly to the console (`/dev/tty'), whereas `echo='\a'' sends it
3389 to the standard error.
3391 The `ttyout=STRING' action outputs STRING to `/dev/tty', so it can
3392 be used even if the standard output is redirected elsewhere. The
3393 STRING is subject to the same modifications as with `echo' action. In
3394 contrast to the latter, `ttyout' does not prepend `tar' executable name
3395 to the string, nor does it output a newline after it. For example, the
3396 following action will print the checkpoint message at the same screen
3397 line, overwriting any previous message:
3399 --checkpoint-action="ttyout=\rHit %s checkpoint #%u"
3401 Another available checkpoint action is `dot' (or `.'). It instructs
3402 `tar' to print a single dot on the standard listing stream, e.g.:
3404 $ tar -c --checkpoint=1000 --checkpoint-action=dot /var
3407 For compatibility with previous GNU `tar' versions, this action can
3408 be abbreviated by placing a dot in front of the checkpoint frequency,
3409 as shown in the previous section.
3411 Yet another action, `sleep', pauses `tar' for a specified amount of
3412 seconds. The following example will stop for 30 seconds at each
3415 $ tar -c --checkpoint=1000 --checkpoint-action=sleep=30
3417 Finally, the `exec' action executes a given external command. For
3420 $ tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint
3422 The supplied command can be any valid command invocation, with or
3423 without additional command line arguments. If it does contain
3424 arguments, don't forget to quote it to prevent it from being split by
3425 the shell. *Note Running External Commands: external, for more detail.
3427 The command gets a copy of `tar''s environment plus the following
3431 GNU `tar' version number.
3434 The name of the archive `tar' is processing.
3436 `TAR_BLOCKING_FACTOR'
3437 Current blocking factor (*note Blocking::).
3440 Number of the checkpoint.
3443 A short option describing the operation `tar' is executing. *Note
3444 Operations::, for a complete list of subcommand options.
3447 Format of the archive being processed. *Note Formats::, for a
3448 complete list of archive format names.
3450 These environment variables can also be passed as arguments to the
3451 command, provided that they are properly escaped, for example:
3454 --checkpoint-action='exec=/sbin/cpoint $TAR_FILENAME'
3456 Notice single quotes to prevent variable names from being expanded by
3457 the shell when invoking `tar'.
3459 Any number of actions can be defined, by supplying several
3460 `--checkpoint-action' options in the command line. For example, the
3461 command below displays two messages, pauses execution for 30 seconds
3462 and executes the `/sbin/cpoint' script:
3464 $ tar -c -f arc.tar \
3465 --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
3466 --checkpoint-action='echo=Sleeping for 30 seconds' \
3467 --checkpoint-action='sleep=30' \
3468 --checkpoint-action='exec=/sbin/cpoint'
3470 This example also illustrates the fact that `--checkpoint-action'
3471 can be used without `--checkpoint'. In this case, the default
3472 checkpoint frequency (at each 10th record) is assumed.
3475 File: tar.info, Node: warnings, Next: interactive, Prev: checkpoints, Up: tar invocation
3477 3.9 Controlling Warning Messages
3478 ================================
3480 Sometimes, while performing the requested task, GNU `tar' notices some
3481 conditions that are not exactly errors, but which the user should be
3482 aware of. When this happens, `tar' issues a "warning message"
3483 describing the condition. Warning messages are output to the standard
3484 error and they do not affect the exit code of `tar' command.
3486 GNU `tar' allows the user to suppress some or all of its warning
3490 Control display of the warning messages identified by KEYWORD. If
3491 KEYWORD starts with the prefix `no-', such messages are
3492 suppressed. Otherwise, they are enabled.
3494 Multiple `--warning' messages accumulate.
3496 The tables below list allowed values for KEYWORD along with the
3497 warning messages they control.
3499 Keywords controlling `tar' operation
3500 ------------------------------------
3503 Enable all warning messages. This is the default.
3506 Disable all warning messages.
3509 `%s: file name read contains nul character'
3512 `A lone zero block at %s'
3514 Keywords applicable for `tar --create'
3515 --------------------------------------
3518 `%s: contains a cache directory tag %s; %s'
3521 `%s: File shrank by %s bytes; padding with zeros'
3524 `%s: file is on a different filesystem; not dumped'
3527 `%s: Unknown file type; file ignored'
3528 `%s: socket ignored'
3532 `%s: file is unchanged; not dumped'
3535 `%s: file is the archive; not dumped'
3538 `%s: File removed before we read it'
3541 `%s: file changed as we read it'
3543 Keywords applicable for `tar --extract'
3544 ---------------------------------------
3547 `%s: implausibly old time stamp %s'
3548 `%s: time stamp %s is %s s in the future'
3551 `Extracting contiguous files as regular files'
3554 `Attempting extraction of symbolic links as hard links'
3557 `%s: Unknown file type '%c', extracted as normal file'
3560 `Current %s is newer or same age'
3563 `Ignoring unknown extended header keyword '%s''
3566 Controls verbose description of failures occurring when trying to
3567 run alternative decompressor programs (*note alternative
3568 decompression programs::). This warning is disabled by default
3569 (unless `--verbose' is used). A common example of what you can get
3570 when using this warning is:
3572 $ tar --warning=decompress-program -x -f archive.Z
3573 tar (child): cannot run compress: No such file or directory
3574 tar (child): trying gzip
3576 This means that `tar' first tried to decompress `archive.Z' using
3577 `compress', and, when that failed, switched to `gzip'.
3580 `Record size = %lu blocks'
3582 Keywords controlling incremental extraction:
3583 --------------------------------------------
3586 `%s: Directory has been renamed from %s'
3587 `%s: Directory has been renamed'
3590 `%s: Directory is new'
3593 `%s: directory is on a different device: not purging'
3596 `Malformed dumpdir: 'X' never used'
3599 File: tar.info, Node: interactive, Next: external, Prev: warnings, Up: tar invocation
3601 3.10 Asking for Confirmation During Operations
3602 ==============================================
3604 Typically, `tar' carries out a command without stopping for further
3605 instructions. In some situations however, you may want to exclude some
3606 files and archive members from the operation (for instance if disk or
3607 storage space is tight). You can do this by excluding certain files
3608 automatically (*note Choosing::), or by performing an operation
3609 interactively, using the `--interactive' (`-w') option. `tar' also
3610 accepts `--confirmation' for this option.
3612 When the `--interactive' (`-w') option is specified, before reading,
3613 writing, or deleting files, `tar' first prints a message for each such
3614 file, telling what operation it intends to take, then asks for
3615 confirmation on the terminal. The actions which require confirmation
3616 include adding a file to the archive, extracting a file from the
3617 archive, deleting a file from the archive, and deleting a file from
3618 disk. To confirm the action, you must type a line of input beginning
3619 with `y'. If your input line begins with anything other than `y',
3620 `tar' skips that file.
3622 If `tar' is reading the archive from the standard input, `tar' opens
3623 the file `/dev/tty' to support the interactive communications.
3625 Verbose output is normally sent to standard output, separate from
3626 other error messages. However, if the archive is produced directly on
3627 standard output, then verbose output is mixed with errors on `stderr'.
3628 Producing the archive on standard output may be used as a way to avoid
3629 using disk space, when the archive is soon to be consumed by another
3630 process reading it, say. Some people felt the need of producing an
3631 archive on stdout, still willing to segregate between verbose output
3632 and error output. A possible approach would be using a named pipe to
3633 receive the archive, and having the consumer process to read from that
3634 named pipe. This has the advantage of letting standard output free to
3635 receive verbose output, all separate from errors.
3638 File: tar.info, Node: external, Prev: interactive, Up: tar invocation
3640 3.11 Running External Commands
3641 ==============================
3643 Certain GNU `tar' operations imply running external commands that you
3644 supply on the command line. One of such operations is checkpointing,
3645 described above (*note checkpoint exec::). Another example of this
3646 feature is the `-I' option, which allows you to supply the program to
3647 use for compressing or decompressing the archive (*note
3648 use-compress-program::).
3650 Whenever such operation is requested, `tar' first splits the
3651 supplied command into words much like the shell does. It then treats
3652 the first word as the name of the program or the shell script to execute
3653 and the rest of words as its command line arguments. The program,
3654 unless given as an absolute file name, is searched in the shell's
3657 Any additional information is normally supplied to external commands
3658 in environment variables, specific to each particular operation. For
3659 example, the `--checkpoint-action=exec' option, defines the
3660 `TAR_ARCHIVE' variable to the name of the archive being worked upon.
3661 You can, should the need be, use these variables in the command line of
3662 the external command. For example:
3664 $ tar -x -f archive.tar \
3665 --checkpoint=exec='printf "%04d in %32s\r" $TAR_CHECKPOINT $TAR_ARCHIVE'
3667 This command prints for each checkpoint its number and the name of the
3668 archive, using the same output line on the screen.
3670 Notice the use of single quotes to prevent variable names from being
3671 expanded by the shell when invoking `tar'.
3674 File: tar.info, Node: operations, Next: Backups, Prev: tar invocation, Up: Top
3676 4 GNU `tar' Operations
3677 **********************
3690 File: tar.info, Node: Basic tar, Next: Advanced tar, Up: operations
3692 4.1 Basic GNU `tar' Operations
3693 ==============================
3695 The basic `tar' operations, `--create' (`-c'), `--list' (`-t') and
3696 `--extract' (`--get', `-x'), are currently presented and described in
3697 the tutorial chapter of this manual. This section provides some
3698 complementary notes for these operations.
3702 Creating an empty archive would have some kind of elegance. One
3703 can initialize an empty archive and later use `--append' (`-r')
3704 for adding all members. Some applications would not welcome
3705 making an exception in the way of adding the first archive member.
3706 On the other hand, many people reported that it is dangerously too
3707 easy for `tar' to destroy a magnetic tape with an empty
3708 archive(1). The two most common errors are:
3710 1. Mistakingly using `create' instead of `extract', when the
3711 intent was to extract the full contents of an archive. This
3712 error is likely: keys `c' and `x' are right next to each
3713 other on the QWERTY keyboard. Instead of being unpacked, the
3714 archive then gets wholly destroyed. When users speak about
3715 "exploding" an archive, they usually mean something else :-).
3717 2. Forgetting the argument to `file', when the intent was to
3718 create an archive with a single file in it. This error is
3719 likely because a tired user can easily add the `f' key to the
3720 cluster of option letters, by the mere force of habit,
3721 without realizing the full consequence of doing so. The
3722 usual consequence is that the single file, which was meant to
3723 be saved, is rather destroyed.
3725 So, recognizing the likelihood and the catastrophic nature of these
3726 errors, GNU `tar' now takes some distance from elegance, and
3727 cowardly refuses to create an archive when `--create' option is
3728 given, there are no arguments besides options, and `--files-from'
3729 (`-T') option is _not_ used. To get around the cautiousness of
3730 GNU `tar' and nevertheless create an archive with nothing in it,
3731 one may still use, as the value for the `--files-from' option, a
3732 file with no names in it, as shown in the following commands:
3734 tar --create --file=empty-archive.tar --files-from=/dev/null
3735 tar -cf empty-archive.tar -T /dev/null
3740 A socket is stored, within a GNU `tar' archive, as a pipe.
3743 GNU `tar' now shows dates as `1996-08-30', while it used to show
3744 them as `Aug 30 1996'. Preferably, people should get used to ISO
3745 8601 dates. Local American dates should be made available again
3746 with full date localization support, once ready. In the meantime,
3747 programs not being localizable for dates should prefer
3748 international dates, that's really the way to go.
3750 Look up `http://www.cl.cam.ac.uk/~mgk25/iso-time.html' if you are
3751 curious, it contains a detailed explanation of the ISO 8601
3755 ---------- Footnotes ----------
3757 (1) This is well described in `Unix-haters Handbook', by Simson
3758 Garfinkel, Daniel Weise & Steven Strassmann, IDG Books, ISBN
3762 File: tar.info, Node: Advanced tar, Next: create options, Prev: Basic tar, Up: operations
3764 4.2 Advanced GNU `tar' Operations
3765 =================================
3767 Now that you have learned the basics of using GNU `tar', you may want
3768 to learn about further ways in which `tar' can help you.
3770 This chapter presents five, more advanced operations which you
3771 probably won't use on a daily basis, but which serve more specialized
3772 functions. We also explain the different styles of options and why you
3773 might want to use one or another, or a combination of them in your `tar'
3774 commands. Additionally, this chapter includes options which allow you
3775 to define the output from `tar' more carefully, and provide help and
3776 error correction in special circumstances.
3788 File: tar.info, Node: Operations, Next: append, Up: Advanced tar
3790 4.2.1 The Five Advanced `tar' Operations
3791 ----------------------------------------
3793 In the last chapter, you learned about the first three operations to
3794 `tar'. This chapter presents the remaining five operations to `tar':
3795 `--append', `--update', `--concatenate', `--delete', and `--compare'.
3797 You are not likely to use these operations as frequently as those
3798 covered in the last chapter; however, since they perform specialized
3799 functions, they are quite useful when you do need to use them. We will
3800 give examples using the same directory and files that you created in
3801 the last chapter. As you may recall, the directory is called
3802 `practice', the files are `jazz', `blues', `folk', and the two archive
3803 files you created are `collection.tar' and `music.tar'.
3805 We will also use the archive files `afiles.tar' and `bfiles.tar'.
3806 The archive `afiles.tar' contains the members `apple', `angst', and
3807 `aspic'; `bfiles.tar' contains the members `./birds', `baboon', and
3810 Unless we state otherwise, all practicing you do and examples you
3811 follow in this chapter will take place in the `practice' directory that
3812 you created in the previous chapter; see *note prepare for examples::.
3813 (Below in this section, we will remind you of the state of the examples
3814 where the last chapter left them.)
3816 The five operations that we will cover in this chapter are:
3820 Add new entries to an archive that already exists.
3824 Add more recent copies of archive members to the end of an
3825 archive, if they exist.
3830 Add one or more pre-existing archives to the end of another
3834 Delete items from an archive (does not work on tapes).
3839 Compare archive members to their counterparts in the file system.
3842 File: tar.info, Node: append, Next: update, Prev: Operations, Up: Advanced tar
3844 4.2.2 How to Add Files to Existing Archives: `--append'
3845 -------------------------------------------------------
3847 If you want to add files to an existing archive, you don't need to
3848 create a new archive; you can use `--append' (`-r'). The archive must
3849 already exist in order to use `--append'. (A related operation is the
3850 `--update' operation; you can use this to add newer versions of archive
3851 members to an existing archive. To learn how to do this with
3852 `--update', *note update::.)
3854 If you use `--append' to add a file that has the same name as an
3855 archive member to an archive containing that archive member, then the
3856 old member is not deleted. What does happen, however, is somewhat
3857 complex. `tar' _allows_ you to have infinite number of files with the
3858 same name. Some operations treat these same-named members no
3859 differently than any other set of archive members: for example, if you
3860 view an archive with `--list' (`-t'), you will see all of those members
3861 listed, with their data modification times, owners, etc.
3863 Other operations don't deal with these members as perfectly as you
3864 might prefer; if you were to use `--extract' to extract the archive,
3865 only the most recently added copy of a member with the same name as
3866 other members would end up in the working directory. This is because
3867 `--extract' extracts an archive in the order the members appeared in
3868 the archive; the most recently archived members will be extracted last.
3869 Additionally, an extracted member will _replace_ a file of the same
3870 name which existed in the directory already, and `tar' will not prompt
3871 you about this(1). Thus, only the most recently archived member will
3872 end up being extracted, as it will replace the one extracted before it,
3875 There exists a special option that allows you to get around this
3876 behavior and extract (or list) only a particular copy of the file.
3877 This is `--occurrence' option. If you run `tar' with this option, it
3878 will extract only the first copy of the file. You may also give this
3879 option an argument specifying the number of copy to be extracted.
3880 Thus, for example if the archive `archive.tar' contained three copies
3881 of file `myfile', then the command
3883 tar --extract --file archive.tar --occurrence=2 myfile
3885 would extract only the second copy. *Note --occurrence: Option
3886 Summary, for the description of `--occurrence' option.
3888 If you want to replace an archive member, use `--delete' to delete
3889 the member you want to remove from the archive, and then use `--append'
3890 to add the member you want to be in the archive. Note that you can not
3891 change the order of the archive; the most recently added member will
3892 still appear last. In this sense, you cannot truly "replace" one
3893 member with another. (Replacing one member with another will not work
3894 on certain types of media, such as tapes; see *note delete:: and *note
3895 Media::, for more information.)
3899 * appending files:: Appending Files to an Archive
3902 ---------- Footnotes ----------
3904 (1) Unless you give it `--keep-old-files' (or `--skip-old-files')
3905 option, or the disk copy is newer than the one in the archive and you
3906 invoke `tar' with `--keep-newer-files' option.
3909 File: tar.info, Node: appending files, Next: multiple, Up: append
3911 4.2.2.1 Appending Files to an Archive
3912 .....................................
3914 The simplest way to add a file to an already existing archive is the
3915 `--append' (`-r') operation, which writes specified files into the
3916 archive whether or not they are already among the archived files.
3918 When you use `--append', you _must_ specify file name arguments, as
3919 there is no default. If you specify a file that already exists in the
3920 archive, another copy of the file will be added to the end of the
3921 archive. As with other operations, the member names of the newly added
3922 files will be exactly the same as their names given on the command
3923 line. The `--verbose' (`-v') option will print out the names of the
3924 files as they are written into the archive.
3926 `--append' cannot be performed on some tape drives, unfortunately,
3927 due to deficiencies in the formats those tape drives use. The archive
3928 must be a valid `tar' archive, or else the results of using this
3929 operation will be unpredictable. *Note Media::.
3931 To demonstrate using `--append' to add a file to an archive, create
3932 a file called `rock' in the `practice' directory. Make sure you are in
3933 the `practice' directory. Then, run the following `tar' command to add
3934 `rock' to `collection.tar':
3936 $ tar --append --file=collection.tar rock
3938 If you now use the `--list' (`-t') operation, you will see that `rock'
3939 has been added to the archive:
3941 $ tar --list --file=collection.tar
3942 -rw-r--r-- me/user 28 1996-10-18 16:31 jazz
3943 -rw-r--r-- me/user 21 1996-09-23 16:44 blues
3944 -rw-r--r-- me/user 20 1996-09-23 16:44 folk
3945 -rw-r--r-- me/user 20 1996-09-23 16:44 rock
3948 File: tar.info, Node: multiple, Prev: appending files, Up: append
3950 4.2.2.2 Multiple Members with the Same Name
3951 ...........................................
3953 You can use `--append' (`-r') to add copies of files which have been
3954 updated since the archive was created. (However, we do not recommend
3955 doing this since there is another `tar' option called `--update'; *Note
3956 update::, for more information. We describe this use of `--append'
3957 here for the sake of completeness.) When you extract the archive, the
3958 older version will be effectively lost. This works because files are
3959 extracted from an archive in the order in which they were archived.
3960 Thus, when the archive is extracted, a file archived later in time will
3961 replace a file of the same name which was archived earlier, even though
3962 the older version of the file will remain in the archive unless you
3963 delete all versions of the file.
3965 Supposing you change the file `blues' and then append the changed
3966 version to `collection.tar'. As you saw above, the original `blues' is
3967 in the archive `collection.tar'. If you change the file and append the
3968 new version of the file to the archive, there will be two copies in the
3969 archive. When you extract the archive, the older version of the file
3970 will be extracted first, and then replaced by the newer version when it
3973 You can append the new, changed copy of the file `blues' to the
3974 archive in this way:
3976 $ tar --append --verbose --file=collection.tar blues
3979 Because you specified the `--verbose' option, `tar' has printed the
3980 name of the file being appended as it was acted on. Now list the
3981 contents of the archive:
3983 $ tar --list --verbose --file=collection.tar
3984 -rw-r--r-- me/user 28 1996-10-18 16:31 jazz
3985 -rw-r--r-- me/user 21 1996-09-23 16:44 blues
3986 -rw-r--r-- me/user 20 1996-09-23 16:44 folk
3987 -rw-r--r-- me/user 20 1996-09-23 16:44 rock
3988 -rw-r--r-- me/user 58 1996-10-24 18:30 blues
3990 The newest version of `blues' is now at the end of the archive (note
3991 the different creation dates and file sizes). If you extract the
3992 archive, the older version of the file `blues' will be replaced by the
3993 newer version. You can confirm this by extracting the archive and
3994 running `ls' on the directory.
3996 If you wish to extract the first occurrence of the file `blues' from
3997 the archive, use `--occurrence' option, as shown in the following
4000 $ tar --extract -vv --occurrence --file=collection.tar blues
4001 -rw-r--r-- me/user 21 1996-09-23 16:44 blues
4003 *Note Writing::, for more information on `--extract' and see *note
4004 -occurrence: Option Summary, for a description of `--occurrence' option.
4007 File: tar.info, Node: update, Next: concatenate, Prev: append, Up: Advanced tar
4009 4.2.3 Updating an Archive
4010 -------------------------
4012 In the previous section, you learned how to use `--append' to add a
4013 file to an existing archive. A related operation is `--update' (`-u').
4014 The `--update' operation updates a `tar' archive by comparing the date
4015 of the specified archive members against the date of the file with the
4016 same name. If the file has been modified more recently than the
4017 archive member, then the newer version of the file is added to the
4018 archive (as with `--append').
4020 Unfortunately, you cannot use `--update' with magnetic tape drives.
4021 The operation will fail.
4023 Both `--update' and `--append' work by adding to the end of the
4024 archive. When you extract a file from the archive, only the version
4025 stored last will wind up in the file system, unless you use the
4026 `--backup' option. *Note multiple::, for a detailed discussion.
4033 File: tar.info, Node: how to update, Up: update
4035 4.2.3.1 How to Update an Archive Using `--update'
4036 .................................................
4038 You must use file name arguments with the `--update' (`-u') operation.
4039 If you don't specify any files, `tar' won't act on any files and won't
4040 tell you that it didn't do anything (which may end up confusing you).
4042 To see the `--update' option at work, create a new file,
4043 `classical', in your practice directory, and some extra text to the
4044 file `blues', using any text editor. Then invoke `tar' with the
4045 `update' operation and the `--verbose' (`-v') option specified, using
4046 the names of all the files in the `practice' directory as file name
4049 $ tar --update -v -f collection.tar blues folk rock classical
4054 Because we have specified verbose mode, `tar' prints out the names of
4055 the files it is working on, which in this case are the names of the
4056 files that needed to be updated. If you run `tar --list' and look at
4057 the archive, you will see `blues' and `classical' at its end. There
4058 will be a total of two versions of the member `blues'; the one at the
4059 end will be newer and larger, since you added text before updating it.
4061 The reason `tar' does not overwrite the older file when updating it
4062 is because writing to the middle of a section of tape is a difficult
4063 process. Tapes are not designed to go backward. *Note Media::, for
4064 more information about tapes.
4066 `--update' (`-u') is not suitable for performing backups for two
4067 reasons: it does not change directory content entries, and it lengthens
4068 the archive every time it is used. The GNU `tar' options intended
4069 specifically for backups are more efficient. If you need to run
4070 backups, please consult *note Backups::.
4073 File: tar.info, Node: concatenate, Next: delete, Prev: update, Up: Advanced tar
4075 4.2.4 Combining Archives with `--concatenate'
4076 ---------------------------------------------
4078 Sometimes it may be convenient to add a second archive onto the end of
4079 an archive rather than adding individual files to the archive. To add
4080 one or more archives to the end of another archive, you should use the
4081 `--concatenate' (`--catenate', `-A') operation.
4083 To use `--concatenate', give the first archive with `--file' option
4084 and name the rest of archives to be concatenated on the command line.
4085 The members, and their member names, will be copied verbatim from those
4086 archives to the first one(1). The new, concatenated archive will be
4087 called by the same name as the one given with the `--file' option. As
4088 usual, if you omit `--file', `tar' will use the value of the environment
4089 variable `TAPE', or, if this has not been set, the default archive name.
4091 To demonstrate how `--concatenate' works, create two small archives
4092 called `bluesrock.tar' and `folkjazz.tar', using the relevant files
4095 $ tar -cvf bluesrock.tar blues rock
4098 $ tar -cvf folkjazz.tar folk jazz
4102 If you like, You can run `tar --list' to make sure the archives contain
4103 what they are supposed to:
4105 $ tar -tvf bluesrock.tar
4106 -rw-r--r-- melissa/user 105 1997-01-21 19:42 blues
4107 -rw-r--r-- melissa/user 33 1997-01-20 15:34 rock
4108 $ tar -tvf jazzfolk.tar
4109 -rw-r--r-- melissa/user 20 1996-09-23 16:44 folk
4110 -rw-r--r-- melissa/user 65 1997-01-30 14:15 jazz
4112 We can concatenate these two archives with `tar':
4115 $ tar --concatenate --file=bluesrock.tar jazzfolk.tar
4117 If you now list the contents of the `bluesrock.tar', you will see
4118 that now it also contains the archive members of `jazzfolk.tar':
4120 $ tar --list --file=bluesrock.tar
4126 When you use `--concatenate', the source and target archives must
4127 already exist and must have been created using compatible format
4128 parameters. Notice, that `tar' does not check whether the archives it
4129 concatenates have compatible formats, it does not even check if the
4130 files are really tar archives.
4132 Like `--append' (`-r'), this operation cannot be performed on some
4133 tape drives, due to deficiencies in the formats those tape drives use.
4135 It may seem more intuitive to you to want or try to use `cat' to
4136 concatenate two archives instead of using the `--concatenate'
4137 operation; after all, `cat' is the utility for combining files.
4139 However, `tar' archives incorporate an end-of-file marker which must
4140 be removed if the concatenated archives are to be read properly as one
4141 archive. `--concatenate' removes the end-of-archive marker from the
4142 target archive before each new archive is appended. If you use `cat'
4143 to combine the archives, the result will not be a valid `tar' format
4144 archive. If you need to retrieve files from an archive that was added
4145 to using the `cat' utility, use the `--ignore-zeros' (`-i') option.
4146 *Note Ignore Zeros::, for further information on dealing with archives
4147 improperly combined using the `cat' shell utility.
4149 ---------- Footnotes ----------
4151 (1) This can cause multiple members to have the same name. For
4152 information on how this affects reading the archive, see *note
4156 File: tar.info, Node: delete, Next: compare, Prev: concatenate, Up: Advanced tar
4158 4.2.5 Removing Archive Members Using `--delete'
4159 -----------------------------------------------
4161 You can remove members from an archive by using the `--delete' option.
4162 Specify the name of the archive with `--file' (`-f') and then specify
4163 the names of the members to be deleted; if you list no member names,
4164 nothing will be deleted. The `--verbose' option will cause `tar' to
4165 print the names of the members as they are deleted. As with
4166 `--extract', you must give the exact member names when using `tar
4167 --delete'. `--delete' will remove all versions of the named file from
4168 the archive. The `--delete' operation can run very slowly.
4170 Unlike other operations, `--delete' has no short form.
4172 This operation will rewrite the archive. You can only use
4173 `--delete' on an archive if the archive device allows you to write to
4174 any point on the media, such as a disk; because of this, it does not
4175 work on magnetic tapes. Do not try to delete an archive member from a
4176 magnetic tape; the action will not succeed, and you will be likely to
4177 scramble the archive and damage your tape. There is no safe way
4178 (except by completely re-writing the archive) to delete files from most
4179 kinds of magnetic tape. *Note Media::.
4181 To delete all versions of the file `blues' from the archive
4182 `collection.tar' in the `practice' directory, make sure you are in that
4183 directory, and then,
4185 $ tar --list --file=collection.tar
4190 $ tar --delete --file=collection.tar blues
4191 $ tar --list --file=collection.tar
4196 The `--delete' option has been reported to work properly when `tar'
4197 acts as a filter from `stdin' to `stdout'.
4200 File: tar.info, Node: compare, Prev: delete, Up: Advanced tar
4202 4.2.6 Comparing Archive Members with the File System
4203 ----------------------------------------------------
4205 The `--compare' (`-d'), or `--diff' operation compares specified
4206 archive members against files with the same names, and then reports
4207 differences in file size, mode, owner, modification date and contents.
4208 You should _only_ specify archive member names, not file names. If you
4209 do not name any members, then `tar' will compare the entire archive.
4210 If a file is represented in the archive but does not exist in the file
4211 system, `tar' reports a difference.
4213 You have to specify the record size of the archive when modifying an
4214 archive with a non-default record size.
4216 `tar' ignores files in the file system that do not have
4217 corresponding members in the archive.
4219 The following example compares the archive members `rock', `blues'
4220 and `funk' in the archive `bluesrock.tar' with files of the same name
4221 in the file system. (Note that there is no file, `funk'; `tar' will
4222 report an error message.)
4224 $ tar --compare --file=bluesrock.tar rock blues funk
4227 tar: funk not found in archive
4229 The spirit behind the `--compare' (`--diff', `-d') option is to
4230 check whether the archive represents the current state of files on
4231 disk, more than validating the integrity of the archive media. For
4232 this latter goal, see *note verify::.
4235 File: tar.info, Node: create options, Next: extract options, Prev: Advanced tar, Up: operations
4237 4.3 Options Used by `--create'
4238 ==============================
4240 The previous chapter described the basics of how to use `--create'
4241 (`-c') to create an archive from a set of files. *Note create::. This
4242 section described advanced options to be used with `--create'.
4246 * override:: Overriding File Metadata.
4247 * Ignore Failed Read::
4250 File: tar.info, Node: override, Next: Ignore Failed Read, Up: create options
4252 4.3.1 Overriding File Metadata
4253 ------------------------------
4255 As described above, a `tar' archive keeps, for each member it contains,
4256 its "metadata", such as modification time, mode and ownership of the
4257 file. GNU `tar' allows to replace these data with other values when
4258 adding files to the archive. The options described in this section
4259 affect creation of archives of any type. For POSIX archives, see also
4260 *note PAX keywords::, for additional ways of controlling metadata,
4261 stored in the archive.
4263 `--mode=PERMISSIONS'
4264 When adding files to an archive, `tar' will use PERMISSIONS for
4265 the archive members, rather than the permissions from the files.
4266 PERMISSIONS can be specified either as an octal number or as
4267 symbolic permissions, like with `chmod' (*Note Permissions:
4268 (fileutils)File permissions. This reference also has useful
4269 information for those not being overly familiar with the UNIX
4270 permission system). Using latter syntax allows for more
4271 flexibility. For example, the value `a+rw' adds read and write
4272 permissions for everybody, while retaining executable bits on
4273 directories or on any other file already marked as executable:
4275 $ tar -c -f archive.tar --mode='a+rw' .
4278 When adding files to an archive, `tar' will use DATE as the
4279 modification time of members when creating archives, instead of
4280 their actual modification times. The argument DATE can be either
4281 a textual date representation in almost arbitrary format (*note
4282 Date input formats::) or a name of an existing file, starting with
4283 `/' or `.'. In the latter case, the modification time of that
4286 The following example will set the modification date to 00:00:00,
4289 $ tar -c -f archive.tar --mtime='1970-01-01' .
4291 When used with `--verbose' (*note verbose tutorial::) GNU `tar'
4292 will try to convert the specified date back to its textual
4293 representation and compare it with the one given with `--mtime'
4294 options. If the two dates differ, `tar' will print a warning
4295 saying what date it will use. This is to help user ensure he is
4296 using the right date.
4300 $ tar -c -f archive.tar -v --mtime=yesterday .
4301 tar: Option --mtime: Treating date 'yesterday' as 2006-06-20
4306 Specifies that `tar' should use USER as the owner of members when
4307 creating archives, instead of the user associated with the source
4310 If USER contains a colon, it is taken to be of the form NAME:ID
4311 where a nonempty NAME specifies the user name and a nonempty ID
4312 specifies the decimal numeric user ID. If USER does not contain a
4313 colon, it is taken to be a user number if it is one or more
4314 decimal digits; otherwise it is taken to be a user name.
4316 If a name is given but no number, the number is inferred from the
4317 current host's user database if possible, and the file's user
4318 number is used otherwise. If a number is given but no name, the
4319 name is inferred from the number if possible, and an empty name is
4320 used otherwise. If both name and number are given, the user
4321 database is not consulted, and the name and number need not be
4322 valid on the current host.
4324 There is no value indicating a missing number, and `0' usually
4325 means `root'. Some people like to force `0' as the value to offer
4326 in their distributions for the owner of files, because the `root'
4327 user is anonymous anyway, so that might as well be the owner of
4328 anonymous archives. For example:
4330 $ tar -c -f archive.tar --owner=0 .
4334 $ tar -c -f archive.tar --owner=root .
4337 Files added to the `tar' archive will have a group ID of GROUP,
4338 rather than the group from the source file. As with `--owner',
4339 the argument GROUP can be an existing group symbolic name, or a
4340 decimal numeric group ID, or NAME:ID.
4343 File: tar.info, Node: Ignore Failed Read, Prev: override, Up: create options
4345 4.3.2 Ignore Fail Read
4346 ----------------------
4348 `--ignore-failed-read'
4349 Do not exit with nonzero on unreadable files or directories.
4352 File: tar.info, Node: extract options, Next: backup, Prev: create options, Up: operations
4354 4.4 Options Used by `--extract'
4355 ===============================
4357 The previous chapter showed how to use `--extract' to extract an
4358 archive into the file system. Various options cause `tar' to extract
4359 more information than just file contents, such as the owner, the
4360 permissions, the modification date, and so forth. This section
4361 presents options to be used with `--extract' when certain special
4362 considerations arise. You may review the information presented in
4363 *note extract:: for more basic information about the `--extract'
4368 * Reading:: Options to Help Read Archives
4369 * Writing:: Changing How `tar' Writes Files
4370 * Scarce:: Coping with Scarce Resources
4373 File: tar.info, Node: Reading, Next: Writing, Up: extract options
4375 4.4.1 Options to Help Read Archives
4376 -----------------------------------
4378 Normally, `tar' will request data in full record increments from an
4379 archive storage device. If the device cannot return a full record,
4380 `tar' will report an error. However, some devices do not always return
4381 full records, or do not require the last record of an archive to be
4382 padded out to the next record boundary. To keep reading until you
4383 obtain a full record, or to accept an incomplete record if it contains
4384 an end-of-archive marker, specify the `--read-full-records' (`-B')
4385 option in conjunction with the `--extract' or `--list' operations.
4388 The `--read-full-records' (`-B') option is turned on by default when
4389 `tar' reads an archive from standard input, or from a remote machine.
4390 This is because on BSD Unix systems, attempting to read a pipe returns
4391 however much happens to be in the pipe, even if it is less than was
4392 requested. If this option were not enabled, `tar' would fail as soon
4393 as it read an incomplete record from the pipe.
4395 If you're not sure of the blocking factor of an archive, you can
4396 read the archive by specifying `--read-full-records' (`-B') and
4397 `--blocking-factor=512-SIZE' (`-b 512-SIZE'), using a blocking factor
4398 larger than what the archive uses. This lets you avoid having to
4399 determine the blocking factor of an archive. *Note Blocking Factor::.
4403 * read full records::
4407 File: tar.info, Node: read full records, Next: Ignore Zeros, Up: Reading
4409 Reading Full Records
4410 ....................
4412 `--read-full-records'
4415 Use in conjunction with `--extract' (`--get', `-x') to read an
4416 archive which contains incomplete records, or one which has a
4417 blocking factor less than the one specified.
4420 File: tar.info, Node: Ignore Zeros, Prev: read full records, Up: Reading
4422 Ignoring Blocks of Zeros
4423 ........................
4425 Normally, `tar' stops reading when it encounters a block of zeros
4426 between file entries (which usually indicates the end of the archive).
4427 `--ignore-zeros' (`-i') allows `tar' to completely read an archive
4428 which contains a block of zeros before the end (i.e., a damaged
4429 archive, or one that was created by concatenating several archives
4432 The `--ignore-zeros' (`-i') option is turned off by default because
4433 many versions of `tar' write garbage after the end-of-archive entry,
4434 since that part of the media is never supposed to be read. GNU `tar'
4435 does not write after the end of an archive, but seeks to maintain
4436 compatibility among archiving utilities.
4440 To ignore blocks of zeros (i.e., end-of-archive entries) which may
4441 be encountered while reading an archive. Use in conjunction with
4442 `--extract' or `--list'.
4445 File: tar.info, Node: Writing, Next: Scarce, Prev: Reading, Up: extract options
4447 4.4.2 Changing How `tar' Writes Files
4448 -------------------------------------
4450 _(This message will disappear, once this node revised.)_
4454 * Dealing with Old Files::
4455 * Overwrite Old Files::
4457 * Keep Newer Files::
4459 * Recursive Unlink::
4460 * Data Modification Times::
4461 * Setting Access Permissions::
4462 * Directory Modification Times and Permissions::
4463 * Writing to Standard Output::
4464 * Writing to an External Program::
4468 File: tar.info, Node: Dealing with Old Files, Next: Overwrite Old Files, Up: Writing
4470 Options Controlling the Overwriting of Existing Files
4471 .....................................................
4473 When extracting files, if `tar' discovers that the extracted file
4474 already exists, it normally replaces the file by removing it before
4475 extracting it, to prevent confusion in the presence of hard or symbolic
4476 links. (If the existing file is a symbolic link, it is removed, not
4477 followed.) However, if a directory cannot be removed because it is
4478 nonempty, `tar' normally overwrites its metadata (ownership,
4479 permission, etc.). The `--overwrite-dir' option enables this default
4480 behavior. To be more cautious and preserve the metadata of such a
4481 directory, use the `--no-overwrite-dir' option.
4483 To be even more cautious and prevent existing files from being
4484 replaced, use the `--keep-old-files' (`-k') option. It causes `tar' to
4485 refuse to replace or update a file that already exists, i.e., a file
4486 with the same name as an archive member prevents extraction of that
4487 archive member. Instead, it reports an error. For example:
4491 $ tar -x -k -f archive.tar
4492 tar: blues: Cannot open: File exists
4493 tar: Exiting with failure status due to previous errors
4495 If you wish to preserve old files untouched, but don't want `tar' to
4496 treat them as errors, use the `--skip-old-files' option. This option
4497 causes `tar' to silently skip extracting over existing files.
4499 To be more aggressive about altering existing files, use the
4500 `--overwrite' option. It causes `tar' to overwrite existing files and
4501 to follow existing symbolic links when extracting.
4503 Some people argue that GNU `tar' should not hesitate to overwrite
4504 files with other files when extracting. When extracting a `tar'
4505 archive, they expect to see a faithful copy of the state of the file
4506 system when the archive was created. It is debatable that this would
4507 always be a proper behavior. For example, suppose one has an archive
4508 in which `usr/local' is a link to `usr/local2'. Since then, maybe the
4509 site removed the link and renamed the whole hierarchy from
4510 `/usr/local2' to `/usr/local'. Such things happen all the time. I
4511 guess it would not be welcome at all that GNU `tar' removes the whole
4512 hierarchy just to make room for the link to be reinstated (unless it
4513 _also_ simultaneously restores the full `/usr/local2', of course!) GNU
4514 `tar' is indeed able to remove a whole hierarchy to reestablish a
4515 symbolic link, for example, but _only if_ `--recursive-unlink' is
4516 specified to allow this behavior. In any case, single files are
4519 Finally, the `--unlink-first' (`-U') option can improve performance
4520 in some cases by causing `tar' to remove files unconditionally before
4524 File: tar.info, Node: Overwrite Old Files, Next: Keep Old Files, Prev: Dealing with Old Files, Up: Writing
4530 Overwrite existing files and directory metadata when extracting
4531 files from an archive.
4533 This causes `tar' to write extracted files into the file system
4534 without regard to the files already on the system; i.e., files
4535 with the same names as archive members are overwritten when the
4536 archive is extracted. It also causes `tar' to extract the
4537 ownership, permissions, and time stamps onto any preexisting files
4538 or directories. If the name of a corresponding file name is a
4539 symbolic link, the file pointed to by the symbolic link will be
4540 overwritten instead of the symbolic link itself (if this is
4541 possible). Moreover, special devices, empty directories and even
4542 symbolic links are automatically removed if they are in the way of
4545 Be careful when using the `--overwrite' option, particularly when
4546 combined with the `--absolute-names' (`-P') option, as this
4547 combination can change the contents, ownership or permissions of
4548 any file on your system. Also, many systems do not take kindly to
4549 overwriting files that are currently being executed.
4552 Overwrite the metadata of directories when extracting files from an
4553 archive, but remove other files before extracting.
4556 File: tar.info, Node: Keep Old Files, Next: Keep Newer Files, Prev: Overwrite Old Files, Up: Writing
4561 GNU `tar' provides two options to control its actions in a situation
4562 when it is about to extract a file which already exists on disk.
4566 Do not replace existing files from archive. When such a file is
4567 encountered, `tar' issues an error message. Upon end of
4568 extraction, `tar' exits with code 2 (*note exit status::).
4571 Do not replace existing files from archive, but do not treat that
4572 as error. Such files are silently skipped and do not affect `tar'
4575 Additional verbosity can be obtained using
4576 `--warning=existing-file' together with that option (*note
4580 File: tar.info, Node: Keep Newer Files, Next: Unlink First, Prev: Keep Old Files, Up: Writing
4585 `--keep-newer-files'
4586 Do not replace existing files that are newer than their archive
4587 copies. This option is meaningless with `--list' (`-t').
4590 File: tar.info, Node: Unlink First, Next: Recursive Unlink, Prev: Keep Newer Files, Up: Writing
4597 Remove files before extracting over them. This can make `tar' run
4598 a bit faster if you know in advance that the extracted files all
4599 need to be removed. Normally this option slows `tar' down
4600 slightly, so it is disabled by default.
4603 File: tar.info, Node: Recursive Unlink, Next: Data Modification Times, Prev: Unlink First, Up: Writing
4608 `--recursive-unlink'
4609 When this option is specified, try removing files and directory
4610 hierarchies before extracting over them. _This is a dangerous
4613 If you specify the `--recursive-unlink' option, `tar' removes
4614 _anything_ that keeps you from extracting a file as far as current
4615 permissions will allow it. This could include removal of the contents
4616 of a full directory hierarchy.
4619 File: tar.info, Node: Data Modification Times, Next: Setting Access Permissions, Prev: Recursive Unlink, Up: Writing
4621 Setting Data Modification Times
4622 ...............................
4624 Normally, `tar' sets the data modification times of extracted files to
4625 the corresponding times recorded for the files in the archive, but
4626 limits the permissions of extracted files by the current `umask'
4629 To set the data modification times of extracted files to the time
4630 when the files were extracted, use the `--touch' (`-m') option in
4631 conjunction with `--extract' (`--get', `-x').
4635 Sets the data modification time of extracted archive members to
4636 the time they were extracted, not the time recorded for them in
4637 the archive. Use in conjunction with `--extract' (`--get', `-x').
4640 File: tar.info, Node: Setting Access Permissions, Next: Directory Modification Times and Permissions, Prev: Data Modification Times, Up: Writing
4642 Setting Access Permissions
4643 ..........................
4645 To set the modes (access permissions) of extracted files to those
4646 recorded for those files in the archive, use `--same-permissions' in
4647 conjunction with the `--extract' (`--get', `-x') operation.
4649 `--preserve-permissions'
4650 `--same-permissions'
4652 Set modes of extracted archive members to those recorded in the
4653 archive, instead of current umask settings. Use in conjunction
4654 with `--extract' (`--get', `-x').
4657 File: tar.info, Node: Directory Modification Times and Permissions, Next: Writing to Standard Output, Prev: Setting Access Permissions, Up: Writing
4659 Directory Modification Times and Permissions
4660 ............................................
4662 After successfully extracting a file member, GNU `tar' normally
4663 restores its permissions and modification times, as described in the
4664 previous sections. This cannot be done for directories, because after
4665 extracting a directory `tar' will almost certainly extract files into
4666 that directory and this will cause the directory modification time to
4667 be updated. Moreover, restoring that directory permissions may not
4668 permit file creation within it. Thus, restoring directory permissions
4669 and modification times must be delayed at least until all files have
4670 been extracted into that directory. GNU `tar' restores directories
4671 using the following approach.
4673 The extracted directories are created with the mode specified in the
4674 archive, as modified by the umask of the user, which gives sufficient
4675 permissions to allow file creation. The meta-information about the
4676 directory is recorded in the temporary list of directories. When
4677 preparing to extract next archive member, GNU `tar' checks if the
4678 directory prefix of this file contains the remembered directory. If it
4679 does not, the program assumes that all files have been extracted into
4680 that directory, restores its modification time and permissions and
4681 removes its entry from the internal list. This approach allows to
4682 correctly restore directory meta-information in the majority of cases,
4683 while keeping memory requirements sufficiently small. It is based on
4684 the fact, that most `tar' archives use the predefined order of members:
4685 first the directory, then all the files and subdirectories in that
4688 However, this is not always true. The most important exception are
4689 incremental archives (*note Incremental Dumps::). The member order in
4690 an incremental archive is reversed: first all directory members are
4691 stored, followed by other (non-directory) members. So, when extracting
4692 from incremental archives, GNU `tar' alters the above procedure. It
4693 remembers all restored directories, and restores their meta-data only
4694 after the entire archive has been processed. Notice, that you do not
4695 need to specify any special options for that, as GNU `tar'
4696 automatically detects archives in incremental format.
4698 There may be cases, when such processing is required for normal
4699 archives too. Consider the following example:
4701 $ tar --no-recursion -cvf archive \
4702 foo foo/file1 bar bar/file foo/file2
4709 During the normal operation, after encountering `bar' GNU `tar' will
4710 assume that all files from the directory `foo' were already extracted
4711 and will therefore restore its timestamp and permission bits. However,
4712 after extracting `foo/file2' the directory timestamp will be offset
4715 To correctly restore directory meta-information in such cases, use
4716 the `--delay-directory-restore' command line option:
4718 `--delay-directory-restore'
4719 Delays restoring of the modification times and permissions of
4720 extracted directories until the end of extraction. This way,
4721 correct meta-information is restored even if the archive has
4722 unusual member ordering.
4724 `--no-delay-directory-restore'
4725 Cancel the effect of the previous `--delay-directory-restore'.
4726 Use this option if you have used `--delay-directory-restore' in
4727 `TAR_OPTIONS' variable (*note TAR_OPTIONS::) and wish to
4728 temporarily disable it.
4731 File: tar.info, Node: Writing to Standard Output, Next: Writing to an External Program, Prev: Directory Modification Times and Permissions, Up: Writing
4733 Writing to Standard Output
4734 ..........................
4736 To write the extracted files to the standard output, instead of
4737 creating the files on the file system, use `--to-stdout' (`-O') in
4738 conjunction with `--extract' (`--get', `-x'). This option is useful if
4739 you are extracting files to send them through a pipe, and do not need to
4740 preserve them in the file system. If you extract multiple members,
4741 they appear on standard output concatenated, in the order they are
4742 found in the archive.
4746 Writes files to the standard output. Use only in conjunction with
4747 `--extract' (`--get', `-x'). When this option is used, instead of
4748 creating the files specified, `tar' writes the contents of the
4749 files extracted to its standard output. This may be useful if you
4750 are only extracting the files in order to send them through a
4751 pipe. This option is meaningless with `--list' (`-t').
4753 This can be useful, for example, if you have a tar archive containing
4754 a big file and don't want to store the file on disk before processing
4755 it. You can use a command like this:
4757 tar -xOzf foo.tgz bigfile | process
4759 or even like this if you want to process the concatenation of the
4762 tar -xOzf foo.tgz bigfile1 bigfile2 | process
4764 However, `--to-command' may be more convenient for use with multiple
4765 files. See the next section.
4768 File: tar.info, Node: Writing to an External Program, Next: remove files, Prev: Writing to Standard Output, Up: Writing
4770 Writing to an External Program
4771 ..............................
4773 You can instruct `tar' to send the contents of each extracted file to
4774 the standard input of an external program:
4776 `--to-command=COMMAND'
4777 Extract files and pipe their contents to the standard input of
4778 COMMAND. When this option is used, instead of creating the files
4779 specified, `tar' invokes COMMAND and pipes the contents of the
4780 files to its standard output. The COMMAND may contain command
4781 line arguments (see *note Running External Commands: external, for
4784 Notice, that COMMAND is executed once for each regular file
4785 extracted. Non-regular files (directories, etc.) are ignored when
4786 this option is used.
4788 The command can obtain the information about the file it processes
4789 from the following environment variables:
4792 Type of the file. It is a single letter with the following meaning:
4801 Currently only regular files are supported.
4804 File mode, an octal number.
4807 The name of the file.
4810 Name of the file as stored in the archive.
4813 Name of the file owner.
4816 Name of the file owner group.
4819 Time of last access. It is a decimal number, representing seconds
4820 since the Epoch. If the archive provides times with nanosecond
4821 precision, the nanoseconds are appended to the timestamp after a
4825 Time of last modification.
4828 Time of last status change.
4834 UID of the file owner.
4837 GID of the file owner.
4839 Additionally, the following variables contain information about tar
4840 mode and the archive being processed:
4843 GNU `tar' version number.
4846 The name of the archive `tar' is processing.
4848 `TAR_BLOCKING_FACTOR'
4849 Current blocking factor (*note Blocking::).
4852 Ordinal number of the volume `tar' is processing.
4855 Format of the archive being processed. *Note Formats::, for a
4856 complete list of archive format names.
4858 These variables are defined prior to executing the command, so you
4859 can pass them as arguments, if you prefer. For example, if the command
4860 PROC takes the member name and size as its arguments, then you could do:
4862 $ tar -x -f archive.tar \
4863 --to-command='proc $TAR_FILENAME $TAR_SIZE'
4865 Notice single quotes to prevent variable names from being expanded by
4866 the shell when invoking `tar'.
4868 If COMMAND exits with a non-0 status, `tar' will print an error
4869 message similar to the following:
4871 tar: 2345: Child returned status 1
4873 Here, `2345' is the PID of the finished process.
4875 If this behavior is not wanted, use `--ignore-command-error':
4877 `--ignore-command-error'
4878 Ignore exit codes of subprocesses. Notice that if the program
4879 exits on signal or otherwise terminates abnormally, the error
4880 message will be printed even if this option is used.
4882 `--no-ignore-command-error'
4883 Cancel the effect of any previous `--ignore-command-error' option.
4884 This option is useful if you have set `--ignore-command-error' in
4885 `TAR_OPTIONS' (*note TAR_OPTIONS::) and wish to temporarily cancel
4889 File: tar.info, Node: remove files, Prev: Writing to an External Program, Up: Writing
4895 Remove files after adding them to the archive.
4898 File: tar.info, Node: Scarce, Prev: Writing, Up: extract options
4900 4.4.3 Coping with Scarce Resources
4901 ----------------------------------
4903 _(This message will disappear, once this node revised.)_
4911 File: tar.info, Node: Starting File, Next: Same Order, Up: Scarce
4916 `--starting-file=NAME'
4918 Starts an operation in the middle of an archive. Use in
4919 conjunction with `--extract' (`--get', `-x') or `--list' (`-t').
4921 If a previous attempt to extract files failed due to lack of disk
4922 space, you can use `--starting-file=NAME' (`-K NAME') to start
4923 extracting only after member NAME of the archive. This assumes, of
4924 course, that there is now free space, or that you are now extracting
4925 into a different file system. (You could also choose to suspend `tar',
4926 remove unnecessary files from the file system, and then resume the same
4927 `tar' operation. In this case, `--starting-file' is not necessary.)
4928 See also *note interactive::, and *note exclude::.
4931 File: tar.info, Node: Same Order, Prev: Starting File, Up: Scarce
4939 To process large lists of file names on machines with small
4940 amounts of memory. Use in conjunction with `--compare' (`--diff',
4941 `-d'), `--list' (`-t') or `--extract' (`--get', `-x').
4943 The `--same-order' (`--preserve-order', `-s') option tells `tar'
4944 that the list of file names to be listed or extracted is sorted in the
4945 same order as the files in the archive. This allows a large list of
4946 names to be used, even on a small machine that would not otherwise be
4947 able to hold all the names in memory at the same time. Such a sorted
4948 list can easily be created by running `tar -t' on the archive and
4951 This option is probably never needed on modern computer systems.
4954 File: tar.info, Node: backup, Next: Applications, Prev: extract options, Up: operations
4959 GNU `tar' offers options for making backups of files before writing new
4960 versions. These options control the details of these backups. They
4961 may apply to the archive itself before it is created or rewritten, as
4962 well as individual extracted members. Other GNU programs (`cp',
4963 `install', `ln', and `mv', for example) offer similar options.
4965 Backup options may prove unexpectedly useful when extracting archives
4966 containing many members having identical name, or when extracting
4967 archives on systems having file name limitations, making different
4968 members appear as having similar names through the side-effect of name
4971 When any existing file is backed up before being overwritten by
4972 extraction, then clashing files are automatically be renamed to be
4973 unique, and the true name is kept for only the last file of a series of
4974 clashing files. By using verbose mode, users may track exactly what
4977 At the detail level, some decisions are still experimental, and may
4978 change in the future, we are waiting comments from our users. So,
4979 please do not learn to depend blindly on the details of the backup
4980 features. For example, currently, directories themselves are never
4981 renamed through using these options, so, extracting a file over a
4982 directory still has good chances to fail. Also, backup options apply
4983 to created archives, not only to extracted members. For created
4984 archives, backups will not be attempted when the archive is a block or
4985 character device, or when it refers to a remote file.
4987 For the sake of simplicity and efficiency, backups are made by
4988 renaming old files prior to creation or extraction, and not by copying.
4989 The original name is restored if the file creation fails. If a failure
4990 occurs after a partial extraction of a file, both the backup and the
4991 partially extracted file are kept.
4994 Back up files that are about to be overwritten or removed.
4995 Without this option, the original versions are destroyed.
4997 Use METHOD to determine the type of backups made. If METHOD is
4998 not specified, use the value of the `VERSION_CONTROL' environment
4999 variable. And if `VERSION_CONTROL' is not set, use the `existing'
5002 This option corresponds to the Emacs variable `version-control';
5003 the same values for METHOD are accepted as in Emacs. This option
5004 also allows more descriptive names. The valid METHODs are:
5008 Always make numbered backups.
5012 Make numbered backups of files that already have them, simple
5013 backups of the others.
5017 Always make simple backups.
5021 Append SUFFIX to each backup file made with `--backup'. If this
5022 option is not specified, the value of the `SIMPLE_BACKUP_SUFFIX'
5023 environment variable is used. And if `SIMPLE_BACKUP_SUFFIX' is not
5024 set, the default is `~', just as in Emacs.
5028 File: tar.info, Node: Applications, Next: looking ahead, Prev: backup, Up: operations
5030 4.6 Notable `tar' Usages
5031 ========================
5033 _(This message will disappear, once this node revised.)_
5035 You can easily use archive files to transport a group of files from one
5036 system to another: put all relevant files into an archive on one
5037 computer system, transfer the archive to another system, and extract
5038 the contents there. The basic transfer medium might be magnetic tape,
5039 Internet FTP, or even electronic mail (though you must encode the
5040 archive with `uuencode' in order to transport it properly by mail).
5041 Both machines do not have to use the same operating system, as long as
5042 they both support the `tar' program.
5044 For example, here is how you might copy a directory's contents from
5045 one disk to another, while preserving the dates, modes, owners and
5046 link-structure of all the files therein. In this case, the transfer
5049 $ (cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)
5051 You can avoid subshells by using `-C' option:
5053 $ tar -C sourcedir -cf - . | tar -C targetdir -xf -
5055 The command also works using long option forms:
5057 $ (cd sourcedir; tar --create --file=- . ) \
5058 | (cd targetdir; tar --extract --file=-)
5062 $ tar --directory sourcedir --create --file=- . \
5063 | tar --directory targetdir --extract --file=-
5065 This is one of the easiest methods to transfer a `tar' archive.
5068 File: tar.info, Node: looking ahead, Prev: Applications, Up: operations
5070 4.7 Looking Ahead: The Rest of this Manual
5071 ==========================================
5073 You have now seen how to use all eight of the operations available to
5074 `tar', and a number of the possible options. The next chapter explains
5075 how to choose and change file and archive names, how to use files to
5076 store names of other files which you can then call as arguments to
5077 `tar' (this can help you save time if you expect to archive the same
5078 list of files a number of times), and so forth.
5080 If there are too many files to conveniently list on the command line,
5081 you can list the names in a file, and `tar' will read that file. *Note
5084 There are various ways of causing `tar' to skip over some files, and
5085 not archive them. *Note Choosing::.
5088 File: tar.info, Node: Backups, Next: Choosing, Prev: operations, Up: Top
5090 5 Performing Backups and Restoring Files
5091 ****************************************
5093 GNU `tar' is distributed along with the scripts for performing backups
5094 and restores. Even if there is a good chance those scripts may be
5095 satisfying to you, they are not the only scripts or methods available
5096 for doing backups and restore. You may well create your own, or use
5097 more sophisticated packages dedicated to that purpose.
5099 Some users are enthusiastic about `Amanda' (The Advanced Maryland
5100 Automatic Network Disk Archiver), a backup system developed by James da
5101 Silva `jds@cs.umd.edu' and available on many Unix systems. This is
5102 free software, and it is available from `http://www.amanda.org'.
5104 This chapter documents both the provided shell scripts and `tar'
5105 options which are more specific to usage as a backup tool.
5107 To "back up" a file system means to create archives that contain all
5108 the files in that file system. Those archives can then be used to
5109 restore any or all of those files (for instance if a disk crashes or a
5110 file is accidentally deleted). File system "backups" are also called
5115 * Full Dumps:: Using `tar' to Perform Full Dumps
5116 * Incremental Dumps:: Using `tar' to Perform Incremental Dumps
5117 * Backup Levels:: Levels of Backups
5118 * Backup Parameters:: Setting Parameters for Backups and Restoration
5119 * Scripted Backups:: Using the Backup Scripts
5120 * Scripted Restoration:: Using the Restore Script
5123 File: tar.info, Node: Full Dumps, Next: Incremental Dumps, Up: Backups
5125 5.1 Using `tar' to Perform Full Dumps
5126 =====================================
5128 _(This message will disappear, once this node revised.)_
5130 Full dumps should only be made when no other people or programs are
5131 modifying files in the file system. If files are modified while `tar'
5132 is making the backup, they may not be stored properly in the archive,
5133 in which case you won't be able to restore them if you have to. (Files
5134 not being modified are written with no trouble, and do not corrupt the
5137 You will want to use the `--label=ARCHIVE-LABEL' (`-V
5138 ARCHIVE-LABEL') option to give the archive a volume label, so you can
5139 tell what this archive is even if the label falls off the tape, or
5142 Unless the file system you are dumping is guaranteed to fit on one
5143 volume, you will need to use the `--multi-volume' (`-M') option. Make
5144 sure you have enough tapes on hand to complete the backup.
5146 If you want to dump each file system separately you will need to use
5147 the `--one-file-system' option to prevent `tar' from crossing file
5148 system boundaries when storing (sub)directories.
5150 The `--incremental' (`-G') (*note Incremental Dumps::) option is not
5151 needed, since this is a complete copy of everything in the file system,
5152 and a full restore from this backup would only be done onto a completely
5155 Unless you are in a hurry, and trust the `tar' program (and your
5156 tapes), it is a good idea to use the `--verify' (`-W') option, to make
5157 sure your files really made it onto the dump properly. This will also
5158 detect cases where the file was modified while (or just after) it was
5159 being archived. Not all media (notably cartridge tapes) are capable of
5160 being verified, unfortunately.
5163 File: tar.info, Node: Incremental Dumps, Next: Backup Levels, Prev: Full Dumps, Up: Backups
5165 5.2 Using `tar' to Perform Incremental Dumps
5166 ============================================
5168 "Incremental backup" is a special form of GNU `tar' archive that stores
5169 additional metadata so that exact state of the file system can be
5170 restored when extracting the archive.
5172 GNU `tar' currently offers two options for handling incremental
5173 backups: `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') and
5174 `--incremental' (`-G').
5176 The option `--listed-incremental' instructs tar to operate on an
5177 incremental archive with additional metadata stored in a standalone
5178 file, called a "snapshot file". The purpose of this file is to help
5179 determine which files have been changed, added or deleted since the
5180 last backup, so that the next incremental backup will contain only
5181 modified files. The name of the snapshot file is given as an argument
5184 `--listed-incremental=FILE'
5186 Handle incremental backups with snapshot data in FILE.
5188 To create an incremental backup, you would use
5189 `--listed-incremental' together with `--create' (*note create::). For
5193 --file=archive.1.tar \
5194 --listed-incremental=/var/log/usr.snar \
5197 This will create in `archive.1.tar' an incremental backup of the
5198 `/usr' file system, storing additional metadata in the file
5199 `/var/log/usr.snar'. If this file does not exist, it will be created.
5200 The created archive will then be a "level 0 backup"; please see the
5201 next section for more on backup levels.
5203 Otherwise, if the file `/var/log/usr.snar' exists, it determines
5204 which files are modified. In this case only these files will be stored
5205 in the archive. Suppose, for example, that after running the above
5206 command, you delete file `/usr/doc/old' and create directory
5207 `/usr/local/db' with the following contents:
5213 Some time later you create another incremental backup. You will
5217 --file=archive.2.tar \
5218 --listed-incremental=/var/log/usr.snar \
5220 tar: usr/local/db: Directory is new
5225 The created archive `archive.2.tar' will contain only these three
5226 members. This archive is called a "level 1 backup". Notice that
5227 `/var/log/usr.snar' will be updated with the new data, so if you plan
5228 to create more `level 1' backups, it is necessary to create a working
5229 copy of the snapshot file before running `tar'. The above example will
5230 then be modified as follows:
5232 $ cp /var/log/usr.snar /var/log/usr.snar-1
5234 --file=archive.2.tar \
5235 --listed-incremental=/var/log/usr.snar-1 \
5238 You can force `level 0' backups either by removing the snapshot file
5239 before running `tar', or by supplying the `--level=0' option, e.g.:
5242 --file=archive.2.tar \
5243 --listed-incremental=/var/log/usr.snar-0 \
5247 Incremental dumps depend crucially on time stamps, so the results are
5248 unreliable if you modify a file's time stamps during dumping (e.g.,
5249 with the `--atime-preserve=replace' option), or if you set the clock
5252 Metadata stored in snapshot files include device numbers, which,
5253 obviously are supposed to be non-volatile values. However, it turns
5254 out that NFS devices have undependable values when an automounter gets
5255 in the picture. This can lead to a great deal of spurious redumping in
5256 incremental dumps, so it is somewhat useless to compare two NFS devices
5257 numbers over time. The solution implemented currently is to consider
5258 all NFS devices as being equal when it comes to comparing directories;
5259 this is fairly gross, but there does not seem to be a better way to go.
5261 Apart from using NFS, there are a number of cases where relying on
5262 device numbers can cause spurious redumping of unmodified files. For
5263 example, this occurs when archiving LVM snapshot volumes. To avoid
5264 this, use `--no-check-device' option:
5267 Do not rely on device numbers when preparing a list of changed
5268 files for an incremental dump.
5271 Use device numbers when preparing a list of changed files for an
5272 incremental dump. This is the default behavior. The purpose of
5273 this option is to undo the effect of the `--no-check-device' if it
5274 was given in `TAR_OPTIONS' environment variable (*note
5277 There is also another way to cope with changing device numbers. It
5278 is described in detail in *note Fixing Snapshot Files::.
5280 Note that incremental archives use `tar' extensions and may not be
5281 readable by non-GNU versions of the `tar' program.
5283 To extract from the incremental dumps, use `--listed-incremental'
5284 together with `--extract' option (*note extracting files::). In this
5285 case, `tar' does not need to access snapshot file, since all the data
5286 necessary for extraction are stored in the archive itself. So, when
5287 extracting, you can give whatever argument to `--listed-incremental',
5288 the usual practice is to use `--listed-incremental=/dev/null'.
5289 Alternatively, you can use `--incremental', which needs no arguments.
5290 In general, `--incremental' (`-G') can be used as a shortcut for
5291 `--listed-incremental' when listing or extracting incremental backups
5292 (for more information regarding this option, *note incremental-op::).
5294 When extracting from the incremental backup GNU `tar' attempts to
5295 restore the exact state the file system had when the archive was
5296 created. In particular, it will _delete_ those files in the file
5297 system that did not exist in their directories when the archive was
5298 created. If you have created several levels of incremental files, then
5299 in order to restore the exact contents the file system had when the
5300 last level was created, you will need to restore from all backups in
5301 turn. Continuing our example, to restore the state of `/usr' file
5302 system, one would do(1):
5305 --listed-incremental=/dev/null \
5306 --file archive.1.tar
5308 --listed-incremental=/dev/null \
5309 --file archive.2.tar
5311 To list the contents of an incremental archive, use `--list' (*note
5312 list::), as usual. To obtain more information about the archive, use
5313 `--listed-incremental' or `--incremental' combined with two `--verbose'
5316 tar --list --incremental --verbose --verbose archive.tar
5318 This command will print, for each directory in the archive, the list
5319 of files in that directory at the time the archive was created. This
5320 information is put out in a format which is both human-readable and
5321 unambiguous for a program: each file name is printed as
5325 where X is a letter describing the status of the file: `Y' if the file
5326 is present in the archive, `N' if the file is not included in the
5327 archive, or a `D' if the file is a directory (and is included in the
5328 archive). *Note Dumpdir::, for the detailed description of dumpdirs
5329 and status codes. Each such line is terminated by a newline character.
5330 The last line is followed by an additional newline to indicate the end
5333 The option `--incremental' (`-G') gives the same behavior as
5334 `--listed-incremental' when used with `--list' and `--extract' options.
5335 When used with `--create' option, it creates an incremental archive
5336 without creating snapshot file. Thus, it is impossible to create
5337 several levels of incremental backups with `--incremental' option.
5339 ---------- Footnotes ----------
5341 (1) Notice, that since both archives were created without `-P'
5342 option (*note absolute::), these commands should be run from the root
5345 (2) Two `--verbose' options were selected to avoid breaking usual
5346 verbose listing output (`--list --verbose') when using in scripts.
5348 Versions of GNU `tar' up to 1.15.1 used to dump verbatim binary
5349 contents of the DUMPDIR header (with terminating nulls) when
5350 `--incremental' or `--listed-incremental' option was given, no matter
5351 what the verbosity level. This behavior, and, especially, the binary
5352 output it produced were considered inconvenient and were changed in
5356 File: tar.info, Node: Backup Levels, Next: Backup Parameters, Prev: Incremental Dumps, Up: Backups
5358 5.3 Levels of Backups
5359 =====================
5361 An archive containing all the files in the file system is called a
5362 "full backup" or "full dump". You could insure your data by creating a
5363 full dump every day. This strategy, however, would waste a substantial
5364 amount of archive media and user time, as unchanged files are daily
5367 It is more efficient to do a full dump only occasionally. To back up
5368 files between full dumps, you can use "incremental dumps". A "level
5369 one" dump archives all the files that have changed since the last full
5372 A typical dump strategy would be to perform a full dump once a week,
5373 and a level one dump once a day. This means some versions of files
5374 will in fact be archived more than once, but this dump strategy makes
5375 it possible to restore a file system to within one day of accuracy by
5376 only extracting two archives--the last weekly (full) dump and the last
5377 daily (level one) dump. The only information lost would be in files
5378 changed or created since the last daily backup. (Doing dumps more than
5379 once a day is usually not worth the trouble.)
5381 GNU `tar' comes with scripts you can use to do full and level-one
5382 (actually, even level-two and so on) dumps. Using scripts (shell
5383 programs) to perform backups and restoration is a convenient and
5384 reliable alternative to typing out file name lists and `tar' commands
5387 Before you use these scripts, you need to edit the file
5388 `backup-specs', which specifies parameters used by the backup scripts
5389 and by the restore script. This file is usually located in
5390 `/etc/backup' directory. *Note Backup Parameters::, for its detailed
5391 description. Once the backup parameters are set, you can perform
5392 backups or restoration by running the appropriate script.
5394 The name of the backup script is `backup'. The name of the restore
5395 script is `restore'. The following sections describe their use in
5398 _Please Note:_ The backup and restoration scripts are designed to be
5399 used together. While it is possible to restore files by hand from an
5400 archive which was created using a backup script, and to create an
5401 archive by hand which could then be extracted using the restore script,
5402 it is easier to use the scripts. *Note Incremental Dumps::, before
5403 making such an attempt.
5406 File: tar.info, Node: Backup Parameters, Next: Scripted Backups, Prev: Backup Levels, Up: Backups
5408 5.4 Setting Parameters for Backups and Restoration
5409 ==================================================
5411 The file `backup-specs' specifies backup parameters for the backup and
5412 restoration scripts provided with `tar'. You must edit `backup-specs'
5413 to fit your system configuration and schedule before using these
5416 Syntactically, `backup-specs' is a shell script, containing mainly
5417 variable assignments. However, any valid shell construct is allowed in
5418 this file. Particularly, you may wish to define functions within that
5419 script (e.g., see `RESTORE_BEGIN' below). For more information about
5420 shell script syntax, please refer to the definition of the Shell
5422 (http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
5423 g_02). See also *note Bash Features: (bashref)Top.
5425 The shell variables controlling behavior of `backup' and `restore'
5426 are described in the following subsections.
5430 * General-Purpose Variables::
5431 * Magnetic Tape Control::
5433 * backup-specs example:: An Example Text of `Backup-specs'
5436 File: tar.info, Node: General-Purpose Variables, Next: Magnetic Tape Control, Up: Backup Parameters
5438 5.4.1 General-Purpose Variables
5439 -------------------------------
5441 -- Backup variable: ADMINISTRATOR
5442 The user name of the backup administrator. `Backup' scripts sends
5443 a backup report to this address.
5445 -- Backup variable: BACKUP_HOUR
5446 The hour at which the backups are done. This can be a number from
5447 0 to 23, or the time specification in form HOURS:MINUTES, or the
5450 This variable is used by `backup'. Its value may be overridden
5451 using `--time' option (*note Scripted Backups::).
5453 -- Backup variable: TAPE_FILE
5454 The device `tar' writes the archive to. If TAPE_FILE is a remote
5455 archive (*note remote-dev::), backup script will suppose that your
5456 `mt' is able to access remote devices. If RSH (*note RSH::) is
5457 set, `--rsh-command' option will be added to invocations of `mt'.
5459 -- Backup variable: BLOCKING
5460 The blocking factor `tar' will use when writing the dump archive.
5461 *Note Blocking Factor::.
5463 -- Backup variable: BACKUP_DIRS
5464 A list of file systems to be dumped (for `backup'), or restored
5465 (for `restore'). You can include any directory name in the list
5466 -- subdirectories on that file system will be included, regardless
5467 of how they may look to other networked machines. Subdirectories
5468 on other file systems will be ignored.
5470 The host name specifies which host to run `tar' on, and should
5471 normally be the host that actually contains the file system.
5472 However, the host machine must have GNU `tar' installed, and must
5473 be able to access the directory containing the backup scripts and
5474 their support files using the same file name that is used on the
5475 machine where the scripts are run (i.e., what `pwd' will print
5476 when in that directory on that machine). If the host that contains
5477 the file system does not have this capability, you can specify
5478 another host as long as it can access the file system through NFS.
5480 If the list of file systems is very long you may wish to put it in
5481 a separate file. This file is usually named `/etc/backup/dirs',
5482 but this name may be overridden in `backup-specs' using `DIRLIST'
5485 -- Backup variable: DIRLIST
5486 The name of the file that contains a list of file systems to backup
5487 or restore. By default it is `/etc/backup/dirs'.
5489 -- Backup variable: BACKUP_FILES
5490 A list of individual files to be dumped (for `backup'), or restored
5491 (for `restore'). These should be accessible from the machine on
5492 which the backup script is run.
5494 If the list of individual files is very long you may wish to store
5495 it in a separate file. This file is usually named
5496 `/etc/backup/files', but this name may be overridden in
5497 `backup-specs' using `FILELIST' variable.
5499 -- Backup variable: FILELIST
5500 The name of the file that contains a list of individual files to
5501 backup or restore. By default it is `/etc/backup/files'.
5503 -- Backup variable: MT
5504 Full file name of `mt' binary.
5506 -- Backup variable: RSH
5507 Full file name of `rsh' binary or its equivalent. You may wish to
5508 set it to `ssh', to improve security. In this case you will have
5509 to use public key authentication.
5511 -- Backup variable: RSH_COMMAND
5512 Full file name of `rsh' binary on remote machines. This will be
5513 passed via `--rsh-command' option to the remote invocation of GNU
5516 -- Backup variable: VOLNO_FILE
5517 Name of temporary file to hold volume numbers. This needs to be
5518 accessible by all the machines which have file systems to be
5521 -- Backup variable: XLIST
5522 Name of "exclude file list". An "exclude file list" is a file
5523 located on the remote machine and containing the list of files to
5524 be excluded from the backup. Exclude file lists are searched in
5525 /etc/tar-backup directory. A common use for exclude file lists is
5526 to exclude files containing security-sensitive information (e.g.,
5527 `/etc/shadow' from backups).
5529 This variable affects only `backup'.
5531 -- Backup variable: SLEEP_TIME
5532 Time to sleep between dumps of any two successive file systems
5534 This variable affects only `backup'.
5536 -- Backup variable: DUMP_REMIND_SCRIPT
5537 Script to be run when it's time to insert a new tape in for the
5538 next volume. Administrators may want to tailor this script for
5539 their site. If this variable isn't set, GNU `tar' will display
5540 its built-in prompt, and will expect confirmation from the
5541 console. For the description of the default prompt, see *note
5542 change volume prompt::.
5545 -- Backup variable: SLEEP_MESSAGE
5546 Message to display on the terminal while waiting for dump time.
5547 Usually this will just be some literal text.
5549 -- Backup variable: TAR
5550 Full file name of the GNU `tar' executable. If this is not set,
5551 backup scripts will search `tar' in the current shell path.
5554 File: tar.info, Node: Magnetic Tape Control, Next: User Hooks, Prev: General-Purpose Variables, Up: Backup Parameters
5556 5.4.2 Magnetic Tape Control
5557 ---------------------------
5559 Backup scripts access tape device using special "hook functions".
5560 These functions take a single argument -- the name of the tape device.
5561 Their names are kept in the following variables:
5563 -- Backup variable: MT_BEGIN
5564 The name of "begin" function. This function is called before
5565 accessing the drive. By default it retensions the tape:
5570 mt -f "$1" retension
5573 -- Backup variable: MT_REWIND
5574 The name of "rewind" function. The default definition is as
5584 -- Backup variable: MT_OFFLINE
5585 The name of the function switching the tape off line. By default
5586 it is defined as follows:
5588 MT_OFFLINE=mt_offline
5594 -- Backup variable: MT_STATUS
5595 The name of the function used to obtain the status of the archive
5596 device, including error count. Default definition:
5605 File: tar.info, Node: User Hooks, Next: backup-specs example, Prev: Magnetic Tape Control, Up: Backup Parameters
5610 "User hooks" are shell functions executed before and after each `tar'
5611 invocation. Thus, there are "backup hooks", which are executed before
5612 and after dumping each file system, and "restore hooks", executed
5613 before and after restoring a file system. Each user hook is a shell
5614 function taking four arguments:
5616 -- User Hook Function: hook LEVEL HOST FS FSNAME
5620 Current backup or restore level.
5623 Name or IP address of the host machine being dumped or
5627 Full file name of the file system being dumped or restored.
5630 File system name with directory separators replaced with
5631 colons. This is useful, e.g., for creating unique files.
5633 Following variables keep the names of user hook functions:
5635 -- Backup variable: DUMP_BEGIN
5636 Dump begin function. It is executed before dumping the file
5639 -- Backup variable: DUMP_END
5640 Executed after dumping the file system.
5642 -- Backup variable: RESTORE_BEGIN
5643 Executed before restoring the file system.
5645 -- Backup variable: RESTORE_END
5646 Executed after restoring the file system.
5649 File: tar.info, Node: backup-specs example, Prev: User Hooks, Up: Backup Parameters
5651 5.4.4 An Example Text of `Backup-specs'
5652 ---------------------------------------
5654 The following is an example of `backup-specs':
5656 # site-specific parameters for file system backup.
5658 ADMINISTRATOR=friedman
5660 TAPE_FILE=/dev/nrsmt0
5662 # Use `ssh' instead of the less secure `rsh'
5664 RSH_COMMAND=/usr/bin/ssh
5666 # Override MT_STATUS function:
5672 # Disable MT_OFFLINE function
5689 apple-gunkies:/com/mailer/gnu
5690 apple-gunkies:/com/archive/gnu"
5692 BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
5695 File: tar.info, Node: Scripted Backups, Next: Scripted Restoration, Prev: Backup Parameters, Up: Backups
5697 5.5 Using the Backup Scripts
5698 ============================
5700 The syntax for running a backup script is:
5702 backup --level=LEVEL --time=TIME
5704 The `--level' option requests the dump level. Thus, to produce a
5705 full dump, specify `--level=0' (this is the default, so `--level' may
5706 be omitted if its value is `0')(1).
5708 The `--time' option determines when should the backup be run. TIME
5709 may take three forms:
5712 The dump must be run at HH hours MM minutes.
5715 The dump must be run at HH hours.
5718 The dump must be run immediately.
5720 You should start a script with a tape or disk mounted. Once you
5721 start a script, it prompts you for new tapes or disks as it needs them.
5722 Media volumes don't have to correspond to archive files -- a
5723 multi-volume archive can be started in the middle of a tape that
5724 already contains the end of another multi-volume archive. The
5725 `restore' script prompts for media by its archive volume, so to avoid
5726 an error message you should keep track of which tape (or disk) contains
5727 which volume of the archive (*note Scripted Restoration::).
5729 The backup scripts write two files on the file system. The first is
5730 a record file in `/etc/tar-backup/', which is used by the scripts to
5731 store and retrieve information about which files were dumped. This
5732 file is not meant to be read by humans, and should not be deleted by
5733 them. *Note Snapshot Files::, for a more detailed explanation of this
5736 The second file is a log file containing the names of the file
5737 systems and files dumped, what time the backup was made, and any error
5738 messages that were generated, as well as how much space was left in the
5739 media volume after the last volume of the archive was written. You
5740 should check this log file after every backup. The file name is
5741 `log-MM-DD-YYYY-level-N', where MM-DD-YYYY represents current date, and
5742 N represents current dump level number.
5744 The script also prints the name of each system being dumped to the
5747 Following is the full list of options accepted by `backup' script:
5751 Do backup level LEVEL (default 0).
5755 Force backup even if today's log file already exists.
5759 Set verbosity level. The higher the level is, the more debugging
5760 information will be output during execution. Default LEVEL is
5761 100, which means the highest debugging level.
5765 Wait till TIME, then do backup.
5769 Display short help message and exit.
5773 Display information about the program's name, version, origin and
5774 legal status, all on standard output, and then exit successfully.
5776 ---------- Footnotes ----------
5778 (1) For backward compatibility, the `backup' will also try to deduce
5779 the requested dump level from the name of the script itself. If the
5780 name consists of a string `level-' followed by a single decimal digit,
5781 that digit is taken as the dump level number. Thus, you may create a
5782 link from `backup' to `level-1' and then run `level-1' whenever you
5783 need to create a level one dump.
5786 File: tar.info, Node: Scripted Restoration, Prev: Scripted Backups, Up: Backups
5788 5.6 Using the Restore Script
5789 ============================
5791 To restore files that were archived using a scripted backup, use the
5792 `restore' script. Its usage is quite straightforward. In the simplest
5793 form, invoke `restore --all', it will then restore all the file systems
5794 and files specified in `backup-specs' (*note BACKUP_DIRS:
5795 General-Purpose Variables.).
5797 You may select the file systems (and/or files) to restore by giving
5798 `restore' a list of "patterns" in its command line. For example,
5803 will restore all file systems on the machine `albert'. A more
5804 complicated example:
5806 restore 'albert:*' '*:/var'
5808 This command will restore all file systems on the machine `albert' as
5809 well as `/var' file system on all machines.
5811 By default `restore' will start restoring files from the lowest
5812 available dump level (usually zero) and will continue through all
5813 available dump levels. There may be situations where such a thorough
5814 restore is not necessary. For example, you may wish to restore only
5815 files from the recent level one backup. To do so, use `--level'
5816 option, as shown in the example below:
5820 The full list of options accepted by `restore' follows:
5824 Restore all file systems and files specified in `backup-specs'.
5828 Start restoring from the given backup level, instead of the
5833 Set verbosity level. The higher the level is, the more debugging
5834 information will be output during execution. Default LEVEL is
5835 100, which means the highest debugging level.
5839 Display short help message and exit.
5843 Display information about the program's name, version, origin and
5844 legal status, all on standard output, and then exit successfully.
5846 You should start the restore script with the media containing the
5847 first volume of the archive mounted. The script will prompt for other
5848 volumes as they are needed. If the archive is on tape, you don't need
5849 to rewind the tape to to its beginning--if the tape head is positioned
5850 past the beginning of the archive, the script will rewind the tape as
5851 needed. *Note Tape Positioning::, for a discussion of tape positioning.
5853 *Warning:* The script will delete files from the active file
5854 system if they were not in the file system when the archive was
5857 *Note Incremental Dumps::, for an explanation of how the script makes
5861 File: tar.info, Node: Choosing, Next: Date input formats, Prev: Backups, Up: Top
5863 6 Choosing Files and Names for `tar'
5864 ************************************
5866 Certain options to `tar' enable you to specify a name for your archive.
5867 Other options let you decide which files to include or exclude from the
5868 archive, based on when or whether files were modified, whether the file
5869 names do or don't match specified patterns, or whether files are in
5870 specified directories.
5872 This chapter discusses these options in detail.
5876 * file:: Choosing the Archive's Name
5877 * Selecting Archive Members::
5878 * files:: Reading Names from a File
5879 * exclude:: Excluding Some Files
5880 * wildcards:: Wildcards Patterns and Matching
5881 * quoting styles:: Ways of Quoting Special Characters in Names
5882 * transform:: Modifying File and Member Names
5883 * after:: Operating Only on New Files
5884 * recurse:: Descending into Directories
5885 * one:: Crossing File System Boundaries
5888 File: tar.info, Node: file, Next: Selecting Archive Members, Up: Choosing
5890 6.1 Choosing and Naming Archive Files
5891 =====================================
5893 By default, `tar' uses an archive file name that was compiled when it
5894 was built on the system; usually this name refers to some physical tape
5895 drive on the machine. However, the person who installed `tar' on the
5896 system may not have set the default to a meaningful value as far as
5897 most users are concerned. As a result, you will usually want to tell
5898 `tar' where to find (or create) the archive. The `--file=ARCHIVE-NAME'
5899 (`-f ARCHIVE-NAME') option allows you to either specify or name a file
5900 to use as the archive instead of the default archive file location.
5902 `--file=ARCHIVE-NAME'
5904 Name the archive to create or operate on. Use in conjunction with
5907 For example, in this `tar' command,
5909 $ tar -cvf collection.tar blues folk jazz
5911 `collection.tar' is the name of the archive. It must directly follow
5912 the `-f' option, since whatever directly follows `-f' _will_ end up
5913 naming the archive. If you neglect to specify an archive name, you may
5914 end up overwriting a file in the working directory with the archive you
5915 create since `tar' will use this file's name for the archive name.
5917 An archive can be saved as a file in the file system, sent through a
5918 pipe or over a network, or written to an I/O device such as a tape,
5919 floppy disk, or CD write drive.
5921 If you do not name the archive, `tar' uses the value of the
5922 environment variable `TAPE' as the file name for the archive. If that
5923 is not available, `tar' uses a default, compiled-in archive name,
5924 usually that for tape unit zero (i.e., `/dev/tu00').
5926 If you use `-' as an ARCHIVE-NAME, `tar' reads the archive from
5927 standard input (when listing or extracting files), or writes it to
5928 standard output (when creating an archive). If you use `-' as an
5929 ARCHIVE-NAME when modifying an archive, `tar' reads the original
5930 archive from its standard input and writes the entire new archive to
5931 its standard output.
5933 The following example is a convenient way of copying directory
5934 hierarchy from `sourcedir' to `targetdir'.
5936 $ (cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)
5938 The `-C' option allows to avoid using subshells:
5940 $ tar -C sourcedir -cf - . | tar -C targetdir -xpf -
5942 In both examples above, the leftmost `tar' invocation archives the
5943 contents of `sourcedir' to the standard output, while the rightmost one
5944 reads this archive from its standard input and extracts it. The `-p'
5945 option tells it to restore permissions of the extracted files.
5947 To specify an archive file on a device attached to a remote machine,
5950 --file=HOSTNAME:/DEV/FILE-NAME
5952 `tar' will set up the remote connection, if possible, and prompt you
5953 for a username and password. If you use
5954 `--file=@HOSTNAME:/DEV/FILE-NAME', `tar' will attempt to set up the
5955 remote connection using your username as the username on the remote
5958 If the archive file name includes a colon (`:'), then it is assumed
5959 to be a file on another machine. If the archive file is
5960 `USER@HOST:FILE', then FILE is used on the host HOST. The remote host
5961 is accessed using the `rsh' program, with a username of USER. If the
5962 username is omitted (along with the `@' sign), then your user name will
5963 be used. (This is the normal `rsh' behavior.) It is necessary for the
5964 remote machine, in addition to permitting your `rsh' access, to have
5965 the `rmt' program installed (this command is included in the GNU `tar'
5966 distribution and by default is installed under `PREFIX/libexec/rmt',
5967 where PREFIX means your installation prefix). If you need to use a
5968 file whose name includes a colon, then the remote tape drive behavior
5969 can be inhibited by using the `--force-local' option.
5971 When the archive is being created to `/dev/null', GNU `tar' tries to
5972 minimize input and output operations. The Amanda backup system, when
5973 used with GNU `tar', has an initial sizing pass which uses this feature.
5976 File: tar.info, Node: Selecting Archive Members, Next: files, Prev: file, Up: Choosing
5978 6.2 Selecting Archive Members
5979 =============================
5981 "File Name arguments" specify which files in the file system `tar'
5982 operates on, when creating or adding to an archive, or which archive
5983 members `tar' operates on, when reading or deleting from an archive.
5986 To specify file names, you can include them as the last arguments on
5987 the command line, as follows:
5988 tar OPERATION [OPTION1 OPTION2 ...] [FILE NAME-1 FILE NAME-2 ...]
5990 If a file name begins with dash (`-'), precede it with `--add-file'
5991 option to prevent it from being treated as an option.
5993 By default GNU `tar' attempts to "unquote" each file or member name,
5994 replacing "escape sequences" according to the following table:
5996 Escape Replaced with
5997 -----------------------------------------------------------
5998 \a Audible bell (ASCII 7)
5999 \b Backspace (ASCII 8)
6000 \f Form feed (ASCII 12)
6001 \n New line (ASCII 10)
6002 \r Carriage return (ASCII 13)
6003 \t Horizontal tabulation (ASCII 9)
6004 \v Vertical tabulation (ASCII 11)
6006 \N ASCII N (N should be an octal number
6009 A backslash followed by any other symbol is retained.
6011 This default behavior is controlled by the following command line
6015 Enable unquoting input file or member names (default).
6018 Disable unquoting input file or member names.
6020 If you specify a directory name as a file name argument, all the
6021 files in that directory are operated on by `tar'.
6023 If you do not specify files, `tar' behavior differs depending on the
6024 operation mode as described below:
6026 When `tar' is invoked with `--create' (`-c'), `tar' will stop
6027 immediately, reporting the following:
6030 tar: Cowardly refusing to create an empty archive
6031 Try 'tar --help' or 'tar --usage' for more information.
6033 If you specify either `--list' (`-t') or `--extract' (`--get',
6034 `-x'), `tar' operates on all the archive members in the archive.
6036 If run with `--diff' option, tar will compare the archive with the
6037 contents of the current working directory.
6039 If you specify any other operation, `tar' does nothing.
6041 By default, `tar' takes file names from the command line. However,
6042 there are other ways to specify file or member names, or to modify the
6043 manner in which `tar' selects the files or members upon which to
6044 operate. In general, these methods work both for specifying the names
6045 of files and archive members.
6048 File: tar.info, Node: files, Next: exclude, Prev: Selecting Archive Members, Up: Choosing
6050 6.3 Reading Names from a File
6051 =============================
6053 Instead of giving the names of files or archive members on the command
6054 line, you can put the names into a file, and then use the
6055 `--files-from=FILE-OF-NAMES' (`-T FILE-OF-NAMES') option to `tar'.
6056 Give the name of the file which contains the list of files to include
6057 as the argument to `--files-from'. In the list, the file names should
6058 be separated by newlines. You will frequently use this option when you
6059 have generated the list of files to archive with the `find' utility.
6061 `--files-from=FILE-NAME'
6063 Get names to extract or create from file FILE-NAME.
6065 If you give a single dash as a file name for `--files-from', (i.e.,
6066 you specify either `--files-from=-' or `-T -'), then the file names are
6067 read from standard input.
6069 Unless you are running `tar' with `--create', you can not use both
6070 `--files-from=-' and `--file=-' (`-f -') in the same command.
6072 Any number of `-T' options can be given in the command line.
6074 The following example shows how to use `find' to generate a list of
6075 files smaller than 400K in length and put that list into a file called
6076 `small-files'. You can then use the `-T' option to `tar' to specify
6077 the files from that file, `small-files', to create the archive
6078 `little.tgz'. (The `-z' option to `tar' compresses the archive with
6079 `gzip'; *note gzip:: for more information.)
6081 $ find . -size -400 -print > small-files
6082 $ tar -c -v -z -T small-files -f little.tgz
6084 In the file list given by `-T' option, any file name beginning with `-'
6085 character is considered a `tar' option and is processed accordingly(1).
6086 For example, the common use of this feature is to change to another
6087 directory by specifying `-C' option:
6095 $ tar -c -f foo.tar --files-from list
6097 In this example, `tar' will first switch to `/etc' directory and add
6098 files `passwd' and `hosts' to the archive. Then it will change to
6099 `/lib' directory and will archive the file `libc.a'. Thus, the
6100 resulting archive `foo.tar' will contain:
6107 If you happen to have a file whose name starts with `-', precede it
6108 with `--add-file' option to prevent it from being recognized as an
6109 option. For example: `--add-file=--my-file'.
6115 ---------- Footnotes ----------
6117 (1) Versions of GNU `tar' up to 1.15.1 recognized only `-C' option
6118 in file lists, and only if the option and its argument occupied two
6122 File: tar.info, Node: nul, Up: files
6124 6.3.1 `NUL'-Terminated File Names
6125 ---------------------------------
6127 The `--null' option causes `--files-from=FILE-OF-NAMES' (`-T
6128 FILE-OF-NAMES') to read file names terminated by a `NUL' instead of a
6129 newline, so files whose names contain newlines can be archived using
6133 Only consider `NUL'-terminated file names, instead of files that
6134 terminate in a newline.
6137 Undo the effect of any previous `--null' option.
6139 The `--null' option is just like the one in GNU `xargs' and `cpio',
6140 and is useful with the `-print0' predicate of GNU `find'. In `tar',
6141 `--null' also disables special handling for file names that begin with
6144 This example shows how to use `find' to generate a list of files
6145 larger than 800K in length and put that list into a file called
6146 `long-files'. The `-print0' option to `find' is just like `-print',
6147 except that it separates files with a `NUL' rather than with a newline.
6148 You can then run `tar' with both the `--null' and `-T' options to
6149 specify that `tar' gets the files from that file, `long-files', to
6150 create the archive `big.tgz'. The `--null' option to `tar' will cause
6151 `tar' to recognize the `NUL' separator between files.
6153 $ find . -size +800 -print0 > long-files
6154 $ tar -c -v --null --files-from=long-files --file=big.tar
6156 The `--no-null' option can be used if you need to read both
6157 `NUL'-terminated and newline-terminated files on the same command line.
6158 For example, if `flist' is a newline-terminated file, then the
6159 following command can be used to combine it with the above command:
6161 $ find . -size +800 -print0 |
6162 tar -c -f big.tar --null -T - --no-null -T flist
6164 This example uses short options for typographic reasons, to avoid
6167 GNU `tar' is tries to automatically detect `NUL'-terminated file
6168 lists, so in many cases it is safe to use them even without the
6169 `--null' option. In this case `tar' will print a warning and continue
6170 reading such a file as if `--null' were actually given:
6172 $ find . -size +800 -print0 | tar -c -f big.tar -T -
6173 tar: -: file name read contains nul character
6175 The null terminator, however, remains in effect only for this
6176 particular file, any following `-T' options will assume newline
6177 termination. Of course, the null autodetection applies to these
6178 eventual surplus `-T' options as well.
6181 File: tar.info, Node: exclude, Next: wildcards, Prev: files, Up: Choosing
6183 6.4 Excluding Some Files
6184 ========================
6186 To avoid operating on files whose names match a particular pattern, use
6187 the `--exclude' or `--exclude-from' options.
6190 Causes `tar' to ignore files that match the PATTERN.
6192 The `--exclude=PATTERN' option prevents any file or member whose
6193 name matches the shell wildcard (PATTERN) from being operated on. For
6194 example, to create an archive with all the contents of the directory
6195 `src' except for files whose names end in `.o', use the command `tar
6196 -cf src.tar --exclude='*.o' src'.
6198 You may give multiple `--exclude' options.
6200 `--exclude-from=FILE'
6202 Causes `tar' to ignore files that match the patterns listed in
6205 Use the `--exclude-from' option to read a list of patterns, one per
6206 line, from FILE; `tar' will ignore files matching those patterns. Thus
6207 if `tar' is called as `tar -c -X foo .' and the file `foo' contains a
6208 single line `*.o', no files whose names end in `.o' will be added to
6211 Notice, that lines from FILE are read verbatim. One of the frequent
6212 errors is leaving some extra whitespace after a file name, which is
6213 difficult to catch using text editors.
6215 However, empty lines are OK.
6218 Exclude files and directories used by following version control
6219 systems: `CVS', `RCS', `SCCS', `SVN', `Arch', `Bazaar',
6220 `Mercurial', and `Darcs'.
6222 As of version 1.27, the following files are excluded:
6224 * `CVS/', and everything under it
6226 * `RCS/', and everything under it
6228 * `SCCS/', and everything under it
6230 * `.git/', and everything under it
6236 * `.svn/', and everything under it
6238 * `.arch-ids/', and everything under it
6240 * `{arch}/', and everything under it
6263 Exclude backup and lock files. This option causes exclusion of
6264 files that match the following shell globbing patterns:
6273 When creating an archive, the `--exclude-caches' option family
6274 causes `tar' to exclude all directories that contain a "cache directory
6275 tag". A cache directory tag is a short file with the well-known name
6276 `CACHEDIR.TAG' and having a standard header specified in
6277 `http://www.brynosaurus.com/cachedir/spec.html'. Various applications
6278 write cache directory tags into directories they use to hold
6279 regenerable, non-precious data, so that such data can be more easily
6280 excluded from backups.
6282 There are three `exclude-caches' options, each providing a different
6283 exclusion semantics:
6286 Do not archive the contents of the directory, but archive the
6287 directory itself and the `CACHEDIR.TAG' file.
6289 `--exclude-caches-under'
6290 Do not archive the contents of the directory, nor the
6291 `CACHEDIR.TAG' file, archive only the directory itself.
6293 `--exclude-caches-all'
6294 Omit directories containing `CACHEDIR.TAG' file entirely.
6296 Another option family, `--exclude-tag', provides a generalization of
6297 this concept. It takes a single argument, a file name to look for.
6298 Any directory that contains this file will be excluded from the dump.
6299 Similarly to `exclude-caches', there are three options in this option
6302 `--exclude-tag=FILE'
6303 Do not dump the contents of the directory, but dump the directory
6304 itself and the FILE.
6306 `--exclude-tag-under=FILE'
6307 Do not dump the contents of the directory, nor the FILE, archive
6308 only the directory itself.
6310 `--exclude-tag-all=FILE'
6311 Omit directories containing FILE file entirely.
6313 Multiple `--exclude-tag*' options can be given.
6315 For example, given this directory:
6326 The `--exclude-tag' will produce the following:
6328 $ tar -cf archive.tar --exclude-tag=tagfile -v dir
6333 tar: dir/folk/: contains a cache directory tag tagfile;
6337 Both the `dir/folk' directory and its tagfile are preserved in the
6338 archive, however the rest of files in this directory are not.
6340 Now, using the `--exclude-tag-under' option will exclude `tagfile'
6341 from the dump, while still preserving the directory itself, as shown in
6344 $ tar -cf archive.tar --exclude-tag-under=tagfile -v dir
6349 ./tar: dir/folk/: contains a cache directory tag tagfile;
6352 Finally, using `--exclude-tag-all' omits the `dir/folk' directory
6355 $ tar -cf archive.tar --exclude-tag-all=tagfile -v dir
6359 ./tar: dir/folk/: contains a cache directory tag tagfile;
6360 directory not dumped
6364 * problems with exclude::
6367 File: tar.info, Node: problems with exclude, Up: exclude
6369 Problems with Using the `exclude' Options
6370 -----------------------------------------
6372 Some users find `exclude' options confusing. Here are some common
6375 * The main operating mode of `tar' does not act on a file name
6376 explicitly listed on the command line, if one of its file name
6377 components is excluded. In the example above, if you create an
6378 archive and exclude files that end with `*.o', but explicitly name
6379 the file `dir.o/foo' after all the options have been listed,
6380 `dir.o/foo' will be excluded from the archive.
6382 * You can sometimes confuse the meanings of `--exclude' and
6383 `--exclude-from'. Be careful: use `--exclude' when files to be
6384 excluded are given as a pattern on the command line. Use
6385 `--exclude-from' to introduce the name of a file which contains a
6386 list of patterns, one per line; each of these patterns can exclude
6387 zero, one, or many files.
6389 * When you use `--exclude=PATTERN', be sure to quote the PATTERN
6390 parameter, so GNU `tar' sees wildcard characters like `*'. If you
6391 do not do this, the shell might expand the `*' itself using files
6392 at hand, so `tar' might receive a list of files instead of one
6393 pattern, or none at all, making the command somewhat illegal.
6394 This might not correspond to what you want.
6398 $ tar -c -f ARCHIVE.TAR --exclude '*.o' DIRECTORY
6403 $ tar -c -f ARCHIVE.TAR --exclude *.o DIRECTORY
6405 * You must use use shell syntax, or globbing, rather than `regexp'
6406 syntax, when using exclude options in `tar'. If you try to use
6407 `regexp' syntax to describe files to be excluded, your command
6410 * In earlier versions of `tar', what is now the `--exclude-from'
6411 option was called `--exclude' instead. Now, `--exclude' applies
6412 to patterns listed on the command line and `--exclude-from'
6413 applies to patterns listed in a file.
6417 File: tar.info, Node: wildcards, Next: quoting styles, Prev: exclude, Up: Choosing
6419 6.5 Wildcards Patterns and Matching
6420 ===================================
6422 "Globbing" is the operation by which "wildcard" characters, `*' or `?'
6423 for example, are replaced and expanded into all existing files matching
6424 the given pattern. GNU `tar' can use wildcard patterns for matching
6425 (or globbing) archive members when extracting from or listing an
6426 archive. Wildcard patterns are also used for verifying volume labels
6427 of `tar' archives. This section has the purpose of explaining wildcard
6430 A PATTERN should be written according to shell syntax, using wildcard
6431 characters to effect globbing. Most characters in the pattern stand
6432 for themselves in the matched string, and case is significant: `a' will
6433 match only `a', and not `A'. The character `?' in the pattern matches
6434 any single character in the matched string. The character `*' in the
6435 pattern matches zero, one, or more single characters in the matched
6436 string. The character `\' says to take the following character of the
6437 pattern _literally_; it is useful when one needs to match the `?', `*',
6438 `[' or `\' characters, themselves.
6440 The character `[', up to the matching `]', introduces a character
6441 class. A "character class" is a list of acceptable characters for the
6442 next single character of the matched string. For example, `[abcde]'
6443 would match any of the first five letters of the alphabet. Note that
6444 within a character class, all of the "special characters" listed above
6445 other than `\' lose their special meaning; for example, `[-\\[*?]]'
6446 would match any of the characters, `-', `\', `[', `*', `?', or `]'.
6447 (Due to parsing constraints, the characters `-' and `]' must either
6448 come _first_ or _last_ in a character class.)
6450 If the first character of the class after the opening `[' is `!' or
6451 `^', then the meaning of the class is reversed. Rather than listing
6452 character to match, it lists those characters which are _forbidden_ as
6453 the next single character of the matched string.
6455 Other characters of the class stand for themselves. The special
6456 construction `[A-E]', using an hyphen between two letters, is meant to
6457 represent all characters between A and E, inclusive.
6459 Periods (`.') or forward slashes (`/') are not considered special
6460 for wildcard matches. However, if a pattern completely matches a
6461 directory prefix of a matched string, then it matches the full matched
6462 string: thus, excluding a directory also excludes all the files beneath
6467 * controlling pattern-matching::
6470 File: tar.info, Node: controlling pattern-matching, Up: wildcards
6472 Controlling Pattern-Matching
6473 ----------------------------
6475 For the purposes of this section, we call "exclusion members" all
6476 member names obtained while processing `--exclude' and `--exclude-from'
6477 options, and "inclusion members" those member names that were given in
6478 the command line or read from the file specified with `--files-from'
6481 These two pairs of member lists are used in the following operations:
6482 `--diff', `--extract', `--list', `--update'.
6484 There are no inclusion members in create mode (`--create' and
6485 `--append'), since in this mode the names obtained from the command
6486 line refer to _files_, not archive members.
6488 By default, inclusion members are compared with archive members
6489 literally (1) and exclusion members are treated as globbing patterns.
6497 # Member names are used verbatim:
6498 $ tar -xf foo.tar -v '[remarks]'
6500 # Exclude member names are globbed:
6501 $ tar -xf foo.tar -v --exclude '*.c'
6505 This behavior can be altered by using the following options:
6508 Treat all member names as wildcards.
6511 Treat all member names as literal strings.
6513 Thus, to extract files whose names end in `.c', you can use:
6515 $ tar -xf foo.tar -v --wildcards '*.c'
6519 Notice quoting of the pattern to prevent the shell from interpreting it.
6521 The effect of `--wildcards' option is canceled by `--no-wildcards'.
6522 This can be used to pass part of the command line arguments verbatim
6523 and other part as globbing patterns. For example, the following
6526 $ tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'
6528 instructs `tar' to extract from `foo.tar' all files whose names end in
6529 `.txt' and the file named `[remarks]'.
6531 Normally, a pattern matches a name if an initial subsequence of the
6532 name's components matches the pattern, where `*', `?', and `[...]' are
6533 the usual shell wildcards, `\' escapes wildcards, and wildcards can
6536 Other than optionally stripping leading `/' from names (*note
6537 absolute::), patterns and names are used as-is. For example, trailing
6538 `/' is not trimmed from a user-specified name before deciding whether
6541 However, this matching procedure can be altered by the options listed
6542 below. These options accumulate. For example:
6544 --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
6546 ignores case when excluding `makefile', but not when excluding `readme'.
6550 If anchored, a pattern must match an initial subsequence of the
6551 name's components. Otherwise, the pattern can match any
6552 subsequence. Default is `--no-anchored' for exclusion members and
6553 `--anchored' inclusion members.
6557 When ignoring case, upper-case patterns match lower-case names and
6558 vice versa. When not ignoring case (the default), matching is
6561 `--wildcards-match-slash'
6562 `--no-wildcards-match-slash'
6563 When wildcards match slash (the default for exclusion members), a
6564 wildcard like `*' in the pattern can match a `/' in the name.
6565 Otherwise, `/' is matched only by `/'.
6568 The `--recursion' and `--no-recursion' options (*note recurse::)
6569 also affect how member patterns are interpreted. If recursion is in
6570 effect, a pattern matches a name if it matches any of the name's parent
6573 The following table summarizes pattern-matching default values:
6575 Members Default settings
6576 --------------------------------------------------------------------------
6577 Inclusion `--no-wildcards --anchored
6578 --no-wildcards-match-slash'
6579 Exclusion `--wildcards --no-anchored
6580 --wildcards-match-slash'
6582 ---------- Footnotes ----------
6584 (1) Notice that earlier GNU `tar' versions used globbing for
6585 inclusion members, which contradicted to UNIX98 specification and was
6586 not documented. *Note Changes::, for more information on this and other
6590 File: tar.info, Node: quoting styles, Next: transform, Prev: wildcards, Up: Choosing
6592 6.6 Quoting Member Names
6593 ========================
6595 When displaying member names, `tar' takes care to avoid ambiguities
6596 caused by certain characters. This is called "name quoting". The
6597 characters in question are:
6599 * Non-printable control characters:
6600 Character ASCII Character name
6601 ---------------------------------------------------------------
6606 \r 13 Carriage return
6607 \t 9 Horizontal tabulation
6608 \v 11 Vertical tabulation
6612 * Single and double quotes (`'' and `"')
6616 The exact way `tar' uses to quote these characters depends on the
6617 "quoting style". The default quoting style, called "escape" (see
6618 below), uses backslash notation to represent control characters, space
6619 and backslash. Using this quoting style, control characters are
6620 represented as listed in column `Character' in the above table, a space
6621 is printed as `\ ' and a backslash as `\\'.
6623 GNU `tar' offers seven distinct quoting styles, which can be selected
6624 using `--quoting-style' option:
6626 `--quoting-style=STYLE'
6627 Sets quoting style. Valid values for STYLE argument are: literal,
6628 shell, shell-always, c, escape, locale, clocale.
6630 These styles are described in detail below. To illustrate their
6631 effect, we will use an imaginary tar archive `arch.tar' containing the
6634 # 1. Contains horizontal tabulation character.
6636 # 2. Contains newline character
6639 # 3. Contains a space
6641 # 4. Contains double quotes
6643 # 5. Contains single quotes
6645 # 6. Contains a backslash character:
6648 Here is how usual `ls' command would have listed them, if they had
6649 existed in the current working directory:
6662 No quoting, display each character as is:
6664 $ tar tf arch.tar --quoting-style=literal
6675 Display characters the same way Bourne shell does: control
6676 characters, except `\t' and `\n', are printed using backslash
6677 escapes, `\t' and `\n' are printed as is, and a single quote is
6678 printed as `\''. If a name contains any quoted characters, it is
6679 enclosed in single quotes. In particular, if a name contains
6680 single quotes, it is printed as several single-quoted strings:
6682 $ tar tf arch.tar --quoting-style=shell
6685 './a'\''single'\''quote'
6693 Same as `shell', but the names are always enclosed in single
6696 $ tar tf arch.tar --quoting-style=shell-always
6699 './a'\''single'\''quote'
6707 Use the notation of the C programming language. All names are
6708 enclosed in double quotes. Control characters are quoted using
6709 backslash notations, double quotes are represented as `\"',
6710 backslash characters are represented as `\\'. Single quotes and
6711 spaces are not quoted:
6713 $ tar tf arch.tar --quoting-style=c
6717 "./a\"double\"quote"
6723 Control characters are printed using backslash notation, a space is
6724 printed as `\ ' and a backslash as `\\'. This is the default
6725 quoting style, unless it was changed when configured the package.
6727 $ tar tf arch.tar --quoting-style=escape
6737 Control characters, single quote and backslash are printed using
6738 backslash notation. All names are quoted using left and right
6739 quotation marks, appropriate to the current locale. If it does not
6740 define quotation marks, use `'' as left and as right quotation
6741 marks. Any occurrences of the right quotation mark in a name are
6742 escaped with `\', for example:
6746 $ tar tf arch.tar --quoting-style=locale
6749 './a\'single\'quote'
6756 Same as `locale', but `"' is used for both left and right
6757 quotation marks, if not provided by the currently selected locale:
6759 $ tar tf arch.tar --quoting-style=clocale
6763 "./a\"double\"quote"
6768 You can specify which characters should be quoted in addition to
6769 those implied by the current quoting style:
6771 `--quote-chars=STRING'
6772 Always quote characters from STRING, even if the selected quoting
6773 style would not quote them.
6775 For example, using `escape' quoting (compare with the usual escape
6778 $ tar tf arch.tar --quoting-style=escape --quote-chars=' "'
6787 To disable quoting of such additional characters, use the following
6790 `--no-quote-chars=STRING'
6791 Remove characters listed in STRING from the list of quoted
6792 characters set by the previous `--quote-chars' option.
6794 This option is particularly useful if you have added `--quote-chars'
6795 to your `TAR_OPTIONS' (*note TAR_OPTIONS::) and wish to disable it for
6796 the current invocation.
6798 Note, that `--no-quote-chars' does _not_ disable those characters
6799 that are quoted by default in the selected quoting style.
6802 File: tar.info, Node: transform, Next: after, Prev: quoting styles, Up: Choosing
6804 6.7 Modifying File and Member Names
6805 ===================================
6807 `Tar' archives contain detailed information about files stored in them
6808 and full file names are part of that information. When storing a file
6809 to an archive, its file name is recorded in it, along with the actual
6810 file contents. When restoring from an archive, a file is created on
6811 disk with exactly the same name as that stored in the archive. In the
6812 majority of cases this is the desired behavior of a file archiver.
6813 However, there are some cases when it is not.
6815 First of all, it is often unsafe to extract archive members with
6816 absolute file names or those that begin with a `../'. GNU `tar' takes
6817 special precautions when extracting such names and provides a special
6818 option for handling them, which is described in *note absolute::.
6820 Secondly, you may wish to extract file names without some leading
6821 directory components, or with otherwise modified names. In other cases
6822 it is desirable to store files under differing names in the archive.
6824 GNU `tar' provides several options for these needs.
6826 `--strip-components=NUMBER'
6827 Strip given NUMBER of leading components from file names before
6830 For example, suppose you have archived whole `/usr' hierarchy to a
6831 tar archive named `usr.tar'. Among other files, this archive contains
6832 `usr/include/stdlib.h', which you wish to extract to the current
6833 working directory. To do so, you type:
6835 $ tar -xf usr.tar --strip=2 usr/include/stdlib.h
6837 The option `--strip=2' instructs `tar' to strip the two leading
6838 components (`usr/' and `include/') off the file name.
6840 If you add the `--verbose' (`-v') option to the invocation above,
6841 you will note that the verbose listing still contains the full file
6842 name, with the two removed components still in place. This can be
6843 inconvenient, so `tar' provides a special option for altering this
6846 `--show-transformed-names'
6847 Display file or member names with all requested transformations
6852 $ tar -xf usr.tar -v --strip=2 usr/include/stdlib.h
6853 usr/include/stdlib.h
6854 $ tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h
6857 Notice that in both cases the file `stdlib.h' is extracted to the
6858 current working directory, `--show-transformed-names' affects only the
6859 way its name is displayed.
6861 This option is especially useful for verifying whether the invocation
6862 will have the desired effect. Thus, before running
6866 it is often advisable to run
6868 $ tar -t -v --show-transformed --strip=N
6870 to make sure the command will produce the intended results.
6872 In case you need to apply more complex modifications to the file
6873 name, GNU `tar' provides a general-purpose transformation option:
6875 `--transform=EXPRESSION'
6876 `--xform=EXPRESSION'
6877 Modify file names using supplied EXPRESSION.
6879 The EXPRESSION is a `sed'-like replace expression of the form:
6881 s/REGEXP/REPLACE/[FLAGS]
6883 where REGEXP is a "regular expression", REPLACE is a replacement for
6884 each file name part that matches REGEXP. Both REGEXP and REPLACE are
6885 described in detail in *note The "s" Command: (sed)The "s" Command.
6887 Any delimiter can be used in lieu of `/', the only requirement being
6888 that it be used consistently throughout the expression. For example,
6889 the following two expressions are equivalent:
6894 Changing delimiters is often useful when the REGEX contains slashes.
6895 For example, it is more convenient to write `s,/,-,' than `s/\//-/'.
6897 As in `sed', you can give several replace expressions, separated by
6900 Supported FLAGS are:
6903 Apply the replacement to _all_ matches to the REGEXP, not just the
6907 Use case-insensitive matching.
6910 REGEXP is an "extended regular expression" (*note Extended regular
6911 expressions: (sed)Extended regexps.).
6914 Only replace the NUMBERth match of the REGEXP.
6916 Note: the POSIX standard does not specify what should happen when
6917 you mix the `g' and NUMBER modifiers. GNU `tar' follows the GNU
6918 `sed' implementation in this regard, so the interaction is defined
6919 to be: ignore matches before the NUMBERth, and then match and
6920 replace all matches from the NUMBERth on.
6923 In addition, several "transformation scope" flags are supported,
6924 that control to what files transformations apply. These are:
6927 Apply transformation to regular archive members.
6930 Do not apply transformation to regular archive members.
6933 Apply transformation to symbolic link targets.
6936 Do not apply transformation to symbolic link targets.
6939 Apply transformation to hard link targets.
6942 Do not apply transformation to hard link targets.
6944 Default is `rsh', which means to apply tranformations to both archive
6945 members and targets of symbolic and hard links.
6947 Default scope flags can also be changed using `flags=' statement in
6948 the transform expression. The flags set this way remain in force until
6949 next `flags=' statement or end of expression, whichever occurs first.
6952 --transform 'flags=S;s|^|/usr/local/|'
6954 Here are several examples of `--transform' usage:
6956 1. Extract `usr/' hierarchy into `usr/local/':
6958 $ tar --transform='s,usr/,usr/local/,' -x -f arch.tar
6960 2. Strip two leading directory components (equivalent to
6961 `--strip-components=2'):
6963 $ tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar
6965 3. Convert each file name to lower case:
6967 $ tar --transform 's/.*/\L&/' -x -f arch.tar
6969 4. Prepend `/prefix/' to each file name:
6971 $ tar --transform 's,^,/prefix/,' -x -f arch.tar
6973 5. Archive the `/lib' directory, prepending `/usr/local' to each
6976 $ tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib
6978 Notice the use of flags in the last example. The `/lib' directory
6979 often contains many symbolic links to files within it. It may look,
6980 for example, like this:
6983 drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/
6984 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so
6985 lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so
6988 Using the expression `s,^,/usr/local/,' would mean adding
6989 `/usr/local' to both regular archive members and to link targets. In
6990 this case, `/lib/libc.so.6' would become:
6992 /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so
6994 This is definitely not desired. To avoid this, the `S' flag is
6995 used, which excludes symbolic link targets from filename
6996 transformations. The result is:
6998 $ tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \
6999 --show-transformed /lib
7000 drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/
7001 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so
7002 lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 \
7005 Unlike `--strip-components', `--transform' can be used in any GNU
7006 `tar' operation mode. For example, the following command adds files to
7007 the archive while replacing the leading `usr/' component with `var/':
7009 $ tar -cf arch.tar --transform='s,^usr/,var/,' /
7011 To test `--transform' effect we suggest using
7012 `--show-transformed-names' option:
7014 $ tar -cf arch.tar --transform='s,^usr/,var/,' \
7015 --verbose --show-transformed-names /
7017 If both `--strip-components' and `--transform' are used together,
7018 then `--transform' is applied first, and the required number of
7019 components is then stripped from its result.
7021 You can use as many `--transform' options in a single command line
7022 as you want. The specified expressions will then be applied in order
7023 of their appearance. For example, the following two invocations are
7026 $ tar -cf arch.tar --transform='s,/usr/var,/var/' \
7027 --transform='s,/usr/local,/usr/,'
7028 $ tar -cf arch.tar \
7029 --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'
7032 File: tar.info, Node: after, Next: recurse, Prev: transform, Up: Choosing
7034 6.8 Operating Only on New Files
7035 ===============================
7037 The `--after-date=DATE' (`--newer=DATE', `-N DATE') option causes `tar'
7038 to only work on files whose data modification or status change times
7039 are newer than the DATE given. If DATE starts with `/' or `.', it is
7040 taken to be a file name; the data modification time of that file is
7041 used as the date. If you use this option when creating or appending to
7042 an archive, the archive will only include new files. If you use
7043 `--after-date' when extracting an archive, `tar' will only extract
7044 files newer than the DATE you specify.
7046 If you only want `tar' to make the date comparison based on
7047 modification of the file's data (rather than status changes), then use
7048 the `--newer-mtime=DATE' option.
7050 You may use these options with any operation. Note that these
7051 options differ from the `--update' (`-u') operation in that they allow
7052 you to specify a particular date against which `tar' can compare when
7053 deciding whether or not to archive the files.
7058 Only store files newer than DATE.
7060 Acts on files only if their data modification or status change
7061 times are later than DATE. Use in conjunction with any operation.
7063 If DATE starts with `/' or `.', it is taken to be a file name; the
7064 data modification time of that file is used as the date.
7066 `--newer-mtime=DATE'
7067 Acts like `--after-date', but only looks at data modification
7070 These options limit `tar' to operate only on files which have been
7071 modified after the date specified. A file's status is considered to
7072 have changed if its contents have been modified, or if its owner,
7073 permissions, and so forth, have been changed. (For more information on
7074 how to specify a date, see *note Date input formats::; remember that the
7075 entire date argument must be quoted if it contains any spaces.)
7077 Gurus would say that `--after-date' tests both the data modification
7078 time (`mtime', the time the contents of the file were last modified)
7079 and the status change time (`ctime', the time the file's status was
7080 last changed: owner, permissions, etc.) fields, while `--newer-mtime'
7081 tests only the `mtime' field.
7083 To be precise, `--after-date' checks _both_ `mtime' and `ctime' and
7084 processes the file if either one is more recent than DATE, while
7085 `--newer-mtime' only checks `mtime' and disregards `ctime'. Neither
7086 does it use `atime' (the last time the contents of the file were looked
7089 Date specifiers can have embedded spaces. Because of this, you may
7090 need to quote date arguments to keep the shell from parsing them as
7091 separate arguments. For example, the following command will add to the
7092 archive all the files modified less than two days ago:
7094 $ tar -cf foo.tar --newer-mtime '2 days ago'
7096 When any of these options is used with the option `--verbose' (*note
7097 verbose tutorial::) GNU `tar' will try to convert the specified date
7098 back to its textual representation and compare that with the one given
7099 with the option. If the two dates differ, `tar' will print a warning
7100 saying what date it will use. This is to help user ensure he is using
7101 the right date. For example:
7103 $ tar -c -f archive.tar --after-date='10 days ago' .
7104 tar: Option --after-date: Treating date '10 days ago' as 2006-06-11
7107 *Please Note:* `--after-date' and `--newer-mtime' should not be
7108 used for incremental backups. *Note Incremental Dumps::, for
7109 proper way of creating incremental backups.
7112 File: tar.info, Node: recurse, Next: one, Prev: after, Up: Choosing
7114 6.9 Descending into Directories
7115 ===============================
7117 Usually, `tar' will recursively explore all directories (either those
7118 given on the command line or through the `--files-from' option) for the
7119 various files they contain. However, you may not always want `tar' to
7122 The `--no-recursion' option inhibits `tar''s recursive descent into
7123 specified directories. If you specify `--no-recursion', you can use
7124 the `find' (*note find: (find)Top.) utility for hunting through levels
7125 of directories to construct a list of file names which you could then
7126 pass to `tar'. `find' allows you to be more selective when choosing
7127 which files to archive; see *note files::, for more information on
7128 using `find' with `tar'.
7131 Prevents `tar' from recursively descending directories.
7134 Requires `tar' to recursively descend directories. This is the
7137 When you use `--no-recursion', GNU `tar' grabs directory entries
7138 themselves, but does not descend on them recursively. Many people use
7139 `find' for locating files they want to back up, and since `tar'
7140 _usually_ recursively descends on directories, they have to use the
7141 `-not -type d' test in their `find' invocation (*note Type:
7142 (find)Type.), as they usually do not want all the files in a directory.
7143 They then use the `--files-from' option to archive the files located
7146 The problem when restoring files archived in this manner is that the
7147 directories themselves are not in the archive; so the
7148 `--same-permissions' (`--preserve-permissions', `-p') option does not
7149 affect them--while users might really like it to. Specifying
7150 `--no-recursion' is a way to tell `tar' to grab only the directory
7151 entries given to it, adding no new files on its own. To summarize, if
7152 you use `find' to create a list of files to be stored in an archive,
7155 $ find DIR TESTS | \
7156 tar -cf ARCHIVE -T - --no-recursion
7158 The `--no-recursion' option also applies when extracting: it causes
7159 `tar' to extract only the matched directory entries, not the files
7160 under those directories.
7162 The `--no-recursion' option also affects how globbing patterns are
7163 interpreted (*note controlling pattern-matching::).
7165 The `--no-recursion' and `--recursion' options apply to later
7166 options and operands, and can be overridden by later occurrences of
7167 `--no-recursion' and `--recursion'. For example:
7169 $ tar -cf jams.tar --no-recursion grape --recursion grape/concord
7171 creates an archive with one entry for `grape', and the recursive
7172 contents of `grape/concord', but no entries under `grape' other than
7176 File: tar.info, Node: one, Prev: recurse, Up: Choosing
7178 6.10 Crossing File System Boundaries
7179 ====================================
7181 `tar' will normally automatically cross file system boundaries in order
7182 to archive files which are part of a directory tree. You can change
7183 this behavior by running `tar' and specifying `--one-file-system'.
7184 This option only affects files that are archived because they are in a
7185 directory that is being archived; `tar' will still archive files
7186 explicitly named on the command line or through `--files-from',
7187 regardless of where they reside.
7190 Prevents `tar' from crossing file system boundaries when
7191 archiving. Use in conjunction with any write operation.
7193 The `--one-file-system' option causes `tar' to modify its normal
7194 behavior in archiving the contents of directories. If a file in a
7195 directory is not on the same file system as the directory itself, then
7196 `tar' will not archive that file. If the file is a directory itself,
7197 `tar' will not archive anything beneath it; in other words, `tar' will
7198 not cross mount points.
7200 This option is useful for making full or incremental archival
7201 backups of a file system. If this option is used in conjunction with
7202 `--verbose' (`-v'), files that are excluded are mentioned by name on
7207 * directory:: Changing Directory
7208 * absolute:: Absolute File Names
7211 File: tar.info, Node: directory, Next: absolute, Up: one
7213 6.10.1 Changing the Working Directory
7214 -------------------------------------
7216 To change the working directory in the middle of a list of file names,
7217 either on the command line or in a file specified using `--files-from'
7218 (`-T'), use `--directory' (`-C'). This will change the working
7219 directory to the specified directory after that point in the list.
7221 `--directory=DIRECTORY'
7223 Changes the working directory in the middle of a command line.
7227 $ tar -c -f jams.tar grape prune -C food cherry
7229 will place the files `grape' and `prune' from the current directory
7230 into the archive `jams.tar', followed by the file `cherry' from the
7231 directory `food'. This option is especially useful when you have
7232 several widely separated files that you want to store in the same
7235 Note that the file `cherry' is recorded in the archive under the
7236 precise name `cherry', _not_ `food/cherry'. Thus, the archive will
7237 contain three files that all appear to have come from the same
7238 directory; if the archive is extracted with plain `tar --extract', all
7239 three files will be written in the current directory.
7241 Contrast this with the command,
7243 $ tar -c -f jams.tar grape prune -C food red/cherry
7245 which records the third file in the archive under the name `red/cherry'
7246 so that, if the archive is extracted using `tar --extract', the third
7247 file will be written in a subdirectory named `red'.
7249 You can use the `--directory' option to make the archive independent
7250 of the original name of the directory holding the files. The following
7251 command places the files `/etc/passwd', `/etc/hosts', and `/lib/libc.a'
7252 into the archive `foo.tar':
7254 $ tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a
7256 However, the names of the archive members will be exactly what they were
7257 on the command line: `passwd', `hosts', and `libc.a'. They will not
7258 appear to be related by file name to the original directories where
7259 those files were located.
7261 Note that `--directory' options are interpreted consecutively. If
7262 `--directory' specifies a relative file name, it is interpreted
7263 relative to the then current directory, which might not be the same as
7264 the original current working directory of `tar', due to a previous
7265 `--directory' option.
7267 When using `--files-from' (*note files::), you can put various `tar'
7268 options (including `-C') in the file list. Notice, however, that in
7269 this case the option and its argument may not be separated by
7270 whitespace. If you use short option, its argument must either follow
7271 the option letter immediately, without any intervening whitespace, or
7272 occupy the next line. Otherwise, if you use long option, separate its
7273 argument by an equal sign.
7275 For instance, the file list for the above example will be:
7283 To use it, you would invoke `tar' as follows:
7285 $ tar -c -f foo.tar --files-from list
7287 The interpretation of `--directory' is disabled by `--null' option.
7290 File: tar.info, Node: absolute, Prev: directory, Up: one
7292 6.10.2 Absolute File Names
7293 --------------------------
7295 By default, GNU `tar' drops a leading `/' on input or output, and
7296 complains about file names containing a `..' component. There is an
7297 option that turns off this behavior:
7301 Do not strip leading slashes from file names, and permit file names
7302 containing a `..' file name component.
7304 When `tar' extracts archive members from an archive, it strips any
7305 leading slashes (`/') from the member name. This causes absolute
7306 member names in the archive to be treated as relative file names. This
7307 allows you to have such members extracted wherever you want, instead of
7308 being restricted to extracting the member in the exact directory named
7309 in the archive. For example, if the archive member has the name
7310 `/etc/passwd', `tar' will extract it as if the name were really
7313 File names containing `..' can cause problems when extracting, so
7314 `tar' normally warns you about such files when creating an archive, and
7315 rejects attempts to extracts such files.
7317 Other `tar' programs do not do this. As a result, if you create an
7318 archive whose member names start with a slash, they will be difficult
7319 for other people with a non-GNU `tar' program to use. Therefore, GNU
7320 `tar' also strips leading slashes from member names when putting
7321 members into the archive. For example, if you ask `tar' to add the file
7322 `/bin/ls' to an archive, it will do so, but the member name will be
7325 Symbolic links containing `..' or leading `/' can also cause
7326 problems when extracting, so `tar' normally extracts them last; it may
7327 create empty files as placeholders during extraction.
7329 If you use the `--absolute-names' (`-P') option, `tar' will do none
7330 of these transformations.
7332 To archive or extract files relative to the root directory, specify
7333 the `--absolute-names' (`-P') option.
7335 Normally, `tar' acts on files relative to the working
7336 directory--ignoring superior directory names when archiving, and
7337 ignoring leading slashes when extracting.
7339 When you specify `--absolute-names' (`-P'), `tar' stores file names
7340 including all superior directory names, and preserves leading slashes.
7341 If you only invoked `tar' from the root directory you would never need
7342 the `--absolute-names' option, but using this option may be more
7343 convenient than switching to root.
7346 Preserves full file names (including superior directory names) when
7347 archiving and extracting files.
7350 `tar' prints out a message about removing the `/' from file names.
7351 This message appears once per GNU `tar' invocation. It represents
7352 something which ought to be told; ignoring what it means can cause very
7353 serious surprises, later.
7355 Some people, nevertheless, do not want to see this message. Wanting
7356 to play really dangerously, one may of course redirect `tar' standard
7357 error to the sink. For example, under `sh':
7359 $ tar -c -f archive.tar /home 2> /dev/null
7361 Another solution, both nicer and simpler, would be to change to the `/'
7362 directory first, and then avoid absolute notation. For example:
7364 $ tar -c -f archive.tar -C / home
7366 *Note Integrity::, for some of the security-related implications of
7369 ---------- Footnotes ----------
7371 (1) A side effect of this is that when `--create' is used with
7372 `--verbose' the resulting output is not, generally speaking, the same
7373 as the one you'd get running `tar --list' command. This may be
7374 important if you use some scripts for comparing both outputs. *Note
7375 listing member and file names::, for the information on how to handle
7379 File: tar.info, Node: Date input formats, Next: Formats, Prev: Choosing, Up: Top
7381 7 Date input formats
7382 ********************
7386 Our units of temporal measurement, from seconds on up to months,
7387 are so complicated, asymmetrical and disjunctive so as to make
7388 coherent mental reckoning in time all but impossible. Indeed, had
7389 some tyrannical god contrived to enslave our minds to time, to
7390 make it all but impossible for us to escape subjection to sodden
7391 routines and unpleasant surprises, he could hardly have done
7392 better than handing down our present system. It is like a set of
7393 trapezoidal building blocks, with no vertical or horizontal
7394 surfaces, like a language in which the simplest thought demands
7395 ornate constructions, useless particles and lengthy
7396 circumlocutions. Unlike the more successful patterns of language
7397 and science, which enable us to face experience boldly or at least
7398 level-headedly, our system of temporal calculation silently and
7399 persistently encourages our terror of time.
7401 ... It is as though architects had to measure length in feet,
7402 width in meters and height in ells; as though basic instruction
7403 manuals demanded a knowledge of five different languages. It is
7404 no wonder then that we often look into our own immediate past or
7405 future, last Tuesday or a week from Sunday, with feelings of
7406 helpless confusion. ...
7408 --Robert Grudin, `Time and the Art of Living'.
7410 This section describes the textual date representations that GNU
7411 programs accept. These are the strings you, as a user, can supply as
7412 arguments to the various programs. The C interface (via the
7413 `parse_datetime' function) is not described here.
7417 * General date syntax:: Common rules.
7418 * Calendar date items:: 19 Dec 1994.
7419 * Time of day items:: 9:20pm.
7420 * Time zone items:: EST, PDT, UTC, ...
7421 * Combined date and time of day items:: 1972-09-24T20:02:00,000000-0500.
7422 * Day of week items:: Monday and others.
7423 * Relative items in date strings:: next tuesday, 2 years ago.
7424 * Pure numbers in date strings:: 19931219, 1440.
7425 * Seconds since the Epoch:: @1078100502.
7426 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
7427 * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al.
7430 File: tar.info, Node: General date syntax, Next: Calendar date items, Up: Date input formats
7432 7.1 General date syntax
7433 =======================
7435 A "date" is a string, possibly empty, containing many items separated
7436 by whitespace. The whitespace may be omitted when no ambiguity arises.
7437 The empty string means the beginning of today (i.e., midnight). Order
7438 of the items is immaterial. A date string may contain many flavors of
7441 * calendar date items
7447 * combined date and time of day items
7449 * day of the week items
7455 We describe each of these item types in turn, below.
7457 A few ordinal numbers may be written out in words in some contexts.
7458 This is most useful for specifying day of the week items or relative
7459 items (see below). Among the most commonly used ordinal numbers, the
7460 word `last' stands for -1, `this' stands for 0, and `first' and `next'
7461 both stand for 1. Because the word `second' stands for the unit of
7462 time there is no way to write the ordinal number 2, but for convenience
7463 `third' stands for 3, `fourth' for 4, `fifth' for 5, `sixth' for 6,
7464 `seventh' for 7, `eighth' for 8, `ninth' for 9, `tenth' for 10,
7465 `eleventh' for 11 and `twelfth' for 12.
7467 When a month is written this way, it is still considered to be
7468 written numerically, instead of being "spelled in full"; this changes
7469 the allowed strings.
7471 In the current implementation, only English is supported for words
7472 and abbreviations like `AM', `DST', `EST', `first', `January',
7473 `Sunday', `tomorrow', and `year'.
7475 The output of the `date' command is not always acceptable as a date
7476 string, not only because of the language problem, but also because
7477 there is no standard meaning for time zone items like `IST'. When using
7478 `date' to generate a date string intended to be parsed later, specify a
7479 date format that is independent of language and that does not use time
7480 zone items other than `UTC' and `Z'. Here are some ways to do this:
7482 $ LC_ALL=C TZ=UTC0 date
7483 Mon Mar 1 00:21:42 UTC 2004
7484 $ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ'
7485 2004-03-01 00:21:42Z
7486 $ date --rfc-3339=ns # --rfc-3339 is a GNU extension.
7487 2004-02-29 16:21:42.692722128-08:00
7488 $ date --rfc-2822 # a GNU extension
7489 Sun, 29 Feb 2004 16:21:42 -0800
7490 $ date +'%Y-%m-%d %H:%M:%S %z' # %z is a GNU extension.
7491 2004-02-29 16:21:42 -0800
7492 $ date +'@%s.%N' # %s and %N are GNU extensions.
7493 @1078100502.692722128
7495 Alphabetic case is completely ignored in dates. Comments may be
7496 introduced between round parentheses, as long as included parentheses
7497 are properly nested. Hyphens not followed by a digit are currently
7498 ignored. Leading zeros on numbers are ignored.
7500 Invalid dates like `2005-02-29' or times like `24:00' are rejected.
7501 In the typical case of a host that does not support leap seconds, a
7502 time like `23:59:60' is rejected even if it corresponds to a valid leap
7506 File: tar.info, Node: Calendar date items, Next: Time of day items, Prev: General date syntax, Up: Date input formats
7508 7.2 Calendar date items
7509 =======================
7511 A "calendar date item" specifies a day of the year. It is specified
7512 differently, depending on whether the month is specified numerically or
7513 literally. All these strings specify the same calendar date:
7515 1972-09-24 # ISO 8601.
7516 72-9-24 # Assume 19xx for 69 through 99,
7517 # 20xx for 00 through 68.
7518 72-09-24 # Leading zeros are ignored.
7519 9/24/72 # Common U.S. writing.
7521 24 Sept 72 # September has a special abbreviation.
7522 24 Sep 72 # Three-letter abbreviations always allowed.
7527 The year can also be omitted. In this case, the last specified year
7528 is used, or the current year if none. For example:
7535 For numeric months, the ISO 8601 format `YEAR-MONTH-DAY' is allowed,
7536 where YEAR is any positive number, MONTH is a number between 01 and 12,
7537 and DAY is a number between 01 and 31. A leading zero must be present
7538 if a number is less than ten. If YEAR is 68 or smaller, then 2000 is
7539 added to it; otherwise, if YEAR is less than 100, then 1900 is added to
7540 it. The construct `MONTH/DAY/YEAR', popular in the United States, is
7541 accepted. Also `MONTH/DAY', omitting the year.
7543 Literal months may be spelled out in full: `January', `February',
7544 `March', `April', `May', `June', `July', `August', `September',
7545 `October', `November' or `December'. Literal months may be abbreviated
7546 to their first three letters, possibly followed by an abbreviating dot.
7547 It is also permitted to write `Sept' instead of `September'.
7549 When months are written literally, the calendar date may be given as
7550 any of the following:
7557 Or, omitting the year:
7562 File: tar.info, Node: Time of day items, Next: Time zone items, Prev: Calendar date items, Up: Date input formats
7564 7.3 Time of day items
7565 =====================
7567 A "time of day item" in date strings specifies the time on a given day.
7568 Here are some examples, all of which represent the same time:
7573 20:02-0500 # In EST (U.S. Eastern Standard Time).
7575 More generally, the time of day may be given as
7576 `HOUR:MINUTE:SECOND', where HOUR is a number between 0 and 23, MINUTE
7577 is a number between 0 and 59, and SECOND is a number between 0 and 59
7578 possibly followed by `.' or `,' and a fraction containing one or more
7579 digits. Alternatively, `:SECOND' can be omitted, in which case it is
7580 taken to be zero. On the rare hosts that support leap seconds, SECOND
7583 If the time is followed by `am' or `pm' (or `a.m.' or `p.m.'), HOUR
7584 is restricted to run from 1 to 12, and `:MINUTE' may be omitted (taken
7585 to be zero). `am' indicates the first half of the day, `pm' indicates
7586 the second half of the day. In this notation, 12 is the predecessor of
7587 1: midnight is `12am' while noon is `12pm'. (This is the zero-oriented
7588 interpretation of `12am' and `12pm', as opposed to the old tradition
7589 derived from Latin which uses `12m' for noon and `12pm' for midnight.)
7591 The time may alternatively be followed by a time zone correction,
7592 expressed as `SHHMM', where S is `+' or `-', HH is a number of zone
7593 hours and MM is a number of zone minutes. The zone minutes term, MM,
7594 may be omitted, in which case the one- or two-digit correction is
7595 interpreted as a number of hours. You can also separate HH from MM
7596 with a colon. When a time zone correction is given this way, it forces
7597 interpretation of the time relative to Coordinated Universal Time
7598 (UTC), overriding any previous specification for the time zone or the
7599 local time zone. For example, `+0530' and `+05:30' both stand for the
7600 time zone 5.5 hours ahead of UTC (e.g., India). This is the best way to
7601 specify a time zone correction by fractional parts of an hour. The
7602 maximum zone correction is 24 hours.
7604 Either `am'/`pm' or a time zone correction may be specified, but not
7608 File: tar.info, Node: Time zone items, Next: Combined date and time of day items, Prev: Time of day items, Up: Date input formats
7613 A "time zone item" specifies an international time zone, indicated by a
7614 small set of letters, e.g., `UTC' or `Z' for Coordinated Universal
7615 Time. Any included periods are ignored. By following a
7616 non-daylight-saving time zone by the string `DST' in a separate word
7617 (that is, separated by some white space), the corresponding daylight
7618 saving time zone may be specified. Alternatively, a
7619 non-daylight-saving time zone can be followed by a time zone
7620 correction, to add the two values. This is normally done only for
7621 `UTC'; for example, `UTC+05:30' is equivalent to `+05:30'.
7623 Time zone items other than `UTC' and `Z' are obsolescent and are not
7624 recommended, because they are ambiguous; for example, `EST' has a
7625 different meaning in Australia than in the United States. Instead,
7626 it's better to use unambiguous numeric time zone corrections like
7627 `-0500', as described in the previous section.
7629 If neither a time zone item nor a time zone correction is supplied,
7630 time stamps are interpreted using the rules of the default time zone
7631 (*note Specifying time zone rules::).
7634 File: tar.info, Node: Combined date and time of day items, Next: Day of week items, Prev: Time zone items, Up: Date input formats
7636 7.5 Combined date and time of day items
7637 =======================================
7639 The ISO 8601 date and time of day extended format consists of an ISO
7640 8601 date, a `T' character separator, and an ISO 8601 time of day.
7641 This format is also recognized if the `T' is replaced by a space.
7643 In this format, the time of day should use 24-hour notation.
7644 Fractional seconds are allowed, with either comma or period preceding
7645 the fraction. ISO 8601 fractional minutes and hours are not supported.
7646 Typically, hosts support nanosecond timestamp resolution; excess
7647 precision is silently discarded.
7649 Here are some examples:
7651 2012-09-24T20:02:00.052-0500
7652 2012-12-31T23:59:59,999999999+1100
7656 File: tar.info, Node: Day of week items, Next: Relative items in date strings, Prev: Combined date and time of day items, Up: Date input formats
7658 7.6 Day of week items
7659 =====================
7661 The explicit mention of a day of the week will forward the date (only
7662 if necessary) to reach that day of the week in the future.
7664 Days of the week may be spelled out in full: `Sunday', `Monday',
7665 `Tuesday', `Wednesday', `Thursday', `Friday' or `Saturday'. Days may
7666 be abbreviated to their first three letters, optionally followed by a
7667 period. The special abbreviations `Tues' for `Tuesday', `Wednes' for
7668 `Wednesday' and `Thur' or `Thurs' for `Thursday' are also allowed.
7670 A number may precede a day of the week item to move forward
7671 supplementary weeks. It is best used in expression like `third
7672 monday'. In this context, `last DAY' or `next DAY' is also acceptable;
7673 they move one week before or after the day that DAY by itself would
7676 A comma following a day of the week item is ignored.