X-Git-Url: https://git.gag.com/?a=blobdiff_plain;f=doc%2Fgzip.texi;fp=doc%2Fgzip.texi;h=9be2aa38d3d5d8d4a2c2501662dceff9094eeef9;hb=0d5a754ba8f2cc33e98d48d559f0ad6cd18a43a3;hp=0000000000000000000000000000000000000000;hpb=ad96056bdcf62abd585cdb53768fbabdde75d1b5;p=debian%2Fgzip diff --git a/doc/gzip.texi b/doc/gzip.texi new file mode 100644 index 0000000..9be2aa3 --- /dev/null +++ b/doc/gzip.texi @@ -0,0 +1,505 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header +@setfilename gzip.info +@include version.texi +@settitle Gzip User's Manual +@finalout +@setchapternewpage odd +@c %**end of header +@copying +This manual is for Gzip +(version @value{VERSION}, @value{UPDATED}), +and documents commands for compressing and decompressing data. + +Copyright @copyright{} 1998, 1999, 2001, 2002, 2006 Free Software +Foundation, Inc. + +Copyright @copyright{} 1992, 1993 Jean-loup Gailly + +@quotation +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no +Invariant Sections, with no Front-Cover Texts, and with no Back-Cover +Texts. A copy of the license is included in the section entitled ``GNU +Free Documentation License''. +@end quotation +@end copying + +@c Debian install-info (up through at least version 1.9.20) uses only the +@c first dircategory. Put this one first, as it is more useful in practice. +@dircategory Individual utilities +@direntry +* gzip: (gzip)Invoking gzip. Compress files. +@end direntry + +@dircategory Utilities +@direntry +* Gzip: (gzip). The gzip command for compressing files. +@end direntry + +@titlepage +@title gzip +@subtitle The data compression program +@subtitle for Gzip Version @value{VERSION} +@subtitle @value{UPDATED} +@author by Jean-loup Gailly + +@page +@vskip 0pt plus 1filll +@insertcopying +@end titlepage + +@contents + +@ifnottex +@node Top, , , (dir) +@top Compressing Files + +@insertcopying +@end ifnottex + +@menu +* Overview:: Preliminary information. +* Sample:: Sample output from @code{gzip}. +* Invoking gzip:: How to run @code{gzip}. +* Advanced usage:: Concatenated files. +* Environment:: The @code{GZIP} environment variable +* Tapes:: Using @code{gzip} on tapes. +* Problems:: Reporting bugs. +* Copying This Manual:: How to make copies of this manual. +* Concept Index:: Index of concepts. +@end menu + +@node Overview, Sample, , Top +@chapter Overview +@cindex overview + +@code{gzip} reduces the size of the named files using Lempel-Ziv coding +(LZ77). Whenever possible, each file is replaced by one with the +extension @samp{.gz}, while keeping the same ownership modes, access and +modification times. (The default extension is @samp{-gz} for VMS, +@samp{z} for MSDOS, OS/2 FAT and Atari.) If no files are specified or +if a file name is "-", the standard input is compressed to the standard +output. @code{gzip} will only attempt to compress regular files. In +particular, it will ignore symbolic links. + +If the new file name is too long for its file system, @code{gzip} +truncates it. @code{gzip} attempts to truncate only the parts of the +file name longer than 3 characters. (A part is delimited by dots.) If +the name consists of small parts only, the longest parts are truncated. +For example, if file names are limited to 14 characters, gzip.msdos.exe +is compressed to gzi.msd.exe.gz. Names are not truncated on systems +which do not have a limit on file name length. + +By default, @code{gzip} keeps the original file name and timestamp in +the compressed file. These are used when decompressing the file with the +@samp{-N} option. This is useful when the compressed file name was +truncated or when the time stamp was not preserved after a file +transfer. However, due to limitations in the current @code{gzip} file +format, fractional seconds are discarded. Also, time stamps must fall +within the range 1970-01-01 00:00:00 through 2106-02-07 06:28:15 +@acronym{UTC}, and hosts whose operating systems use 32-bit time +stamps are further restricted to time stamps no later than 2038-01-19 +03:14:07 @acronym{UTC}. The upper bounds assume the typical case +where leap seconds are ignored. + +Compressed files can be restored to their original form using @samp{gzip -d} +or @code{gunzip} or @code{zcat}. If the original name saved in the +compressed file is not suitable for its file system, a new name is +constructed from the original one to make it legal. + +@code{gunzip} takes a list of files on its command line and replaces +each file whose name ends with @samp{.gz}, @samp{.z}, @samp{.Z}, +@samp{-gz}, @samp{-z} or @samp{_z} and which begins with the correct +magic number with an uncompressed file without the original extension. +@code{gunzip} also recognizes the special extensions @samp{.tgz} and +@samp{.taz} as shorthands for @samp{.tar.gz} and @samp{.tar.Z} +respectively. When compressing, @code{gzip} uses the @samp{.tgz} +extension if necessary instead of truncating a file with a @samp{.tar} +extension. + +@code{gunzip} can currently decompress files created by @code{gzip}, +@code{zip}, @code{compress} or @code{pack}. The detection of the input +format is automatic. When using the first two formats, @code{gunzip} +checks a 32 bit CRC (cyclic redundancy check). For @code{pack}, +@code{gunzip} checks the uncompressed length. The @code{compress} format +was not designed to allow consistency checks. However @code{gunzip} is +sometimes able to detect a bad @samp{.Z} file. If you get an error when +uncompressing a @samp{.Z} file, do not assume that the @samp{.Z} file is +correct simply because the standard @code{uncompress} does not complain. +This generally means that the standard @code{uncompress} does not check +its input, and happily generates garbage output. The SCO @samp{compress +-H} format (@code{lzh} compression method) does not include a CRC but +also allows some consistency checks. + +Files created by @code{zip} can be uncompressed by @code{gzip} only if +they have a single member compressed with the 'deflation' method. This +feature is only intended to help conversion of @code{tar.zip} files to +the @code{tar.gz} format. To extract a @code{zip} file with a single +member, use a command like @samp{gunzip . +@end example + +This is the output of the command @samp{gzip -v texinfo.tex}: + +@example +texinfo.tex: 69.7% -- replaced with texinfo.tex.gz +@end example + +The following command will find all @code{gzip} files in the current +directory and subdirectories, and extract them in place without +destroying the original: + +@example +find . -name '*.gz' -print | sed 's/^\(.*\)[.]gz$/gunzip < "&" > "\1"/' | sh +@end example + +@node Invoking gzip, Advanced usage, Sample, Top +@chapter Invoking @code{gzip} +@cindex invoking +@cindex options + +The format for running the @code{gzip} program is: + +@example +gzip @var{option} @dots{} +@end example + +@code{gzip} supports the following options: + +@table @samp +@item --stdout +@itemx --to-stdout +@itemx -c +Write output on standard output; keep original files unchanged. +If there are several input files, the output consists of a sequence of +independently compressed members. To obtain better compression, +concatenate all input files before compressing them. + +@item --decompress +@itemx --uncompress +@itemx -d +Decompress. + +@item --force +@itemx -f +Force compression or decompression even if the file has multiple links +or the corresponding file already exists, or if the compressed data +is read from or written to a terminal. If the input data is not in +a format recognized by @code{gzip}, and if the option @samp{--stdout} is also +given, copy the input data without change to the standard output: let +@code{zcat} behave as @code{cat}. If @samp{-f} is not given, and +when not running in the background, @code{gzip} prompts to verify +whether an existing file should be overwritten. + +@item --help +@itemx -h +Print an informative help message describing the options then quit. + +@item --list +@itemx -l +For each compressed file, list the following fields: + +@example +compressed size: size of the compressed file +uncompressed size: size of the uncompressed file +ratio: compression ratio (0.0% if unknown) +uncompressed_name: name of the uncompressed file +@end example + +The uncompressed size is given as @samp{-1} for files not in @code{gzip} +format, such as compressed @samp{.Z} files. To get the uncompressed size for +such a file, you can use: + +@example +zcat file.Z | wc -c +@end example + +In combination with the @samp{--verbose} option, the following fields are also +displayed: + +@example +method: compression method (deflate,compress,lzh,pack) +crc: the 32-bit CRC of the uncompressed data +date & time: time stamp for the uncompressed file +@end example + +The crc is given as ffffffff for a file not in gzip format. + +With @samp{--verbose}, the size totals and compression ratio for all files +is also displayed, unless some sizes are unknown. With @samp{--quiet}, +the title and totals lines are not displayed. + +The @code{gzip} format represents the input size modulo +@math{2^32}, so the uncompressed size and compression ratio are listed +incorrectly for uncompressed files 4 GB and larger. To work around +this problem, you can use the following command to discover a large +uncompressed file's true size: + +@example +zcat file.gz | wc -c +@end example + +@item --license +@itemx -L +Display the @code{gzip} license then quit. + +@item --no-name +@itemx -n +When compressing, do not save the original file name and time stamp by +default. (The original name is always saved if the name had to be +truncated.) When decompressing, do not restore the original file name +if present (remove only the @code{gzip} +suffix from the compressed file name) and do not restore the original +time stamp if present (copy it from the compressed file). This option +is the default when decompressing. + +@item --name +@itemx -N +When compressing, always save the original file name and time stamp; this +is the default. When decompressing, restore the original file name and +time stamp if present. This option is useful on systems which have +a limit on file name length or when the time stamp has been lost after +a file transfer. + +@item --quiet +@itemx -q +Suppress all warning messages. + +@item --recursive +@itemx -r +Travel the directory structure recursively. If any of the file names +specified on the command line are directories, @code{gzip} will descend +into the directory and compress all the files it finds there (or +decompress them in the case of @code{gunzip}). + +@item --suffix @var{suf} +@itemx -S @var{suf} +Use suffix @samp{@var{suf}} instead of @samp{.gz}. Any suffix can be +given, but suffixes other than @samp{.z} and @samp{.gz} should be +avoided to avoid confusion when files are transferred to other systems. +A null suffix forces gunzip to try decompression on all given files +regardless of suffix, as in: + +@example +gunzip -S "" * (*.* for MSDOS) +@end example + +Previous versions of gzip used the @samp{.z} suffix. This was changed to +avoid a conflict with @code{pack}. + +@item --test +@itemx -t +Test. Check the compressed file integrity. + +@item --verbose +@itemx -v +Verbose. Display the name and percentage reduction for each file compressed. + +@item --version +@itemx -V +Version. Display the version number and compilation options, then quit. + +@item --fast +@itemx --best +@itemx -@var{n} +Regulate the speed of compression using the specified digit @var{n}, +where @samp{-1} or @samp{--fast} indicates the fastest compression +method (less compression) and @samp{--best} or @samp{-9} indicates the +slowest compression method (optimal compression). The default +compression level is @samp{-6} (that is, biased towards high compression at +expense of speed). +@end table + +@node Advanced usage, Environment, Invoking gzip, Top +@chapter Advanced usage +@cindex concatenated files + +Multiple compressed files can be concatenated. In this case, +@code{gunzip} will extract all members at once. If one member is +damaged, other members might still be recovered after removal of the +damaged member. Better compression can be usually obtained if all +members are decompressed and then recompressed in a single step. + +This is an example of concatenating @code{gzip} files: + +@example +gzip -c file1 > foo.gz +gzip -c file2 >> foo.gz +@end example + +Then + +@example +gunzip -c foo +@end example + +is equivalent to + +@example +cat file1 file2 +@end example + +In case of damage to one member of a @samp{.gz} file, other members can +still be recovered (if the damaged member is removed). However, +you can get better compression by compressing all members at once: + +@example +cat file1 file2 | gzip > foo.gz +@end example + +compresses better than + +@example +gzip -c file1 file2 > foo.gz +@end example + +If you want to recompress concatenated files to get better compression, do: + +@example +zcat old.gz | gzip > new.gz +@end example + +If a compressed file consists of several members, the uncompressed +size and CRC reported by the @samp{--list} option applies to the last member +only. If you need the uncompressed size for all members, you can use: + +@example +zcat file.gz | wc -c +@end example + +If you wish to create a single archive file with multiple members so +that members can later be extracted independently, use an archiver such +as @code{tar} or @code{zip}. GNU @code{tar} supports the @samp{-z} +option to invoke @code{gzip} transparently. @code{gzip} is designed as a +complement to @code{tar}, not as a replacement. + +@node Environment, Tapes, Advanced usage, Top +@chapter Environment +@cindex Environment + +The environment variable @code{GZIP} can hold a set of default options for +@code{gzip}. These options are interpreted first and can be overwritten by +explicit command line parameters. For example: + +@example +for sh: GZIP="-8v --name"; export GZIP +for csh: setenv GZIP "-8v --name" +for MSDOS: set GZIP=-8v --name +@end example + +On Vax/VMS, the name of the environment variable is @code{GZIP_OPT}, to +avoid a conflict with the symbol set for invocation of the program. + +@node Tapes, Problems, Environment, Top +@chapter Using @code{gzip} on tapes +@cindex tapes + +When writing compressed data to a tape, it is generally necessary to pad +the output with zeroes up to a block boundary. When the data is read and +the whole block is passed to @code{gunzip} for decompression, +@code{gunzip} detects that there is extra trailing garbage after the +compressed data and emits a warning by default if the garbage contains +nonzero bytes. You have to use the +@samp{--quiet} option to suppress the warning. This option can be set in the +@code{GZIP} environment variable, as in: + +@example +for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0 +for csh: (setenv GZIP "-q"; tar -xfz --block-compress /dev/rst0) +@end example + +In the above example, @code{gzip} is invoked implicitly by the @samp{-z} +option of GNU @code{tar}. Make sure that the same block size (@samp{-b} +option of @code{tar}) is used for reading and writing compressed data on +tapes. (This example assumes you are using the GNU version of +@code{tar}.) + +@node Problems, Copying This Manual, Tapes, Top +@chapter Reporting Bugs +@cindex bugs + +If you find a bug in @code{gzip}, please send electronic mail to +@email{bug-gzip@@gnu.org}. Include the version number, +which you can find by running @w{@samp{gzip -V}}. Also include in your +message the hardware and operating system, the compiler used to compile +@code{gzip}, +a description of the bug behavior, and the input to @code{gzip} that triggered +the bug.@refill + +@node Copying This Manual, Concept Index, Problems, Top +@appendix Copying This Manual + +@menu +* GNU Free Documentation License:: License for copying this manual. +@end menu + +@include fdl.texi + +@node Concept Index, , Copying This Manual, Top +@appendix Concept Index + +@printindex cp + +@bye