-.PU
.TH GZIP 1 local
.SH NAME
gzip, gunzip, zcat \- compress or expand files
.SH SYNOPSIS
.ll +8
.B gzip
-.RB [ " \-acdfhlLnNrtvV19 " ]
+.RB [ " \-acdfhklLnNrtvV19 " ]
.RB [ \-S\ suffix ]
[
.I "name \&..."
.ll -8
.br
.B gunzip
-.RB [ " \-acfhlLnNrtvV " ]
+.RB [ " \-acfhklLnNrtvV " ]
.RB [ \-S\ suffix ]
[
.I "name \&..."
reduces the size of the named files using Lempel-Ziv coding (LZ77).
Whenever possible,
each file is replaced by one with the extension
-.B "\&.gz,"
+.BR "\&.gz" ,
while keeping the same ownership modes, access and modification times.
(The default extension is
-.B "\-gz"
-for VMS,
.B "z"
for MSDOS, OS/2 FAT, Windows NT FAT and Atari.)
If no files are specified, or if a file name is "-", the standard input is
or
.I gunzip
or
-.I zcat.
+.IR 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.
.PP
.I gunzip
takes a list of files on its command line and replaces each
-file whose name ends with .gz, -gz, .z, -z, _z or .Z
+file whose name ends with .gz, -gz, .z, -z, or _z (ignoring case)
and which begins with the correct magic number with an uncompressed
file without the original extension.
.I gunzip
.PP
.I gunzip
can currently decompress files created by
-.I gzip, zip, compress, compress -H
+.IR gzip ,
+.IR zip ,
+.IR compress ,
+.I "compress -H"
or
-.I pack.
+.IR pack .
The detection of the input format is automatic. When using
the first two formats,
.I gunzip
checks a 32 bit CRC. For
-.I pack, gunzip
+.I pack
+and
+.I gunzip
checks the uncompressed length. The standard
.I compress
format was not designed to allow consistency checks. However
.I zip
can be uncompressed by gzip only if they have a single member compressed
with the 'deflation' method. This feature is only intended to help
-conversion of tar.zip files to the tar.gz format. To extract zip files
+conversion of tar.zip files to the tar.gz format. To extract a
+.I zip
+file with a single member, use a command like
+.I "gunzip <foo.zip"
+or
+.IR "gunzip -S .zip foo.zip" .
+To extract zip files
with several members, use
.I unzip
instead of
-.I gunzip.
+.IR gunzip .
.PP
.I zcat
is identical to
.I gunzip
-.B \-c.
+.BR \-c .
(On some systems,
.I zcat
may be installed as
.I gzcat
to preserve the original link to
-.I compress.)
+.IR compress .)
.I zcat
uncompresses either a list of files on the command line or its
standard input and writes the uncompressed data on standard output.
Typically, text such as source code or English
is reduced by 60\-70%.
Compression is generally much better than that achieved by
-LZW (as used in
+LZW (as used in
.IR compress ),
Huffman coding (as used in
.IR pack ),
.I gzip
preserves the mode, ownership and timestamps of files when compressing
or decompressing.
-
.SH OPTIONS
.TP
.B \-a --ascii
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
-.I gzip,
+.IR gzip ,
and if the option --stdout is also given, copy the input data without change
-to the standard ouput: let
+to the standard output: let
.I zcat
behave as
-.I cat.
+.IR cat .
If
.B \-f
is not given,
.B \-h --help
Display a help screen and quit.
.TP
+.B \-k --keep
+Keep (don't delete) input files during compression or decompression.
+.TP
.B \-l --list
For each compressed file, list the following fields:
.TP
.B \-r --recursive
Travel the directory structure recursively. If any of the file names
-specified on the command line are directories,
+specified on the command line are directories,
.I gzip
will descend into the directory and compress all the files it finds there
(or decompress them in the case of
).
.TP
.B \-S .suf --suffix .suf
-Use suffix .suf instead of .gz. Any suffix can be given, but suffixes
+When compressing, use suffix .suf instead of .gz.
+Any non-empty suffix can be given, but suffixes
other than .z and .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:
-
- gunzip -S "" * (*.* for MSDOS)
+are transferred to other systems.
-Previous versions of gzip used
-the .z suffix. This was changed to avoid a conflict with
-.IR pack "(1)".
+When decompressing, add .suf to the beginning of the list of
+suffixes to try, when deriving an output file name from an input file name.
+.TP
+.B --synchronous
+Use synchronous output. With this option,
+.I gzip
+is less likely to lose data during a system crash, but it can be
+considerably slower.
.TP
.B \-t --test
Test. Check the compressed file integrity.
The default compression level is
.BR \-6
(that is, biased towards high compression at expense of speed).
+.TP
+.B \-\-rsyncable
+When you synchronize a compressed file between two computers, this option allows rsync to transfer only files that were changed in the archive instead of the entire archive.
+Normally, after a change is made to any file in the archive, the compression algorithm can generate a new version of the archive that does not match the previous version of the archive. In this case, rsync transfers the entire new version of the archive to the remote computer.
+With this option, rsync can transfer only the changed files as well as a small amount of metadata that is required to update the archive structure in the area that was changed.
.SH "ADVANCED USAGE"
Multiple compressed files can be concatenated. In this case,
.I gunzip
gzip -c file2 >> foo.gz
Then
+
gunzip -c foo
is equivalent to
transparently. gzip is designed as a complement to tar, not as a
replacement.
.SH "ENVIRONMENT"
-The environment variable
+The obsolescent environment variable
.B GZIP
can hold a set of default options for
-.I gzip.
-These options are interpreted first and can be overwritten by
-explicit command line parameters. For example:
- for sh: GZIP="-8v --name"; export GZIP
- for csh: setenv GZIP "-8v --name"
- for MSDOS: set GZIP=-8v --name
+.IR gzip .
+These options are interpreted first and can be overwritten by explicit
+command line parameters. As this can cause problems when using
+scripts, this feature is supported only for options that are
+reasonably likely to not cause too much harm, and
+.I gzip
+warns if it is used.
+This feature will be removed in a future release of
+.IR gzip .
+.PP
+You can use an alias or script instead. For example, if
+.I gzip
+is in the directory
+.B /usr/bin
+you can prepend
+.B $HOME/bin
+to your
+.B PATH
+and create an executable script
+.B $HOME/bin/gzip
+containing the following:
-On Vax/VMS, the name of the environment variable is GZIP_OPT, to
-avoid a conflict with the symbol set for invocation of the program.
+ #! /bin/sh
+ export PATH=/usr/bin
+ exec gzip \-9 "$@"
.SH "SEE ALSO"
-znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1),
-pack(1), compact(1)
+znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1)
+.PP
+The
+.I gzip
+file format is specified in P. Deutsch, \s-1GZIP\s0 file format
+specification version 4.3,
+.BR <http://www.ietf.org/rfc/rfc1952.txt> ,
+Internet RFC 1952 (May 1996).
+The
+.I zip
+deflation format is specified in P. Deutsch, \s-1DEFLATE\s0 Compressed
+Data Format Specification version 1.3,
+.BR <http://www.ietf.org/rfc/rfc1951.txt> ,
+Internet RFC 1951 (May 1996).
.SH "DIAGNOSTICS"
Exit status is normally 0;
if an error occurs, exit status is 1. If a warning occurs, exit status is 2.
-.PP
-Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
-.in +8
+.TP
+Usage: gzip [-cdfhklLnNrtvV19] [-S suffix] [file ...]
Invalid options were specified on the command line.
-.in -8
-.IR file :
-not in gzip format
-.in +8
+.TP
+\fIfile\fP\^: not in gzip format
The file specified to
.I gunzip
has not been compressed.
-.in -8
-.IR file:
-Corrupt input. Use zcat to recover some data.
-.in +8
+.TP
+\fIfile\fP\^: Corrupt input. Use zcat to recover some data.
The compressed file has been damaged. The data up to the point of failure
can be recovered using
-.in +8
-zcat file > recover
-.in -16
-.IR file :
-compressed with
-.I xx
-bits, can only handle
-.I yy
-bits
-.in +8
+
+ zcat \fIfile\fP > recover
+.TP
+\fIfile\fP\^: compressed with \fIxx\fP bits, can only handle \fIyy\fP bits
.I File
was compressed (using LZW) by a program that could deal with
-more
+more
.I bits
than the decompress code on this machine.
Recompress the file with gzip, which compresses better and uses
less memory.
-.in -8
-.IR file :
-already has .gz suffix -- no change
-.in +8
+.TP
+\fIfile\fP\^: already has .gz suffix -- unchanged
The file is assumed to be already compressed.
Rename the file and try again.
-.in -8
-.I file
-already exists; do you wish to overwrite (y or n)?
-.in +8
+.TP
+\fIfile\fP already exists; do you wish to overwrite (y or n)?
Respond "y" if you want the output file to be replaced; "n" if not.
-.in -8
+.TP
gunzip: corrupt input
-.in +8
A SIGSEGV violation was detected which usually means that the input file has
been corrupted.
-.in -8
-.I "xx.x%"
-.in +8
-Percentage of the input saved by compression.
+.TP
+\fIxx.x%\fP Percentage of the input saved by compression.
(Relevant only for
.BR \-v
and
.BR \-l \.)
-.in -8
+.TP
-- not a regular file or directory: ignored
-.in +8
When the input file is not a regular file or directory,
(e.g. a symbolic link, socket, FIFO, device file), it is
left unaltered.
-.in -8
--- has
-.I xx
-other links: unchanged
-.in +8
+.TP
+-- has \fIxx\fP other links: unchanged
The input file has links; it is left unchanged. See
.IR ln "(1)"
for more information. Use the
.B \-f
flag to force compression of multiply-linked files.
-.in -8
.SH CAVEATS
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
for decompression,
.I gunzip
detects that there is extra trailing garbage after the compressed data
-and emits a warning by default. You have to use the --quiet option to
-suppress the warning. This option can be set in the
-.B GZIP
-environment variable as in:
- for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
- for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
-
-In the above example, gzip is invoked implicitly by the -z option of
-GNU tar. Make sure that the same block size (-b option of tar) is used
-for reading and writing compressed data on tapes. (This example
-assumes you are using the GNU version of tar.)
+and emits a warning by default. You can use the --quiet option to
+suppress the warning.
.SH BUGS
-The --list option reports incorrect sizes if they exceed 2 gigabytes.
+The gzip format represents the input size modulo 2^32, so the
+--list option reports incorrect uncompressed sizes and compression
+ratios 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:
+
+ zcat file.gz | wc -c
+
The --list option reports sizes as -1 and crc as ffffffff if the
compressed file is on a non seekable media.
the default compression level (-6). On some highly redundant files,
.I compress
compresses better than
-.I gzip.
+.IR gzip .
+.SH "COPYRIGHT NOTICE"
+Copyright \(co 1998-1999, 2001-2002, 2012, 2015-2016 Free Software Foundation,
+Inc.
+.br
+Copyright \(co 1992, 1993 Jean-loup Gailly
+.PP
+Permission is granted to make and distribute verbatim copies of
+this manual provided the copyright notice and this permission notice
+are preserved on all copies.
+.ig
+Permission is granted to process this file through troff and print the
+results, provided the printed document carries copying permission
+notice identical to this one except for the removal of this paragraph
+(this paragraph not being relevant to the printed manual).
+..
+.PP
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided that the entire
+resulting derived work is distributed under the terms of a permission
+notice identical to this one.
+.PP
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation approved
+by the Foundation.
projects / debian / gzip / blobdiff