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Info file gzip.info, produced by Makeinfo, -*- Text -*- from input
file gzip.texi.
This file documents the the GNU `gzip' command for compressing
files.
Copyright (C) 1992-1993 Jean-loup Gailly
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.
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.
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.

File: gzip.info, Node: Top, Up: (dir)
This file documents the `gzip' command to compress files.
* Menu:
* Copying:: How you can copy and share `gzip'.
* Overview:: Preliminary information.
* Sample:: Sample output from `gzip'.
* Invoking gzip:: How to run `gzip'.
* Advanced usage:: Concatenated files.
* Environment:: The `GZIP' environment variable
* Tapes:: Using `gzip' on tapes.
* Problems:: Reporting bugs.
* Concept Index:: Index of concepts.

File: gzip.info, Node: Copying, Next: Overview, Up: Top
GNU GENERAL PUBLIC LICENSE
**************************
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
675 Mass Ave, Cambridge, MA 02139, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
Preamble
========
The licenses for most software are designed to take away your
freedom to share and change it. By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users. This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it. (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.) You can apply it to
your programs, too.
When we speak of free software, we are referring to freedom, not
price. Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
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in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid
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These restrictions translate to certain responsibilities for you if you
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For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have. You must make sure that they, too, receive or can get the
source code. And you must show them these terms so they know their
rights.
We protect your rights with two steps: (1) copyright the software,
and (2) offer you this license which gives you legal permission to
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Also, for each author's protection and ours, we want to make certain
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Finally, any free program is threatened constantly by software
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The precise terms and conditions for copying, distribution and
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TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
1. This License applies to any program or other work which contains
a notice placed by the copyright holder saying it may be
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2. You may copy and distribute verbatim copies of the Program's
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absence of any warranty; and give any other recipients of the
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redistribute the program under these conditions, and telling
the user how to view a copy of this License. (Exception: if
the Program itself is interactive but does not normally
print such an announcement, your work based on the Program
is not required to print an announcement.)
These requirements apply to the modified work as a whole. If
identifiable sections of that work are not derived from the
Program, and can be reasonably considered independent and
separate works in themselves, then this License, and its terms,
do not apply to those sections when you distribute them as
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part of a whole which is a work based on the Program, the
distribution of the whole must be on the terms of this License,
whose permissions for other licensees extend to the entire whole,
and thus to each and every part regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or
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intent is to exercise the right to control the distribution of
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In addition, mere aggregation of another work not based on the
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4. You may copy and distribute the Program (or a work based on it,
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1. Accompany it with the complete corresponding machine-readable
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distribute the Program at all. For example, if a patent license
would not permit royalty-free redistribution of the Program by
all those who receive copies directly or indirectly through you,
then the only way you could satisfy both it and this License
would be to refrain entirely from distribution of the Program.
If any portion of this section is held invalid or
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It is not the purpose of this section to induce you to
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This section is intended to make thoroughly clear what is
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NO WARRANTY
12. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
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WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
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END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
=============================================
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.
ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES.
Copyright (C) 19YY NAME OF AUTHOR
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Also add information on how to contact you by electronic and paper
mail.
If the program is interactive, make it output a short notice like
this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'. This is free software, and you are welcome
to redistribute it under certain conditions; type `show c'
for details.
The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License. Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.
You should also get your employer (if you work as a programmer) or
your school, if any, to sign a "copyright disclaimer" for the program,
if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written
by James Hacker.
SIGNATURE OF TY COON, 1 April 1989
Ty Coon, President of Vice
This General Public License does not permit incorporating your
program into proprietary programs. If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library. If this is what you want to do, use
the GNU Library General Public License instead of this License.

File: gzip.info, Node: Overview, Next: Sample, Prev: Copying, Up: Top
Overview
********
`gzip' reduces the size of the named files using Lempel-Ziv coding
(LZ77). Whenever possible, each file is replaced by one with the
extension `.gz', while keeping the same ownership modes, access and
modification times. (The default extension is `-gz' for VMS, `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.
`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, `gzip'
truncates it. `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, `gzip' keeps the original file name and timestamp in
the compressed file. These are used when decompressing the file with
the `-N' option. This is useful when the compressed file name was
truncated or when the time stamp was not preserved after a file
transfer.
Compressed files can be restored to their original form using `gzip
-d' or `gunzip' or `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.
`gunzip' takes a list of files on its command line and replaces
each file whose name ends with `.gz', `.z', `.Z', `-gz', `-z' or `_z'
and which begins with the correct magic number with an uncompressed
file without the original extension. `gunzip' also recognizes the
special extensions `.tgz' and `.taz' as shorthands for `.tar.gz' and
`.tar.Z' respectively. When compressing, `gzip' uses the `.tgz'
extension if necessary instead of truncating a file with a `.tar'
extension.
`gunzip' can currently decompress files created by `gzip', `zip',
`compress' or `pack'. The detection of the input format is automatic.
When using the first two formats, `gunzip' checks a 32 bit CRC (cyclic
redundancy check). For `pack', `gunzip' checks the uncompressed
length. The `compress' format was not designed to allow consistency
checks. However `gunzip' is sometimes able to detect a bad `.Z' file.
If you get an error when uncompressing a `.Z' file, do not assume that
the `.Z' file is correct simply because the standard `uncompress' does
not complain. This generally means that the standard `uncompress'
does not check its input, and happily generates garbage output. The
SCO `compress -H' format (`lzh' compression method) does not include a
CRC but also allows some consistency checks.
Files created by `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 with several members, use
`unzip' instead of `gunzip'.
`zcat' is identical to `gunzip -c'. `zcat' uncompresses either a
list of files on the command line or its standard input and writes the
uncompressed data on standard output. `zcat' will uncompress files
that have the correct magic number whether they have a `.gz' suffix or
not.
`gzip' uses the Lempel-Ziv algorithm used in `zip' and PKZIP. The
amount of compression obtained depends on the size of the input and
the distribution of common substrings. 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 `compress'), Huffman
coding (as used in `pack'), or adaptive Huffman coding (`compact').
Compression is always performed, even if the compressed file is
slightly larger than the original. The worst case expansion is a few
bytes for the `gzip' file header, plus 5 bytes every 32K block, or an
expansion ratio of 0.015% for large files. Note that the actual number
of used disk blocks almost never increases. `gzip' preserves the mode,
ownership and timestamps of files when compressing or decompressing.

File: gzip.info, Node: Sample, Next: Invoking gzip, Prev: Overview, Up: Top
Sample Output
*************
Here are some realistic examples of running `gzip'.
This is the output of the command `gzip -h':
gzip 1.2.4 (18 Aug 93)
usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
-c --stdout write on standard output, keep original files unchanged
-d --decompress decompress
-f --force force overwrite of output file and compress links
-h --help give this help
-l --list list compressed file contents
-L --license display software license
-n --no-name do not save or restore the original name and time stamp
-N --name save or restore the original name and time stamp
-q --quiet suppress all warnings
-r --recursive operate recursively on directories
-S .suf --suffix .suf use suffix .suf on compressed files
-t --test test compressed file integrity
-v --verbose verbose mode
-V --version display version number
-1 --fast compress faster
-9 --best compress better
file... files to (de)compress. If none given, use standard input.
This is the output of the command `gzip -v texinfo.tex':
texinfo.tex: 71.6% -- replaced with texinfo.tex.gz
The following command will find all `gzip' files in the current
directory and subdirectories, and extract them in place without
destroying the original:
find . -name '*.gz' -print | sed 's/^\(.*\)[.]gz$/gunzip < "&" > "\1"/' | sh

File: gzip.info, Node: Invoking gzip, Next: Advanced usage, Prev: Sample, Up: Top
Invoking `gzip'
***************
The format for running the `gzip' program is:
gzip OPTION ...
`gzip' supports the following options:
`--stdout'
`--to-stdout'
`-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.
`--decompress'
`--uncompress'
`-d'
Decompress.
`--force'
`-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 `gzip', and if the
option --stdout is also given, copy the input data without change
to the standard ouput: let `zcat' behave as `cat'. If `-f' is not
given, and when not running in the background, `gzip' prompts to
verify whether an existing file should be overwritten.
`--help'
`-h'
Print an informative help message describing the options then
quit.
`--list'
`-l'
For each compressed file, list the following fields:
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
The uncompressed size is given as `-1' for files not in `gzip'
format, such as compressed `.Z' files. To get the uncompressed
size for such a file, you can use:
zcat file.Z | wc -c
In combination with the --verbose option, the following fields
are also displayed:
method: compression method (deflate,compress,lzh,pack)
crc: the 32-bit CRC of the uncompressed data
date & time: time stamp for the uncompressed file
The crc is given as ffffffff for a file not in gzip format.
With --verbose, the size totals and compression ratio for all
files is also displayed, unless some sizes are unknown. With
--quiet, the title and totals lines are not displayed.
`--license'
`-L'
Display the `gzip' license then quit.
`--no-name'
`-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 `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.
`--name'
`-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.
`--quiet'
`-q'
Suppress all warning messages.
`--recursive'
`-r'
Travel the directory structure recursively. If any of the file
names specified on the command line are directories, `gzip' will
descend into the directory and compress all the files it finds
there (or decompress them in the case of `gunzip').
`--suffix SUF'
`-S SUF'
Use suffix `SUF' instead of `.gz'. Any 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)
Previous versions of gzip used the `.z' suffix. This was changed
to avoid a conflict with `pack'.
`--test'
`-t'
Test. Check the compressed file integrity.
`--verbose'
`-v'
Verbose. Display the name and percentage reduction for each file
compressed.
`--version'
`-V'
Version. Display the version number and compilation options, then
quit.
`--fast'
`--best'
`-N'
Regulate the speed of compression using the specified digit N,
where `-1' or `--fast' indicates the fastest compression method
(less compression) and `--best' or `-9' indicates the slowest
compression method (optimal compression). The default
compression level is `-6' (that is, biased towards high
compression at expense of speed).

File: gzip.info, Node: Advanced usage, Next: Environment, Prev: Invoking gzip, Up: Top
Advanced usage
**************
Multiple compressed files can be concatenated. In this case,
`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 `gzip' files:
gzip -c file1 > foo.gz
gzip -c file2 >> foo.gz
Then
gunzip -c foo
is equivalent to
cat file1 file2
In case of damage to one member of a `.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:
cat file1 file2 | gzip > foo.gz
compresses better than
gzip -c file1 file2 > foo.gz
If you want to recompress concatenated files to get better
compression, do:
zcat old.gz | gzip > new.gz
If a compressed file consists of several members, the uncompressed
size and CRC reported by the `--list' option applies to the last member
only. If you need the uncompressed size for all members, you can use:
zcat file.gz | wc -c
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 `tar' or `zip'. GNU `tar' supports the `-z' option to invoke `gzip'
transparently. `gzip' is designed as a complement to `tar', not as a
replacement.

File: gzip.info, Node: Environment, Next: Tapes, Prev: Advanced usage, Up: Top
Environment
***********
The environment variable `GZIP' can hold a set of default options
for `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
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.

File: gzip.info, Node: Tapes, Next: Problems, Prev: Environment, Up: Top
Using `gzip' on 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 `gunzip' for decompression,
`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
`GZIP' environment variable, as in:
for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
for csh: (setenv GZIP "-q"; tar -xfz --block-compress /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'.)

File: gzip.info, Node: Problems, Next: Concept Index, Prev: Tapes, Up: Top
Reporting Bugs
**************
If you find a bug in `gzip', please send electronic mail to
`jloup@chorus.fr' or, if this fails, to
`bug-gnu-utils@prep.ai.mit.edu'. Include the version number, which
you can find by running `gzip -V'. Also include in your message the
hardware and operating system, the compiler used to compile `gzip', a
description of the bug behavior, and the input to `gzip' that triggered
the bug.

File: gzip.info, Node: Concept Index, Prev: Problems, Up: Top
Concept Index
*************
* Menu:
* Environment: Environment.
* bugs: Problems.
* concatenated files: Advanced usage.
* invoking: Invoking gzip.
* options: Invoking gzip.
* overview: Overview.
* sample: Sample.
* tapes: Tapes.

Tag Table:
Node: Top864
Node: Copying1344
Node: Overview20602
Node: Sample24911
Node: Invoking gzip26528
Node: Advanced usage31183
Node: Environment32772
Node: Tapes33340
Node: Problems34317
Node: Concept Index34822

End Tag Table