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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
* 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
if you want it, that you can change the software or use pieces of it
in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.
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
copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software. If the software is modified by someone else and passed on,
we want its recipients to know that what they have is not the
original, so that any problems introduced by others will not reflect
on the original authors' reputations.
Finally, any free program is threatened constantly by software
patents. We wish to avoid the danger that redistributors of a free
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program proprietary. To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and
modification follow.
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
distributed under the terms of this General Public License. The
"Program", below, refers to any such program or work, and a "work
based on the Program" means either the Program or any derivative
work under copyright law: that is to say, a work containing the
Program or a portion of it, either verbatim or with modifications
and/or translated into another language. (Hereinafter,
translation is included without limitation in the term
"modification".) Each licensee is addressed as "you".
Activities other than copying, distribution and modification
are not covered by this License; they are outside its scope. The
act of running the Program is not restricted, and the output from
the Program is covered only if its contents constitute a work
based on the Program (independent of having been made by running
the Program). Whether that is true depends on what the Program
does.
2. You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an
appropriate copyright notice and disclaimer of warranty; keep
intact all the notices that refer to this License and to the
absence of any warranty; and give any other recipients of the
Program a copy of this License along with the Program.
You may charge a fee for the physical act of transferring a
copy, and you may at your option offer warranty protection in
exchange for a fee.
3. You may modify your copy or copies of the Program or any portion
of it, thus forming a work based on the Program, and copy and
distribute such modifications or work under the terms of Section 1
above, provided that you also meet all of these conditions:
1. You must cause the modified files to carry prominent notices
stating that you changed the files and the date of any
change.
2. You must cause any work that you distribute or publish, that
in whole or in part contains or is derived from the Program
or any part thereof, to be licensed as a whole at no charge
to all third parties under the terms of this License.
3. If the modified program normally reads commands interactively
when run, you must cause it, when started running for such
interactive use in the most ordinary way, to print or
display an announcement including an appropriate copyright
notice and a notice that there is no warranty (or else,
saying that you provide a warranty) and that users may
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
separate works. But when you distribute the same sections as
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
contest your rights to work written entirely by you; rather, the
intent is to exercise the right to control the distribution of
derivative or collective works based on the Program.
In addition, mere aggregation of another work not based on the
Program with the Program (or with a work based on the Program) on
a volume of a storage or distribution medium does not bring the
other work under the scope of this License.
4. You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the
terms of Sections 1 and 2 above provided that you also do one of
the following:
1. Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of
Sections 1 and 2 above on a medium customarily used for
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2. Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than
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complete machine-readable copy of the corresponding source
code, to be distributed under the terms of Sections 1 and 2
above on a medium customarily used for software interchange;
or,
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offer to distribute corresponding source code. (This
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If distribution of executable or object code is made by
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5. You may not copy, modify, sublicense, or distribute the Program
except as expressly provided under this License. Any attempt
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License. However, parties who have received copies, or rights,
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or distribute the Program or its derivative works. These actions
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simultaneously your obligations under this License and any other
pertinent obligations, then as a consequence you may not
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
unenforceable under any particular circumstance, the balance of
the section is intended to apply and the section as a whole is
intended to apply in other circumstances.
It is not the purpose of this section to induce you to
infringe any patents or other property right claims or to contest
validity of any such claims; this section has the sole purpose of
protecting the integrity of the free software distribution
system, which is implemented by public license practices. Many
people have made generous contributions to the wide range of
software distributed through that system in reliance on
consistent application of that system; it is up to the
author/donor to decide if he or she is willing to distribute
software through any other system and a licensee cannot impose
that choice.
This section is intended to make thoroughly clear what is
believed to be a consequence of the rest of this License.
9. If the distribution and/or use of the Program is restricted in
certain countries either by patents or by copyrighted interfaces,
the original copyright holder who places the Program under this
License may add an explicit geographical distribution limitation
excluding those countries, so that distribution is permitted only
in or among countries not thus excluded. In such case, this
License incorporates the limitation as if written in the body of
this License.
10. The Free Software Foundation may publish revised and/or new
versions of the General Public License from time to time. Such
new versions will be similar in spirit to the present version,
but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the
Program specifies a version number of this License which applies
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Foundation.
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NO WARRANTY
12. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE
QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY
SERVICING, REPAIR OR CORRECTION.
13. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS
OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH
ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
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 ".z", while keeping the same ownership modes, access and
modification times. (The extension is "-z" for VMS, "z" for MSDOS,
OS/2 and Atari.) If no files are specified, the standard input is
compressed to the standard output. If the new file name is too long,
`gzip' truncates it and keeps the original file name in the compressed
file. `gzip' will only attempt to compress regular files. In
particular, it will ignore symbolic links.
Compressed files can be restored to their original form using
"`gzip' -d" or `gunzip' or `zcat'.
`gunzip' takes a list of files on its command line and replaces
each file whose name ends with ".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.z" or ".tar.Z".
`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.
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.z' 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 ".z" 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. `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':
usage: gzip [-cdfhLrv19] [file ...]
For more help, type: gzip -h
This is the output of the command `gzip -h':
gzip 1.0.7 (18 Mar 93)
usage: gzip [-cdfhLrtvV19] [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 --license display software license
-q --quiet suppress all warnings
-r --recurse recurse through directories
-t --test test compressed file integrity (implies -d)
-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 gzip.c':
gzip.c: 69.8% -- replaced with gzip.c.z

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:
`--help'
`-h'
Print an informative help message describing the options.
`--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'
`-d'
Decompress.
`--force'
`-f'
Force compression or decompression even if the file has multiple
links or the corresponding file already exists. 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'
Display a help screen.
`--license'
`-L'
Display the `gzip' license.
`--recurse'
`-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').
`--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.
`--fast'
`--best'
`-#'
Regulate the speed of compression using the specified digit #,
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
-5.

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 then recompressed in a single step.
This is an example of concatenating gzip files:
gzip -c file1 > foo.z
gzip -c file2 >> foo.z
Then
gunzip -c foo
is equivalent to
cat file1 file2
In case of damage to one member of a .z 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.z
compresses better than
gzip -c file1 file2 > foo.z
If you want to recompress concatenated files to get better
compression, do:
zcat old.z | gzip > new.z

File: gzip.info, Node: Environment, Next: Problems, 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="-8 -v"; export GZIP
for csh: setenv GZIP "-8 -v"
for MSDOS: set GZIP=-8 -v
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: Problems, Next: Concept Index, Prev: Environment, 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, 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.

Tag Table:
Node: Top864
Node: Copying1297
Node: Overview20555
Node: Sample23686
Node: Invoking gzip24890
Node: Advanced usage26752
Node: Environment27788
Node: Problems28342
Node: Concept Index28844

End Tag Table
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