144 lines
7.1 KiB
Plaintext
144 lines
7.1 KiB
Plaintext
This is the file README for the gzip distribution, version 1.2.4.
|
|
|
|
gzip (GNU zip) is a compression utility designed to be a replacement
|
|
for 'compress'. Its main advantages over compress are much better
|
|
compression and freedom from patented algorithms. The GNU Project
|
|
uses it as the standard compression program for its system.
|
|
|
|
gzip currently uses by default the LZ77 algorithm used in zip 1.9 (the
|
|
portable pkzip compatible archiver). The gzip format was however
|
|
designed to accommodate several compression algorithms. See below
|
|
for a comparison of zip and gzip.
|
|
|
|
gunzip can currently decompress files created by gzip, compress or
|
|
pack. The detection of the input format is automatic. For the
|
|
gzip format, gunzip checks a 32 bit CRC. 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 because there is some redundancy in the .Z compression format.
|
|
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.
|
|
|
|
gzip produces files with a .gz extension. Previous versions of gzip
|
|
used the .z extension, which was already used by the 'pack'
|
|
Huffman encoder. gunzip is able to decompress .z files (packed
|
|
or gzip'ed).
|
|
|
|
Several planned features are not yet supported (see the file TODO).
|
|
See the file NEWS for a summary of changes since 0.5. See the file
|
|
INSTALL for installation instructions. Some answers to frequently
|
|
asked questions are given in the file INSTALL, please read it. (In
|
|
particular, please don't ask me once more for an /etc/magic entry.)
|
|
|
|
WARNING: on several systems, compiler bugs cause gzip to fail, in
|
|
particular when optimization options are on. See the section "Special
|
|
targets" at the end of the INSTALL file for a list of known problems.
|
|
For all machines, use "make check" to check that gzip was compiled
|
|
correctly. Try compiling gzip without any optimization if you have a
|
|
problem.
|
|
|
|
Please send all comments and bug reports by electronic mail to
|
|
<bug-gzip@gnu.org>.
|
|
|
|
Bug reports should ideally include:
|
|
|
|
* The complete output of "gzip -V" (or the contents of revision.h
|
|
if you can't get gzip to compile)
|
|
* The hardware and operating system (try "uname -a")
|
|
* The compiler used to compile (if it is gcc, use "gcc -v")
|
|
* A description of the bug behavior
|
|
* The input to gzip, that triggered the bug
|
|
|
|
If you send me patches for machines I don't have access to, please test them
|
|
very carefully. gzip is used for backups, it must be extremely reliable.
|
|
|
|
The package crypt++.el is highly recommended to manipulate gzip'ed
|
|
file from emacs. It recognizes automatically encrypted and compressed
|
|
files when they are first visited or written. It is available via
|
|
anonymous ftp to roebling.poly.edu [128.238.5.31] in /pub/crypt++.el.
|
|
The same directory contains also patches to dired, ange-ftp and info.
|
|
GNU tar 1.11.2 has a -z option to invoke directly gzip, so you don't have to
|
|
patch it. The package ftp.uu.net:/languages/emacs-lisp/misc/jka-compr19.el.Z
|
|
also supports gzip'ed files.
|
|
|
|
The znew and gzexe shell scripts provided with gzip benefit from
|
|
(but do not require) the cpmod utility to transfer file attributes.
|
|
It is available by anonymous ftp on gatekeeper.dec.com in
|
|
/.0/usenet/comp.sources.unix/volume11/cpmod.Z.
|
|
|
|
The sample programs zread.c, sub.c and add.c in subdirectory sample
|
|
are provided as examples of useful complements to gzip. Read the
|
|
comments inside each source file. The perl script ztouch is also
|
|
provided as example (not installed by default since it relies on perl).
|
|
|
|
|
|
gzip is free software, you can redistribute it and/or modify it under
|
|
the terms of the GNU General Public License, a copy of which is
|
|
provided under the name COPYING. The latest version of gzip are always
|
|
available by ftp in prep.ai.mit.edu:/pub/gnu, or in any of the prep
|
|
mirror sites:
|
|
|
|
- sources in gzip-*.tar (or .shar or .tar.gz).
|
|
- Solaris 2 executables in sparc-sun-solaris2/gzip-binaries-*.tar
|
|
- MSDOS lha self-extracting exe in gzip-msdos-*.exe. Once extracted,
|
|
copy gzip.exe to gunzip.exe and zcat.exe, or use "gzip -d" to decompress.
|
|
gzip386.exe runs much faster but only on 386 and above; it is compiled with
|
|
djgpp 1.10 available in directory omnigate.clarkson.edu:/pub/msdos/djgpp.
|
|
|
|
A VMS executable is available in ftp.spc.edu:[.macro32.savesets]gzip-1-*.zip
|
|
(use [.macro32]unzip.exe to extract). A PRIMOS executable is available
|
|
in ftp.lysator.liu.se:/pub/primos/run/gzip.run.
|
|
OS/2 executables (16 and 32 bits versions) are available in
|
|
ftp.tu-muenchen.de:/pub/comp/os/os2/archiver/gz*-[16,32].zip
|
|
|
|
Some ftp servers can automatically make a tar.Z from a tar file. If
|
|
you are getting gzip for the first time, you can ask for a tar.Z file
|
|
instead of the much larger tar file.
|
|
|
|
Many thanks to those who provided me with bug reports and feedback.
|
|
See the files THANKS and ChangeLog for more details.
|
|
|
|
|
|
Note about zip vs. gzip:
|
|
|
|
The name 'gzip' was a very unfortunate choice, because zip and gzip
|
|
are two really different programs, although the actual compression and
|
|
decompression sources were written by the same persons. A different
|
|
name should have been used for gzip, but it is too late to change now.
|
|
|
|
zip is an archiver: it compresses several files into a single archive
|
|
file. gzip is a simple compressor: each file is compressed separately.
|
|
Both share the same compression and decompression code for the
|
|
'deflate' method. unzip can also decompress old zip archives
|
|
(implode, shrink and reduce methods). gunzip can also decompress files
|
|
created by compress and pack. zip 1.9 and gzip do not support
|
|
compression methods other than deflation. (zip 1.0 supports shrink and
|
|
implode). Better compression methods may be added in future versions
|
|
of gzip. zip will always stick to absolute compatibility with pkzip,
|
|
it is thus constrained by PKWare, which is a commercial company. The
|
|
gzip header format is deliberately different from that of pkzip to
|
|
avoid such a constraint.
|
|
|
|
On Unix, gzip is mostly useful in combination with tar. GNU tar
|
|
1.11.2 has a -z option to invoke gzip automatically. "tar -z"
|
|
compresses better than zip, since gzip can then take advantage of
|
|
redundancy between distinct files. The drawback is that you must
|
|
scan the whole tar.gz file in order to extract a single file near
|
|
the end; unzip can directly seek to the end of the zip file. There
|
|
is no overhead when you extract the whole archive anyway.
|
|
If a member of a .zip archive is damaged, other files can still
|
|
be recovered. If a .tar.gz file is damaged, files beyond the failure
|
|
point cannot be recovered. (Future versions of gzip will have
|
|
error recovery features.)
|
|
|
|
gzip and gunzip are distributed as a single program. zip and unzip
|
|
are, for historical reasons, two separate programs, although the
|
|
authors of these two programs work closely together in the info-zip
|
|
team. zip and unzip are not associated with the GNU project.
|
|
The sources are available by ftp in
|
|
|
|
oak.oakland.edu:/pub/misc/unix/zip19p1.zip
|
|
oak.oakland.edu:/pub/misc/unix/unz50p1.tar-z
|