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