Commit | Line | Data |
---|---|---|
24c2f017 C |
1 | This is the file README for the gzip distribution, version 1.2.4. |
2 | ||
3 | gzip (GNU zip) is a compression utility designed to be a replacement | |
4 | for 'compress'. Its main advantages over compress are much better | |
5 | compression and freedom from patented algorithms. The GNU Project | |
6 | uses it as the standard compression program for its system. | |
7 | ||
8 | gzip currently uses by default the LZ77 algorithm used in zip 1.9 (the | |
9 | portable pkzip compatible archiver). The gzip format was however | |
10 | designed to accommodate several compression algorithms. See below | |
11 | for a comparison of zip and gzip. | |
12 | ||
13 | gunzip can currently decompress files created by gzip, compress or | |
14 | pack. The detection of the input format is automatic. For the | |
15 | gzip format, gunzip checks a 32 bit CRC. For pack, gunzip checks the | |
16 | uncompressed length. The 'compress' format was not designed to allow | |
17 | consistency checks. However gunzip is sometimes able to detect a bad | |
18 | .Z file because there is some redundancy in the .Z compression format. | |
19 | If you get an error when uncompressing a .Z file, do not assume that | |
20 | the .Z file is correct simply because the standard uncompress does not | |
21 | complain. This generally means that the standard uncompress does not | |
22 | check its input, and happily generates garbage output. | |
23 | ||
24 | gzip produces files with a .gz extension. Previous versions of gzip | |
25 | used the .z extension, which was already used by the 'pack' | |
26 | Huffman encoder. gunzip is able to decompress .z files (packed | |
27 | or gzip'ed). | |
28 | ||
29 | Several planned features are not yet supported (see the file TODO). | |
30 | See the file NEWS for a summary of changes since 0.5. See the file | |
31 | INSTALL for installation instructions. Some answers to frequently | |
32 | asked questions are given in the file INSTALL, please read it. (In | |
33 | particular, please don't ask me once more for an /etc/magic entry.) | |
34 | ||
35 | WARNING: on several systems, compiler bugs cause gzip to fail, in | |
36 | particular when optimization options are on. See the section "Special | |
37 | targets" at the end of the INSTALL file for a list of known problems. | |
38 | For all machines, use "make check" to check that gzip was compiled | |
39 | correctly. Try compiling gzip without any optimization if you have a | |
40 | problem. | |
41 | ||
42 | Please send all comments and bug reports by electronic mail to: | |
43 | Jean-loup Gailly <jloup@chorus.fr> | |
44 | ||
45 | or, if this fails, to bug-gnu-utils@prep.ai.mit.edu. | |
46 | Bug reports should ideally include: | |
47 | ||
48 | * The complete output of "gzip -V" (or the contents of revision.h | |
49 | if you can't get gzip to compile) | |
50 | * The hardware and operating system (try "uname -a") | |
51 | * The compiler used to compile (if it is gcc, use "gcc -v") | |
52 | * A description of the bug behavior | |
53 | * The input to gzip, that triggered the bug | |
54 | ||
55 | If you send me patches for machines I don't have access to, please test them | |
56 | very carefully. gzip is used for backups, it must be extremely reliable. | |
57 | ||
58 | The package crypt++.el is highly recommended to manipulate gzip'ed | |
59 | file from emacs. It recognizes automatically encrypted and compressed | |
60 | files when they are first visited or written. It is available via | |
61 | anonymous ftp to roebling.poly.edu [128.238.5.31] in /pub/crypt++.el. | |
62 | The same directory contains also patches to dired, ange-ftp and info. | |
63 | GNU tar 1.11.2 has a -z option to invoke directly gzip, so you don't have to | |
64 | patch it. The package ftp.uu.net:/languages/emacs-lisp/misc/jka-compr19.el.Z | |
65 | also supports gzip'ed files. | |
66 | ||
67 | The znew and gzexe shell scripts provided with gzip benefit from | |
68 | (but do not require) the cpmod utility to transfer file attributes. | |
69 | It is available by anonymous ftp on gatekeeper.dec.com in | |
70 | /.0/usenet/comp.sources.unix/volume11/cpmod.Z. | |
71 | ||
72 | The sample programs zread.c, sub.c and add.c in subdirectory sample | |
73 | are provided as examples of useful complements to gzip. Read the | |
74 | comments inside each source file. The perl script ztouch is also | |
75 | provided as example (not installed by default since it relies on perl). | |
76 | ||
77 | ||
78 | gzip is free software, you can redistribute it and/or modify it under | |
79 | the terms of the GNU General Public License, a copy of which is | |
80 | provided under the name COPYING. The latest version of gzip are always | |
81 | available by ftp in prep.ai.mit.edu:/pub/gnu, or in any of the prep | |
82 | mirror sites: | |
83 | ||
84 | - sources in gzip-*.tar (or .shar or .tar.gz). | |
85 | - Solaris 2 executables in sparc-sun-solaris2/gzip-binaries-*.tar | |
86 | - MSDOS lha self-extracting exe in gzip-msdos-*.exe. Once extracted, | |
87 | copy gzip.exe to gunzip.exe and zcat.exe, or use "gzip -d" to decompress. | |
88 | gzip386.exe runs much faster but only on 386 and above; it is compiled with | |
89 | djgpp 1.10 available in directory omnigate.clarkson.edu:/pub/msdos/djgpp. | |
90 | ||
91 | A VMS executable is available in ftp.spc.edu:[.macro32.savesets]gzip-1-*.zip | |
92 | (use [.macro32]unzip.exe to extract). A PRIMOS executable is available | |
93 | in ftp.lysator.liu.se:/pub/primos/run/gzip.run. | |
94 | OS/2 executables (16 and 32 bits versions) are available in | |
95 | ftp.tu-muenchen.de:/pub/comp/os/os2/archiver/gz*-[16,32].zip | |
96 | ||
97 | Some ftp servers can automatically make a tar.Z from a tar file. If | |
98 | you are getting gzip for the first time, you can ask for a tar.Z file | |
99 | instead of the much larger tar file. | |
100 | ||
101 | Many thanks to those who provided me with bug reports and feedback. | |
102 | See the files THANKS and ChangeLog for more details. | |
103 | ||
104 | ||
105 | Note about zip vs. gzip: | |
106 | ||
107 | The name 'gzip' was a very unfortunate choice, because zip and gzip | |
108 | are two really different programs, although the actual compression and | |
109 | decompression sources were written by the same persons. A different | |
110 | name should have been used for gzip, but it is too late to change now. | |
111 | ||
112 | zip is an archiver: it compresses several files into a single archive | |
113 | file. gzip is a simple compressor: each file is compressed separately. | |
114 | Both share the same compression and decompression code for the | |
115 | 'deflate' method. unzip can also decompress old zip archives | |
116 | (implode, shrink and reduce methods). gunzip can also decompress files | |
117 | created by compress and pack. zip 1.9 and gzip do not support | |
118 | compression methods other than deflation. (zip 1.0 supports shrink and | |
119 | implode). Better compression methods may be added in future versions | |
120 | of gzip. zip will always stick to absolute compatibility with pkzip, | |
121 | it is thus constrained by PKWare, which is a commercial company. The | |
122 | gzip header format is deliberately different from that of pkzip to | |
123 | avoid such a constraint. | |
124 | ||
125 | On Unix, gzip is mostly useful in combination with tar. GNU tar | |
126 | 1.11.2 has a -z option to invoke gzip automatically. "tar -z" | |
127 | compresses better than zip, since gzip can then take advantage of | |
128 | redundancy between distinct files. The drawback is that you must | |
129 | scan the whole tar.gz file in order to extract a single file near | |
130 | the end; unzip can directly seek to the end of the zip file. There | |
131 | is no overhead when you extract the whole archive anyway. | |
132 | If a member of a .zip archive is damaged, other files can still | |
133 | be recovered. If a .tar.gz file is damaged, files beyond the failure | |
134 | point cannot be recovered. (Future versions of gzip will have | |
135 | error recovery features.) | |
136 | ||
137 | gzip and gunzip are distributed as a single program. zip and unzip | |
138 | are, for historical reasons, two separate programs, although the | |
139 | authors of these two programs work closely together in the info-zip | |
140 | team. zip and unzip are not associated with the GNU project. | |
141 | The sources are available by ftp in | |
142 | ||
143 | oak.oakland.edu:/pub/misc/unix/zip19p1.zip | |
144 | oak.oakland.edu:/pub/misc/unix/unz50p1.tar-z |