1 \input texinfo @c -*-texinfo-*-
4 @settitle Gzip User's Manual
10 This file documents the the GNU @code{gzip} command for compressing files.
12 Copyright (C) 1992-1993 Jean-loup Gailly
14 Permission is granted to make and distribute verbatim copies of
15 this manual provided the copyright notice and this permission notice
16 are preserved on all copies.
19 Permission is granted to process this file through TeX and print the
20 results, provided the printed document carries copying permission
21 notice identical to this one except for the removal of this paragraph
22 (this paragraph not being relevant to the printed manual).
25 Permission is granted to copy and distribute modified versions of this
26 manual under the conditions for verbatim copying, provided that the entire
27 resulting derived work is distributed under the terms of a permission
28 notice identical to this one.
30 Permission is granted to copy and distribute translations of this manual
31 into another language, under the above conditions for modified versions,
32 except that this permission notice may be stated in a translation approved
38 @subtitle The data compression program
39 @subtitle Edition 1.2.4, for Gzip Version 1.2.4
41 @author by Jean-loup Gailly
44 @vskip 0pt plus 1filll
45 Copyright @copyright{} 1992-1993 Jean-loup Gailly
47 Permission is granted to make and distribute verbatim copies of
48 this manual provided the copyright notice and this permission notice
49 are preserved on all copies.
51 Permission is granted to copy and distribute modified versions of this
52 manual under the conditions for verbatim copying, provided that the entire
53 resulting derived work is distributed under the terms of a permission
54 notice identical to this one.
56 Permission is granted to copy and distribute translations of this manual
57 into another language, under the above conditions for modified versions,
58 except that this permission notice may be stated in a translation approved
65 This file documents the @code{gzip} command to compress files.
69 * Copying:: How you can copy and share @code{gzip}.
70 * Overview:: Preliminary information.
71 * Sample:: Sample output from @code{gzip}.
72 * Invoking gzip:: How to run @code{gzip}.
73 * Advanced usage:: Concatenated files.
74 * Environment:: The @code{GZIP} environment variable
75 * Tapes:: Using @code{gzip} on tapes.
76 * Problems:: Reporting bugs.
77 * Concept Index:: Index of concepts.
80 @node Copying, Overview, , Top
83 @node Overview, Sample, Copying, Top
87 @code{gzip} reduces the size of the named files using Lempel-Ziv coding
88 (LZ77). Whenever possible, each file is replaced by one with the
89 extension @samp{.gz}, while keeping the same ownership modes, access and
90 modification times. (The default extension is @samp{-gz} for VMS,
91 @samp{z} for MSDOS, OS/2 FAT and Atari.) If no files are specified or
92 if a file name is "-", the standard input is compressed to the standard
93 output. @code{gzip} will only attempt to compress regular files. In
94 particular, it will ignore symbolic links.
96 If the new file name is too long for its file system, @code{gzip}
97 truncates it. @code{gzip} attempts to truncate only the parts of the
98 file name longer than 3 characters. (A part is delimited by dots.) If
99 the name consists of small parts only, the longest parts are truncated.
100 For example, if file names are limited to 14 characters, gzip.msdos.exe
101 is compressed to gzi.msd.exe.gz. Names are not truncated on systems
102 which do not have a limit on file name length.
104 By default, @code{gzip} keeps the original file name and timestamp in
105 the compressed file. These are used when decompressing the file with the
106 @samp{-N} option. This is useful when the compressed file name was
107 truncated or when the time stamp was not preserved after a file
110 Compressed files can be restored to their original form using @samp{gzip -d}
111 or @code{gunzip} or @code{zcat}. If the original name saved in the
112 compressed file is not suitable for its file system, a new name is
113 constructed from the original one to make it legal.
115 @code{gunzip} takes a list of files on its command line and replaces
116 each file whose name ends with @samp{.gz}, @samp{.z}, @samp{.Z},
117 @samp{-gz}, @samp{-z} or @samp{_z} and which begins with the correct
118 magic number with an uncompressed file without the original extension.
119 @code{gunzip} also recognizes the special extensions @samp{.tgz} and
120 @samp{.taz} as shorthands for @samp{.tar.gz} and @samp{.tar.Z}
121 respectively. When compressing, @code{gzip} uses the @samp{.tgz}
122 extension if necessary instead of truncating a file with a @samp{.tar}
125 @code{gunzip} can currently decompress files created by @code{gzip},
126 @code{zip}, @code{compress} or @code{pack}. The detection of the input
127 format is automatic. When using the first two formats, @code{gunzip}
128 checks a 32 bit CRC (cyclic redundancy check). For @code{pack},
129 @code{gunzip} checks the uncompressed length. The @code{compress} format
130 was not designed to allow consistency checks. However @code{gunzip} is
131 sometimes able to detect a bad @samp{.Z} file. If you get an error when
132 uncompressing a @samp{.Z} file, do not assume that the @samp{.Z} file is
133 correct simply because the standard @code{uncompress} does not complain.
134 This generally means that the standard @code{uncompress} does not check
135 its input, and happily generates garbage output. The SCO @samp{compress
136 -H} format (@code{lzh} compression method) does not include a CRC but
137 also allows some consistency checks.
139 Files created by @code{zip} can be uncompressed by @code{gzip} only if
140 they have a single member compressed with the 'deflation' method. This
141 feature is only intended to help conversion of @code{tar.zip} files to
142 the @code{tar.gz} format. To extract @code{zip} files with several
143 members, use @code{unzip} instead of @code{gunzip}.
145 @code{zcat} is identical to @samp{gunzip -c}. @code{zcat}
146 uncompresses either a list of files on the command line or its standard
147 input and writes the uncompressed data on standard output. @code{zcat}
148 will uncompress files that have the correct magic number whether they
149 have a @samp{.gz} suffix or not.
151 @code{gzip} uses the Lempel-Ziv algorithm used in @code{zip} and PKZIP.
152 The amount of compression obtained depends on the size of the input and
153 the distribution of common substrings. Typically, text such as source
154 code or English is reduced by 60-70%. Compression is generally much
155 better than that achieved by LZW (as used in @code{compress}), Huffman
156 coding (as used in @code{pack}), or adaptive Huffman coding
159 Compression is always performed, even if the compressed file is slightly
160 larger than the original. The worst case expansion is a few bytes for
161 the @code{gzip} file header, plus 5 bytes every 32K block, or an expansion
162 ratio of 0.015% for large files. Note that the actual number of used
163 disk blocks almost never increases. @code{gzip} preserves the mode,
164 ownership and timestamps of files when compressing or decompressing.
166 @node Sample, Invoking gzip, Overview, Top
167 @chapter Sample Output
170 Here are some realistic examples of running @code{gzip}.
172 This is the output of the command @samp{gzip -h}:
175 gzip 1.2.4 (18 Aug 93)
176 usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
177 -c --stdout write on standard output, keep original files unchanged
178 -d --decompress decompress
179 -f --force force overwrite of output file and compress links
180 -h --help give this help
181 -l --list list compressed file contents
182 -L --license display software license
183 -n --no-name do not save or restore the original name and time stamp
184 -N --name save or restore the original name and time stamp
185 -q --quiet suppress all warnings
186 -r --recursive operate recursively on directories
187 -S .suf --suffix .suf use suffix .suf on compressed files
188 -t --test test compressed file integrity
189 -v --verbose verbose mode
190 -V --version display version number
191 -1 --fast compress faster
192 -9 --best compress better
193 file... files to (de)compress. If none given, use standard input.
196 This is the output of the command @samp{gzip -v texinfo.tex}:
199 texinfo.tex: 71.6% -- replaced with texinfo.tex.gz
202 The following command will find all @code{gzip} files in the current
203 directory and subdirectories, and extract them in place without
204 destroying the original:
207 find . -name '*.gz' -print | sed 's/^\(.*\)[.]gz$/gunzip < "&" > "\1"/' | sh
210 @node Invoking gzip, Advanced usage, Sample, Top
211 @chapter Invoking @code{gzip}
215 The format for running the @code{gzip} program is:
218 gzip @var{option} @dots{}
221 @code{gzip} supports the following options:
227 Write output on standard output; keep original files unchanged.
228 If there are several input files, the output consists of a sequence of
229 independently compressed members. To obtain better compression,
230 concatenate all input files before compressing them.
239 Force compression or decompression even if the file has multiple links
240 or the corresponding file already exists, or if the compressed data
241 is read from or written to a terminal. If the input data is not in
242 a format recognized by @code{gzip}, and if the option --stdout is also
243 given, copy the input data without change to the standard ouput: let
244 @code{zcat} behave as @code{cat}. If @samp{-f} is not given, and
245 when not running in the background, @code{gzip} prompts to verify
246 whether an existing file should be overwritten.
250 Print an informative help message describing the options then quit.
254 For each compressed file, list the following fields:
257 compressed size: size of the compressed file
258 uncompressed size: size of the uncompressed file
259 ratio: compression ratio (0.0% if unknown)
260 uncompressed_name: name of the uncompressed file
263 The uncompressed size is given as @samp{-1} for files not in @code{gzip}
264 format, such as compressed @samp{.Z} files. To get the uncompressed size for
265 such a file, you can use:
271 In combination with the --verbose option, the following fields are also
275 method: compression method (deflate,compress,lzh,pack)
276 crc: the 32-bit CRC of the uncompressed data
277 date & time: time stamp for the uncompressed file
280 The crc is given as ffffffff for a file not in gzip format.
282 With --verbose, the size totals and compression ratio for all files
283 is also displayed, unless some sizes are unknown. With --quiet,
284 the title and totals lines are not displayed.
288 Display the @code{gzip} license then quit.
292 When compressing, do not save the original file name and time stamp by
293 default. (The original name is always saved if the name had to be
294 truncated.) When decompressing, do not restore the original file name
295 if present (remove only the @code{gzip}
296 suffix from the compressed file name) and do not restore the original
297 time stamp if present (copy it from the compressed file). This option
298 is the default when decompressing.
302 When compressing, always save the original file name and time stamp; this
303 is the default. When decompressing, restore the original file name and
304 time stamp if present. This option is useful on systems which have
305 a limit on file name length or when the time stamp has been lost after
310 Suppress all warning messages.
314 Travel the directory structure recursively. If any of the file names
315 specified on the command line are directories, @code{gzip} will descend
316 into the directory and compress all the files it finds there (or
317 decompress them in the case of @code{gunzip}).
319 @item --suffix @var{suf}
321 Use suffix @samp{@var{suf}} instead of @samp{.gz}. Any suffix can be
322 given, but suffixes other than @samp{.z} and @samp{.gz} should be
323 avoided to avoid confusion when files are transferred to other systems.
324 A null suffix forces gunzip to try decompression on all given files
325 regardless of suffix, as in:
328 gunzip -S "" * (*.* for MSDOS)
331 Previous versions of gzip used the @samp{.z} suffix. This was changed to
332 avoid a conflict with @code{pack}.
336 Test. Check the compressed file integrity.
340 Verbose. Display the name and percentage reduction for each file compressed.
344 Version. Display the version number and compilation options, then quit.
349 Regulate the speed of compression using the specified digit @var{n},
350 where @samp{-1} or @samp{--fast} indicates the fastest compression
351 method (less compression) and @samp{--best} or @samp{-9} indicates the
352 slowest compression method (optimal compression). The default
353 compression level is @samp{-6} (that is, biased towards high compression at
357 @node Advanced usage, Environment, Invoking gzip, Top
358 @chapter Advanced usage
359 @cindex concatenated files
361 Multiple compressed files can be concatenated. In this case,
362 @code{gunzip} will extract all members at once. If one member is
363 damaged, other members might still be recovered after removal of the
364 damaged member. Better compression can be usually obtained if all
365 members are decompressed and then recompressed in a single step.
367 This is an example of concatenating @code{gzip} files:
370 gzip -c file1 > foo.gz
371 gzip -c file2 >> foo.gz
386 In case of damage to one member of a @samp{.gz} file, other members can
387 still be recovered (if the damaged member is removed). However,
388 you can get better compression by compressing all members at once:
391 cat file1 file2 | gzip > foo.gz
394 compresses better than
397 gzip -c file1 file2 > foo.gz
400 If you want to recompress concatenated files to get better compression, do:
403 zcat old.gz | gzip > new.gz
406 If a compressed file consists of several members, the uncompressed
407 size and CRC reported by the @samp{--list} option applies to the last member
408 only. If you need the uncompressed size for all members, you can use:
414 If you wish to create a single archive file with multiple members so
415 that members can later be extracted independently, use an archiver such
416 as @code{tar} or @code{zip}. GNU @code{tar} supports the @samp{-z}
417 option to invoke @code{gzip} transparently. @code{gzip} is designed as a
418 complement to @code{tar}, not as a replacement.
420 @node Environment, Tapes, Advanced usage, Top
424 The environment variable @code{GZIP} can hold a set of default options for
425 @code{gzip}. These options are interpreted first and can be overwritten by
426 explicit command line parameters. For example:
429 for sh: GZIP="-8v --name"; export GZIP
430 for csh: setenv GZIP "-8v --name"
431 for MSDOS: set GZIP=-8v --name
434 On Vax/VMS, the name of the environment variable is @code{GZIP_OPT}, to
435 avoid a conflict with the symbol set for invocation of the program.
437 @node Tapes, Problems, Environment, Top
438 @chapter Using @code{gzip} on tapes
441 When writing compressed data to a tape, it is generally necessary to pad
442 the output with zeroes up to a block boundary. When the data is read and
443 the whole block is passed to @code{gunzip} for decompression,
444 @code{gunzip} detects that there is extra trailing garbage after the
445 compressed data and emits a warning by default. You have to use the
446 @samp{--quiet} option to suppress the warning. This option can be set in the
447 @code{GZIP} environment variable, as in:
450 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
451 for csh: (setenv GZIP "-q"; tar -xfz --block-compress /dev/rst0)
454 In the above example, @code{gzip} is invoked implicitly by the @samp{-z}
455 option of GNU @code{tar}. Make sure that the same block size (@samp{-b}
456 option of @code{tar}) is used for reading and writing compressed data on
457 tapes. (This example assumes you are using the GNU version of
460 @node Problems, Concept Index, Tapes, Top
461 @chapter Reporting Bugs
464 If you find a bug in @code{gzip}, please send electronic mail to
465 @w{@samp{jloup@@chorus.fr}} or, if this fails, to
466 @w{@samp{bug-gnu-utils@@prep.ai.mit.edu}}. Include the version number,
467 which you can find by running @w{@samp{gzip -V}}. Also include in your
468 message the hardware and operating system, the compiler used to compile
470 a description of the bug behavior, and the input to @code{gzip} that triggered
473 @node Concept Index, , Problems, Top
474 @unnumbered Concept Index