1 GZIP(1) General Commands Manual GZIP(1)
4 gzip, gunzip, zcat - compress or expand files
7 1mgzip 22m[ 1m-acdfhklLnNrtvV19 22m] [1m-S suffix22m] [ 4mname24m 4m...24m ]
8 1mgunzip 22m[ 1m-acfhklLnNrtvV 22m] [1m-S suffix22m] [ 4mname24m 4m...24m ]
9 1mzcat 22m[ 1m-fhLV 22m] [ 4mname24m 4m...24m ]
12 4mGzip24m reduces the size of the named files using Lempel-Ziv coding
13 (LZ77). Whenever possible, each file is replaced by one with the
14 extension 1m.gz22m, while keeping the same ownership modes, access and modi-
15 fication times. (The default extension is 1m-gz 22mfor VMS, 1mz 22mfor MSDOS,
16 OS/2 FAT, Windows NT FAT and Atari.) If no files are specified, or if
17 a file name is "-", the standard input is compressed to the standard
18 output. 4mGzip24m will only attempt to compress regular files. In particu-
19 lar, it will ignore symbolic links.
21 If the compressed file name is too long for its file system, 4mgzip24m trun-
22 cates it. 4mGzip24m attempts to truncate only the parts of the file name
23 longer than 3 characters. (A part is delimited by dots.) If the name
24 consists of small parts only, the longest parts are truncated. For
25 example, if file names are limited to 14 characters, gzip.msdos.exe is
26 compressed to gzi.msd.exe.gz. Names are not truncated on systems which
27 do not have a limit on file name length.
29 By default, 4mgzip24m keeps the original file name and timestamp in the com-
30 pressed file. These are used when decompressing the file with the 1m-N0m
31 option. This is useful when the compressed file name was truncated or
32 when the time stamp was not preserved after a file transfer.
34 Compressed files can be restored to their original form using 4mgzip24m 4m-d0m
35 or 4mgunzip24m or 4mzcat24m. If the original name saved in the compressed file
36 is not suitable for its file system, a new name is constructed from the
37 original one to make it legal.
39 4mgunzip24m takes a list of files on its command line and replaces each file
40 whose name ends with .gz, -gz, .z, -z, or _z (ignoring case) and which
41 begins with the correct magic number with an uncompressed file without
42 the original extension. 4mgunzip24m also recognizes the special extensions
43 1m.tgz 22mand 1m.taz 22mas shorthands for 1m.tar.gz 22mand 1m.tar.Z 22mrespectively. When
44 compressing, 4mgzip24m uses the 1m.tgz 22mextension if necessary instead of trun-
45 cating a file with a 1m.tar 22mextension.
47 4mgunzip24m can currently decompress files created by 4mgzip24m, 4mzip24m, 4mcompress24m,
48 4mcompress24m 4m-H24m or 4mpack24m. The detection of the input format is automatic.
49 When using the first two formats, 4mgunzip24m checks a 32 bit CRC. For 4mpack0m
50 and 4mgunzip24m checks the uncompressed length. The standard 4mcompress24m format
51 was not designed to allow consistency checks. However 4mgunzip24m is some-
52 times able to detect a bad .Z file. If you get an error when uncom-
53 pressing a .Z file, do not assume that the .Z file is correct simply
54 because the standard 4muncompress24m does not complain. This generally means
55 that the standard 4muncompress24m does not check its input, and happily gen-
56 erates garbage output. The SCO compress -H format (lzh compression
57 method) does not include a CRC but also allows some consistency checks.
59 Files created by 4mzip24m can be uncompressed by gzip only if they have a
60 single member compressed with the 'deflation' method. This feature is
61 only intended to help conversion of tar.zip files to the tar.gz format.
62 To extract a 4mzip24m file with a single member, use a command like 4mgunzip0m
63 4m<foo.zip24m or 4mgunzip24m 4m-S24m 4m.zip24m 4mfoo.zip24m. To extract zip files with several
64 members, use 4munzip24m instead of 4mgunzip24m.
66 4mzcat24m is identical to 4mgunzip24m 1m-c22m. (On some systems, 4mzcat24m may be
67 installed as 4mgzcat24m to preserve the original link to 4mcompress24m.) 4mzcat0m
68 uncompresses either a list of files on the command line or its standard
69 input and writes the uncompressed data on standard output. 4mzcat24m will
70 uncompress files that have the correct magic number whether they have a
71 1m.gz 22msuffix or not.
73 4mGzip24m uses the Lempel-Ziv algorithm used in 4mzip24m and PKZIP. The amount
74 of compression obtained depends on the size of the input and the dis-
75 tribution of common substrings. Typically, text such as source code or
76 English is reduced by 60-70%. Compression is generally much better
77 than that achieved by LZW (as used in 4mcompress24m), Huffman coding (as
78 used in 4mpack24m), or adaptive Huffman coding (4mcompact24m).
80 Compression is always performed, even if the compressed file is
81 slightly larger than the original. The worst case expansion is a few
82 bytes for the gzip file header, plus 5 bytes every 32K block, or an
83 expansion ratio of 0.015% for large files. Note that the actual number
84 of used disk blocks almost never increases. 4mgzip24m preserves the mode,
85 ownership and timestamps of files when compressing or decompressing.
89 Ascii text mode: convert end-of-lines using local conventions.
90 This option is supported only on some non-Unix systems. For
91 MSDOS, CR LF is converted to LF when compressing, and LF is con-
92 verted to CR LF when decompressing.
94 1m-c --stdout --to-stdout0m
95 Write output on standard output; keep original files unchanged.
96 If there are several input files, the output consists of a
97 sequence of independently compressed members. To obtain better
98 compression, concatenate all input files before compressing
101 1m-d --decompress --uncompress0m
105 Force compression or decompression even if the file has multiple
106 links or the corresponding file already exists, or if the com-
107 pressed data is read from or written to a terminal. If the input
108 data is not in a format recognized by 4mgzip24m, and if the option
109 --stdout is also given, copy the input data without change to
110 the standard output: let 4mzcat24m behave as 4mcat24m. If 1m-f 22mis not
111 given, and when not running in the background, 4mgzip24m prompts to
112 verify whether an existing file should be overwritten.
115 Display a help screen and quit.
118 Keep (don't delete) input files during compression or decompres-
122 For each compressed file, list the following fields:
124 compressed size: size of the compressed file
125 uncompressed size: size of the uncompressed file
126 ratio: compression ratio (0.0% if unknown)
127 uncompressed_name: name of the uncompressed file
129 The uncompressed size is given as -1 for files not in gzip for-
130 mat, such as compressed .Z files. To get the uncompressed size
131 for such a file, you can use:
135 In combination with the --verbose option, the following fields
138 method: compression method
139 crc: the 32-bit CRC of the uncompressed data
140 date & time: time stamp for the uncompressed file
142 The compression methods currently supported are deflate, com-
143 press, lzh (SCO compress -H) and pack. The crc is given as
144 ffffffff for a file not in gzip format.
146 With --name, the uncompressed name, date and time are those
147 stored within the compress file if present.
149 With --verbose, the size totals and compression ratio for all
150 files is also displayed, unless some sizes are unknown. With
151 --quiet, the title and totals lines are not displayed.
154 Display the 4mgzip24m license and quit.
157 When compressing, do not save the original file name and time
158 stamp by default. (The original name is always saved if the name
159 had to be truncated.) When decompressing, do not restore the
160 original file name if present (remove only the 4mgzip24m suffix from
161 the compressed file name) and do not restore the original time
162 stamp if present (copy it from the compressed file). This option
163 is the default when decompressing.
166 When compressing, always save the original file name and time
167 stamp; this is the default. When decompressing, restore the
168 original file name and time stamp if present. This option is
169 useful on systems which have a limit on file name length or when
170 the time stamp has been lost after a file transfer.
173 Suppress all warnings.
176 Travel the directory structure recursively. If any of the file
177 names specified on the command line are directories, 4mgzip24m will
178 descend into the directory and compress all the files it finds
179 there (or decompress them in the case of 4mgunzip24m ).
181 1m-S .suf --suffix .suf0m
182 When compressing, use suffix .suf instead of .gz. Any non-empty
183 suffix can be given, but suffixes other than .z and .gz should
184 be avoided to avoid confusion when files are transferred to
187 When decompressing, add .suf to the beginning of the list of
188 suffixes to try, when deriving an output file name from an input
192 Test. Check the compressed file integrity.
195 Verbose. Display the name and percentage reduction for each file
196 compressed or decompressed.
199 Version. Display the version number and compilation options then
203 Regulate the speed of compression using the specified digit 4m#24m,
204 where 1m-1 22mor 1m--fast 22mindicates the fastest compression method
205 (less compression) and 1m-9 22mor 1m--best 22mindicates the slowest com-
206 pression method (best compression). The default compression
207 level is 1m-6 22m(that is, biased towards high compression at expense
211 Multiple compressed files can be concatenated. In this case, 4mgunzip0m
212 will extract all members at once. For example:
214 gzip -c file1 > foo.gz
215 gzip -c file2 >> foo.gz
225 In case of damage to one member of a .gz file, other members can still
226 be recovered (if the damaged member is removed). However, you can get
227 better compression by compressing all members at once:
229 cat file1 file2 | gzip > foo.gz
231 compresses better than
233 gzip -c file1 file2 > foo.gz
235 If you want to recompress concatenated files to get better compression,
238 gzip -cd old.gz | gzip > new.gz
240 If a compressed file consists of several members, the uncompressed size
241 and CRC reported by the --list option applies to the last member only.
242 If you need the uncompressed size for all members, you can use:
244 gzip -cd file.gz | wc -c
246 If you wish to create a single archive file with multiple members so
247 that members can later be extracted independently, use an archiver such
248 as tar or zip. GNU tar supports the -z option to invoke gzip transpar-
249 ently. gzip is designed as a complement to tar, not as a replacement.
252 The environment variable 1mGZIP 22mcan hold a set of default options for
253 4mgzip24m. These options are interpreted first and can be overwritten by
254 explicit command line parameters. For example:
255 for sh: GZIP="-8v --name"; export GZIP
256 for csh: setenv GZIP "-8v --name"
257 for MSDOS: set GZIP=-8v --name
259 On Vax/VMS, the name of the environment variable is GZIP_OPT, to avoid
260 a conflict with the symbol set for invocation of the program.
263 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), com-
266 The 4mgzip24m file format is specified in P. Deutsch, GZIP file format spec-
267 ification version 4.3, 1m<http://www.ietf.org/rfc/rfc1952.txt>22m, Internet
268 RFC 1952 (May 1996). The 4mzip24m deflation format is specified in P.
269 Deutsch, DEFLATE Compressed Data Format Specification version 1.3,
270 1m<http://www.ietf.org/rfc/rfc1951.txt>22m, Internet RFC 1951 (May 1996).
273 Exit status is normally 0; if an error occurs, exit status is 1. If a
274 warning occurs, exit status is 2.
276 Usage: gzip [-cdfhklLnNrtvV19] [-S suffix] [file ...]
277 Invalid options were specified on the command line.
279 4mfile24m: not in gzip format
280 The file specified to 4mgunzip24m has not been compressed.
282 4mfile24m: Corrupt input. Use zcat to recover some data.
283 The compressed file has been damaged. The data up to the point
284 of failure can be recovered using
286 zcat 4mfile24m > recover
288 4mfile24m: compressed with 4mxx24m bits, can only handle 4myy24m bits
289 4mFile24m was compressed (using LZW) by a program that could deal
290 with more 4mbits24m than the decompress code on this machine. Recom-
291 press the file with gzip, which compresses better and uses less
294 4mfile24m: already has .gz suffix -- no change
295 The file is assumed to be already compressed. Rename the file
298 4mfile24m already exists; do you wish to overwrite (y or n)?
299 Respond "y" if you want the output file to be replaced; "n" if
302 gunzip: corrupt input
303 A SIGSEGV violation was detected which usually means that the
304 input file has been corrupted.
306 4mxx.x%24m Percentage of the input saved by compression.
307 (Relevant only for 1m-v 22mand 1m-l22m.)
309 -- not a regular file or directory: ignored
310 When the input file is not a regular file or directory, (e.g. a
311 symbolic link, socket, FIFO, device file), it is left unaltered.
313 -- has 4mxx24m other links: unchanged
314 The input file has links; it is left unchanged. See 4mln24m(1) for
315 more information. Use the 1m-f 22mflag to force compression of multi-
319 When writing compressed data to a tape, it is generally necessary to
320 pad the output with zeroes up to a block boundary. When the data is
321 read and the whole block is passed to 4mgunzip24m for decompression, 4mgunzip0m
322 detects that there is extra trailing garbage after the compressed data
323 and emits a warning by default. You have to use the --quiet option to
324 suppress the warning. This option can be set in the 1mGZIP 22menvironment
326 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
327 for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
329 In the above example, gzip is invoked implicitly by the -z option of
330 GNU tar. Make sure that the same block size (-b option of tar) is used
331 for reading and writing compressed data on tapes. (This example
332 assumes you are using the GNU version of tar.)
335 The gzip format represents the input size modulo 2^32, so the --list
336 option reports incorrect uncompressed sizes and compression ratios for
337 uncompressed files 4 GB and larger. To work around this problem, you
338 can use the following command to discover a large uncompressed file's
343 The --list option reports sizes as -1 and crc as ffffffff if the com-
344 pressed file is on a non seekable media.
346 In some rare cases, the --best option gives worse compression than the
347 default compression level (-6). On some highly redundant files, 4mcom-0m
348 4mpress24m compresses better than 4mgzip24m.
351 Copyright (C) 1998, 1999, 2001, 2002, 2012 Free Software Foundation,
353 Copyright (C) 1992, 1993 Jean-loup Gailly
355 Permission is granted to make and distribute verbatim copies of this
356 manual provided the copyright notice and this permission notice are
357 preserved on all copies.
359 Permission is granted to copy and distribute modified versions of this
360 manual under the conditions for verbatim copying, provided that the
361 entire resulting derived work is distributed under the terms of a per-
362 mission notice identical to this one.
364 Permission is granted to copy and distribute translations of this man-
365 ual into another language, under the above conditions for modified ver-
366 sions, except that this permission notice may be stated in a transla-
367 tion approved by the Foundation.