4 gzip, gunzip, zcat - compress or expand files
7 1mgzip 22m[ 1m-acdfhlLnNrtvV19 22m] [1m-S suffix22m] [ 4mname24m 4m...24m ]
8 1mgunzip 22m[ 1m-acfhlLnNrtvV 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.gz, 22mwhile 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 4mzcat.24m 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 4mgzip,24m 4mzip,24m 4mcompress,0m
48 4mcompress24m 4m-H24m or 4mpack.24m The detection of the input format is automatic.
49 When using the first two formats, 4mgunzip24m checks a 32 bit CRC. For 4mpack,0m
50 4mgunzip24m checks the uncompressed length. The standard 4mcompress24m format was
51 not designed to allow consistency checks. However 4mgunzip24m is sometimes
52 able to detect a bad .Z file. If you get an error when uncompressing a
53 .Z file, do not assume that the .Z file is correct simply because the
54 standard 4muncompress24m does not complain. This generally means that the
55 standard 4muncompress24m does not check its input, and happily generates
56 garbage output. The SCO compress -H format (lzh compression method)
57 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 4mgunzip.0m
66 4mzcat24m is identical to 4mgunzip24m 1m-c. 22m(On some systems, 4mzcat24m may be
67 installed as 4mgzcat24m to preserve the original link to 4mcompress.)24m 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.
87 The 4mgzip24m file format is specified in P. Deutsch, GZIP file format spec-
88 ification version 4.3, <ftp://ftp.isi.edu/in-notes/rfc1952.txt>, Inter-
89 net RFC 1952 (May 1996). The 4mzip24m deflation format is specified in P.
90 Deutsch, DEFLATE Compressed Data Format Specification version 1.3,
91 <ftp://ftp.isi.edu/in-notes/rfc1951.txt>, Internet RFC 1951 (May 1996).
95 Ascii text mode: convert end-of-lines using local conventions.
96 This option is supported only on some non-Unix systems. For
97 MSDOS, CR LF is converted to LF when compressing, and LF is con-
98 verted to CR LF when decompressing.
100 1m-c --stdout --to-stdout0m
101 Write output on standard output; keep original files unchanged.
102 If there are several input files, the output consists of a
103 sequence of independently compressed members. To obtain better
104 compression, concatenate all input files before compressing
107 1m-d --decompress --uncompress0m
111 Force compression or decompression even if the file has multiple
112 links or the corresponding file already exists, or if the com-
113 pressed data is read from or written to a terminal. If the input
114 data is not in a format recognized by 4mgzip,24m and if the option
115 --stdout is also given, copy the input data without change to
116 the standard output: let 4mzcat24m behave as 4mcat.24m If 1m-f 22mis not
117 given, and when not running in the background, 4mgzip24m prompts to
118 verify whether an existing file should be overwritten.
121 Display a help screen and quit.
124 For each compressed file, list the following fields:
126 compressed size: size of the compressed file
127 uncompressed size: size of the uncompressed file
128 ratio: compression ratio (0.0% if unknown)
129 uncompressed_name: name of the uncompressed file
131 The uncompressed size is given as -1 for files not in gzip for-
132 mat, such as compressed .Z files. To get the uncompressed size
133 for such a file, you can use:
137 In combination with the --verbose option, the following fields
140 method: compression method
141 crc: the 32-bit CRC of the uncompressed data
142 date & time: time stamp for the uncompressed file
144 The compression methods currently supported are deflate, com-
145 press, lzh (SCO compress -H) and pack. The crc is given as
146 ffffffff for a file not in gzip format.
148 With --name, the uncompressed name, date and time are those
149 stored within the compress file if present.
151 With --verbose, the size totals and compression ratio for all
152 files is also displayed, unless some sizes are unknown. With
153 --quiet, the title and totals lines are not displayed.
156 Display the 4mgzip24m license and quit.
159 When compressing, do not save the original file name and time
160 stamp by default. (The original name is always saved if the name
161 had to be truncated.) When decompressing, do not restore the
162 original file name if present (remove only the 4mgzip24m suffix from
163 the compressed file name) and do not restore the original time
164 stamp if present (copy it from the compressed file). This option
165 is the default when decompressing.
168 When compressing, always save the original file name and time
169 stamp; this is the default. When decompressing, restore the
170 original file name and time stamp if present. This option is
171 useful on systems which have a limit on file name length or when
172 the time stamp has been lost after a file transfer.
175 Suppress all warnings.
178 Travel the directory structure recursively. If any of the file
179 names specified on the command line are directories, 4mgzip24m will
180 descend into the directory and compress all the files it finds
181 there (or decompress them in the case of 4mgunzip24m ).
183 1m-S .suf --suffix .suf0m
184 When compressing, use suffix .suf instead of .gz. Any non-empty
185 suffix can be given, but suffixes other than .z and .gz should
186 be avoided to avoid confusion when files are transferred to
189 When decompressing, add .suf to the beginning of the list of
190 suffixes to try, when deriving an output file name from an input
196 Test. Check the compressed file integrity.
199 Verbose. Display the name and percentage reduction for each file
200 compressed or decompressed.
203 Version. Display the version number and compilation options then
207 Regulate the speed of compression using the specified digit 4m#24m,
208 where 1m-1 22mor 1m--fast 22mindicates the fastest compression method
209 (less compression) and 1m-9 22mor 1m--best 22mindicates the slowest com-
210 pression method (best compression). The default compression
211 level is 1m-6 22m(that is, biased towards high compression at expense
215 Multiple compressed files can be concatenated. In this case, 4mgunzip0m
216 will extract all members at once. For example:
218 gzip -c file1 > foo.gz
219 gzip -c file2 >> foo.gz
229 In case of damage to one member of a .gz file, other members can still
230 be recovered (if the damaged member is removed). However, you can get
231 better compression by compressing all members at once:
233 cat file1 file2 | gzip > foo.gz
235 compresses better than
237 gzip -c file1 file2 > foo.gz
239 If you want to recompress concatenated files to get better compression,
242 gzip -cd old.gz | gzip > new.gz
244 If a compressed file consists of several members, the uncompressed size
245 and CRC reported by the --list option applies to the last member only.
246 If you need the uncompressed size for all members, you can use:
248 gzip -cd file.gz | wc -c
250 If you wish to create a single archive file with multiple members so
251 that members can later be extracted independently, use an archiver such
252 as tar or zip. GNU tar supports the -z option to invoke gzip transpar-
253 ently. gzip is designed as a complement to tar, not as a replacement.
256 The environment variable 1mGZIP 22mcan hold a set of default options for
257 4mgzip.24m These options are interpreted first and can be overwritten by
258 explicit command line parameters. For example:
259 for sh: GZIP="-8v --name"; export GZIP
260 for csh: setenv GZIP "-8v --name"
261 for MSDOS: set GZIP=-8v --name
263 On Vax/VMS, the name of the environment variable is GZIP_OPT, to avoid
264 a conflict with the symbol set for invocation of the program.
267 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), com-
268 press(1), pack(1), compact(1)
270 The 4mgzip24m file format is specified in P. Deutsch, GZIP file format spec-
271 ification version 4.3, 1m<ftp://ftp.isi.edu/in-notes/rfc1952.txt>22m, Inter-
272 net RFC 1952 (May 1996). The 4mzip24m deflation format is specified in P.
273 Deutsch, DEFLATE Compressed Data Format Specification version 1.3,
274 1m<ftp://ftp.isi.edu/in-notes/rfc1951.txt>22m, Internet RFC 1951 (May 1996).
277 Exit status is normally 0; if an error occurs, exit status is 1. If a
278 warning occurs, exit status is 2.
280 Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
281 Invalid options were specified on the command line.
283 4mfile24m: not in gzip format
284 The file specified to 4mgunzip24m has not been compressed.
286 4mfile24m: Corrupt input. Use zcat to recover some data.
287 The compressed file has been damaged. The data up to the point
288 of failure can be recovered using
290 zcat 4mfile24m > recover
292 4mfile24m: compressed with 4mxx24m bits, can only handle 4myy24m bits
293 4mFile24m was compressed (using LZW) by a program that could deal
294 with more 4mbits24m than the decompress code on this machine. Recom-
295 press the file with gzip, which compresses better and uses less
298 4mfile24m: already has .gz suffix -- no change
299 The file is assumed to be already compressed. Rename the file
302 4mfile24m already exists; do you wish to overwrite (y or n)?
303 Respond "y" if you want the output file to be replaced; "n" if
306 gunzip: corrupt input
307 A SIGSEGV violation was detected which usually means that the
308 input file has been corrupted.
310 4mxx.x%24m Percentage of the input saved by compression.
311 (Relevant only for 1m-v 22mand 1m-l22m.)
313 -- not a regular file or directory: ignored
314 When the input file is not a regular file or directory, (e.g. a
315 symbolic link, socket, FIFO, device file), it is left unaltered.
317 -- has 4mxx24m other links: unchanged
318 The input file has links; it is left unchanged. See 4mln24m(1) for
319 more information. Use the 1m-f 22mflag to force compression of multi-
323 When writing compressed data to a tape, it is generally necessary to
324 pad the output with zeroes up to a block boundary. When the data is
325 read and the whole block is passed to 4mgunzip24m for decompression, 4mgunzip0m
326 detects that there is extra trailing garbage after the compressed data
327 and emits a warning by default. You have to use the --quiet option to
328 suppress the warning. This option can be set in the 1mGZIP 22menvironment
330 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
331 for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
333 In the above example, gzip is invoked implicitly by the -z option of
334 GNU tar. Make sure that the same block size (-b option of tar) is used
335 for reading and writing compressed data on tapes. (This example
336 assumes you are using the GNU version of tar.)
339 The gzip format represents the input size modulo 2^32, so the --list
340 option reports incorrect uncompressed sizes and compression ratios for
341 uncompressed files 4 GB and larger. To work around this problem, you
342 can use the following command to discover a large uncompressed file's
347 The --list option reports sizes as -1 and crc as ffffffff if the com-
348 pressed file is on a non seekable media.
350 In some rare cases, the --best option gives worse compression than the
351 default compression level (-6). On some highly redundant files, 4mcom-0m
352 4mpress24m compresses better than 4mgzip.0m
355 Copyright (C) 1998, 1999, 2001, 2002 Free Software Foundation, Inc.
356 Copyright (C) 1992, 1993 Jean-loup Gailly
358 Permission is granted to make and distribute verbatim copies of this
359 manual provided the copyright notice and this permission notice are
360 preserved on all copies.
362 Permission is granted to copy and distribute modified versions of this
363 manual under the conditions for verbatim copying, provided that the
364 entire resulting derived work is distributed under the terms of a per-
365 mission notice identical to this one.
367 Permission is granted to copy and distribute translations of this man-
368 ual into another language, under the above conditions for modified ver-
369 sions, except that this permission notice may be stated in a transla-
370 tion approved by the Foundation.