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1 perry 1 GZIP
2 !!!GZIP
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 OPTIONS
7 ADVANCED USAGE
8 ENVIRONMENT
9 SEE ALSO
10 DIAGNOSTICS
11 CAVEATS
12 BUGS
13 COPYRIGHT NOTICE
14 ----
15 !!NAME
16
17
18 gzip, gunzip, zcat - compress or expand files
19 !!SYNOPSIS
20
21
22 __gzip__ [[ __-acdfhlLnNrtvV19__ ] [[__-S suffix__] [[
23 ''name ...'' ]__
24 gunzip__ [[ __-acfhlLnNrtvV__ ] [[__-S suffix__] [[
25 ''name ...'' ]__
26 zcat__ [[ __-fhLV__ ] [[ ''name ...'' ]
27 !!DESCRIPTION
28
29
30 ''Gzip'' reduces the size of the named files using
31 Lempel-Ziv coding (LZ77). Whenever possible, each file is
32 replaced by one with the extension __.gz,__ while keeping
33 the same ownership modes, access and modification times.
34 (The default extension is __-gz__ for VMS, __z__ for
35 MSDOS, OS/2 FAT, Windows NT FAT and Atari.) If no files are
36 specified, or if a file name is
37 __Gzip'' will
38 only attempt to compress regular files. In particular, it
39 will ignore symbolic links.
40
41
42 If the compressed file name is too long for its file system,
43 ''gzip'' truncates it. ''Gzip'' attempts to truncate
44 only the parts of the file name longer than 3 characters. (A
45 part is delimited by dots.) If the name consists of small
46 parts only, the longest parts are truncated. For example, if
47 file names are limited to 14 characters, gzip.msdos.exe is
48 compressed to gzi.msd.exe.gz. Names are not truncated on
49 systems which do not have a limit on file name
50 length.
51
52
53 By default, ''gzip'' keeps the original file name and
54 timestamp in the compressed file. These are used when
55 decompressing the file with the __-N__ option. This is
56 useful when the compressed file name was truncated or when
57 the time stamp was not preserved after a file
58 transfer.
59
60
61 Compressed files can be restored to their original form
62 using ''gzip -d'' or ''gunzip'' or ''zcat.'' If the
63 original name saved in the compressed file is not suitable
64 for its file system, a new name is constructed from the
65 original one to make it legal.
66
67
68 ''gunzip'' takes a list of files on its command line and
69 replaces each file whose name ends with .gz, -gz, .z, -z, _z
70 or .Z and which begins with the correct magic number with an
71 uncompressed file without the original extension.
72 ''gunzip'' also recognizes the special extensions
73 __.tgz__ and __.taz__ as shorthands for __.tar.gz__
74 and __.tar.Z__ respectively. When compressing,
75 ''gzip'' uses the __.tgz__ extension if necessary
76 instead of truncating a file with a __.tar__
77 extension.
78
79
80 ''gunzip'' can currently decompress files created by
81 ''gzip, zip, compress, compress -H'' or ''pack.'' The
82 detection of the input format is automatic. When using the
83 first two formats, ''gunzip'' checks a 32 bit CRC. For
84 ''pack, gunzip'' checks the uncompressed length. The
85 standard ''compress'' format was not designed to allow
86 consistency checks. However ''gunzip'' is sometimes able
87 to detect a bad .Z file. If you get an error when
88 uncompressing a .Z file, do not assume that the .Z file is
89 correct simply because the standard ''uncompress'' does
90 not complain. This generally means that the standard
91 ''uncompress'' does not check its input, and happily
92 generates garbage output. The SCO compress -H format (lzh
93 compression method) does not include a CRC but also allows
94 some consistency checks.
95
96
97 Files created by ''zip'' can be uncompressed by gzip only
98 if they have a single member compressed with the 'deflation'
99 method. This feature is only intended to help conversion of
100 tar.zip files to the tar.gz format. To extract zip files
101 with several members, use ''unzip'' instead of
102 ''gunzip.''
103
104
105 ''zcat'' is identical to ''gunzip'' __-c.__ (On
106 some systems, ''zcat'' may be installed as ''gzcat''
107 to preserve the original link to ''compress.) zcat''
108 uncompresses either a list of files on the command line or
109 its standard input and writes the uncompressed data on
110 standard output. ''zcat'' will uncompress files that have
111 the correct magic number whether they have a __.gz__
112 suffix or not.
113
114
115 ''Gzip'' uses the Lempel-Ziv algorithm used in ''zip''
116 and PKZIP. The amount of compression obtained depends on the
117 size of the input and the distribution of common substrings.
118 Typically, text such as source code or English is reduced by
119 60-70%. Compression is generally much better than that
120 achieved by LZW (as used in ''compress''), Huffman coding
121 (as used in ''pack''), or adaptive Huffman coding
122 (''compact'').
123
124
125 Compression is always performed, even if the compressed file
126 is slightly larger than the original. The worst case
127 expansion is a few bytes for the gzip file header, plus 5
128 bytes every 32K block, or an expansion ratio of 0.015% for
129 large files. Note that the actual number of used disk blocks
130 almost never increases. ''gzip'' preserves the mode,
131 ownership and timestamps of files when compressing or
132 decompressing.
133 !!OPTIONS
134
135
136 __-a --ascii__
137
138
139 Ascii text mode: convert end-of-lines using local
140 conventions. This option is supported only on some non-Unix
141 systems. For MSDOS, CR LF is converted to LF when
142 compressing, and LF is converted to CR LF when
143 decompressing.
144
145
146 __-c --stdout --to-stdout__
147
148
149 Write output on standard output; keep original files
150 unchanged. If there are several input files, the output
151 consists of a sequence of independently compressed members.
152 To obtain better compression, concatenate all input files
153 before compressing them.
154
155
156 __-d --decompress --uncompress__
157
158
159 Decompress.
160
161
162 __-f --force__
163
164
165 Force compression or decompression even if the file has
166 multiple links or the corresponding file already exists, or
167 if the compressed data is read from or written to a
168 terminal. If the input data is not in a format recognized by
169 ''gzip,'' and if the option --stdout is also given, copy
170 the input data without change to the standard ouput: let
171 ''zcat'' behave as ''cat.'' If __-f__ is not given,
172 and when not running in the background, ''gzip'' prompts
173 to verify whether an existing file should be
174 overwritten.
175
176
177 __-h --help__
178
179
180 Display a help screen and quit.
181
182
183 __-l --list__
184
185
186 For each compressed file, list the following
187 fields:
188
189
190 compressed size: size of the compressed file uncompressed
191 size: size of the uncompressed file ratio: compression ratio
192 (0.0% if unknown) uncompressed_name: name of the
193 uncompressed file
194
195
196 The uncompressed size is given as -1 for files not in gzip
197 format, such as compressed .Z files. To get the uncompressed
198 size for such a file, you can use:
199
200
201 zcat file.Z | wc -c
202
203
204 In combination with the --verbose option, the following
205 fields are also displayed:
206
207
208 method: compression method crc: the 32-bit CRC of the
209 uncompressed data date
210
211
212 The compression methods currently supported are deflate,
213 compress, lzh (SCO compress -H) and pack. The crc is given
214 as ffffffff for a file not in gzip format.
215
216
217 With --name, the uncompressed name, date and time are those
218 stored within the compress file if present.
219
220
221 With --verbose, the size totals and compression ratio for
222 all files is also displayed, unless some sizes are unknown.
223 With --quiet, the title and totals lines are not
224 displayed.
225
226
227 __-L --license__
228
229
230 Display the ''gzip'' license and quit.
231
232
233 __-n --no-name__
234
235
236 When compressing, do not save the original file name and
237 time stamp by default. (The original name is always saved if
238 the name had to be truncated.) When decompressing, do not
239 restore the original file name if present (remove only the
240 ''gzip'' suffix from the compressed file name) and do not
241 restore the original time stamp if present (copy it from the
242 compressed file). This option is the default when
243 decompressing.
244
245
246 __-N --name__
247
248
249 When compressing, always save the original file name and
250 time stamp; this is the default. When decompressing, restore
251 the original file name and time stamp if present. This
252 option is useful on systems which have a limit on file name
253 length or when the time stamp has been lost after a file
254 transfer.
255
256
257 __-q --quiet__
258
259
260 Suppress all warnings.
261
262
263 __-r --recursive__
264
265
266 Travel the directory structure recursively. If any of the
267 file names specified on the command line are directories,
268 ''gzip'' will descend into the directory and compress all
269 the files it finds there (or decompress them in the case of
270 ''gunzip'' ).
271
272
273 __-S .suf --suffix .suf__
274
275
276 Use suffix .suf instead of .gz. Any suffix can be given, but
277 suffixes other than .z and .gz should be avoided to avoid
278 confusion when files are transferred to other systems. A
279 null suffix forces gunzip to try decompression on all given
280 files regardless of suffix, as in:
281
282
283 gunzip -S
284
285
286 Previous versions of gzip used the .z suffix. This was
287 changed to avoid a conflict with
288 pack(1)''.''
289
290
291 __-t --test__
292
293
294 Test. Check the compressed file integrity.
295
296
297 __-v --verbose__
298
299
300 Verbose. Display the name and percentage reduction for each
301 file compressed or decompressed.
302
303
304 __-V --version__
305
306
307 Version. Display the version number and compilation options
308 then quit.
309
310
311 __-# --fast --best__
312
313
314 Regulate the speed of compression using the specified digit
315 ''#'', where __-1__ or __--fast__ indicates the
316 fastest compression method (less compression) and __-9__
317 or __--best__ indicates the slowest compression method
318 (best compression). The default compression level is
319 __-6__ (that is, biased towards high compression at
320 expense of speed).
321 !!ADVANCED USAGE
322
323
324 Multiple compressed files can be concatenated. In this case,
325 ''gunzip'' will extract all members at once. For
326 example:
327
328
329 gzip -c file1
330
331
332 Then
333
334
335 gunzip -c foo
336
337
338 is equivalent to
339
340
341 cat file1 file2
342
343
344 In case of damage to one member of a .gz file, other members
345 can still be recovered (if the damaged member is removed).
346 However, you can get better compression by compressing all
347 members at once:
348
349
350 cat file1 file2 | gzip
351
352
353 compresses better than
354
355
356 gzip -c file1 file2
357
358
359 If you want to recompress concatenated files to get better
360 compression, do:
361
362
363 gzip -cd old.gz | gzip
364
365
366 If a compressed file consists of several members, the
367 uncompressed size and CRC reported by the --list option
368 applies to the last member only. If you need the
369 uncompressed size for all members, you can use:
370
371
372 gzip -cd file.gz | wc -c
373
374
375 If you wish to create a single archive file with multiple
376 members so that members can later be extracted
377 independently, use an archiver such as tar or zip. GNU tar
378 supports the -z option to invoke gzip transparently. gzip is
379 designed as a complement to tar, not as a
380 replacement.
381 !!ENVIRONMENT
382
383
384 The environment variable __GZIP__ can hold a set of
385 default options for ''gzip.'' These options are
386 interpreted first and can be overwritten by explicit command
387 line parameters. For example: for sh: GZIP=
388 ''
389
390
391 On Vax/VMS, the name of the environment variable is
392 GZIP_OPT, to avoid a conflict with the symbol set for
393 invocation of the program.
394 !!SEE ALSO
395
396
397 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1),
398 unzip(1), compress(1), pack(1), compact(1)
399
400
401 The ''gzip'' file format is specified in P. Deutsch,
402 GZIP file format specification version 4.3,
403 ____,
404 Internet RFC 1952 (May 1996). The ''zip'' deflation
405 format is specified in P. Deutsch, DEFLATE
406 Compressed Data Format Specification version 1.3,
407 ____,
408 Internet RFC 1951 (May 1996).
409 !!DIAGNOSTICS
410
411
412 Exit status is normally 0; if an error occurs, exit status
413 is 1. If a warning occurs, exit status is 2.
414
415
416 Usage: gzip [[-cdfhlLnNrtvV19] [[-S suffix] [[file
417 ...]
418
419
420 Invalid options were specified on the command
421 line.
422
423
424 ''file'': not in gzip format
425
426
427 The file specified to ''gunzip'' has not been
428 compressed.
429
430
431 ''file'': Corrupt input. Use zcat to recover some
432 data.
433
434
435 The compressed file has been damaged. The data up to the
436 point of failure can be recovered using
437
438
439 zcat ''file'' ''
440
441
442 ''file'': compressed with ''xx'' bits, can only handle
443 ''yy'' bits
444
445
446 ''File'' was compressed (using LZW) by a program that
447 could deal with more ''bits'' than the decompress code on
448 this machine. Recompress the file with gzip, which
449 compresses better and uses less memory.
450
451
452 ''file'': already has .gz suffix -- no
453 change
454
455
456 The file is assumed to be already compressed. Rename the
457 file and try again.
458
459
460 ''file'' already exists; do you wish to overwrite (y or
461 n)?
462
463
464 Respond
465
466
467 gunzip: corrupt input
468
469
470 A SIGSEGV violation was detected which usually means that
471 the input file has been corrupted.
472
473
474 ''xx.x%'' Percentage of the input saved by
475 compression.
476
477
478 (Relevant only for __-v__ and __-l__.)
479
480
481 -- not a regular file or directory: ignored
482
483
484 When the input file is not a regular file or directory,
485 (e.g. a symbolic link, socket, FIFO, device file), it is
486 left unaltered.
487
488
489 -- has ''xx'' other links: unchanged
490
491
492 The input file has links; it is left unchanged. See
493 ln(1) for more information. Use the __-f__ flag to
494 force compression of multiply-linked files.
495 !!CAVEATS
496
497
498 When writing compressed data to a tape, it is generally
499 necessary to pad the output with zeroes up to a block
500 boundary. When the data is read and the whole block is
501 passed to ''gunzip'' for decompression, ''gunzip''
502 detects that there is extra trailing garbage after the
503 compressed data and emits a warning by default. You have to
504 use the --quiet option to suppress the warning. This option
505 can be set in the __GZIP__ environment variable as in:
506 for sh: GZIP=
507 __
508
509
510 In the above example, gzip is invoked implicitly by the -z
511 option of GNU tar. Make sure that the same block size (-b
512 option of tar) is used for reading and writing compressed
513 data on tapes. (This example assumes you are using the GNU
514 version of tar.)
515 !!BUGS
516
517
518 The gzip format represents the the input size modulo 2^32,
519 so the --list option reports incorrect uncompressed sizes
520 and compression ratios for uncompressed files 4 GB and
521 larger. To work around this problem, you can use the
522 following command to discover a large uncompressed file's
523 true size:
524
525
526 zcat file.gz | wc -c
527
528
529 The --list option reports sizes as -1 and crc as ffffffff if
530 the compressed file is on a non seekable media.
531
532
533 In some rare cases, the --best option gives worse
534 compression than the default compression level (-6). On some
535 highly redundant files, ''compress'' compresses better
536 than ''gzip.''
537 !!COPYRIGHT NOTICE
538
539
540 Copyright 1998, 1999, 2001 Free Software Foundation,
541 Inc.
542 Copyright 1992, 1993 Jean-loup Gailly
543
544
545 Permission is granted to make and distribute verbatim copies
546 of this manual provided the copyright notice and this
547 permission notice are preserved on all copies.
548
549
550 Permission is granted to copy and distribute modified
551 versions of this manual under the conditions for verbatim
552 copying, provided that the entire resulting derived work is
553 distributed under the terms of a permission notice identical
554 to this one.
555
556
557 Permission is granted to copy and distribute translations of
558 this manual into another language, under the above
559 conditions for modified versions, except that this
560 permission notice may be stated in a translation approved by
561 the Foundation.
562 ----
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