![[BACK]](/cvsweb/icons/back.gif){kind=icon}
Return to gzip.doc CVS log ![[TXT]](/cvsweb/icons/text.gif){kind=icon}
![[DIR]](/cvsweb/icons/dir.gif){kind=icon}
Up to [MW Coherent from dump] / coherent / g / usr / bin / gzip|
Return to gzip.doc CVS log | Up to [MW Coherent from dump] / coherent / g / usr / bin / gzip |
1.1 root 1:
2: GZIP(1) USER COMMANDS GZIP(1)
3:
4: NAME
5: gzip, gunzip, zcat - compress or expand files
6:
7: SYNOPSIS
8: gzip [ -cdfhLrtvV19 ] [ name ... ]
9: gunzip [ -cfhLrtvV ] [ name ... ]
10: zcat [ -hLV ] [ name ... ]
11:
12: DESCRIPTION
13: Gzip reduces the size of the named files using Lempel-Ziv
14: coding (LZ77). Whenever possible, each file is replaced by
15: one with the extension .z, while keeping the same ownership
16: modes, access and modification times. (The extension is -z
17: for VMS, z for MSDOS, OS/2 and Atari.) If no files are
18: specified, the standard input is compressed to the standard
19: output. If the new file name is too long, gzip truncates it
20: and keeps the original file name in the compressed file.
21: Gzip will only attempt to compress regular files. In par-
22: ticular, it will ignore symbolic links.
23:
24: Compressed files can be restored to their original form
25: using gzip -d or gunzip or zcat.
26:
27: gunzip takes a list of files on its command line and
28: replaces each file whose name ends with .z or .Z or -z and
29: which begins with the correct magic number with an
30: uncompressed file without the original extension. gunzip
31: also recognizes the special extensions .tgz and .taz as
32: shorthands for .tar.z or .tar.Z
33:
34: gunzip can currently decompress files created by gzip, zip,
35: compress or pack. The detection of the input format is
36: automatic. When using the first two formats, gunzip checks
37: a 32 bit CRC. For pack, gunzip checks the uncompressed
38: length. The compress format was not designed to allow con-
39: sistency checks. However gunzip is sometimes able to detect
40: a bad .Z file. If you get an error when uncompressing a .Z
41: file, do not assume that the .Z file is correct simply
42: because the standard uncompress does not complain. This gen-
43: erally means that the standard uncompress does not check its
44: input, and happily generates garbage output.
45:
46: Files created by zip can be uncompressed by gzip only if
47: they have a single member compressed with the 'deflation'
48: method. This feature is only intended to help conversion of
49: tar.zip files to the tar.z format. To extract zip files with
50: several members, use unzip instead of gunzip.
51:
52: zcat is identical to gunzip -c. (On some systems, zcat may
53: be installed as gzcat to preserve the original link to
54: compress.) zcat uncompresses either a list of files on the
55: command line or its standard input and writes the
56:
57: Sun Release 4.1 Last change: local 1
58:
59: GZIP(1) USER COMMANDS GZIP(1)
60:
61: uncompressed data on standard output. zcat will uncompress
62: files that have the correct magic number whether they have a
63: .z suffix or not.
64:
65: Gzip uses the Lempel-Ziv algorithm used in zip and PKZIP.
66: The amount of compression obtained depends on the size of
67: the input and the distribution of common substrings. Typi-
68: cally, text such as source code or English is reduced by
69: 60-70%. Compression is generally much better than that
70: achieved by LZW (as used in compress), Huffman coding (as
71: used in pack), or adaptive Huffman coding (compact).
72:
73: Compression is always performed, even if the compressed file
74: is slightly larger than the original. The worst case expan-
75: sion is a few bytes for the gzip file header, plus 5 bytes
76: every 32K block, or an expansion ratio of 0.015% for large
77: files. gzip preserves the mode, ownership and timestamps of
78: files when compressing or decompressing.
79:
80: OPTIONS
81: -c --stdout
82: Write output on standard output; keep original files
83: unchanged. If there are several input files, the out-
84: put consists of a sequence of independently compressed
85: members. To obtain better compression, concatenate all
86: input files before compressing them.
87:
88: -d --decompress
89: Decompress.
90:
91: -f --force
92: Force compression or decompression even if the file has
93: multiple links or the corresponding file already
94: exists. If -f is not given, and when not running in
95: the background, gzip prompts to verify whether an
96: existing file should be overwritten.
97:
98: -h --help
99: Display a help screen.
100:
101: -L --license
102: Display the gzip license.
103:
104: -q --quiet
105: Suppress all warnings.
106:
107: -r --recurse
108: Travel the directory structure recursively. If any of
109: the file names specified on the command line are direc-
110: tories, gzip will descend into the directory and
111: compress all the files it finds there (or decompress
112:
113: Sun Release 4.1 Last change: local 2
114:
115: GZIP(1) USER COMMANDS GZIP(1)
116:
117: them in the case of gunzip ).
118:
119: -t --test
120: Test. Check the compressed file integrity.
121:
122: -v --verbose
123: Verbose. Display the name and percentage reduction for
124: each file compressed.
125:
126: -V --version
127: Version. Display the version number and compilation
128: options.
129:
130: -# --fast --best
131: Regulate the speed of compression using the specified
132: digit #, where -1 or --fast indicates the fastest
133: compression method (less compression) and -9 or --best
134: indicates the slowest compression method (optimal
135: compression). The default compression level is -5.
136:
137: ADVANCED USAGE
138: Multiple compressed files can be concatenated. In this case,
139: gunzip will extract all members at once. For example:
140:
141: gzip -c file1 > foo.z
142: gzip -c file2 >> foo.z Then
143: gunzip -c foo
144:
145: is equivalent to
146:
147: cat file1 file2
148:
149: In case of damage to one member of a .z file, other members
150: can still be recovered (if the damaged member is removed).
151: However, you can get better compression by compressing all
152: members at once:
153:
154: cat file1 file2 | gzip > foo.z
155:
156: compresses better than
157:
158: gzip -c file1 file2 > foo.z
159:
160: If you want to recompress concatenated files to get better
161: compression, do:
162:
163: zcat old.z | gzip > new.z
164:
165: ENVIRONMENT
166: The environment variable GZIP can hold a set of default
167: options for gzip. These options are interpreted first and
168: can be ovewritten by explicit command line parameters. For
169:
170: Sun Release 4.1 Last change: local 3
171:
172: GZIP(1) USER COMMANDS GZIP(1)
173:
174: example:
175: for sh: GZIP="-8 -v"; export GZIP
176: for csh: setenv GZIP "-8 -v"
177: for MSDOS: set GZIP=-8 -v
178:
179: On Vax/VMS, the name of the environment variable is
180: GZIP_OPT, to avoid a conflict with the symbol set for invo-
181: cation of the program.
182:
183: SEE ALSO
184: znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1),
185: unzip(1), compress(1), pack(1), compact(1)
186:
187: DIAGNOSTICS
188: Exit status is normally 0; if an error occurs, exit status
189: is 1. If a warning occurs, exit status is 2.
190:
191: Usage: gzip [-cdfhLrtvV19] [file ...]
192: Invalid options were specified on the command line.
193: file: not in gzip format
194: The file specified to gunzip has not been
195: compressed.
196: file: Corrupt input. Use zcat to recover some data.
197: The compressed file has been damaged. The data up to
198: the point of failure can be recovered using
199: zcat file > recover
200: file: compressed with xx bits, can only handle yy bits
201: File was compressed (using LZW) by a program that
202: could deal with more bits than the decompress code
203: on this machine. Recompress the file with gzip,
204: which compresses better and uses less memory.
205: file: already has z suffix -- no change
206: The file is assumed to be already compressed.
207: Rename the file and try again or use zcat.
208: file already exists; do you wish to overwrite (y or n)?
209: Respond "y" if you want the output file to be
210: replaced; "n" if not.
211: gunzip: corrupt input
212: A SIGSEGV violation was detected which usually means
213: that the input file has been corrupted.
214: xx.x%
215: Percentage of the input saved by compression.
216: (Relevant only for -v.)
217: -- not a regular file or directory: ignored
218: When the input file is not a regular file or direc-
219: tory, (e.g. a symbolic link, socket, FIFO, device
220: file), it is left unaltered.
221: -- has xx other links: unchanged
222: The input file has links; it is left unchanged. See
223: ln(1) for more information. Use the -f flag to force
224: compression of multiply-linked files.
225:
226: Sun Release 4.1 Last change: local 4
227:
228: GZIP(1) USER COMMANDS GZIP(1)
229:
230: CAVEATS
231: The .z extension is already used by pack(1). You can link
232: gzip to pcat to get transparent decompression for programs
233: expecting .z files to be in pack format.
234:
235: Sun Release 4.1 Last change: local 5
236:
This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.