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47 .TH COMPRESS 1 "Mar 13, 2008"
48 .SH NAME
49 compress, uncompress, zcat \- compress, uncompress files or display expanded
50 files
51 .SH SYNOPSIS
52 .LP
53 .nf
54 \fBcompress\fR [\fB-fv/\fR] [\fB-b\fR \fIbits\fR] [\fIfile\fR]...
55 .fi
57 .LP
58 .nf
59 \fBcompress\fR \fB-c\fR [\fB-fv\fR] [\fB-b\fR \fIbits\fR] [\fIfile\fR]
60 .fi
62 .LP
63 .nf
64 \fBuncompress\fR [\fB-fv\fR] [\fB-c | -/\fR] [\fIfile\fR]...
65 .fi
67 .LP
68 .nf
69 \fBzcat\fR [\fIfile\fR]...
70 .fi
72 .SH DESCRIPTION
73 .SS "compress"
74 .sp
75 .LP
76 The \fBcompress\fR utility attempts to reduce the size of the named files by
77 using adaptive Lempel-Ziv coding. Except when the output is to the standard
78 output, each file is replaced by one with the extension \fB\&.Z\fR, while
79 keeping the same ownership modes, change times and modification times, ACLs,
80 and extended attributes. The compress utility also attempt to set the owner and
81 group of \fIfile\fR\fB\&.z\fR to the owner and group of file, but does not fail
82 if this cannot be done. If appending the \fB\&.Z\fR to the file pathname would
83 make the pathname exceed \fB1023\fR bytes, the command fails. If no files are
84 specified, the standard input is compressed to the standard output.
85 .sp
86 .LP
87 The amount of compression obtained depends on the size of the input, the number
88 of \fIbits\fR per code, and the distribution of common substrings. Typically,
89 text such as source code or English is reduced by 50\(mi60%. Compression is
90 generally much better than that achieved by Huffman coding (as used in
91 \fBpack\fR(1)) and it takes less time to compute. The \fIbits\fR parameter
92 specified during compression is encoded within the compressed file, along with
93 a magic number to ensure that neither decompression of random data nor
94 recompression of compressed data is subsequently allowed.
95 .SS "uncompress"
96 .sp
97 .LP
98 The \fBuncompress\fR utility restores files to their original state after they
99 have been compressed using the \fBcompress\fR utility. If no files are
100 specified, the standard input is uncompressed to the standard output.
101 .sp
102 .LP
103 This utility supports the uncompressing of any files produced by
104 \fBcompress\fR. For files produced by \fBcompress\fR on other systems,
105 \fBuncompress\fR supports 9- to 16-bit compression (see \fB-b\fR).
106 .SS "zcat"
107 .sp
108 .LP
109 The \fBzcat\fR utility writes to standard output the uncompressed form of files
110 that have been compressed using \fBcompress\fR. It is the equivalent of
111 \fBuncompress\fR\fB-c\fR. Input files are not affected.
112 .SH OPTIONS
113 .sp
114 .LP
115 The following options are supported:
116 .sp
117 .ne 2
118 .na
119 \fB\fB-b\fR \fIbits\fR\fR
120 .ad
121 .RS 11n
122 Sets the upper limit (in bits) for common substring codes. \fIbits\fR must be
123 between 9 and 16 (16 is the default). Lowering the number of bits result in
124 larger, less compressed files.
125 .RE
127 .sp
128 .ne 2
129 .na
130 \fB\fB-c\fR\fR
131 .ad
132 .RS 11n
133 Writes to the standard output; no files are changed and no \fB\&.Z\fR files are
134 created. The behavior of \fBzcat\fR is identical to that of `\fBuncompress\fR
135 \fB-c\fR'.
136 .RE
138 .sp
139 .ne 2
140 .na
141 \fB\fB-f\fR\fR
142 .ad
143 .RS 11n
144 When compressing, forces compression of \fIfile\fR, even if it does not
145 actually reduce the size of the file, or if the corresponding
146 \fIfile\fR\fB\&.Z\fR file already exists.
147 .sp
148 If the \fB-f\fR option is not specified, and the process is not running in the
149 background, prompts to verify whether an existing file should be overwritten.
150 If the response is affirmative, the existing file is overwritten. When
151 uncompressing, does not prompt for overwriting files. If the \fB-f\fR option is
152 not specified, and the process is not running in the background, prompts to
153 verify whether an existing file should be overwritten. If the standard input is
154 not a terminal and \fB-f\fR is not specified, writes a diagnostic message to
155 standard error and exits with a status greater than \fB0\fR.
156 .RE
158 .sp
159 .ne 2
160 .na
161 \fB\fB-v\fR\fR
162 .ad
163 .RS 11n
164 Verbose. Writes to standard error messages concerning the percentage reduction
165 or expansion of each file.
166 .RE
168 .sp
169 .ne 2
170 .na
171 \fB\fB-/\fR\fR
172 .ad
173 .RS 11n
174 When compressing or decompressing, copies any extended system attributes
175 associated with the source file to the target file and copies any extended
176 system attributes associated with extended attributes of the source file to the
177 corresponding extended attributes associated with the target file. If any
178 extended system attributes cannot be copied, the original file is retained, a
179 diagnostic is written to \fBstderr\fR, and the final exit status is
180 \fBnon-zero\fR.
181 .RE
183 .SH OPERANDS
184 .sp
185 .LP
186 The following operand is supported:
187 .sp
188 .ne 2
189 .na
190 \fB\fIfile\fR\fR
191 .ad
192 .RS 8n
193 A path name of a file to be compressed by \fBcompress\fR, uncompressed by
194 \fBuncompress\fR, or whose uncompressed form is written to standard out by
195 \fBzcat\fR. If \fIfile\fR is \fB\(mi\fR, or if no \fIfile\fR is specified, the
196 standard input is used.
197 .RE
199 .SH USAGE
200 .sp
201 .LP
202 See \fBlargefile\fR(5) for the description of the behavior of \fBcompress\fR,
203 \fBuncompress\fR, and \fBzcat\fR when encountering files greater than or equal
204 to 2 Gbyte ( 2^31 bytes).
205 .SH ENVIRONMENT VARIABLES
206 .sp
207 .LP
208 See \fBenviron\fR(5) for descriptions of the following environment variables
209 that affect the execution of \fBcompress\fR, \fBuncompress\fR, and \fBzcat\fR:
210 \fBLANG\fR, \fBLC_ALL\fR, \fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR,
211 and \fBNLSPATH\fR.
212 .sp
213 .LP
214 Affirmative responses are processed using the extended regular expression
215 defined for the \fByesexpr\fR keyword in the \fBLC_MESSAGES\fR category of the
216 user's locale. The locale specified in the \fBLC_COLLATE\fR category defines
217 the behavior of ranges, equivalence classes, and multi-character collating
218 elements used in the expression defined for \fByesexpr\fR. The locale specified
219 in \fBLC_CTYPE\fR determines the locale for interpretation of sequences of
220 bytes of text data a characters, the behavior of character classes used in the
221 expression defined for the \fByesexpr\fR. See \fBlocale\fR(5).
222 .SH EXIT STATUS
223 .sp
224 .LP
225 The following error values are returned:
226 .sp
227 .ne 2
228 .na
229 \fB\fB0\fR\fR
230 .ad
231 .RS 6n
232 Successful completion.
233 .RE
235 .sp
236 .ne 2
237 .na
238 \fB\fB1\fR\fR
239 .ad
240 .RS 6n
241 An error occurred.
242 .RE
244 .sp
245 .ne 2
246 .na
247 \fB\fB2\fR\fR
248 .ad
249 .RS 6n
250 One or more files were not compressed because they would have increased in size
251 (and the \fB-f\fR option was not specified).
252 .RE
254 .sp
255 .ne 2
256 .na
257 \fB\fB>2\fR\fR
258 .ad
259 .RS 6n
260 An error occurred.
261 .RE
263 .SH ATTRIBUTES
264 .sp
265 .LP
266 See \fBattributes\fR(5) for descriptions of the following attributes:
267 .sp
269 .sp
270 .TS
271 box;
272 c | c
273 l | l .
274 ATTRIBUTE TYPE ATTRIBUTE VALUE
275 _
276 CSI Enabled
277 _
278 Interface Stability Committed
279 _
280 Standard See \fBstandards\fR(5).
281 .TE
283 .SH SEE ALSO
284 .sp
285 .LP
286 \fBln\fR(1), \fBpack\fR(1), \fBfgetattr\fR(3C), \fBfsetattr\fR(3C),
287 \fBattributes\fR(5), \fBenviron\fR(5), \fBlargefile\fR(5), \fBlocale\fR(5),
288 \fBstandards\fR(5)
289 .SH DIAGNOSTICS
290 .sp
291 .ne 2
292 .na
293 \fBUsage: \fBcompress [-fv/] [-b\fR \fIbits\fR] [\fIfile\fR\|.\|.\|. ]\fR
294 .ad
295 .br
296 .na
297 \fB\fBcompress c [-fv] [-b\fR \fIbits\fR] [\fIfile\fR\|.\|.\|. ]\fR
298 .ad
299 .sp .6
300 .RS 4n
301 Invalid options were specified on the command line.
302 .RE
304 .sp
305 .ne 2
306 .na
307 \fBUsage: \fBuncompress [-fv] [-c | -/] [\fR\fIfile\fR\fB]...\fR\fR
308 .ad
309 .sp .6
310 .RS 4n
311 Invalid options were specified on the command line.
312 .RE
314 .sp
315 .ne 2
316 .na
317 \fBMissing maxbits\fR
318 .ad
319 .sp .6
320 .RS 4n
321 Maxbits must follow \fB-b\fR, or invalid maxbits, not a numeric value.
322 .RE
324 .sp
325 .ne 2
326 .na
327 \fB\fIfile\fR: not in compressed format\fR
328 .ad
329 .sp .6
330 .RS 4n
331 The file specified to \fBuncompress\fR has not been compressed.
332 .RE
334 .sp
335 .ne 2
336 .na
337 \fB\fIfile\fR: compressed with \fIxx\fRbits, can only handle \fIyy\fRbits\fR
338 .ad
339 .sp .6
340 .RS 4n
341 \fBfile\fR was compressed by a program that could deal with more \fIbits\fR
342 than the compress code on this machine. Recompress the file with smaller
343 \fIbits\fR.
344 .RE
346 .sp
347 .ne 2
348 .na
349 \fB\fIfile\fR: already has .\|Z suffix -- no change\fR
350 .ad
351 .sp .6
352 .RS 4n
353 The file is assumed to be already compressed. Rename the file and try again.
354 .RE
356 .sp
357 .ne 2
358 .na
359 \fB\fIfile\fR: already exists; do you wish to overwrite (y or n)?\fR
360 .ad
361 .sp .6
362 .RS 4n
363 Respond \fBy\fR if you want the output file to be replaced; \fBn\fR if not.
364 .RE
366 .sp
367 .ne 2
368 .na
369 \fBuncompress: corrupt input\fR
370 .ad
371 .sp .6
372 .RS 4n
373 A \fBSIGSEGV\fR violation was detected, which usually means that the input file
374 is corrupted.
375 .RE
377 .sp
378 .ne 2
379 .na
380 \fBCompression:\fIxx.xx\fR\fB%\fR\fR
381 .ad
382 .sp .6
383 .RS 4n
384 Percentage of the input saved by compression. (Relevant only for \fB-v\fR.)
385 .RE
387 .sp
388 .ne 2
389 .na
390 \fB- - not a regular file: unchanged\fR
391 .ad
392 .sp .6
393 .RS 4n
394 When the input file is not a regular file, (such as a directory), it is left
395 unaltered.
396 .RE
398 .sp
399 .ne 2
400 .na
401 \fB- - has \fIxx\fR other links: unchanged\fR
402 .ad
403 .sp .6
404 .RS 4n
405 The input file has links; it is left unchanged. See \fBln\fR(1) for more
406 information.
407 .RE
409 .sp
410 .ne 2
411 .na
412 \fB- - file unchanged\fR
413 .ad
414 .sp .6
415 .RS 4n
416 No savings are achieved by compression. The input remains uncompressed.
417 .RE
419 .sp
420 .ne 2
421 .na
422 \fB- -filename too long to tack on .Z\fR
423 .ad
424 .sp .6
425 .RS 4n
426 The path name is too long to append the \fB\&.Z\fR suffix.
427 .RE
429 .sp
430 .ne 2
431 .na
432 \fB- -cannot preserve extended attributes. file unchanged\fR
433 .ad
434 .sp .6
435 .RS 4n
436 Extended system attributes could not be copied.
437 .RE
439 .SH NOTES
440 .sp
441 .LP
442 Although compressed files are compatible between machines with large memory,
443 \fB-b\fR 12 should be used for file transfer to architectures with a small
444 process data space (64KB or less).
445 .sp
446 .LP
447 \fBcompress\fR should be more flexible about the existence of the \fB\&.\|Z\fR
448 suffix.