1compress(1)                      User Commands                     compress(1)
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3
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NAME

6       compress,  uncompress,  zcat  -  compress,  uncompress files or display
7       expanded files
8

SYNOPSIS

10       compress [-fv/] [-b bits] [file]...
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13       compress -c [-fv] [-b bits] [file]
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16       uncompress [-fv] [-c | -/] [file]...
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19       zcat [file]...
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21

DESCRIPTION

23   compress
24       The compress utility attempts to reduce the size of the named files  by
25       using  adaptive  Lempel-Ziv  coding.  Except  when the output is to the
26       standard output, each file is replaced by one with  the  extension  .Z,
27       while  keeping  the same ownership modes, change times and modification
28       times, ACLs, and extended attributes. The compress utility also attempt
29       to  set  the  owner and group of file.z to the owner and group of file,
30       but does not fail if this cannot be done. If appending the  .Z  to  the
31       file  pathname  would  make the pathname exceed 1023 bytes, the command
32       fails. If no files are specified, the standard input is  compressed  to
33       the standard output.
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35
36       The  amount  of  compression obtained depends on the size of the input,
37       the number of bits per code, and the distribution of common substrings.
38       Typically,  text  such  as source code or English is reduced by 50−60%.
39       Compression is generally much better than that achieved by Huffman cod‐
40       ing  (as  used  in pack(1)) and it takes less time to compute. The bits
41       parameter specified during compression is encoded within the compressed
42       file, along with a magic number to ensure that neither decompression of
43       random data  nor  recompression  of  compressed  data  is  subsequently
44       allowed.
45
46   uncompress
47       The  uncompress  utility  restores  files to their original state after
48       they have been compressed using the compress utility. If no  files  are
49       specified, the standard input is uncompressed to the standard output.
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51
52       This  utility  supports the uncompressing of any files produced by com‐
53       press. For files produced by compress on other systems, uncompress sup‐
54       ports 9- to 16-bit compression (see -b).
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56   zcat
57       The  zcat  utility  writes  to standard output the uncompressed form of
58       files that have been compressed using compress. It is the equivalent of
59       uncompress-c. Input files are not affected.
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OPTIONS

62       The following options are supported:
63
64       -b bits    Sets  the  upper limit (in bits) for common substring codes.
65                  bits must be between 9 and 16 (16 is the default).  Lowering
66                  the number of bits result in larger, less compressed files.
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68
69       -c         Writes  to  the standard output; no files are changed and no
70                  .Z files are created. The behavior of zcat is  identical  to
71                  that of `uncompress -c'.
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73
74       -f         When  compressing,  forces  compression  of file, even if it
75                  does not actually reduce the size of the  file,  or  if  the
76                  corresponding file.Z file already exists.
77
78                  If  the  -f  option is not specified, and the process is not
79                  running in the background,  prompts  to  verify  whether  an
80                  existing  file  should  be  overwritten.  If the response is
81                  affirmative, the existing file is overwritten.  When  uncom‐
82                  pressing,  does  not prompt for overwriting files. If the -f
83                  option is not specified, and the process is not  running  in
84                  the  background,  prompts to verify whether an existing file
85                  should be overwritten. If the standard input is not a termi‐
86                  nal  and -f is not specified, writes a diagnostic message to
87                  standard error and exits with a status greater than 0.
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89
90       -v         Verbose. Writes to standard error  messages  concerning  the
91                  percentage reduction or expansion of each file.
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93
94       -/         When  compressing or decompressing, copies any extended sys‐
95                  tem attributes associated with the source file to the target
96                  file  and  copies  any extended system attributes associated
97                  with extended attributes of the source file  to  the  corre‐
98                  sponding  extended  attributes  associated  with  the target
99                  file. If any extended system attributes  cannot  be  copied,
100                  the  original  file  is retained, a diagnostic is written to
101                  stderr, and the final exit status is non-zero.
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103

OPERANDS

105       The following operand is supported:
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107       file    A path name of a file to  be  compressed  by  compress,  uncom‐
108               pressed by uncompress, or whose uncompressed form is written to
109               standard out by zcat. If file is , or if no file is specified,
110               the standard input is used.
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112

USAGE

114       See  largefile(5)  for  the  description  of  the behavior of compress,
115       uncompress, and zcat when encountering files greater than or equal to 2
116       Gbyte ( 2^31 bytes).
117

ENVIRONMENT VARIABLES

119       See  environ(5) for descriptions of the following environment variables
120       that affect the execution of  compress,  uncompress,  and  zcat:  LANG,
121       LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES, and NLSPATH.
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123
124       Affirmative  responses are processed using the extended regular expres‐
125       sion defined for the yesexpr keyword in the LC_MESSAGES category of the
126       user's  locale. The locale specified in the LC_COLLATE category defines
127       the behavior of ranges, equivalence classes, and  multi-character  col‐
128       lating  elements used in the expression defined for yesexpr. The locale
129       specified in LC_CTYPE  determines  the  locale  for  interpretation  of
130       sequences of bytes of text data a characters, the behavior of character
131       classes used in the expression defined for the yesexpr. See locale(5).
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EXIT STATUS

134       The following error values are returned:
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136       0     Successful completion.
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139       1     An error occurred.
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141
142       2     One or more files were not compressed  because  they  would  have
143             increased in size (and the -f option was not specified).
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145
146       >2    An error occurred.
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148

ATTRIBUTES

150       See attributes(5) for descriptions of the following attributes:
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155       ┌─────────────────────────────┬─────────────────────────────┐
156       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
157       ├─────────────────────────────┼─────────────────────────────┤
158       │Availability                 │SUNWesu                      │
159       ├─────────────────────────────┼─────────────────────────────┤
160       │CSI                          │Enabled                      │
161       ├─────────────────────────────┼─────────────────────────────┤
162       │Interface Stability          │Committed                    │
163       ├─────────────────────────────┼─────────────────────────────┤
164       │Standard                     │See standards(5).            │
165       └─────────────────────────────┴─────────────────────────────┘
166

SEE ALSO

168       ln(1),  pack(1), fgetattr(3C), fsetattr(3C), attributes(5), environ(5),
169       largefile(5), locale(5), standards(5)
170

DIAGNOSTICS

172       Usage: compress [-fv/] [-b bits] [file... ]
173       compress c [-fv] [-b bits] [file... ]
174
175           Invalid options were specified on the command line.
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177
178       Usage: uncompress [-fv] [-c | -/] [file]...
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180           Invalid options were specified on the command line.
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182
183       Missing maxbits
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185           Maxbits must follow -b, or invalid maxbits, not a numeric value.
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187
188       file: not in compressed format
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190           The file specified to uncompress has not been compressed.
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192
193       file: compressed with xxbits, can only handle yybits
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195           file was compressed by a program that could  deal  with  more  bits
196           than  the  compress  code on this machine. Recompress the file with
197           smaller bits.
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199
200       file: already has .Z suffix -- no change
201
202           The file is assumed to be already compressed. Rename the  file  and
203           try again.
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205
206       file: already exists; do you wish to overwrite (y or n)?
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208           Respond y if you want the output file to be replaced; n if not.
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211       uncompress: corrupt input
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213           A  SIGSEGV  violation  was  detected,  which usually means that the
214           input file is corrupted.
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217       Compression:xx.xx%
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219           Percentage of the input saved by compression.  (Relevant  only  for
220           -v.)
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223       - - not a regular file: unchanged
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225           When  the  input file is not a regular file, (such as a directory),
226           it is left unaltered.
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228
229       - - has xx other links: unchanged
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231           The input file has links; it is left unchanged. See ln(1) for  more
232           information.
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235       - - file unchanged
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237           No  savings  are  achieved by compression. The input remains uncom‐
238           pressed.
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241       - -filename too long to tack on .Z
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243           The path name is too long to append the .Z suffix.
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245
246       - -cannot preserve extended attributes. file unchanged
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248           Extended system attributes could not be copied.
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NOTES

252       Although compressed files are compatible between  machines  with  large
253       memory,  -b 12 should be used for file transfer to architectures with a
254       small process data space (64KB or less).
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256
257       compress should be more flexible about the existence of the .Z suffix.
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261SunOS 5.11                        13 Mar 2008                      compress(1)
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