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compress(1)

compress(1)                      User Commands                     compress(1)



NAME
       compress,  uncompress,  zcat  -  compress,  uncompress files or display
       expanded files

SYNOPSIS
       compress [-fv/] [-b bits] [file]...


       compress -c [-fv] [-b bits] [file]


       uncompress [-fv] [-c | -/] [file]...


       zcat [file]...

DESCRIPTION
   compress
       The compress utility attempts to reduce the size of the named files  by
       using  adaptive  Lempel-Ziv  coding.  Except  when the output is to the
       standard output, each file is replaced by one with  the  extension  .Z,
       while  keeping  the same ownership modes, change times and modification
       times, ACLs, and extended attributes. The compress utility also attempt
       to  set  the  owner and group of file.z to the owner and group of file,
       but does not fail if this cannot be done. If appending the  .Z  to  the
       file  pathname  would  make the pathname exceed 1023 bytes, the command
       fails. If no files are specified, the standard input is  compressed  to
       the standard output.


       The  amount  of  compression obtained depends on the size of the input,
       the number of bits per code, and the distribution of common substrings.
       Typically,  text  such  as source code or English is reduced by 50−60%.
       Compression is generally much better than that achieved by Huffman cod‐
       ing  and  it  takes  less time to compute. The bits parameter specified
       during compression is encoded within the compressed file, along with  a
       magic  number  to  ensure that neither decompression of random data nor
       recompression of compressed data is subsequently allowed.

   uncompress
       The uncompress utility restores files to  their  original  state  after
       they  have  been compressed using the compress utility. If no files are
       specified, the standard input is uncompressed to the standard output.


       This utility supports the uncompressing of any files produced  by  com‐
       press. For files produced by compress on other systems, uncompress sup‐
       ports 9- to 16-bit compression (see -b).

   zcat
       The zcat utility writes to standard output  the  uncompressed  form  of
       files that have been compressed using compress. It is the equivalent of
       uncompress-c. Input files are not affected.

OPTIONS
       The following options are supported:

       -b bits    Sets the upper limit (in bits) for common  substring  codes.
                  bits  must be between 9 and 16 (16 is the default). Lowering
                  the number of bits result in larger, less compressed files.


       -c         Writes to the standard output; no files are changed  and  no
                  .Z  files  are created. The behavior of zcat is identical to
                  that of `uncompress  -c'.


       -f         When compressing, forces compression of  file,  even  if  it
                  does  not  actually  reduce  the size of the file, or if the
                  corresponding file.Z file already exists.

                  If the -f option is not specified, and the  process  is  not
                  running  in  the  background,  prompts  to verify whether an
                  existing file should be  overwritten.  If  the  response  is
                  affirmative,  the  existing file is overwritten. When uncom‐
                  pressing, does not prompt for overwriting files. If  the  -f
                  option  is  not specified, and the process is not running in
                  the background, prompts to verify whether an  existing  file
                  should be overwritten. If the standard input is not a termi‐
                  nal and -f is not specified, writes a diagnostic message  to
                  standard error and exits with a status greater than 0.


       -v         Verbose.  Writes  to  standard error messages concerning the
                  percentage reduction or expansion of each file.


       -/         When compressing or decompressing, copies any extended  sys‐
                  tem attributes associated with the source file to the target
                  file and copies any extended  system  attributes  associated
                  with  extended  attributes  of the source file to the corre‐
                  sponding extended  attributes  associated  with  the  target
                  file.  If  any  extended system attributes cannot be copied,
                  the original file is retained, a diagnostic  is  written  to
                  stderr, and the final exit status is non-zero.


OPERANDS
       The following operand is supported:

       file    A  path  name  of  a  file to be compressed by compress, uncom‐
               pressed by uncompress, or whose uncompressed form is written to
               standard out by zcat. If file is −, or if no file is specified,
               the standard input is used.


ENVIRONMENT VARIABLES
       See environ(7) for descriptions of the following environment  variables
       that  affect  the  execution  of  compress, uncompress, and zcat: LANG,
       LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES, and NLSPATH.


       Affirmative responses are processed using the extended regular  expres‐
       sion defined for the yesexpr keyword in the LC_MESSAGES category of the
       user's locale. The locale specified in the LC_COLLATE category  defines
       the  behavior  of ranges, equivalence classes, and multi-character col‐
       lating elements used in the expression defined for yesexpr. The  locale
       specified  in  LC_CTYPE  determines  the  locale  for interpretation of
       sequences of bytes of text data a characters, the behavior of character
       classes used in the expression defined for the yesexpr. See locale(7).

EXIT STATUS
       The following error values are returned:

       0     Successful completion.


       1     An error occurred.


       2     One  or  more  files  were not compressed because they would have
             increased in size (and the -f option was not specified).


       >2    An error occurred.


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE  TYPEAT‐
       TRIBUTE  VALUE  _  Availabilitysystem/core-os  _ CSIEnabled _ Interface
       StabilityCommitted _ StandardSee standards(7).


SEE ALSO
       ln(1),   fgetattr(3C),   fsetattr(3C),    attributes(7),    environ(7),
       locale(7), standards(7)

DIAGNOSTICS
       Usage: compress [-fv/] [-b bits] [file... ]
       compress c [-fv] [-b bits] [file... ]

           Invalid options were specified on the command line.



       Usage: uncompress [-fv] [-c | -/] [file]...

           Invalid options were specified on the command line.


       Missing maxbits

           Maxbits must follow -b, or invalid maxbits, not a numeric value.


       file: not in compressed format

           The file specified to uncompress has not been compressed.


       file: compressed with xxbits, can only handle yybits

           file  was  compressed  by  a program that could deal with more bits
           than the compress code on this machine. Recompress  the  file  with
           smaller bits.


       file: already has .Z suffix -- no change

           The  file  is assumed to be already compressed. Rename the file and
           try again.


       file: already exists; do you wish to overwrite (y or n)?

           Respond y if you want the output file to be replaced; n if not.


       uncompress: corrupt input

           A SIGSEGV violation was detected,  which  usually  means  that  the
           input file is corrupted.


       Compression:xx.xx%

           Percentage  of  the  input saved by compression. (Relevant only for
           -v.)


       - - not a regular file: unchanged

           When the input file is not a regular file, (such as  a  directory),
           it is left unaltered.


       - - has xx other links: unchanged

           The  input file has links; it is left unchanged. See ln(1) for more
           information.


       - - file unchanged

           No savings are achieved by compression. The  input  remains  uncom‐
           pressed.


       - -filename too long to tack on .Z

           The path name is too long to append the .Z suffix.


       - -cannot preserve extended attributes. file unchanged

           Extended system attributes could not be copied.


NOTES
       Although  compressed  files  are compatible between machines with large
       memory, -b 12 should be used for file transfer to architectures with  a
       small process data space (64KB or less).


       compress should be more flexible about the existence of the .Z suffix.



Oracle Solaris 11.4               4 Feb 2015                       compress(1)
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