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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 owner-
     ship 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  coding  (as  used  in
     pack(1)) and it takes less time to compute. The bits parame-
     ter 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  pro-
     duced  by  compress. For files produced by compress on other
     systems, uncompress supports 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  sub-
                string  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  pro-
                cess 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 uncompressing,
                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 terminal 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  con-
                cerning  the percentage reduction or expansion of
                each file.


     -/
                When compressing  or  decompressing,  copies  any
                extended  system  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
                corresponding extended attributes associated with
                the target file. If any  extended  system  attri-
                butes  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,
             uncompressed  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.

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

Environment Variables
     See environ(5) 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 regu-
     lar  expression  defined  for  the  yesexpr  keyword  in the
     LC_MESSAGES category of the user's locale. The locale speci-
     fied  in  the  LC_COLLATE  category  defines the behavior of
     ranges, equivalence classes, and  multi-character  collating
     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 charac-
     ters, the behavior of character classes used in the  expres-
     sion defined for the yesexpr. See locale(5).

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(5) for descriptions of the  following  attri-
     butes:



     tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i)  ATTRI-
     BUTE  TYPEATTRIBUTE  VALUE  _  Availabilitysystem/core-os  _
     CSIEnabled  _  Interface  StabilityCommitted  _  StandardSee
     standards(5).

See Also
     ln(1), pack(1), fgetattr(3C),  fsetattr(3C),  attributes(5),
     environ(5), largefile(5), locale(5), standards(5)

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 uncompressed.


     - -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.
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