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uncompress


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

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

     compress [-cfv] [-b bits] [file]

     uncompress [-cfv] [file...]

     zcat [file...]

DESCRIPTION
  compress
     The compress utility will attempt 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  will  be
     replaced  by  one  with  the extension .Z, while keeping the
     same ownership modes, change times and  modification  times.
     If  appending  the  .Z  to  the file pathname would make the
     pathname exceed 1023 bytes, the command  will  fail.  If  no
     files  are  specified, the standard input will be 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 will restore files to their  original
     state  after  they  have  been compressed using the compress
     utility. If no files are specified, the standard input  will
     be 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  will  write  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:

     -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 given, and the pro-
              cess is not running in the background,  prompts  to
              verify  whether  an  existing file.Z file should be
              overwritten.  When uncompressing, does  not  prompt
              for  overwriting  files.  If  the  -f option is not
              given, and the process is not running in the  back-
              ground,  prompts to verify whether an existing file
              should be overwritten. If the standard input is not
              a terminal and -f is not given, writes a diagnostic
              message to standard error and exits with  a  status
              greater than 0.



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



     -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  will  result
              in larger, less compressed files.




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
              will be 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_CTYPE,    LC_MESSAGES,    and
     NLSPATH.

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:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Availability                | SUNWesu                     |
    |_____________________________|_____________________________|
    | CSI                         | Enabled                     |
    |_____________________________|_____________________________|
    | Interface Stability         | Standard                    |
    |_____________________________|_____________________________|


SEE ALSO
     ln(1),  pack(1),  attributes(5),  environ(5),  largefile(5),
     standards(5)


DIAGNOSTICS
     Usage: compress [-fvc] [-b maxbits] [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.



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.










Man pages from Solaris 10 Update 8. See docs.sun.com and www.oracle.com for further documentation and Solaris information.
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