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COMPRESS(1P)		   POSIX Programmer's Manual		  COMPRESS(1P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       compresscompress data

       compress [−fv] [−b bits] [file...]

       compress [−cfv] [−b bits] [file]

       The compress utility shall attempt to reduce  the  size	of  the	 named
       files by using adaptive Lempel-Ziv coding algorithm.

       Note:	 Lempel-Ziv  is	 US Patent 4464650, issued to William Eastman,
		 Abraham Lempel, Jacob Ziv, Martin Cohn on August  7th,	 1984,
		 and assigned to Sperry Corporation.

		 Lempel-Ziv-Welch compression is covered by US Patent 4558302,
		 issued to Terry A. Welch on December 10th, 1985, and assigned
		 to Sperry Corporation.

       On  systems  not	 supporting  adaptive Lempel-Ziv coding algorithm, the
       input files shall not be changed and an error value  greater  than  two
       shall  be  returned.  Except when the output is to the standard output,
       each file shall be replaced by one  with	 the  extension	 .Z.   If  the
       invoking	 process  has  appropriate  privileges,	 the ownership, modes,
       access time, and modification time of the original file are  preserved.
       If  appending  the  .Z  to  the	filename  would	 make  the name exceed
       {NAME_MAX} bytes, the command shall fail. If no	files  are  specified,
       the standard input shall be compressed to the standard output.

       The  compress  utility  shall conform to the Base Definitions volume of
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       −b bits	 Specify the maximum number of bits to use in a	 code.	For  a
		 conforming application, the bits argument shall be:

		     9 <= bits <= 14

		 The  implementation may allow bits values of greater than 14.
		 The default is 14, 15, or 16.

       −c	 Cause compress to write to the	 standard  output;  the	 input
		 file is not changed, and no .Z files are created.

       −f	 Force	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
		 process is  not  running  in  the  background,	 the  user  is
		 prompted  as  to  whether  an	existing file.Z file should be
		 overwritten. If the response  is  affirmative,	 the  existing
		 file will be overwritten.

       −v	 Write	the  percentage	 reduction  of	each  file to standard

       The following operand shall be supported:

       file	 A pathname of a file to be compressed.

       The standard input shall be used only if no file	 operands  are	speci‐
       fied, or if a file operand is '−'.

       If  file operands are specified, the input files contain the data to be

       The following environment variables shall affect the execution of  com‐

       LANG	 Provide  a  default  value for the internationalization vari‐
		 ables that are unset or null. (See the Base Definitions  vol‐
		 ume  of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
		 ables for the precedence  of  internationalization  variables
		 used to determine the values of locale categories.)

       LC_ALL	 If  set  to  a non-empty string value, override the values of
		 all the other internationalization variables.

		 Determine the locale for the behavior of ranges,  equivalence
		 classes,  and	multi-character collating elements used in the
		 extended regular expression defined for  the  yesexpr	locale
		 keyword in the LC_MESSAGES category.

       LC_CTYPE	 Determine  the	 locale for the interpretation of sequences of
		 bytes of text data as characters (for example, single-byte as
		 opposed  to multi-byte characters in arguments), the behavior
		 of character classes used in the extended regular  expression
		 defined  for  the  yesexpr  locale keyword in the LC_MESSAGES

		 Determine the locale used to process  affirmative  responses,
		 and  the  locale  used	 to  affect the format and contents of
		 diagnostic messages, prompts, and  the	 output	 from  the  −v
		 option written to standard error.

       NLSPATH	 Determine the location of message catalogs for the processing


       If no file operands are specified, or if a file operand is '−',	or  if
       the −c option is specified, the standard output contains the compressed

       The standard error shall be used only for diagnostic  and  prompt  mes‐
       sages and the output from −v.

       The  output  files  shall  contain the compressed output. The format of
       compressed files is unspecified and interchange of such	files  between
       implementations	(including  access via unspecified file sharing mecha‐
       nisms) is not required by POSIX.1‐2008.


       The following exit values shall be 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.

       The input file shall remain unmodified.

       The following sections are informative.

       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  or	adaptive Huffman coding (compact), and takes less time to com‐

       Although compress strictly follows the default actions upon receipt  of
       a signal or when an error occurs, some unexpected results may occur. In
       some implementations it is likely that a partially compressed  file  is
       left in place, alongside its uncompressed input file. Since the general
       operation of compress is to delete the uncompressed file only after the
       .Z  file	 has  been  successfully  filled, an application should always
       carefully check the exit status of compress before arbitrarily deleting
       files that have like-named neighbors with .Z suffixes.

       The  limit  of 14 on the bits option-argument is to achieve portability
       to all systems (within the restrictions	imposed	 by  the  lack	of  an
       explicit	 published  file format). Some implementations based on 16-bit
       architectures cannot support 15 or 16-bit uncompression.




       uncompress, zcat

       The Base Definitions volume of  POSIX.1‐2008,  Chapter  8,  Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the	referee document. The original Standard can be obtained online
       at .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker‐ .

IEEE/The Open Group		     2013			  COMPRESS(1P)

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