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Linux 2.6 - man page for unexpand (linux section 1posix)

UNEXPAND(P)			    POSIX Programmer's Manual			      UNEXPAND(P)

NAME
       unexpand - convert spaces to tabs

SYNOPSIS
       unexpand [ -a| -t tablist][file...]

DESCRIPTION
       The  unexpand  utility  shall  copy files or standard input to standard output, converting
       <blank>s at the beginning of each line into the maximum number of <tab>s followed  by  the
       minimum	number	of <space>s needed to fill the same column positions originally filled by
       the translated <blank>s. By default, tabstops shall be set at every  eighth  column  posi-
       tion.  Each <backspace> shall be copied to the output, and shall cause the column position
       count for tab calculations to be decremented; the count shall never be  decremented  to	a
       value less than one.

OPTIONS
       The unexpand utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001,
       Section 12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       -a     In addition to translating <blank>s at the beginning of each  line,  translate  all
	      sequences  of  two or more <blank>s immediately preceding a tab stop to the maximum
	      number of <tab>s followed by the minimum number of <space>s needed to fill the same
	      column positions originally filled by the translated <blank>s.

       -t  tablist
	      Specify  the  tab stops. The application shall ensure that the tablist option-argu-
	      ment is a single argument consisting of a single positive decimal integer or multi-
	      ple positive decimal integers, separated by <blank>s or commas, in ascending order.
	      If a single number is given, tabs shall  be  set	tablist  column  positions  apart
	      instead  of  the default 8. If multiple numbers are given, the tabs shall be set at
	      those specific column positions.

       The application shall ensure that each tab-stop position N is  an  integer  value  greater
       than  zero, and the list shall be in strictly ascending order. This is taken to mean that,
       from the start of a line of output, tabbing to position N shall cause the  next	character
       output to be in the ( N+1)th column position on that line. When the -t option is not spec-
       ified, the default shall be the equivalent of specifying -t 8 (except for the  interaction
       with -a, described below).

       No  <space>-to-	<tab> conversions shall occur for characters at positions beyond the last
       of those specified in a multiple tab-stop list.

       When -t is specified, the presence or absence of the -a option shall be	ignored;  conver-
       sion shall not be limited to the processing of leading <blank>s.

OPERANDS
       The following operand shall be supported:

       file   A pathname of a text file to be used as input.

STDIN
       See the INPUT FILES section.

INPUT FILES
       The input files shall be text files.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of unexpand:

       LANG   Provide  a  default  value for the internationalization variables that are unset or
	      null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, Inter-
	      nationalization Variables 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  interna-
	      tionalization variables.

       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  argu-
	      ments and input files), the processing of <tab>s and <space>s, and for the determi-
	      nation of the width in column positions each character would occupy  on  an  output
	      device.

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic messages written to standard error.

       NLSPATH
	      Determine the location of message catalogs for the processing of LC_MESSAGES .

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       The standard output shall be equivalent to the input files with the specified  <space>-to-
       <tab> conversions.

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       The following exit values shall be returned:

	0     Successful completion.

       >0     An error occurred.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       One  non-intuitive aspect of unexpand is its restriction to leading spaces when neither -a
       nor -t is specified. Users who always want to convert all spaces  in  a	file  can  easily
       alias unexpand to use the -a or -t 8 option.

EXAMPLES
       None.

RATIONALE
       On  several occasions, consideration was given to adding a -t option to the unexpand util-
       ity to complement the -t in expand (see expand ). The historical intent of unexpand was to
       translate  multiple <blank>s into tab stops, where tab stops were a multiple of eight col-
       umn positions on most UNIX systems. An early proposal omitted -t because it seemed outside
       the  scope  of  the  User Portability Utilities option; it was not described in any of the
       base documents.	However, hard-coding tab stops every eight columns was not  suitable  for
       the  international  community and broke historical precedents for some vendors in the FOR-
       TRAN community, so -t was restored in conjunction with the list of valid  extension  cate-
       gories  considered  by the standard developers. Thus, unexpand is now the logical converse
       of expand.

FUTURE DIRECTIONS
       None.

SEE ALSO
       expand , tabs

COPYRIGHT
       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2003  Edition,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				      UNEXPAND(P)


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