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



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

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 begin-
       ning 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 position.  Each <backspace> shall be copied to the output, and shall cause the column posi-
       tion  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,  Util-
       ity 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-argument is a  single  argu-
              ment consisting of a single positive decimal integer or multiple 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 specified, the default shall be the equivalent of specifying -t 8 (except for the interac-
       tion 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; conversion shall not be lim-
       ited 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, Internationalization Variables for the prece-
              dence 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.

       LC_CTYPE
              Determine  the locale for the interpretation of sequences of bytes of text data as characters (for exam-
              ple, single-byte as opposed to multi-byte characters in arguments and input files),  the  processing  of
              <tab>s  and  <space>s,  and  for the determination 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 diagnostic messages  writ-
              ten 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 utility 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 column positions on most UNIX systems. An early proposal  omit-
       ted  -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  inter-
       national  community  and  broke  historical  precedents  for  some  vendors in the FORTRAN community, so -t was
       restored in conjunction with the list of valid extension categories  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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                         UNEXPAND(1P)