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PROLOG

       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
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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> characters
       at  the beginning of each line into the maximum number of <tab> characters followed by the minimum number
       of <space> characters needed to fill the same  column  positions  originally  filled  by  the  translated
       <blank>  characters.  By default, tabstops shall be set at every eighth column position. 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 POSIX.1‐2017, Section 12.2, Utility
Syntax Guidelines.

The following options shall be supported:

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

-t tablist
Specify the tab stops. The application shall ensure that the tablist option-argument is a
single argument consisting of a single positive decimal integer or multiple positive decimal
integers, separated by <blank> or <comma> characters, 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 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; conversion
shall not be limited to the processing of leading <blank> characters.

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 POSIX.1‐2017, Section 8.2, Internationalization  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  internationalization
                 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 arguments  and  input  files),
                 the  processing  of  <tab>  and  <space>  characters, 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 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 <space> characters when neither -a nor
       -t is specified. Users who always want to convert all <space> characters  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>
       characters into tab stops, where tab stops were a  multiple  of  eight  column  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 for IEEE Std  1003.2‐1992.   However,
       hard-coding  tab  stops  every  eight  columns was not suitable for the international 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.

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                      UNEXPAND(1POSIX)