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



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

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 88
                 (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 88 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.

SEE ALSO
       expand, tabs

       The Base Definitions volume of POSIX.1-2017, Chapter _8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

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(1)
