unexpand(1p) — Linux manual page


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

PROLOG         top

       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.

NAME         top

       unexpand — convert spaces to tabs

SYNOPSIS         top

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

DESCRIPTION         top

       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         top

       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>

OPERANDS         top

       The following operand shall be supported:

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

STDIN         top

       See the INPUT FILES section.

INPUT FILES         top

       The input files shall be text files.


       The following environment variables shall affect the execution of

       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.

                 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.



STDOUT         top

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

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top




EXIT STATUS         top

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.



       The following sections are informative.


       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         top


RATIONALE         top

       On several occasions, consideration was given to adding a -t
       option to the unexpand utility to complement the -t in expand
       (see expand(1p)).  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.



SEE ALSO         top

       expand(1p), tabs(1p)

       The Base Definitions volume of POSIX.1‐2017, Chapter 8,
       Environment Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT         top

       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(1P)

Pages that refer to this page: expand(1p)tabs(1p)