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.1‐2008, 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         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.1‐2008, Section 8.2, Internationalization
                 Variables for the precedence of internationalization
                 variables used to determine the values of locale

       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. 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.1‐2008, 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, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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 .

       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 .

IEEE/The Open Group                 2013                        UNEXPAND(1P)

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