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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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UNEXPAND(1P) POSIX Programmer's Manual UNEXPAND(1P)
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.
unexpand — convert spaces to tabs
unexpand [-a|-t tablist] [file...]
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.
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.
The following operand shall be supported:
file A pathname of a text file to be used as input.
See the INPUT FILES section.
The input files shall be text files.
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.
Default.
The standard output shall be equivalent to the input files with
the specified <space>-to-<tab> conversions.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Default.
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.
None.
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.
None.
expand(1p), tabs(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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