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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 2024-06-26 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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