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unexpand(P) unexpand(P)
NAME
unexpand - convert spaces to tabs
SYNOPSIS
unexpand [ -a| -t tablist][file...]<img
src="../images/opt-end.gif" alt="[Option End]" bor-
der="0">
DESCRIPTION
The unexpand utility shall copy files or standard input
to standard output, converting <blank>s at the beginning
of each line into the maximum number of <tab>s followed
by the minimum number of <space>s needed to fill the
same column positions originally filled by the trans-
lated <blank>s. By default, tabstops shall be set at
every eighth column position. Each <backspace> shall be
copied to the output, and shall cause the column posi-
tion 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 Defini-
tions volume of IEEE Std 1003.1-2001, Section 12.2,
Utility Syntax Guidelines.
The following options shall be supported:
-a In addition to translating <blank>s at the begin-
ning of each line, translate all sequences of two
or more <blank>s immediately preceding a tab stop
to the maximum number of <tab>s followed by the
minimum number of <space>s needed to fill the
same column positions originally filled by the
translated <blank>s.
-t tablist
Specify the tab stops. The application shall
ensure that the tablist option-argument is a sin-
gle argument consisting of a single positive dec-
imal integer or multiple positive decimal inte-
gers, separated by <blank>s or commas, in ascend-
ing 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 interac-
tion with -a, described below).
No <space>-to- <tab> conversions shall occur for charac-
ters 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>s.
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 internationaliza-
tion variables that are unset or null. (See the
Base Definitions volume of IEEE Std 1003.1-2001,
Section 8.2, Internationalization Variables for
the precedence of internationalization variables
used to determine the values of locale cate-
gories.)
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>s and <space>s, and for
the determination of the width in column posi-
tions 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 mes-
sages 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 spaces when neither -a nor -t is specified.
Users who always want to convert all spaces in a file
can easily alias unexpand to use the -a or -t 8 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 unex-
pand was to translate multiple <blank>s into tab stops,
where tab stops were a multiple of eight column posi-
tions on most UNIX systems. An early proposal omitted -t
because it seemed outside the scope of the User Porta-
bility 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 interna-
tional 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
COPYRIGHT
Portions of this text are reprinted and reproduced in
electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operat-
ing System Interface (POSIX), The Open Group Base Speci-
fications Issue 6, Copyright (C) 2001-2003 by the Insti-
tute 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.open-
group.org/unix/online.html .
POSIX 2003 unexpand(P)
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