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NAME
unexpand - convert spaces to tabs
SYNOPSIS
unexpand [ -a| -t tablist][file...]
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 translated <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 position 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 Definitions 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 beginning 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 single
argument consisting of a single positive decimal integer or multiple positive decimal integers,
separated by <blank>s or commas, 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>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 internationalization 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
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>s and <space>s, 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 .
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 unexpand was to translate multiple <blank>s 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.
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 Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
IEEE/The Open Group 2003 UNEXPAND(P)