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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 .