UNEXPAND(P) UNEXPAND(P)
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 posi-
tion. 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-argu-
ment is a single argument consisting of a single positive decimal integer or multi-
ple 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 spec-
ified, 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; conver-
sion 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, Inter-
nationalization 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 interna-
tionalization 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 argu-
ments and input files), the processing of <tab>s and <space>s, and for the determi-
nation 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 diag-
nostic 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 util-
ity 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 col-
umn 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 FOR-
TRAN community, so -t was restored in conjunction with the list of valid extension cate-
gories 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
POSIX 2003 UNEXPAND(P)
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