UNEXPAND(P) POSIX Programmer's Manual UNEXPAND(P)PROLOG
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NAMEunexpand - convert spaces to tabs
SYNOPSISunexpand [ -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 max‐
imum 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 immedi‐
ately preceding a tab stop to the maximum number of <tab>s fol‐
lowed 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 posi‐
tions.
The application shall ensure that each tab-stop position N is an inte‐
ger value greater than zero, and the list shall be in strictly ascend‐
ing order. This is taken to mean that, from the start of a line of out‐
put, 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 posi‐
tions 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 unex‐
pand:
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 Vari‐
ables 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 spa‐
ces when neither -a nor -t is specified. Users who always want to con‐
vert 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 out‐
side 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 commu‐
nity, so -t was restored in conjunction with the list of valid exten‐
sion 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)
