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 .
