UNEXPAND(1P) POSIX Programmer's Manual UNEXPAND(1P)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> characters at the beginning of each line
into the maximum number of <tab> characters followed by the minimum
number of <space> characters needed to fill the same column positions
originally filled by the translated <blank> characters. 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
POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
−a In addition to translating <blank> characters at the begin‐
ning of each line, translate all sequences of two or more
<blank> characters immediately preceding a tab stop to the
maximum number of <tab> characters followed by the minimum
number of <space> characters needed to fill the same column
positions originally filled by the translated <blank> charac‐
ters.
−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> or <comma> characters, 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> characters.
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 vari‐
ables that are unset or null. (See the Base Definitions vol‐
ume of POSIX.1‐2008, 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> and <space> characters, 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
<space> characters when neither −a nor −t is specified. Users who
always want to convert all <space> characters 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> charac‐
ters 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 FOR‐
TRAN 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
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
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IEEE/The Open Group 2013 UNEXPAND(1P)
