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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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UNEXPAND(1P) POSIX Programmer's Manual UNEXPAND(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
unexpand — convert spaces to tabs
unexpand [−a|−t tablist] [file...]
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.
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
beginning 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> characters.
−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.
The following operand shall be supported:
file A pathname of a text file to be used as input.
See the INPUT FILES section.
The input files shall be text files.
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 POSIX.1‐2008, 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> 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.
Default.
The standard output shall be equivalent to the input files with the
specified <space>-to-<tab> conversions.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Default.
The following sections are informative.
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.
None.
On several occasions, consideration was given to adding a −t option
to the unexpand utility to complement the −t in expand (see
expand(1p)). The historical intent of unexpand was to translate
multiple <blank> characters 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.
None.
expand(1p), tabs(1p)
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 UNEXPAND(1P)
Pages that refer to this page: expand(1p), tabs(1p)
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