TABS(1P) POSIX Programmer's Manual TABS(1P)
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This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
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NAME
tabs -- set terminal tabs
SYNOPSIS
tabs [-n|-a|-a2|-c|-c2|-c3|-f|-p|-s|-u] [-T type]
tabs [-T type] n[[sep[+]n]...]
DESCRIPTION
The tabs utility shall display a series of characters that first clears
the hardware terminal tab settings and then initializes the tab stops
at the specified positions and optionally adjusts the margin.
The phrase ``tab-stop position N'' shall be 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. The maximum number of tab stops allowed is terminal-dependent.
It need not be possible to implement tabs on certain terminals. If the
terminal type obtained from the TERM environment variable or -T option
represents such a terminal, an appropriate diagnostic message shall be
written to standard error and tabs shall exit with a status greater
than zero.
OPTIONS
The tabs utility shall conform to the Base Definitions volume of
POSIX.1-2008, Section 12.2, Utility Syntax Guidelines, except for vari-
ous extensions: the options -a2, -c2, and -c3 are multi-character.
The following options shall be supported:
-n Specify repetitive tab stops separated by a uniform number of
column positions, n, where n is a single-digit decimal num-
ber. The default usage of tabs with no arguments shall be
equivalent to tabs -8. When -0 is used, the tab stops shall
be cleared and no new ones set.
-a 1,10,16,36,72
Assembler, applicable to some mainframes.
-a2 1,10,16,40,72
Assembler, applicable to some mainframes.
-c 1,8,12,16,20,55
COBOL, normal format.
-c2 1,6,10,14,49
COBOL, compact format (columns 1 to 6 omitted).
-c3 1,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,67
COBOL compact format (columns 1 to 6 omitted), with more tabs
than -c2.
-f 1,7,11,15,19,23
FORTRAN
-p 1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61
PL/1
-s 1,10,55
SNOBOL
-u 1,12,20,44
Assembler, applicable to some mainframes.
-T type Indicate the type of terminal. If this option is not supplied
and the TERM variable is unset or null, an unspecified
default terminal type shall be used. The setting of type
shall take precedence over the value in TERM.
OPERANDS
The following operand shall be supported:
n[[sep[+]n]...]
A single command line argument that consists of one or more
tab-stop values (n) separated by a separator character (sep)
which is either a <comma> or a <blank> character. The appli-
cation shall ensure that the tab-stop values are positive
decimal integers in strictly ascending order. If any tab-stop
value (except the first one) is preceded by a <plus-sign>, it
is taken as an increment to be added to the previous value.
For example, the tab lists 1,10,20,30 and "110+10+10" are
considered to be identical.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of tabs:
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).
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.
TERM Determine the terminal type. If this variable is unset or
null, and if the -T option is not specified, an unspecified
default terminal type shall be used.
ASYNCHRONOUS EVENTS
Default.
STDOUT
If standard output is a terminal, the appropriate sequence to clear and
set the tab stops may be written to standard output in an unspecified
format. If standard output is not a terminal, undefined results occur.
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
This utility makes use of the terminal's hardware tabs and the stty
tabs option.
This utility is not recommended for application use.
Some integrated display units might not have escape sequences to set
tab stops, but may be set by internal system calls. On these terminals,
tabs works if standard output is directed to the terminal; if output is
directed to another file, however, tabs fails.
EXAMPLES
None.
RATIONALE
Consideration was given to having the tput utility handle all of the
functions described in tabs. However, the separate tabs utility was
retained because it seems more intuitive to use a command named tabs
than tput with a new option. The tput utility does not support setting
or clearing tabs, and no known historical version of tabs supports the
capability of setting arbitrary tab stops.
The System V tabs interface is very complex; the version in this volume
of POSIX.1-2008 has a reduced feature list, but many of the features
omitted were restored as part of the XSI option even though the sup-
ported languages and coding styles are primarily historical.
There was considerable sentiment for specifying only a means of reset-
ting the tabs back to a known state--presumably the ``standard'' of
tabs every eight positions. The following features were omitted:
* Setting tab stops via the first line in a file, using --file.
Since even the SVID has no complete explanation of this feature, it
is doubtful that it is in widespread use.
In an early proposal, a -t tablist option was added for consistency
with expand; this was later removed when inconsistencies with the his-
torical list of tabs were identified.
Consideration was given to adding a -p option that would output the
current tab settings so that they could be saved and then later
restored. This was not accepted because querying the tab stops of the
terminal is not a capability in historical terminfo or termcap facili-
ties and might not be supported on a wide range of terminals.
FUTURE DIRECTIONS
None.
SEE ALSO
expand, stty, tput, unexpand
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-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 TABS(1P)
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