TABS(P) POSIX Programmer's Manual TABS(P)NAMEtabs - set terminal tabsSYNOPSIStabs [ -n| -a| -a2| -c| -c2| -c3| -f| -p| -s| -u][+m[n]] [-T type]
tabs [-T type][ +[n]] n1[,n2,...]
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
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines, except
for various extensions: the options -a2, -c2, and -c3 are multi-charac‐
ter.
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 number.
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:
n1[,n2,...]
A single command line argument that consists of tab-stop values
separated using either commas or <blank>s. The application shall
ensure that the tab-stop values are positive decimal integers in
strictly ascending order. If any number (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 1,10,+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 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).
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 IEEE Std 1003.1-2001 has a reduced feature list, but many of the
features omitted were restored as XSI extensions 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
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 TABS(P)
