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-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 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 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).
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 sttytabs
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 supported languages and coding
styles are primarily historical.
There was considerable sentiment for specifying only a means of resetting
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 -ttablist option was added for
consistency with expand; this was later removed when inconsistencies
with the historical 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 facilities 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 .
