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TABS(1P) POSIX Programmer's Manual TABS(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.
tabs — set terminal tabs
tabs [−n|−a|−a2|−c|−c2|−c3|−f|−p|−s|−u] [−T type]
tabs [−T type] n[[sep[+]n]...]
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.
The tabs utility shall conform to the Base Definitions volume of
POSIX.1‐2008, 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.
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
application 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.
Not used.
None.
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 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).
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.
Default.
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.
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.
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.
None.
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 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 −t tablist 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.
None.
expand(1p), stty(1p), tput(1p), unexpand(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 TABS(1P)
Pages that refer to this page: expand(1p), tput(1p), unexpand(1p)