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tabs(1) General Commands Manual tabs(1)
NAME
tabs - set tabs on a terminal
SYNOPSIS
tabs [options]] [tabstop-list]
DESCRIPTION
The tabs program clears and sets tab-stops on the terminal. This uses the terminfo
clear_all_tabs and set_tab capabilities. If either is absent, tabs is unable to clear/set
tab-stops. The terminal should be configured to use hard tabs, e.g.,
stty tab0
Like clear(1), tabs writes to the standard output. You can redirect the standard output
to a file (which prevents tabs from actually changing the tabstops), and later cat the
file to the screen, setting tabstops at that point.
These are hardware tabs, which cannot be queried rapidly by applications running in the
terminal, if at all. Curses and other full-screen applications may use hardware tabs in
optimizing their output to the terminal. If the hardware tabstops differ from the infor-
mation in the terminal database, the result is unpredictable. Before running curses pro-
grams, you should either reset tab-stops to the standard interval
tabs -8
or use the reset program, since the normal initialization sequences do not ensure that
tab-stops are reset.
OPTIONS
General Options
-Tname
Tell tabs which terminal type to use. If this option is not given, tabs will use the
$TERM environment variable. If that is not set, it will use the ansi+tabs entry.
-d The debugging option shows a ruler line, followed by two data lines. The first data
line shows the expected tab-stops marked with asterisks. The second data line shows
the actual tab-stops, marked with asterisks.
-n This option tells tabs to check the options and run any debugging option, but not to
modify the terminal settings.
-V reports the version of ncurses which was used in this program, and exits.
The tabs program processes a single list of tab stops. The last option to be processed
which defines a list is the one that determines the list to be processed.
Implicit Lists
Use a single number as an option, e.g., "-5" to set tabs at the given interval (in this
case 1, 6, 11, 16, 21, etc.). Tabs are repeated up to the right margin of the screen.
Use "-0" to clear all tabs.
Use "-8" to set tabs to the standard interval.
Explicit Lists
An explicit list can be defined after the options (this does not use a "-"). The values
in the list must be in increasing numeric order, and greater than zero. They are sepa-
rated by a comma or a blank, for example,
tabs 1,6,11,16,21
tabs 1 6 11 16 21
Use a "+" to treat a number as an increment relative to the previous value, e.g.,
tabs 1,+5,+5,+5,+5
which is equivalent to the 1,6,11,16,21 example.
Predefined Tab-Stops
POSIX defines several predefined lists of tab stops.
-a Assembler, IBM S/370, first format
1,10,16,36,72
-a2 Assembler, IBM S/370, second format
1,10,16,40,72
-c COBOL, normal format
1,8,12,16,20,55
-c2 COBOL compact format
1,6,10,14,49
-c3 COBOL compact format extended
1,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,67
-f FORTRAN
1,7,11,15,19,23
-p PL/I
1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61
-s SNOBOL
1,10,55
-u UNIVAC 1100 Assembler
1,12,20,44
Margins
A few terminals provide the capability for changing their left/right margins. The tabs
program has an option to use this feature:
+m margin
The effect depends on whether the terminal has the margin capabilities:
o If the terminal provides the capability for setting the left margin, tabs uses
this, and adjusts the available width for tab-stops.
o If the terminal does not provide the margin capabilities, tabs imitates the ef-
fect, putting the tab stops at the appropriate place on each line. The termi-
nal's left-margin is not modified.
If the margin parameter is omitted, the default is 10. Use +m0 to reset the left
margin, i.e., to the left edge of the terminal's display. Before setting a left-mar-
gin, tabs resets the margin to reduce problems which might arise on moving the cursor
before the current left-margin.
When setting or resetting the left-margin, tabs may reset the right-margin.
PORTABILITY
IEEE Std 1003.1/The Open Group Base Specifications Issue 7 (POSIX.1-2008) describes a tabs
utility. However
o This standard describes a +m option, to set a terminal's left-margin. Very few of the
entries in the terminal database provide the smgl (set_left_margin) or smglp
(set_left_margin_parm) capability needed to support the feature.
o There is no counterpart in X/Open Curses Issue 7 for this utility, unlike tput(1).
The -d (debug) and -n (no-op) options are extensions not provided by other implementa-
tions.
A tabs utility appeared in PWB/Unix 1.0 (1977). There was a reduced version of the tabs
utility in Unix 7th edition and in 3BSD (1979). The latter supported a single "-n" option
(to cause the first tab stop to be set on the left margin). That option is not documented
by POSIX.
The PWB/Unix tabs utility, which was included in System III (1980), used built-in tables
rather than the terminal database, to support a half-dozen hardcopy terminal (printer)
types. It also had built-in logic to support the left-margin, as well as a feature for
copying the tab settings from a file.
Later versions of Unix, e.g., SVr4, added support for the terminal database, but kept the
tables to support the printers. In an earlier development effort, the tab-stop initial-
ization provided by tset (1982) and incorporated into tput uses the terminal database,
The +m option was documented in the Base Specifications Issue 5 (Unix98, 1997), and omit-
ted in Issue 6 (Unix03, 2004) without documenting the rationale, though an introductory
comment "and optionally adjusts the margin" remains, overlooked in the removal. The docu-
mented tabs utility in Issues 6 and later has no mechanism for setting margins. The +m
option in this implementation differs from the feature in SVr4 by using terminal capabili-
ties rather than built-in tables.
POSIX documents no limits on the number of tab stops. Documentation for other implementa-
tions states that there is a limit on the number of tab stops (e.g., 20 in PWB/Unix's tabs
utility). While some terminals may not accept an arbitrary number of tab stops, this im-
plementation will attempt to set tab stops up to the right margin of the screen, if the
given list happens to be that long.
The Rationale section of the POSIX documentation goes into some detail about the ways the
committee considered redesigning the tabs and tput utilities, without proposing an im-
proved solution. It comments that
no known historical version of tabs supports the capability of setting arbitrary tab
stops.
However, the Explicit Lists described in this manual page were implemented in PWB/Unix.
Those provide the capability of setting abitrary tab stops.
SEE ALSO
infocmp(1), tset(1), ncurses(3NCURSES), terminfo(5).
This describes ncurses version 6.3 (patch 20211021).
tabs(1)
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