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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILES | PORTABILITY | HISTORY | SEE ALSO | COLOPHON |
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tabs(1) User commands tabs(1)
tabs - set terminal tab stops
tabs [options] [tabstop-list]
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
information in the terminal database, the result is unpredictable.
Before running curses programs, 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.
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 separated 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.
Standard Tab Stops
POSIX defines several 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 expose a means of changing their left and right
margins. tabs supports this feature with an option.
+m margin
The effect depends on whether the terminal has the margin
capabilities:
• If the terminal provides the capability for setting the
left margin, tabs uses this, and adjusts the available
tab stop widths.
• If the terminal does not provide the margin capabilities,
tabs imitates their effect, putting tab stops at
appropriate places on each line. The terminal's left
margin is not modified.
If the margin parameter is omitted, the default is 10. Use
+m0 to reset the left margin, that is, to make it the left
edge of the terminal's display. Before setting a left
margin, tabs resets the margin to reduce problems that might
arise from moving the cursor to the left of the current left
margin.
When setting or resetting the left margin, tabs may also reset the
right margin.
datadir/tabset
tab stop initialization database
IEEE Std 1003.1/The Open Group Base Specifications Issue 7
(POSIX.1-2008) describes a tabs utility. However,
• this standard describes a +m option to set a terminal's left
margin. Very few of the entries in the terminal database
provide the set_left_margin (smgl) or set_left_margin_parm
(smglp) capabilities needed to support the feature.
• Unlike tput, tabs has no specification in X/Open Curses
Issue 7.
The -d (debug) and -n (no-op) options are ncurses extensions not
provided by other implementations.
A tabs utility appeared in PWB/Unix 1.0 (1977). A reduced version
shipped in Seventh Edition Unix (early 1979) and in 3BSD (later
the same year); it supported an option “-n” to set the first tab
stop at the left margin. That option is not specified by POSIX.
The PWB/Unix tabs utility returned in System III (1980), and used
built-in tables to support a half-dozen hardcopy terminal
(printer) types. It also had logic to support setting the left
margin, as well as a feature for copying the tab settings from a
file.
Versions of the program in later releases of AT&T Unix, such as
SVr4, added support for the terminal database, but retained the
tables to support the printers. By this time, System V tput had
incorporated the tab stop initialization feature of BSD's tset
from 1982, but employed the terminfo database to do so.
The +m option was documented in the POSIX Base Specifications
Issue 5 (Unix98, 1997), then omitted in Issue 6 (Unix03, 2004)
without express motivation, though an introductory comment “and
optionally adjusts the margin” remains, overlooked in the removal.
The tabs utility documented in Issues 6 and later has no mechanism
for setting margins. The +m option in ncurses's implementation
differs from the SVr4 feature by using terminal capabilities
rather than built-in tables.
POSIX documents no limit on the number of tab stops. Other
implementations impose one; the limit is 20 in PWB/Unix's tabs
utility. While some terminals may not accept an arbitrary number
of tab stops, ncurses attempts to set tab stops up to the right
margin if the list thereof is sufficiently long.
The “Rationale” section of the Issue 6 tabs reference page details
how the committee considered redesigning the tabs and tput
utilities, without settling on an improved solution. It claims
that
no known historical version of tabs supports the capability of
setting arbitrary tab stops.
The feature described in subsection “Explicit Lists” above was
implemented in PWB/Unix, and permitted the setting of arbitrary
tab stops nevertheless.
infocmp(1M), tset(1), curses(3X), terminfo(5)
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://invisible-island.net/ncurses/ncurses.html⟩. If you have a
bug report for this manual page, send it to bug-ncurses@gnu.org.
This page was obtained from the tarball ncurses-6.6.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/ncurses/⟩ on 2026-01-16. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information
in this COLOPHON (which is not part of the original manual page),
send a mail to man-pages@man7.org
ncurses @NCURSES_MAJOR@.@NCU... 2025-08-16 tabs(1)
Pages that refer to this page: tput(1), terminfo(5)
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HTML rendering created 2026-01-16 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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