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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.
-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.
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.
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.
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
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:
o If the terminal provides the capability for setting the left
margin, tabs uses this, and adjusts the available tab stop
widths.
o 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.
/usr/share/tabset
tab stop initialization database
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 set_left_margin (smgl) or set_left_margin_parm (smglp)
capabilities needed to support the feature.
o 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 abitrary tab
stops nevertheless.
infocmp(1m), tset(1), curses(3x), terminfo(5)
ncurses 6.5 2024-09-21 tabs(1)