tabs(1) User commands tabs(1)
NAME
tabs - set terminal tab stops
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 ab-
sent, 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 chang-
ing the tabstops), and later cat the file to the screen, setting tab-
stops at that point.
These are hardware tabs, which cannot be queried rapidly by applica-
tions 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.
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 separated by a comma or a blank, for exam-
ple,
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 capabil-
ities:
• If the terminal provides the capability for setting the left
margin, tabs uses this, and adjusts the available width for
tab-stops.
• If the terminal does not provide the margin capabilities, tabs
imitates the effect, putting the tab stops at the appropriate
place on each line. The terminal's left-margin is not modi-
fied.
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-margin, 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.
FILES
/usr/share/tabset
tab stop initialization database
PORTABILITY
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-mar-
gin. 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.
• 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 implementations.
HISTORY
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 a “-n” option to set the first tab stop at the
left margin. That option is not documented by POSIX.
The PWB/Unix tabs utility returned in System III (1980), and 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 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. In an earlier development effort, the tab stop
initialization provided by tset(1) (1982), and incorporated into
tput(1) uses the terminal database,
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 docu-
mented in Issues 6 and later has no mechanism for setting margins. The
+m option in ncurses tabs differs from the SVr4 feature by using termi-
nal capabilities rather than built-in tables.
POSIX documents no limit on the number of tab stops. Other implementa-
tions 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
tabs 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, with-
out settling on an improved solution. It claims that
no known historical version of tabs supports the capability of
setting arbitrary tab stops.
Nevertheless, the feature described in subsection “Explicit Lists”
above was implemented in PWB/Unix, and permits the setting of abitrary
tab stops.
SEE ALSO
infocmp(1), tset(1), ncurses(3NCURSES), terminfo(5)
ncurses 6.4 2023-12-23 tabs(1)
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