Manual: tabs

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 capa‐
       bilities.  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.

OPTIONS
   General Options
       -Tname
	    Tell  tabs	which  terminal type to use.  If this option is not given, tabs will use the $TERM environment vari‐
	    able.  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 set‐
	    tings.

       -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 in‐
       creasing 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  avail‐
		able 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 prob‐
	    lems 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.

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 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.

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 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 initializa‐
       tion 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” re‐
       mains, 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.

SEE ALSO
       infocmp(1), tset(1), ncurses(3NCURSES), terminfo(5)

ncurses 6.6						 2025-08-16						     tabs(1)