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 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 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.

   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 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.

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 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.

SEE ALSO

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

ncurses 6.5                                        2025-02-15                                            tabs(1)