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tabs 1

tabs(1)                     General Commands Manual                    tabs(1)




NAME

       tabs - set tabs on a terminal


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  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
            capabilities:

            o   If  the  terminal provides the capability for setting the left
                margin, tabs uses this, and adjusts the  available  width  for
                tab-stops.

            o   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
                modified.

            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.


PORTABILITY

       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  smgl   (set_left_margin)   or   smglp   (set_left_margin_parm)
           capability needed to support the feature.

       o   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.

       A  tabs  utility  appeared in PWB/Unix 1.0 (1977).  There was a reduced
       version of the tabs utility in Unix 7th edition  and  in  3BSD  (1979).
       The  latter supported a single "-n" option (to cause the first tab stop
       to be set on the left margin).  That option is not documented by POSIX.

       The PWB/Unix tabs utility, which was included  in  System  III  (1980),
       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 the left-margin, as well as a feature for copying the
       tab settings from a file.

       Later versions of Unix, e.g., SVr4,  added  support  for  the  terminal
       database,  but  kept the tables to support the printers.  In an earlier
       development effort, the tab-stop initialization provided by tset (1982)
       and incorporated into tput uses the terminal database,

       The  +m  option  was  documented  in  the  Base  Specifications Issue 5
       (Unix98,  1997),  and  omitted  in  Issue  6  (Unix03,  2004)   without
       documenting   the   rationale,  though  an  introductory  comment  "and
       optionally adjusts the margin" remains, overlooked in the removal.  The
       documented  tabs  utility  in  Issues  6 and later has no mechanism for
       setting margins.  The +m option in this implementation differs from the
       feature  in  SVr4  by  using terminal capabilities rather than built-in
       tables.

       POSIX documents no limits on the number of  tab  stops.   Documentation
       for other implementations states that there is a limit on the number of
       tab stops (e.g., 20 in PWB/Unix's tabs utility).  While some  terminals
       may  not  accept  an arbitrary number of tab stops, this implementation
       will attempt to set tab stops up to the right margin of the screen,  if
       the given list happens to be that long.

       The  Rationale section of the POSIX documentation goes into some detail
       about the ways the committee considered redesigning the tabs  and  tput
       utilities, without proposing an improved solution.  It comments that

            no  known  historical  version  of tabs supports the capability of
            setting arbitrary tab stops.

       However,  the  Explicit  Lists  described  in  this  manual  page  were
       implemented  in  PWB/Unix.   Those  provide  the  capability of setting
       abitrary tab stops.


SEE ALSO

       infocmp(1m), tset(1), curses(3x), terminfo(5).

       This describes ncurses version 6.3 (patch 20220703).



                                                                       tabs(1)