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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 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

       X/Open defines several predefined lists of tab stops.

       -a   Assembler, IBM S/370, first format

       -a2  Assembler, IBM S/370, second format

       -c   COBOL, normal format

       -c2  COBOL compact format

       -c3  COBOL compact format extended

       -f   FORTRAN

       -p   PL/I

       -s   SNOBOL

       -u   UNIVAC 1100 Assembler


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-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.

       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  terminal  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, as a fallback.  In an  earlier  develop-
       ment  effort,  the  tab-stop initialization provided by tset (1982) and
       incorporated into tput uses the terminal database,

       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  imple-
       mented  in  PWB/Unix.  Those provide the capability of setting abitrary
       tab stops.


SEE ALSO

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

       This describes ncurses version 6.1 (patch 20190623).



                                                                       tabs(1)