tabs 1 2024-06-22 ncurses 6.5 User commands

tabs(1)                          User commands                         tabs(1)


       tabs - set terminal tab stops


       tabs [options] [tabstop-list]


       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.


General Options

            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

       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

           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

       -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


       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

            o   If  the  terminal provides the capability for setting the left
                margin, tabs uses this, and adjusts  the  available  tab  stop

            o   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.


              tab stop initialization database


       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   set_left_margin   (smgl)   or   set_left_margin_parm  (smglp)
           capabilities 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 ncurses extensions not
       provided by other implementations.


       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 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 tabs 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  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,
       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  abitrary  tab
       stops nevertheless.


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

ncurses 6.5                       2024-06-22                           tabs(1)