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.

       •   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.

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 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.

SEE ALSO

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