# tabs 1 2025-04-05 ncurses 6.5 User commands

    tabs(1)                          User commands                         tabs(1)

## 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:

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

                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.

## 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,

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

    ncurses 6.5                       2025-04-05                           tabs(1)