# tabs

## 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**
           **-T** _name_
                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:
    
                •   If the terminal provides the capability for setting the
                    left margin, tabs uses this, and adjusts the available
                    width for tab-stops.
    
                •   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
    
           •   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.
    
           •   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.
    


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