TABS(1)                    POSIX Programmer's Manual                   TABS(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       tabs -- set terminal tabs

SYNOPSIS
       tabs [[-_n|-a|-a2|-c|-c2|-c3|-f|-p|-s|-u]] [[-T type]]

       tabs [[-T type]] _n[[[[sep[[+]]_n]]...]]

DESCRIPTION
       The tabs utility shall display a series of characters that first clears
       the hardware terminal tab settings and then initializes the tab stops
       at the specified positions and optionally adjusts the margin.

       The phrase ``tab-stop position _N'' shall be taken to mean that, from
       the start of a line of output, tabbing to position _N shall cause the
       next character output to be in the (_N+1)th column position on that
       line. The maximum number of tab stops allowed is terminal-dependent.

       It need not be possible to implement tabs on certain terminals. If the
       terminal type obtained from the TERM environment variable or -T option
       represents such a terminal, an appropriate diagnostic message shall be
       written to standard error and tabs shall exit with a status greater
       than zero.

OPTIONS
       The tabs utility shall conform to the Base Definitions volume of
       POSIX.1-2017, Section 12.2, Utility Syntax Guidelines, except for
       various extensions: the options -a2, -c2, and -c3 are multi-character.

       The following options shall be supported:

       --_n        Specify repetitive tab stops separated by a uniform number of
                 column positions, _n, where _n is a single-digit decimal
                 number. The default usage of tabs with no arguments shall be
                 equivalent to tabs -8. When --00 is used, the tab stops shall
                 be cleared and no new ones set.

       -a        1,10,16,36,72
                 Assembler, applicable to some mainframes.

       -a2       1,10,16,40,72
                 Assembler, applicable to some mainframes.

       -c        1,8,12,16,20,55
                 COBOL, normal format.

       -c2       1,6,10,14,49
                 COBOL, compact format (columns 1 to 6 omitted).

       -c3       1,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,67
                 COBOL compact format (columns 1 to 6 omitted), with more tabs
                 than -c2.

       -f        1,7,11,15,19,23
                 FORTRAN

       -p        1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61
                 PL/1

       -s        1,10,55
                 SNOBOL

       -u        1,12,20,44
                 Assembler, applicable to some mainframes.

       -T type   Indicate the type of terminal. If this option is not supplied
                 and the TERM variable is unset or null, an unspecified
                 default terminal type shall be used. The setting of type
                 shall take precedence over the value in TERM.

OPERANDS
       The following operand shall be supported:

       _n[[[[sep[[+]]_n]]...]]
                 A single command line argument that consists of one or more
                 tab-stop values (_n) separated by a separator character (sep)
                 which is either a <comma> or a <blank> character. The
                 application shall ensure that the tab-stop values are
                 positive decimal integers in strictly ascending order. If any
                 tab-stop value (except the first one) is preceded by a <plus-
                 sign>, it is taken as an increment to be added to the
                 previous value. For example, the tab lists 1,10,20,30 and
                 ""1110++1100+10" are considered to be identical.

STDIN
       Not used.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of tabs:

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base Definitions
                 volume of POSIX.1-2017, Section 8.2, Internationalization
                 Variables for the precedence of internationalization
                 variables used to determine the values of locale categories.)

       LC__ALL    If set to a non-empty string value, override the values of
                 all the other internationalization variables.

       LC__CTYPE  Determine the locale for the interpretation of sequences of
                 bytes of text data as characters (for example, single-byte as
                 opposed to multi-byte characters in arguments).

       LC__MESSAGES
                 Determine the locale that should be used to affect the format
                 and contents of diagnostic messages written to standard
                 error.

       NLSPATH   Determine the location of message catalogs for the processing
                 of LC__MESSAGES.

       TERM      Determine the terminal type. If this variable is unset or
                 null, and if the -T option is not specified, an unspecified
                 default terminal type shall be used.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       If standard output is a terminal, the appropriate sequence to clear and
       set the tab stops may be written to standard output in an unspecified
       format. If standard output is not a terminal, undefined results occur.

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       This utility makes use of the terminal's hardware tabs and the stty
       tabs option.

       This utility is not recommended for application use.

       Some integrated display units might not have escape sequences to set
       tab stops, but may be set by internal system calls. On these terminals,
       tabs works if standard output is directed to the terminal; if output is
       directed to another file, however, tabs fails.

EXAMPLES
       None.

RATIONALE
       Consideration was given to having the tput utility handle all of the
       functions described in tabs.  However, the separate tabs utility was
       retained because it seems more intuitive to use a command named tabs
       than tput with a new option. The tput utility does not support setting
       or clearing tabs, and no known historical version of tabs supports the
       capability of setting arbitrary tab stops.

       The System V tabs interface is very complex; the version in this volume
       of POSIX.1-2017 has a reduced feature list, but many of the features
       omitted were restored as part of the XSI option even though the
       supported languages and coding styles are primarily historical.

       There was considerable sentiment for specifying only a means of
       resetting the tabs back to a known state--presumably the ``standard''
       of tabs every eight positions. The following features were omitted:

        *  Setting tab stops via the first line in a file, using --file.
           Since even the SVID has no complete explanation of this feature, it
           is doubtful that it is in widespread use.

       In an early proposal, a -t tablist option was added for consistency
       with expand; this was later removed when inconsistencies with the
       historical list of tabs were identified.

       Consideration was given to adding a -p option that would output the
       current tab settings so that they could be saved and then later
       restored. This was not accepted because querying the tab stops of the
       terminal is not a capability in historical terminfo or termcap
       facilities and might not be supported on a wide range of terminals.

FUTURE DIRECTIONS
       None.

SEE ALSO
       expand, stty, tput, unexpand

       The Base Definitions volume of POSIX.1-2017, Chapter _8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                              TABS(1)
