Ubuntu Manpage: tabs - set terminal tabs

NAME

       tabs - set terminal tabs

SYNOPSIS

       tabs [ -n| -a| -a2| -c| -c2| -c3| -f| -p| -s| -u][+m[n]] [-T type]

       tabs [-T type][ +[n]] n1[,n2,...]

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 IEEE Std 1003.1-2001,
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 -0 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:

       n1[,n2,...]
              A single command line argument that consists of  tab-stop  values  separated  using
              either  commas  or  <blank>s. The application shall ensure that the tab-stop values
              are positive decimal integers in strictly ascending order. If  any  number  (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  1,10,+10,+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  IEEE Std 1003.1-2001,  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
IEEE Std 1003.1-2001 has a reduced feature list, but many of the features omitted were
restored as XSI extensions 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.

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .