tabs(C)

tabs -- set tabs on a terminal

Syntax

tabs [ tabspec ] [ -T type ] [ +mn ]

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

Description

The tabs command sets the tab stops on the user's terminal according to the tab specification tabspec, after clearing any previous settings. It also optionally adjusts the margin. The user's terminal must have remotely-settable hardware tabs.

tabspec

The four types of acceptable tab specification for tabspec are canned (-code), repetitive (-n), arbitrary (n1,n2, ...), and file (--file). These are described below. If no tabspec is given, the default value is ``-8'', that is, ``standard'' UNIX tabs. The lowest column number is 1. Note that for tabs, column 1 always refers to the leftmost column on a terminal, even one whose column markers begin at 0, for example, the DASI 300, DASI 300s, and DASI 450.

-code

Select a canned set of tabs with -code set to:

-a: 1,10,16,36,72
Assembler, IBM S/370, first format
-a2: 1,10,16,40,72
Assembler, IBM S/370, second format
-c: 1,8,12,16,20,55
COBOL, normal format
-c2: 1,6,10,14,49
COBOL compact format (columns 1-6 omitted). Using this code, the first typed character corresponds to card column 7, one space gets you to column 8, and a tab reaches column 12. Files using this tab setup should include a format specification as follows (see fspec(F)): <:t-c2 m6 s66 d:>
-c3: 1,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,67
COBOL compact format (columns 1-6 omitted), with more tabs than -c2. This is the recommended format for COBOL. The appropriate format specification is (see fspec(F)): <:t-c3 m6 s66 d:>
-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/I
-s: 1,10,55
SNOBOL
-u: 1,12,20,44
UNIVAC 1100 Assembler

-n

A repetitive specification requests tabs at columns 1+n, 1+2

n, etc. Of particular importance is the value 8: this represents the ``standard'' UNIX tab setting, and is the most likely tab setting to be found at a terminal. Another special case is the value 0, implying no tabs at all.

n1,n2, ...

The arbitrary format permits the user to type any chosen set of numbers, separated by commas, in ascending order. Up to 40 numbers are allowed. 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. Thus, the formats 1,10,20,30, and 1,10,+10,+10 are considered identical.

--file

If the name of a file is given, tabs reads the first line of the file, searching for a format specification (see fspec(F)). If it finds one there, it sets the tab stops according to it: otherwise it sets them as -8. This type of specification may be used to make sure that a tabbed file is printed with correct tab settings, and would be used with the pr(C) command:

tabs -- file; pr file

Any of the following also may be used; if a given flag occurs more than once, the last value given takes effect:

-T type: tabs usually needs to know the type of terminal in order to set tabs and always needs to know the type to set margins. type is a name listed in term(M). If no -T flag is supplied, tabs uses the value of the environment variable TERM. If TERM is not defined in the environment (see environ(M)), tabs tries a sequence that will work for many terminals.
+mn: The margin argument may be used for some terminals. It causes all tabs to be moved over n columns by making column n+1 the left margin. If +m is given without a value of n, the value assumed is 10. For a TermiNet, the first value in the tab list should be 1, or the margin will move even further to the right. The normal (leftmost) margin on most terminals is obtained by +m0. The margin for most terminals is reset only when the +m flag is given explicitly.

Tab and margin setting is performed via the standard output.

Exit values

tabs returns 0 if no error occurred, or 1 if an error took place.

Diagnostics

illegal tabs: When arbitrary tabs are ordered incorrectly.
illegal increment: When a zero or missing increment is found in an arbitrary specification.
unknown tab code: When a canned code cannot be found.
can't open: If --file option used and file can't be opened.
file indirection: If --file option used and the specification in that file points to yet another file. Indirection of this form is not permitted.

Examples

tabs -a: Example using -code (canned specification) to set tabs to the settings required by the IBM assembler:
columns 1, 10, 16, 36, 72.
tabs -8: Example of using -n (repetitive specification), where n is 8, causes tabs to be set every eighth position:
1+(18), 1+(28), ... which evaluate to columns 9, 17, ...
tabs 1,8,36: Example of using n1,n2, ... (arbitrary specification) to set tabs at columns 1, 8, and 36.
tabs --$HOME/fspec.list/att4425: Example of using --file (file specification) to indicate that tabs should be set according to the first line of $HOME/fspec.list/att4425 (see fspec(F)).

Limitations

There is no consistency among different terminals regarding ways of clearing tabs and setting the left margin.

The tabs command clears only 20 tabs (on terminals requiring a long sequence), but is willing to set 64.

The tabspec used with the tabs command is different from the one used with the newform(C) command. For example, tabs -8 sets every eighth position; whereas newform -i-8 indicates that tabs are set every eighth position.

Standards conformance

tabs is conformant with:

ISO/IEC DIS 99452:1992, Information technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (IEEE Std 1003.21992);
AT&T SVID Issue 2;
X/Open CAE Specification, Commands and Utilities, Issue 4, 1992.