The Open Group Base Specifications Issue 7, 2018 edition
IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)
Copyright © 2001-2018 IEEE and The Open Group


tabs - set terminal tabs


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

[-T type] n[[sep[+]n]...]


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 [XSI] [Option Start]  and optionally adjusts the margin. [Option End]

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.


The tabs utility shall conform to XBD Utility Syntax Guidelines , [XSI] [Option Start]  except for various extensions: the options -a2, -c2, and -c3 are multi-character. [Option End]

The following options shall be supported:

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.
[XSI] [Option Start] 1,10,16,36,72
Assembler, applicable to some mainframes. [Option End]
[XSI] [Option Start] 1,10,16,40,72
Assembler, applicable to some mainframes. [Option End]
[XSI] [Option Start] 1,8,12,16,20,55
COBOL, normal format. [Option End]
[XSI] [Option Start] 1,6,10,14,49
COBOL, compact format (columns 1 to 6 omitted). [Option End]
[XSI] [Option Start] 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. [Option End]
[XSI] [Option Start] 1,7,11,15,19,23
FORTRAN [Option End]
[XSI] [Option Start] 1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61
PL/1 [Option End]
[XSI] [Option Start] 1,10,55
SNOBOL [Option End]
[XSI] [Option Start] 1,12,20,44
Assembler, applicable to some mainframes. [Option End]
-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.


The following operand shall be supported:

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 "1 10 +10 +10" are considered to be identical.


Not used.




The following environment variables shall affect the execution of tabs:

Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
If set to a non-empty string value, override the values of all the other internationalization variables.
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).
Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
[XSI] [Option Start] Determine the location of message catalogs for the processing of LC_MESSAGES. [Option End]
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.




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.


The standard error shall be used only for diagnostic messages.






The following exit values shall be returned:

Successful completion.
An error occurred.



The following sections are informative.


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.




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:

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.




expand, stty, tput, unexpand

XBD Environment Variables, Utility Syntax Guidelines


First released in Issue 2.

Issue 6

This utility is marked as part of the User Portability Utilities option.

The normative text is reworded to avoid use of the term "must" for application requirements.

Issue 7

The tabs utility is removed from the User Portability Utilities option. User Portability Utilities is now an option for interactive utilities.

SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.

The SYNOPSIS and OPERANDS sections are updated.

End of informative text.


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