NAME

tsort - topological sort

SYNOPSIS

tsort [file]

DESCRIPTION

The tsort utility shall write to standard output a totally ordered list of items consistent with a partial ordering of items contained in the input.

The application shall ensure that the input consists of pairs of items (non-empty strings) separated by <blank> characters. Pairs of different items indicate ordering. Pairs of identical items indicate presence, but not ordering.

OPTIONS

None.

OPERANDS

The following operand shall be supported:

file

A pathname of a text file to order. If no file operand is given, the standard input shall be used.

STDIN

The standard input shall be used if no file operand is specified, and shall be used if the file operand is '-' and the implementation treats the '-' as meaning standard input. Otherwise, the standard input shall not be used. See the INPUT FILES section.

INPUT FILES

The input file shall be a text file.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of tsort:

LANG

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.)

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 and input files).

LC_MESSAGES

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

NLSPATH

^[XSI] Determine the location of message catalogs for the processing of LC_MESSAGES.

ASYNCHRONOUS EVENTS

Default.

STDOUT

The standard output shall be a text file consisting of the order list produced from the partially ordered input.

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.

APPLICATION USAGE

The LC_COLLATE variable need not affect the actions of tsort. The output ordering is not lexicographic, but depends on the pairs of items given as input.

EXAMPLES

The command:

tsort <<EOF
a b c c d e
g g
f g e f
h h
EOF

produces the output:

a
b
c
d
e
f
g
h

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

XBD Environment Variables

CHANGE HISTORY

First released in Issue 2.

Issue 6

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

Issue 7

Austin Group Interpretation 1003.1-2001 #092 is applied.

The tsort utility is moved from the XSI option to the Base.

POSIX.1-2008, Technical Corrigendum 1, XCU/TC1-2008/0146 [241] is applied.