NAME
tsort —
topological sort
SYNOPSIS
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>s. 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 a text file that is used if no file operand is given.
INPUT FILES
The input file named by the file operand is 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 the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), 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 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- 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:
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
None.
CHANGE HISTORY
First released in Issue 2.
Issue 6
The normative text is reworded to avoid use of the term "must" for application requirements.
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