TSORT(P)

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>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, 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:

0   Successful completion.

>0  An error occurred.

CONSEQUENCES OF ERRORS

Default.

The following sections are informative.

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.

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 .