TSORT(1P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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 the Base Definitions volume of POSIX.1-2017, 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
The Base Definitions volume of POSIX.1-2017, Chapter 8, Environment Variables

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .