TSORT(1P)                  POSIX Programmer's Manual                 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 .

IEEE/The Open Group                  2017                            TSORT(1P)