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 .

IEEE/The Open Group                                   2003                                              TSORT(P)