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 .