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 .