TSORT(1)                FreeBSD General Commands Manual               TSORT(1)

NAME
     tsort - topological sort of a directed graph

SYNOPSIS
     tsort [-dlq] [file]

DESCRIPTION
     The tsort utility takes a list of pairs of node names representing
     directed arcs in a graph and prints the nodes in topological order on
     standard output.  Input is taken from the named file, or from standard
     input if no file is given.

     There must be an even number of nodes in the input.  Node names specified
     on the same line should be white space separated.

     Presence of a node in a graph can be represented by an arc from the node
     to itself.  This is useful when a node is not connected to any other
     nodes.

     If the graph contains a cycle (and therefore cannot be properly sorted),
     one of the arcs in the cycle is ignored and the sort continues.  Cycles
     are reported on standard error.

     The options are as follows:

     -d      Turn on debugging.

     -l      Search for and display the longest cycle.  Can take a very long
             time.

     -q      Do not display informational messages about cycles.  This is
             primarily intended for building libraries, where optimal ordering
             is not critical, and cycles occur often.

EXAMPLES
     Assuming a file named dag with the following contents representing a
     directed acyclic graph:

           A B
           A F
           B C
           B D
           D E

     Sort the nodes of the graph:

           $ tsort dag
           A
           F
           B
           D
           C
           E

     White spaces and new line characters are considered equal.  This file for
     example is considered equal to the one we defined before:

           $ cat dga
           A B A F B C B D D E

     Assume we add a new directed arc from D to A creating a cycle:

           A B
           A F
           B C
           B D
           D E
           D A

     Ordering the graph detects the cycle:

           $ tsort dag
           tsort: cycle in data
           tsort: A
           tsort: B
           tsort: D
           D
           E
           A
           F
           B
           C

     Same as above but silencing the warning about the cycle:

           $ tsort -q dag
           D
           E
           A
           F
           B
           C

SEE ALSO
     ar(1)

HISTORY
     The tsort command appeared in Version 7 AT&T UNIX.  This tsort command
     and manual page are derived from sources contributed to Berkeley by
     Michael Rendell of Memorial University of Newfoundland.

BUGS
     The tsort utility does not recognize multibyte characters.

FreeBSD 13.1-RELEASE-p6         August 30, 2020        FreeBSD 13.1-RELEASE-p6