TSORT(1)                   OpenBSD Reference Manual                   TSORT(1)

NAME
     tsort - topological sort of a directed graph

SYNOPSIS
     tsort [-f] [-h file] [-l] [-q] [-r] [-v] [-w] [file]

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

     Node names in the input are separated by white space and there must be an
     even number of node pairs.

     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:

     -f      Resolve ambiguities by selecting nodes based on the order of ap-
             parition of the first component of the pairs.

     -h file
             Use file, which holds an ordered list of nodes, to resolve ambi-
             guities.  In case of duplicates, the first entry is chosen.

     -l      Search for and display the longest cycle.  Can take a very long
             time, as it may need to solve an NP-complete problem.

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

     -r      Reverse the ordering relation.

     -v      Inform on the exact number of edges broken while breaking cycles.
             If a hints file was used, inform on seen nodes absent from that
             file.

     -w      Exit with exit code the number of cycles tsort had to break.

SEE ALSO
     ar(1), lorder(1)

     Donald E. Knuth, The Art of Computer Programming, Vol. 1, pp 258-268,
     1973.

HISTORY
     A tsort command appeared in Version 7 AT&T UNIX.  This tsort command was
     completely rewritten by Marc Espie for OpenBSD, to finally use the well-
     known optimal algorithms for topological sorting.

OpenBSD 3.0                    November 1, 1999                              1
