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TSORT(1)		     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 out-
     put.  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 pri-
	     marily 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 di-
     rected 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 ports 15.quarterly	 August 30, 2020			TSORT(1)

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