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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	di-
     rected arcs in a graph and	prints the nodes in topological	order on stan-
     dard 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 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	13.0			August 30, 2020			  FreeBSD 13.0
NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | SEE ALSO | HISTORY | BUGS

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