.\" Copyright (c) 1990, 1993, 1994
.\"	The Regents of the University of California.  All rights reserved.
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.\" This manual is derived from one contributed to Berkeley by
.\" Michael Rendell of Memorial University of Newfoundland.
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.\"     @(#)tsort.1	8.3 (Berkeley) 4/1/94
.\" $FreeBSD$
.\"
.Dd December 27, 2006
.Dt TSORT 1
.Os
.Sh NAME
.Nm tsort
.Nd topological sort of a directed graph
.Sh SYNOPSIS
.Nm
.Op Fl dlq
.Op Ar file
.Sh DESCRIPTION
The
.Nm
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
.Ar file ,
or from standard input if no file
is given.
.Pp
There must be an even number of nodes in the input.
Node names specified on the same line should be white space separated.
.Pp
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.
.Pp
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.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl d
Turn on debugging.
.It Fl l
Search for and display the longest cycle.
Can take a very long time.
.It Fl 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.
.El
.Sh SEE ALSO
.Xr ar 1
.Sh HISTORY
The
.Nm
command appeared in
.At v7 .
This
.Nm
command and manual page are derived from sources contributed to Berkeley by
.An Michael Rendell
of Memorial University of Newfoundland.
.Sh BUGS
The
.Nm
utility does not recognize multibyte characters.