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.\" $OpenBSD: tsort.1,v 1.10 2001/07/11 15:15:21 espie Exp $
.\" $NetBSD: tsort.1,v 1.6 1996/01/17 20:37:49 mycroft Exp $
.\"
.\" Copyright (c) 1990, 1993, 1994
.\" The Regents of the University of California. All rights reserved.
.\"
.\" This manual is derived from one contributed to Berkeley by
.\" Michael Rendell of Memorial University of Newfoundland.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)tsort.1 8.3 (Berkeley) 4/1/94
.\"
.Dd November 1, 1999
.Dt TSORT 1
.Os
.Sh NAME
.Nm tsort
.Nd topological sort of a directed graph
.Sh SYNOPSIS
.Nm tsort
.Op Fl f
.Op Fl h Ar file
.Op Fl l
.Op Fl q
.Op Fl r
.Op Fl v
.Op Fl w
.Op Ar file
.Sh DESCRIPTION
.Nm 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.
Input is taken from the named
.Ar file ,
or from standard input if no file
is given.
.Pp
Node names in the input are separated by white space and there must
be an even number of node pairs.
.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 Ds
.It Fl f
Resolve ambiguities by selecting nodes based on the order of apparition
of the first component of the pairs.
.It Fl h Ar file
Use
.Ar file ,
which holds an ordered list of nodes, to resolve ambiguities.
In case of duplicates, the first entry is chosen.
.It Fl l
Search for and display the longest cycle.
Can take a very long time, as it may need to solve an NP-complete problem.
.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.
.It Fl r
Reverse the ordering relation.
.It Fl 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.
.It Fl w
Exit with exit code the number of cycles
.Nm
had to break.
.El
.Sh SEE ALSO
.Xr ar 1 ,
.Xr lorder 1 ,
.Rs
.%A Donald E. Knuth
.%B The Art of Computer Programming
.%V Vol. 1
.%P pp 258-268
.%D 1973
.Re
.Sh HISTORY
A
.Nm
command appeared in
.At v7 .
This
.Nm tsort
command was completely rewritten by Marc Espie for
.Ox ,
to finally use the well-known optimal algorithms for topological sorting.
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