1.\" Copyright (c) 1990, 1993, 1994 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This manual is derived from one contributed to Berkeley by 5.\" Michael Rendell of Memorial University of Newfoundland. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)tsort.1 8.3 (Berkeley) 4/1/94 32.\" $FreeBSD$ 33.\" 34.Dd August 30, 2020 35.Dt TSORT 1 36.Os 37.Sh NAME 38.Nm tsort 39.Nd topological sort of a directed graph 40.Sh SYNOPSIS 41.Nm 42.Op Fl dlq 43.Op Ar file 44.Sh DESCRIPTION 45The 46.Nm 47utility takes a list of pairs of node names representing directed arcs in 48a graph and prints the nodes in topological order on standard output. 49Input is taken from the named 50.Ar file , 51or from standard input if no file 52is given. 53.Pp 54There must be an even number of nodes in the input. 55Node names specified on the same line should be white space separated. 56.Pp 57Presence of a node in a graph can be represented by an arc from the node 58to itself. 59This is useful when a node is not connected to any other nodes. 60.Pp 61If the graph contains a cycle (and therefore cannot be properly sorted), 62one of the arcs in the cycle is ignored and the sort continues. 63Cycles are reported on standard error. 64.Pp 65The options are as follows: 66.Bl -tag -width indent 67.It Fl d 68Turn on debugging. 69.It Fl l 70Search for and display the longest cycle. 71Can take a very long time. 72.It Fl q 73Do not display informational messages about cycles. 74This is primarily 75intended for building libraries, where optimal ordering is not critical, 76and cycles occur often. 77.El 78.Sh EXAMPLES 79Assuming a file named 80.Pa dag 81with the following contents representing a directed acyclic graph: 82.Bd -literal -offset indent 83A B 84A F 85B C 86B D 87D E 88.Ed 89.Pp 90Sort the nodes of the graph: 91.Bd -literal -offset indent 92$ tsort dag 93A 94F 95B 96D 97C 98E 99.Ed 100.Pp 101White spaces and new line characters are considered equal. 102This file for example is considered equal to the one we defined before: 103.Bd -literal -offset indent 104$ cat dga 105A B A F B C B D D E 106.Ed 107.Pp 108Assume we add a new directed arc from D to A creating a cycle: 109.Bd -literal -offset indent 110A B 111A F 112B C 113B D 114D E 115D A 116.Ed 117.Pp 118Ordering the graph detects the cycle: 119.Bd -literal -offset indent 120$ tsort dag 121tsort: cycle in data 122tsort: A 123tsort: B 124tsort: D 125D 126E 127A 128F 129B 130C 131.Ed 132.Pp 133Same as above but silencing the warning about the cycle: 134.Bd -literal -offset indent 135$ tsort -q dag 136D 137E 138A 139F 140B 141C 142.Ed 143.Sh SEE ALSO 144.Xr ar 1 145.Sh HISTORY 146The 147.Nm 148command appeared in 149.At v7 . 150This 151.Nm 152command and manual page are derived from sources contributed to Berkeley by 153.An Michael Rendell 154of Memorial University of Newfoundland. 155.Sh BUGS 156The 157.Nm 158utility does not recognize multibyte characters. 159