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.\" 33.Dd August 30, 2020 34.Dt TSORT 1 35.Os 36.Sh NAME 37.Nm tsort 38.Nd topological sort of a directed graph 39.Sh SYNOPSIS 40.Nm 41.Op Fl dlq 42.Op Ar file 43.Sh DESCRIPTION 44The 45.Nm 46utility takes a list of pairs of node names representing directed arcs in 47a graph and prints the nodes in topological order on standard output. 48Input is taken from the named 49.Ar file , 50or from standard input if no file 51is given. 52.Pp 53There must be an even number of nodes in the input. 54Node names specified on the same line should be white space separated. 55.Pp 56Presence of a node in a graph can be represented by an arc from the node 57to itself. 58This is useful when a node is not connected to any other nodes. 59.Pp 60If the graph contains a cycle (and therefore cannot be properly sorted), 61one of the arcs in the cycle is ignored and the sort continues. 62Cycles are reported on standard error. 63.Pp 64The options are as follows: 65.Bl -tag -width indent 66.It Fl d 67Turn on debugging. 68.It Fl l 69Search for and display the longest cycle. 70Can take a very long time. 71.It Fl q 72Do not display informational messages about cycles. 73This is primarily 74intended for building libraries, where optimal ordering is not critical, 75and cycles occur often. 76.El 77.Sh EXAMPLES 78Assuming a file named 79.Pa dag 80with the following contents representing a directed acyclic graph: 81.Bd -literal -offset indent 82A B 83A F 84B C 85B D 86D E 87.Ed 88.Pp 89Sort the nodes of the graph: 90.Bd -literal -offset indent 91$ tsort dag 92A 93F 94B 95D 96C 97E 98.Ed 99.Pp 100White spaces and new line characters are considered equal. 101This file for example is considered equal to the one we defined before: 102.Bd -literal -offset indent 103$ cat dga 104A B A F B C B D D E 105.Ed 106.Pp 107Assume we add a new directed arc from D to A creating a cycle: 108.Bd -literal -offset indent 109A B 110A F 111B C 112B D 113D E 114D A 115.Ed 116.Pp 117Ordering the graph detects the cycle: 118.Bd -literal -offset indent 119$ tsort dag 120tsort: cycle in data 121tsort: A 122tsort: B 123tsort: D 124D 125E 126A 127F 128B 129C 130.Ed 131.Pp 132Same as above but silencing the warning about the cycle: 133.Bd -literal -offset indent 134$ tsort -q dag 135D 136E 137A 138F 139B 140C 141.Ed 142.Sh SEE ALSO 143.Xr ar 1 144.Sh HISTORY 145The 146.Nm 147command appeared in 148.At v7 . 149This 150.Nm 151command and manual page are derived from sources contributed to Berkeley by 152.An Michael Rendell 153of Memorial University of Newfoundland. 154.Sh BUGS 155The 156.Nm 157utility does not recognize multibyte characters. 158