FreeBSD manual
download PDF document: tsort.1.pdf
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
directed arcs in a graph and prints the nodes in topological order on
standard 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
primarily 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
directed 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:
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 14.0-RELEASE-p11 August 30, 2020 FreeBSD 14.0-RELEASE-p11