|TSORT(1)||General Commands Manual||TSORT(1)|
topological sort of a directed graph
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. That is, the input describes a partial ordering
relation, from which
tsort computes a total order
compatible with this partial ordering.
Input is taken from the named file, or from standard input if no file is given.
Node names in the input are separated by white space and there must be an even number of node names.
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:
tsorthad to break.
tsort utility exits 0 on
success, and >0 if an error occurs.
Faced with the input:
a b b c b d d f c e
a b c e d f
which is one total ordering compatible with the individual relations. There is no unicity, another compatible total ordering would be:
a b c d e f
tsort is commonly used to analyze
dependencies and find a correct build order in a static way, whereas
make(1) accomplishes the same
task in a dynamic way.
Donald E. Knuth, The Art of Computer Programming, Vol. 1, pp. 258–268, 1973.
tsort utility is compliant with the
IEEE Std 1003.1-2008 (“POSIX.1”)
The flags [
-fhlqrvw] are extensions to
tsort command appeared in
Version 7 AT&T UNIX. This
tsort command was completely rewritten by Marc Espie
for OpenBSD, to finally use the well-known optimal
algorithms for topological sorting.
|April 23, 2019||OpenBSD-6.7|