According to its info page, this command was initially written for providing an ordering of object files that allowed the linker to process them sequentially (each one exactly once, and in … 展开

tsort lists the vertices of a directed acyclic graph in such an order that all ordering/direction relations are respected:
Call graph
tsort can help rearranging functions in a source file so that as many as possible are defined before they are … 展开

• Free and open-source software portal
• Sort (Unix)
• Make (software)
• Topological sorting
• List of Unix commands
• Call graph 展开

manual page of tsort on
• FreeBSD,
• OpenBSD,
• NetBSD,
• AIX,
• Solaris, 展开

FreeBSD options can be:
GNU provides the following options only:
There are no options prescribed by POSIX. 展开

tsort reads its input (from the given FILE, or standard input if no input file is given or for a FILE of '-') as pairs of strings, separated by blanks, indicating a partial ordering. The output is a total ordering that corresponds to the given partial ordering.
In other words: for a 展开

Notice the interchangeability of white space separators so the following inputs are equivalent:
Pairs of identical items indicate presence of a vertex, but not ordering (so the following represents one vertex without edges): 展开