pretty-print graph file
reads a stream of graphs and prints each in pretty-printed (canonical) format
on stdout. If no
are given, it reads from stdin.
The following options are supported:
Produce no output - just check the input for valid DOT.
Print usage information.
If any errors occurred while processing any input, such as a file
not found or a file containing illegal DOT, a non-zero exit value
is returned. Otherwise, zero is returned.