connected components with graphivz

I just discovered the gvpr transformation language that comes with graphivz. Up until now, I spend far too much time manipulating dot graphs for various reasons. gvpr is an awk like language to manipulate dot graphs. It seems pretty complete, and allows you to do a lot of simple operations in one line. One small example is to split a graph in its connected components in many graphs, one per file.

The one line is :

ccomps -x dominators.dot | gvpr -f split.gvpr

where ccomps is a tool (that is also part of the graphivz suite) that computes connected components of a dot graph. The option -x creates a digraph for connected component (by default it creates a graph with a lot of subgraphs). The results of this command is piped to gvpr that is the graphivz language interpreter. The program itself is very simple :

BEGIN { int n; }
BEG_G {
  n = nNodes($G);
  if ( n > 2 ) writeG($G,$G.name); 
}
END {}

for each graph, if the graph has more then two nodes, write the graph in a file. and voila !