Digraph6 is a text-based file format for storing one or more directed graphs.

The GraphTheory[ImportGraph] and GraphTheory[ExportGraph] commands can read from and write to this format.

The general-purpose commands Import and Export also support this format.

$G≔\mathrm{Import}\left(''example/dgex.d6''\,\mathrm{base}=\mathrm{datadir}\right)$

$G≔\mathrm{Graph\; 1:\; a\; directed\; unweighted\; graph\; with\; 4\; vertices\; and\; 4\; arc(s)}$

$\mathrm{GraphTheory}:-\mathrm{DrawGraph}\left(G\,\mathrm{style}=\mathrm{spring}\right)$

$G≔\mathrm{GraphTheory}:-\mathrm{Graph}\left(5\,\left\{\left[1\,2\right]\,\left[2\,3\right]\,\left[2\,4\right]\,\left[3\,5\right]\right\}\right)$

$G≔\mathrm{Graph\; 2:\; a\; directed\; unweighted\; graph\; with\; 5\; vertices\; and\; 4\; arc(s)}$

$\mathrm{Export}\left(''graph.d6''\,G\,\mathrm{base}=\mathrm{homedir}\right)$

$8$

McKay, B.D. and Piperno, A., Practical Graph Isomorphism, II, Journal of Symbolic Computation, 60 (2014), pp. 94-112, doi:10.1016/j.jsc.2013.09.003