Software like Blackduck or Scanoss is designed to identify exactly that type of behaviour. It is used very often to scan closed source software and to check whether it contains snippets that are copied from open source with incompatible licenses (e.g. GPL).

To be able to do so, these softwares build a syntax tree of what your code snippet is, and compare the tree structure with similar trees in open source software without being fooled by variable names. To speed up the search, they also compute a signature for these trees so that the signature can be more easily searched in their database of open source code.