This is awful. Code Search is an indispensable tool for finding reference code and real-world uses of various libraries. I don't know of anything on par with it.
IMHO Github code search totally sucks. It's better than nothing, but it feels like the bare minimum - just a normal fulltext index applied to source code.
- It's not case-sensitive, which sucks for searching code.
- It's unable to search for any punctuation characters (searching for "foo()" is the same as searching for "foo"), which totally sucks for searching source code.
- The search finds lots and lots of duplicates. Even multiple matches in one file are listed as completely separate results.
- You can limit the search to one of the languages in dropdown menu, but if your language of choice doesn't happen to be in there, you're out of luck. For example you can't limit your search only to C header files.
Simply by adding package:github.com to Google Code Search search box one can apply a better tool for code in github, but unfortunately the good times seem to be over soon.