Google Code Search
From Seo Wiki - Search Engine Optimization and Programming Languages
|File:Google Code Search.png|
|Operating system||Any (web based application)|
|Type||Code search engine|
Features include the ability to search using operators. These are lang:, package:, license: and file:.
Regular expression engine
The site allows the use of regular expressions in queries, which is not offered by any other search engine for code. This makes it resemble grep, but over the world's public code. The methodology employed has not been disclosed by Google, but appears to have combined precomputed indices with a POSIX compliant regular expression engine.[original research?]
Google Code Search supports POSIX extended regular expression syntax, excluding back-references, collating elements, and collation classes.
Languages not officially supported can still be searched for using the file: operator to match the common file extensions for the language.