a multi-language source code indexing tool
http://ctags.sourceforge.net

Exuberant Ctags generates an index (or tag) file of language objects
found in source files for many popular programming languages. This index
makes it easy for text editors and other tools to locate the indexed
items. Exuberant Ctags improves on traditional ctags because of its
multilanguage support, its ability for the user to define new languages
searched by regular expressions, and its ability to generate emacs-style
TAGS files.