On Linux, you can use Vim in conjunction with ack to search through code bases. ack is the spiritual successor of grep, and is focused on working with code. Install it using your favorite package manager; here's an example of using apt-get:
$ sudo apt-get install ack-grep
For example, you can now use ack from the command line to search for all Python files recursively (starting in the current directory) containing the word Animal:
$ ack --python Animal
The preceding code will produce output similar to grep:
Vim has a plugin that integrates ...