Ack is a recursive grep-replacement Perl script that you can download from: It is somewhat similar to “egrep”, but is much smarter and has ten times nicer output format. It also automatically ignores annoying .svn files and you can teach it different file types.

If you are a Drupal developer you need to put the following line in your /etc/profile:

export ACK_OPTIONS=--type-set=php=.php,.module,.inc,.install

After which you can enjoy yourself some:

ack --php "check_plain"