Search and Replace can search and replace data in very large text files, and it can operate upon thousands of files, recursing down a directory tree. SR has a number of options, including prompted replace and the ability to choose between one file and a whole directory tree. It has the ability to use user-specified setup files (as well as the command line), and has file extension options that provide the ability to 'include or exclude' files with a set of extensions or ignore extensions altogether. It's written in Perl.
