perl -pi.bak -e "s/Old text/New text/g" file1 file2 file3

http://www.debian-administration.org/article/Performing_search_and_replace_operations_across_multiple_files

-p tells perl to assume a simple loop around the code we give it to run.

-i.bak tells perl that we wish to create backups of the files we modify with the suffix .bak.

-e "..." tells perl that we wish to execute the code inside the quotes.

And finally the file list is the list of files that we wish to operate upon.

Escape special characters such as ".", "?", "*", or "/" by preceding them with the "\" character.

Example: change "Bob" to "Steve" on all HTML files in the current directory:

perl -pi.bak -e "s/Bob/Steve/g" *.html

Search and replace across multiple files

Perl