This one is compatible with git repositories, and a bit simpler:
Linux:
git grep -l 'original_text' | xargs sed -i 's/original_text/new_text/g'
Mac:
git grep -l 'original_text' | xargs sed -i '' -e 's/original_text/new_text/g'
(Thanks to http://blog.jasonmeridth.com/posts/use-git-grep-to-replace-strings-in-files-in-your-git-repository/)