search & replace on multiple files

[Scott I. Remick]

Hello... I'm trying to figure out a way to pull off the following:

I have a subdir with many different sorts of text files (some nested in
additional subdirs, so recursion would be necessary) that need to have a
search & replace done on them. What's a quick way to script a global search
& replace on many/all text files in nested subirs? 

Thanks!