recusive ls/search/replace function!!

[bruce]

hi..

can't figure this out. it's basic.. how can i do a find of all files in
underlying recursive dirs. also, how can i do a search/replace of txt in all
files that match a certain extension..

ie, how do i find all files that end in 'int' in the underlying dirs...
or, how do i replace "foo' with 'dog' in all underlying dirs that end in
'ddf'..

i can see that 'ls -R * can/should get me all underlying files... but...

i can also see that find . -name "*.int" would work to find the files... but
i'm not sure how to get the rest.

-bruce
bedouglas at earthlink.net