What do you mean for "specific variable"? Grep by itself is not recursive, but you can consider using find to search for some or all the files inside a directory (and eventually its subdirectory) and issue grep on them. A way to do this is
find . -type f | xargs grep string
where string is any pattern you are looking for. It could be also
find . -type f | xargs grep $var
if the value of $var is the string you are looking for.
Edit: Quakeboy02 was faster than me in posting the replay
Sorry for redundancy!