There are several ways, here are a few:
Code:
grep -r 'search-string' /path/to/dictory/*
find /path/to/dictory -exec grep 'search-string' {} \;
find /path/to/dictory | xargs grep 'search-string'
The -r switch for grep is to run a recursive search, leave it off if you don't want sub-directories searched. find searches recursively by default, but you can limit that as well.