Lots of people ask this in forums and there are various complex answers that come back - enough to make the most hardened GNU cohorts shiver. Anyway, dead easy, just use grep from the command line.
grep -r 'search term in here' *
-r is to recurse sub directories and the * says look in everything. The result is written to the console but you could always redirect it to a file using "> something" at the end (without the quotes of course).