'Just using the blog as a notepad, but you may find it useful.

Here is how to find files according to content, or find a content out of many files, recursively. This is using the egrep tool, available on many operating systems, such at GNU/Linux or Mac OS X.

egrep "pattern" --include=*.txt .

You can adapt or omit the --include=*.txt part if you want to change or remove the file name requirement.

You can also add the -n switch if you want the line number to be printed.