grep is a command line text search utility originally written for Unix. The name is taken from the first letters in global / regular expression / print, a series of instructions for the ed text editor.
grep -rHnE 'my [r]eg+ex' /path/to/folder/ : look for files with this regular expression recursively and print out their name and the line number, as well as the matching line itself.
Awk might do it, or you can -exec it with find, but I've read several times that grep is generally faster, even faster than a simple search with a custom and non-optimized C program.
