Most good text editors have both a "find in files" feature that allows you to search in multiple files or whole directories at a time and also have a "regular expressions" feature that allow you to do what you call "grep" searchs.  I use notepad++ on windows but I can't give you the name of a text editor for Mac as I'm not a Mac user.  The Muktabodha digital library searchable etext library has that feature built in, but only for use on its searchable etext collection.