Using grep on Mac-style text files
You can't change grep's behavior, but you can change the file it sees:

tr '\r' '\n' &lt;file | grep foo


Also, \r line endings are legacy these days; OS X officially uses \n, although there are still things that haven't been updated.  In particular, AppleScript still hasn't quite caught up, which also shows in its using pre-OS X file paths by default and requiring POSIX file to indicate OS X native paths; also, many Carbon applications still use \r, Carbon being a transition framework from Mac OS 9 to OS X.