use warnings;
use strict;

while (<DATA>) {
   if (/do_(add|delete)/) {
      print "Found: $_";
   }
}

##</code><code>##

__DATA__
A line of stuff with do_add in it.
A line of stuff with do_delete in it.
Another line of stuff.
The last line of stuff. It has do_add and do_delete.


Found: A line of stuff with do_add in it.
Found: A line of stuff with do_delete in it.
Found: The last line of stuff. It has do_add and do_delete.