You don't show any (relevant) code, so I have to guess where your problem could lie. See perlvar on @ARGV and/or Getopt::Long for how to parse command line switches. Also see opendir and readdir or Path::Class for how to list files in one directory. See File::Find for how to find files below a given directory. Alternatively see App::Ack for a reimplementation of the grep program in Perl.