#!/usr/bin/perl

use File::Find;
my @dirs = @ARGV;
@ARGV = ();
File::Find::find(
  {
    wanted => sub { push @ARGV, $File::Find::name if -f }
  },
  @dirs
);
$^I = '.bak';
local $_;
while ( defined( $_ = <ARGV> ) ) {
  s/bilbo/frodo/g;
  print;
}