use File::Find;
{
  my @starters = @ARGV ? @ARGV : qw(/home/merlyn);
  @ARGV = ();
  find sub {
    push @ARGV, $File::Find::name if /\.asp$/; # or whatever condition here
  }, @starters;
}
{
  local $/; # slurp it
  local $^I = ".bak";
  while (<>) {
    # $_ now contains the entire file, alter at will
    s/foo/bar/g;
    print;
  }
}