It won't run on Unix because the directory delimiter is not a blackslash. This is why you should use File::Find instead of a hand-rolled directory recursion.

Here's some similar code I just whipped up, doing roughly the same thing:

use File::Find;
my @topdirs = @ARGV;
@ARGV = ();
find sub {
  push @ARGV, $File::Find::name
    if /\.p[lm]\z/ and -f;
}, @topdirs;
my $count = 0;
@ARGV or die "No files to process!\n";
$count++ while <>;
print "Total $count lines\n";
[download]

-- Randal L. Schwartz, Perl hacker