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    sub check_url {
        local $_ = shift;
...
        my $valid = join '|', @$valid_referrers;
        return /$valid/ ? 1 : 0;
    }

    my @referrers =
       ('http://www.foo.com/',
...
    for my $url (@urls_to_check) {
        print $url, ": ", check_url($url, \@referrers), "\n";
    }