index(), in turn, may be a little faster than substr(). And replacing the regex on the error code should help, too. [code removed to protect the innocent] Update:

index() is faster when the match occurs at the beginning of the string, but substr() is much better when there is no match at all, which happens quite a lot in this application.

$dir = "/$dir/";
my $strlen = length $dir;
while (<LOG>) {
    my ($url, $code) = (split)[6,8];
    if (substr($url, 0, $strlen) eq $dir && $code == $error) {
        $report{$url}++;
    }
}
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