my $dir='/acm/';
my $strlen=length ($dir)

while (<LOG>) {
  my $url = (split())[6];
  if ((substr($url,0,$strlen) eq $dir) && ($url=~/$error/)) {
    if (exists $report{$url}) {
      $report{$url}++;
    } else {
      $report{$url} = 1;
    }
  }
}