my @message_type=('error','alert','warning');
my %messages;
my $messages_log='/var/log/messages';

open LOG, $messages_log or die "$!: $messages_log\n";
while (<LOG>) {
  foreach my $msg_type (@message_type) {
    ++$messages{$_} if /\Q$msg_type/;
  }
}
close LOG;