note vinian <p> i don't think there is something to do with regex negative lookahead, the problem lies in the <br /><c>(\w+(,\s)?)+</c><br /> it will match "INFO, FILE, SYSLOG", but not "INFO, FILE".<br /> "+" is greedy, it eaten whatever match by "( ... )" . I don't how to make the above regex match less, but i use this <br /><c>print "has_matched $has\n" if $has =~ /^($start(\w+(,\s)?)+?)$(?<!$end)/;</c><br /> and it will not match <c>$has</c>. </p> 941881 941881