非root用户下执行netstat -apn | grep 9990 | wc -l结果为(Not all processes could be identified, non-owned process info will not be shown, you would have to be root to see it all.)0
为了单独获取最后一个数字,可以
port_count=`netstat -apn 2> /dev/null |grep 9990 |wc -l`