What is the netstat command for particular port if that's connected or not?
Probably the best you can get is 

netstat -f inet -n | grep .port


or 

netstat -f inet | grep .servicename


Examples:

machine:~ user$ netstat -f inet -n | grep .443
tcp4       0      0  192.168.114.5.58471       192.111.0.25.443       ESTABLISHED
tcp4       0      0  192.168.114.5.57990       192.111.0.25.443       ESTABLISHED
tcp4       0      0  192.168.114.5.56813       192.111.0.25.443       ESTABLISHED

machine:~ user$ netstat -f inet | grep .https
tcp4       0      0  machine.example.co.58471 stackoverflow.co.https ESTABLISHED
tcp4       0      0  machine.example.co.57990 stackoverflow.co.https ESTABLISHED
tcp4       0      0  machine.example.co.56813 stackoverflow.co.https ESTABLISHED


Please consider that using port numbers below 256 in the first command may collide with one or more of the 4 octets of IP-numbers.