netcat listen

netcat -l [options] [host] [port]

check if the port is open

 nc -z -v -w5 <ip> <port>

 nc -z -v -w5 <ip> <port>; echo $?

sample

pi@pi-lcd:/usr/local/bin $ nc -z -v -w5 10.11.12.253 22; echo $?
Connection to 10.11.12.253 22 port [tcp/ssh] succeeded!
0
pi@pi-lcd:/usr/local/bin $ nc -z -v -w5 10.11.12.251 22; echo $?
nc: connect to 10.11.12.251 port 22 (tcp) timed out: Operation now in progress
1
pi@pi-lcd:/usr/local/bin $ nc -z -v -w2 10.11.12.21 22; echo $?
nc: connect to 10.11.12.21 port 22 (tcp) timed out: Operation now in progress