https://www.cyberciti.biz/faq/linux-port-scanning/
Check if a port is open
nc -z -v -w5 <host> <port/range>

-w5: 5s timeout is optional

Example: 
nc -zv domain 1-1023

nc -zv domain 443
nc -zv domain 80
nc -zv domain 22
nc -zv domain 21
nc -zv domain smtp
nc -zvn domain ftp