list opened ports, close port and open port under centos

Question

I need to build a bash script to do the following:

• list opened ports
• close opened port
• open port under

What is the plan, packages and configuration to do that?

Answer 1

Use nmap to get the list of host open/close ports

nmap --top-ports 20 hostname

e.g
nmap --top-ports 20 localhost