How to check if a port is open on Linux

Sometimes when writing a script/program you need to know if a port your are interested in has an established connection to it or it's free.

My favorite way to do this is to run the following command ( replace PORT with the port number you want to check for ):

netstat -ln | grep :PORT

-l = Show only listening ports

-n = Show port number

 If this command doesn't return anything, it shows that your PORT is available to use.
In your script you can check $? to see the return code of the above command. If it's non-zero, the PORT is available.

One thing to note though is that, this doesn't tell you the status of your network e.g. if PORT is accessible from outside of your notwork.