[Test if remote TCP port is open from a shell script - Stack Overflow](https://stackoverflow.com/questions/4922943/test-if-remote-tcp-port-is-open-from-a-shell-script) ```shell # Connection successful: $ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/80' $ echo $? 0 # Connection failure prior to the timeout $ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/sfsfdfdff.com/80' bash: sfsfdfdff.com: Name or service not known bash: /dev/tcp/sfsfdfdff.com/80: Invalid argument $ echo $? 1 # Connection not established by the timeout $ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/81' $ echo $? 124 ```