To test a connection use nc
# nc -vz myhost 22 -w 15 > /dev/null 2>&1
-w 15 is the timeout
Will return 0 if the host connects on ssh port 22
or 1 if it does not connect.
Updated: 03/29/2016
The new update to the nc command takes this option away.
Instead the following will work
timeout 60s /bin/bash -c 2>/dev/null >/dev/tcp/myhost/22
Test port connection
*from the man pages
On one console, start nc listening on a specific port for a connection.
# nc -l 1234
nc is now listening on port 1234 for a connection. On a second console (or a second machine), connect to the machine and port being listened on:
# nc 127.0.0.1 1234
There should now be a connection between the ports. Anything typed at the second console will be concatenated to the first, and vice-versa. The connection may be terminated using an EOF.