create ssh tunnel only if it doesn't exist on the port yet

[marchello_lippi2]

Hi all,

I'm looking for a way to create ssh tunnel only in case it doesn't exist on particular port yet.

This is how I would check if the tunnel exists:

nc -z 127.0.0.1 9521 || echo "no tunnel open"

And this is how I would create the tunnel:

ssh user1@example.com -D9521 -C -N -q

Now how do I combine those two or maybe there is another more robust way?... The thing is that I'm not able to install additional software on the system; also I'm not able to copy some pre-compiled executable into the filesystem -- the instance is re-created from scratch every session. I would rather need just to combine those two commands above using bash.

Please advise.

[TheFu]

# Only start SOCKS proxy if necessary

if  [ $(/bin/ps -eaf |/bin/grep ssh |/bin/grep -c $PORT ) = 0 ] ; then
   # Setup SOCKS proxy through home server
   echo "Starting ssh SOCKS Proxy"
   /usr/bin/ssh  -f -C -D $PORT  $SSH_SRV  -NT &
fi

is how I do it.