I found myself wanting to launch and control a port-forwarding ssh session from a shell script today and I eventually figured out how to do it.
The tricky part was that I also wanted the script to do other things (start a Selenium server) and kill off the ssh connection when it was done.
remote_port=1234
local_port=1234
# Start an ssh port-forwarding command in the background
ssh user@host.com -TN -R $remote_port:localhost:$localport >/dev/null /2>&1 &
# Get pid of ssh background process -- tricky
ssh_pid=$!
# kill the ssh process on exit
trap "kill $ssh_pid" EXIT
# Do other stuff that uses the forwarded port.
#
# In my case, start Selenium
java -jar selenium-server-standalone* The SSH command is the trickiest bit, so here it is, more in depth.
ssh user@host.com
# Disable tty allocation (needed for backgrounding)
-T
# Dont run a remote command (i.e. only does port forwarding)
-N
# Setup remote port to forward to local port
-R $remote_port:localhost:$localport
# Redirect stdin and stdout to /dev/null
# and put the process in the background (the &)
>/dev/null /2>&1 &