Create an ssh tunnel using a local port

tunnel.sh

#!/bin/bash

# Suppose you wish to connect to a server X on port 23
# but you have to do this via another server Y like this:
#
#   localhost> ssh -p 22 username@Y
#           Y> ssh -p 23 username@X
#
# Instead, you can create an ssh tunnel on a local port, say 9999:
#   localhost> ssh -nNT -L 9999:X:23 -p 22 username@Y
# (assumes you are using bash)
#
# Then you can connect to the server X as follows:
#   localhost> ssh -p 9999 username@localhost

pL=9999

X=X
pX=23

Y=Y
pY=22

user=username

ssh -nNT -L $pL:$X:$pX -p $pY $user@$Y & echo Tunnel PID: $!

echo Connect using:
echo ssh -p $pL $user@localhost