shell function to robustly get the IP address of the currently connected ssh client (through subshells, user changes, and more)

get_ssh_client_ip.sh

get_ssh_client_ip() {
    # Returns (via stdout) the IP address for the currently connected SSH session
    #  - this relies on the ssh server setting the SSH_CLIENT env var (done by openssh, dropbear, etc)
    
    pid=$$  # current pid will be checked
    while [ "$pid" -ne 1 ]; do
        cip=$(cat /proc/$pid/environ | tr '\0' '\n' | grep 'SSH_CLIENT=' | awk -F'[= ]' '{ print $2 }')
        [ -n "$cip" ] && break # got it!
        pid=$(awk '{ print $4 }' /proc/$pid/stat) # the parent pid for the next try
    done
    echo "$cip" # will be null if we couldn't find it
}