A bash script for managing ssh tunnels for smtp (or whatever)

ssh-tunnel.sh

#!/bin/bash
 
SOCKS_PORT=''
LOCAL_PORT='5525'
SSH_HOST='sccs.swarthmore.edu'
TARGET_HOST='smtp.swarthmore.edu'
TARGET_PORT='25'
 
while getopts 'D:p:s:h:P:' OPTION
do
    case $OPTION in
        D)  SOCKS_PORT="$OPTARG" ;;
        p)  LOCAL_PORT="$OPTARG" ;;
        s)  SSH_HOST="$OPTARG" ;;
        h)  TARGET_HOST="$OPTARG" ;;
        P)  TARGET_PORT="$OPTARG" ;;
        ?)  echo "incorrect usage, dummy"; exit -1 ;;
    esac
done
shift $(($OPTIND - 1))
 
if [[ -n "$1" ]]; then
    do=$1
else
    do='start'
fi
 
if [[ -n $SOCKS_PORT ]]; then
    cmd="ssh -D $SOCKS_PORT -Nf $SSH_HOST"
else
    cmd="ssh -L $LOCAL_PORT:$TARGET_HOST:$TARGET_PORT -Nf $SSH_HOST"
fi
 
function find_pid {
    PID=$(ps aux | grep "$cmd" | grep -v 'grep' | awk '{print $2}')
}
 
function start_tunnel {
    find_pid
    if [[ -n "$PID" ]]; then
        echo "tunnel already running (pid $PID)" 1>&2
        exit 1
    fi
 
    $cmd
    find_pid
    echo "started new process: $PID"
}
 
function stop_tunnel {
    find_pid
    if [[ -z "$PID" ]]; then
        echo "couldn't find a running tunnel" 1>&2
        exit 2
    fi
 
    oldpid=$PID
    kill $PID
    find_pid
    if [[ -z $PID ]]; then
        echo "killed process $oldpid"
    else
        echo "unable to kill process $PID" 1>&2
        exit 3
    fi
 
}
 
case "$do" in
    pid)    find_pid;
            echo $PID ;;

    cmd)    echo $cmd ;;

    start)  start_tunnel ;;

    stop)   stop_tunnel  ;;

    restart) (find_pid && stop_tunnel);
             start_tunnel ;;

    toggle) find_pid;
            if [[ -n "$PID" ]]; then stop_tunnel;
            else start_tunnel;
            fi ;;

    *)      echo "Incorrect usage: unknown command '$do'";
            exit 4 ;;
esac