BASH script to tunnel NNTP connections

nzbtunnel.sh

#!/bin/bash
# Script that attempts to create a tunnel for Usenet (NNTP) to pass through
# This script: creates a tunnel, assigns the host address to local address in /etc/hosts
# For Mac OS X
### CONFIGURATION ###
SERVER='your.nntp.server'
PORT='your.nntp.port'
LOCAL='127.0.0.1'
USER='root'
HOST='your.ssh.server'
### END CONFIGURATION ###

### NOTHING BELOW THIS LINE NEEDS EDITING ###
USER=`whoami`

if [ $USER != 'root' ]
  then
    echo "Sorry - this script must be run as root to function"
    exit
elif [ -z $1 ]
  then
    echo "Usage: nzbtunnel {start|stop}"
fi

GREPSTR='# Entry added for NNTP Tunnel'

case "$1" in
  
  start)
    # Check if the pid file already exists
    if [ -a /tmp/nzbtunnel.pid ]
      then
        echo "PID file exists - tunnel is already running?"
        exit
    fi
    
    # Open the tunnel
    CMSTR="ssh -f $USER@$HOST -L $PORT:$SERVER:$PORT -N"
    $CMSTR

    # Add the entry into /etc/hosts
    echo '' >> /etc/hosts
    echo "$GREPSTR" >> /etc/hosts
    echo $LOCAL $SERVER >> /etc/hosts

    # Flush the DNS cache
    dscacheutil -flushcache

    # Save PID
    PID=`ps aux | grep "$CMSTR" | awk '{print $2}'`
    for a in $PID; do
      echo $a >> /tmp/nzbtunnel.pid
    done
    
    echo "Tunnel is now running"
    ;;
    
  stop)
    # Try and stop the tunnel
    for pid in `cat /tmp/nzbtunnel.pid`; do
      kill -9 $pid &> /dev/null
    done
    
    # Find which line we added text to
    LINE=`grep "$GREPSTR" /etc/hosts -n | tr ':' '\n' | head -n 1`
    LINE=`echo $LINE-1 | bc`
    if [ $LINE != '-1' ]
      then
      NEW=`head -n $LINE /etc/hosts`
      echo "$NEW" > /etc/hosts
    fi
    
    # Flush the DNS cache
    dscacheutil -flushcache
    
    # Delete the pid file
    rm /tmp/nzbtunnel.pid
    
    echo "Tunnel shut down"
    ;;
    
esac