A shell script to establish a ssh tunnel using ssh command.

ssh-tunnel-start

#!/bin/sh

LOCAL_HOST="localhost"
LOCAL_PORT=""

GATEWAY_USER=""
GATEWAY_HOST=""
GATEWAY_PORT=22

TARGET_HOST=""
TARGET_PORT=""

SSH_CTRL_DIR="/tmp"
SSH_CTRL_PATH=""

function usage() {
  echo "Usage:"
  echo "    $(basename $0) [-lh localhost] -lp <local-port> -gu <gateway-user> -gh <gateway-host> [-gp gateway-port] -th <target-host> -tp <target-port>"
  echo "Options:"
  echo "    -lh | --local-host \t The address of the local host. Defaults to localhost if not specified."
  echo "    -lp | --local-port \t The port of the local host to map to. Must be specified."
  echo "    -gu | --gateway-user \t The username to access the gateway host. Must be specified."
  echo "    -gh | --gateway-host \t The address of the gateway host. Must be specified."
  echo "    -gp | --gateway-port \t The address of the gateway port. Defaults to 22 if not specified."
  echo "    -th | --target-host \t The address of the target host. Must be specified."
  echo "    -tp | --target-port \t The port of the target host. Must be specified."
  echo "Examples:"
  echo "    1) tunnel from 192.168.20.8:3389 to localhost:3389 via gateway gateway.yourcompany.org"
  echo "        $(basename $0) -lp 3389 -gu john -gh gateway.yourcompany.org -th 192.168.20.8 -tp 3389"
  echo "    2) tunnel from 192.168.20.8:22 to localhost:22222 via gateway gateway.yourcompany.org"
  echo "        $(basename $0) -lp 22222 -gu john -gh gateway.yourcompany.org -th 192.168.20.8 -tp 22"
}

# parse arguments
while [ $# -gt 0 ]
do
  case $1 in
    -lh|--local-host)
      [[ -z $2 ]] && echo "Error: missing --local-host value." 2>&1 && usage && exit 1
      LOCAL_HOST=$2; shift
      ;;
    -lp|--local-port)
      [[ -z $2 ]] && echo "Error: missing --local-port value." 2>&1 && usage && exit 1
      LOCAL_PORT=$2; shift
      ;;
    -gu|--gateway-user)
      [[ -z $2 ]] && echo "Error: missing --gateway-user value." 2>&1 && usage && exit 1
      GATEWAY_USER=$2; shift
      ;;
    -gh|--gateway-host)
      [[ -z $2 ]] && echo "Error: missing --gateway-host value." 2>&1 && usage && exit 1
      GATEWAY_HOST=$2; shift
      ;;
    -gp|--gateway-port)
      [[ -z $2 ]] && echo "Error: missing --gateway-port value." 2>&1 && usage && exit 1
      GATEWAY_PORT=$2; shift
      ;;
    -th|--target-host)
      [[ -z $2 ]] && echo "Error: missing --target-host value." 2>&1 && usage && exit 1
      TARGET_HOST=$2; shift
      ;;
    -tp|--target-port)
      [[ -z $2 ]] && echo "Error: missing --target-port value." 2>&1 && usage && exit 1
      TARGET_PORT=$2; shift
      ;;
    *)
      break
      ;;
    esac
    shift
done

# check arguments
[[ -z $LOCAL_PORT ]] && echo "Error: --local-port is not specified." 2>&1 && usage && exit 1
[[ -z $GATEWAY_USER ]] && echo "Error: --gateway-user is not specified." 2>&1 && usage && exit 1
[[ -z $GATEWAY_HOST ]] && echo "Error: --gateway-host is not specified." 2>&1 && usage && exit 1
[[ -z $TARGET_HOST ]] && echo "Error: --target-host is not specified." 2>&1 && usage && exit 1
[[ -z $TARGET_PORT ]] && echo "Error: --target-port is not specified." 2>&1 && usage && exit 1

SSH_CTRL_PATH="${SSH_CTRL_DIR}/ssh-tunnel.${LOCAL_HOST}.${LOCAL_PORT}"
if [[ -z $GATEWAY_PORT ]]; then
  CMD="ssh -L ${LOCAL_HOST}:${LOCAL_PORT}:${TARGET_HOST}:${TARGET_PORT} ${GATEWAY_USER}@${GATEWAY_HOST} -N -f -M -S ${SSH_CTRL_PATH}"
else
  CMD="ssh -L ${LOCAL_HOST}:${LOCAL_PORT}:${TARGET_HOST}:${TARGET_PORT} ${GATEWAY_USER}@${GATEWAY_HOST} -p ${GATEWAY_PORT} -N -f -M -S ${SSH_CTRL_PATH}"
fi

$CMD