README

## INSTALL
    curl -o ~/bin/knockp https://gist.github.com/moregeek/7599055/raw/knockp
    chmod +x ~/bin/knockp

## USAGE

### With ssh config (~/.ssh/config)

    host example.org
      ProxyCommand sh -c "~/bin/knockp -s example.org 2000 3000 4000; nc %h %p"

### Without ssh config

    ~/bin/knockp example.org 2000 3000 4000

knockp

#!/usr/bin/env bash
 
################################################################################
#
# knockp / simple portknocking helper script
#
#   Copyright 2013 by Stefan Morgenthaler <stefan_at_morgenthaler_dot_at>
#
#   Licensed under GNU General Public License 3.0 or later.
#   @license GPL-3.0+ <http://spdx.org/licenses/GPL-3.0+>
#
################################################################################
 
function _help () {
  echo "usage: pknock [arguments] {HOST} {port: n n-1}";
  echo "";
  echo "arguments:";
  echo "  -s|silent   just knock, do not show output on screen";
  echo "  -h|help     show this help text";
  exit 0;
}
 
function _knock () {
  if ! [ -o ${_silent} ]; then
    exec > /dev/null 2>&1
  fi
 
  host="$1"; shift;
 
  echo "knocking host: ${host}..."
  for port in "${@}"; do
    echo "=> ${port}... "
    nmap -Pn --host_timeout 100 --max-retries 0 -p ${port} ${host} > /dev/null 2&>1
  done
 
  exit 0;
}

function _check_dependency () {
  which nmap > /dev/null 2>&1 
  if [[ $? -gt 0 ]]; then
    echo "Please install dependency: 'nmap'!";
  fi
  exit 1;
}
 
 
function main () {

  _check_dependency;
 
  while [[ "$1" =~ ^[-]{1,2}[a-z] ]]; do
 
    case ${1/*[-]} in
      s|silent)   shift; _silent=0; ;;
      h|help)     shift; _help      ;;
 
      *)          echo "Unknown option! See 'knockp --help'";
                  exit 1;
    esac
 
  done;
 
  if [ $# -lt 3 ]; then
    echo "Missing argument! See 'knockp --help'";
    exit 1;
  fi
 
  _knock "$@"
 
}
 
main "$@"