Find Free Ports - Linux

find-free-port.py

#!/usr/bin/env python

# Source: http://unix.stackexchange.com/questions/55913/whats-the-easiest-way-to-find-an-unused-local-port#comment271991_132524
# One liner: python -c 'import socket; s=socket.socket(); s.bind(("", 0)); print(s.getsockname()[1]); s.close()'

import socket
s=socket.socket()
s.bind(("", 0))
print(s.getsockname()[1])
s.close()

find-free-port.sh

#!/bin/sh

function isPortFree() {
 PORT_FREE=`/usr/sbin/lsof -i:$1 | grep "LISTEN"`

 if [ "X$PORT_FREE" = "X" ]
 then
   echo "1"
 else
   echo "0"
 fi
}

function findFreeport() {

  # finds a range of port numbers with ip_local_port_range
  read lowerPort upperPort < /proc/sys/net/ipv4/ip_local_port_range

  range=$(($upperPort - $lowerPort))

  IS_PORT_FREE=0

  # generate a random open port in the range
  while [ X"$IS_PORT_FREE" == "X0" ]; do
    random_port=`echo $(($lowerPort+$RANDOM % $range))`
    IS_PORT_FREE=`isPortFree $random_port`
  done
  echo $random_port
}

FREE_PORT=`findFreeport`

echo "$FREE_PORT"