get a random ip within a provided subnet

random_ip.sh

#!/usr/bin/env bash

# https://gist.github.com/jjarmoc/1299906
function atoi {
 #Returns the integer representation of an IP arg, passed in ascii dotted-decimal notation (x.x.x.x)
 IP=$1; IPNUM=0
 for (( i=0 ; i<4 ; ++i )); do
   ((IPNUM+=${IP%%.*}*$((256**$((3-${i}))))))
   IP=${IP#*.}
 done
 echo $IPNUM
}

# https://gist.github.com/jjarmoc/1299906
function itoa {
 #returns the dotted-decimal ascii form of an IP arg passed in integer format
 echo -n $(($(($(($((${1}/256))/256))/256))%256)).
 echo -n $(($(($((${1}/256))/256))%256)).
 echo -n $(($((${1}/256))%256)).
 echo $((${1}%256))
}


function rnd_ip() {
 NET_ADDR=$1
 NET_MASK=$2

 NET_INT=$(atoi $NET_ADDR)
 IP_INT=$(($NET_INT + 1 + $RANDOM % $((2 ** $(( 32 - $NET_MASK)))) ))
 IP=$(itoa $IP_INT)

 echo $IP
}

#usage: rnd_ip 10.0.0.0 8