Return random string from array:
#!/usr/bin/env bash
subnets[0]="subnet1"
subnets[1]="subnet2"
subnets[2]="subnet3"
size=${#subnets[@]}
index=$(($RANDOM % $size))
echo ${subnets[$index]}
Return random rumber from range:
#!/usr/bin/env bash
echo $[ $RANDOM % 3 + 1 ]