cidr2mask.sh

_cidr2mask()
{
    local i mask=""
    local full_octets=$(($1 / 8))
    local partial_octet=$(($1 % 8))

    for((i = 0; i < 4; i += 1))
    do
        if [ $i -lt $full_octets ]
        then
            mask+=255
        elif [ $i -eq $full_octets ]
        then
            mask+=$((256 - 2 ** (8 - $partial_octet)))
        else
            mask+=0
        fi
            test $i -lt 3 && mask+=.
    done
    echo $mask
}