cidr2ip is a small and simple program for converting a CIDR into ip (mask).
Edit config.mk to match your local setup (cidr2ip is installed into the /usr/local namespace by default), then simply enter the following command to install (if necessary as root):
make clean install
Print a complete CIDR to ip conversion table
for i in {1..32}; do printf '\\%-5s' $i; cidr2ip $i;done