check_ip.sh

#!/bin/bash

n='([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])'
m='([0-9]|[12][0-9]|3[012])'

IFS= read -rp 'Input: ' ipaddr

if [[ $ipaddr =~ ^$n(\.$n){3}/$m$ ]]; then
    printf '"%s" is a valid CIDR\n' "$ipaddr"
elif [[ $ipaddr =~ ^$n(\.$n){3}$ ]]; then
    printf '"%s" is a valid IP address\n' "$ipaddr"
else
    printf '"%s" is not valid IP address\n' "$ipaddr"
fi

checks if the address is in the form 22.22.22.22/32 or 22.22.22.22 and discards all invalid combinations.