Taking feedback from timetoexpire

Changed back so that curl is used by default, however dig can be used
as a backup if curl is not installed on the system. Additionally took
my fear of code injection into account by sanitizing the remote input
through a regex.

cloudflare-template.sh

@@ -17,17 +17,15 @@ slackuri=""                                        # URI for Slack WebHook "http
 ###########################################
 ## Check if we have a public IP
 ###########################################
-command -v dig &> /dev/null
-# Use the DNS lookup if dig is available.
-if [[ $? -eq 0 ]]; then 
+# Use curl if curl is available
+if [[ $(command -v curl &> /dev/null; echo $?) ]]; then
+    ip=$(curl -s https://api.ipify.org || curl -s https://ipv4.icanhazip.com/)
+elif [[ $(command -v dig &> /dev/null; echo $?) ]]; then
     ip=$(dig +short myip.opendns.com @resolver1.opendns.com);
 fi
-if [[ $ip -eq "" ]]; then
-    ip=$(curl -s https://api.ipify.org || curl -s https://ipv4.icanhazip.com/)
-fi
 
-if [[ "${ip}" == "" ]]; then 
-  logger -s "DDNS Updater: No public IP found"
+if [[ ! $ip =~ [0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3} ]]; then
+    logger -s "DDNS Updater: Failed to find a valid IP."
     exit 1
 fi