adds rudimentary command checks + documents packages to install for alpine

ddns.sh

@@ -7,6 +7,19 @@ NAMESERVER="1.1.1.1"
 
 # ----- END CONFIG -------------------------------
 
+
+COMMANDS="dirname cat dig"
+for COMMAND in $COMMANDS; do
+  if ! command -v $COMMAND &> /dev/null
+  then
+    echo "$COMMAND could not be found!"
+    exit 1
+  fi
+done
+
+set -e
+
+
 SCRIPTPATH="$( cd "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"
 
 DOMAIN="$1"