improved variable filling

spells/install-service-template

@@ -34,20 +34,27 @@ for arg in "$@"; do
     substitution_cmd="${substitution_cmd}s|\\\$${arg%%=*}|${arg#*=}|g;"
 done
 
-# Perform substitutions
-sudo sh -c "sed \"$substitution_cmd\" \"$template_path\" > \"$service_path\""
+# Perform substitutions into a temporary file in /tmp
+tmp_file="/tmp/tmp_service"
+sed "$substitution_cmd" "$template_path" > "$tmp_file"
 
 # Ask for missing variables
 while IFS= read -r line; do
     if echo "$line" | grep -q '\$'; then
         var=$(echo "$line" | sed -n -e 's/^.*\$\([A-Z_]*\).*$/\1/p')
         if [ -n "$var" ]; then
+            value="${!var}"
+            if [ -z "$value" ]; then
                 echo "Enter a value for $var: "
                 read -r value
-            sed -i "s|\$$var|$value|g" "$service_path"
             fi
+            sed -i "s|\$$var|$value|g" "$tmp_file"
         fi
-done < "$service_path"
+    fi
+done < "$tmp_file"
+
+# Move the temporary file to the final destination
+sudo mv "$tmp_file" "$service_path"
 
 # Set permissions
 sudo chmod 644 "$service_path"