assume default values if xdg dirs not set

.local/bin/rssadd

@@ -2,7 +2,7 @@
 
 ! echo "$1" | grep "https*://\S\+\.[A-Za-z]\+\S*" >/dev/null &&
 	notify-send "That doesn't look like a full URL." && exit
-RSSFILE="$XDG_CONFIG_HOME/newsboat/urls"
+RSSFILE="${XDG_CONFIG_HOME:$HOME/.config}/newsboat/urls"
 if awk '{print $1}' "$RSSFILE" | grep "^$1$" >/dev/null; then
 	notify-send "You already have this RSS feed."
 else