=== modified file 'zsh-functions/confz_ip_init'
--- zsh-functions/confz_ip_init	2016-02-22 11:51:54 +0000
+++ zsh-functions/confz_ip_init	2014-06-29 02:15:38 +0000
@@ -18,16 +18,16 @@
 		read ignored mac rest
 		if [[ ${iface%:} == $vars[name] ]]; then
 			[[ $mac == $vars[mac] ]] || \
-				die "${(qqq)iface%:} already exists with different MAC address"
+				"${(qqq)iface%:} already exists with different MAC address"
 			ok=1
 			break
 		fi
-		if [[ -z $old_name && $mac == $vars[mac] ]]; then
+		if ! (($+old_name)) && [[ $mac == $vars[mac] ]]; then
 			old_name=${iface%:}
 		fi
 	done <<<$out
 
-	[[ -n $old_name ]] || die "could not find interface with MAC: $vars[mac]"
+	(($+old_name)) || die "could not find interface with MAC: $vars[mac]"
 
 	do_command=( ip link set dev $old_name name $vars[name] )
 	(($ok))