Load wlan device to environment variables

i3/.xsession

@@ -0,0 +1,2 @@
+WLAN=/sbin/ifconfig | grep wlp | tail -1 | cut -d ':' -f 1
+i3

polybar/.config/polybar/config

@@ -220,7 +220,7 @@ label = %percentage_used%%
 
 [module/wlan]
 type = internal/network
-interface = wlp3s0
+interface = ${env:WLAN:wlp2s0}
 interval = 3.0
 
 format-connected = <ramp-signal> <label-connected>