Console Crash with this script...

Hi, i want to
:global TX [/interface wireless monitor wlan1 once do={:set TX (tx-signal-strength)}];

or try this as well…

:global TX ([/interface wireless monitor wlan1 once][:set TX (tx-signal-strength)]);

i believe i have wrong some way, the system will show me the console crash, appreciated for you correction to help this work…