clearing down mysql binary logs from a script

Hello all,

I'd like to know how to clear down mysql binary logs from a script.
I have a script which runs this:
"C:\Program Files\mysql\bin\mysql" -uroot -prootpasswd < C:\ClearBinaryLogs.sql

ClearBinaryLogs.sql:
use db
PURGE MASTER LOGS BEFORE 'NOW()';

doesn't clear anything but seems to complete without any errors and all the paths are correct, anyone have any ideas?

Thanks in advance.