Thank you for the response. In fact, I changed the Path variable using Perl by TieRegistry. The system path do changed. But the click-opened command prompt didn't. If it didn't propagate to all users, I've already logged in as administrator, why I should right click opened "run as administrator" to see this change is beyond my understanding. I expect after I added the PATH env, all users can use it, no need to set it manually any more.