How to erase a global variable?

RouterOS General
1

I have set a global variable,now I want to erase it from Mikrotik,how to do?Thanks

2

http://forum.mikrotik.com/t/how-do-you-clear-a-global-variable/25265/1

Still works on 4.5:

[admin@rb750g] /system script> pri  
Flags: I - invalid 
 0   name="test" owner="admin" 
     policy=ftp,reboot,read,write,policy,test,winbox,password,sniff,sensitive 
     run-count=0 source=
       :global test "This is a test"
       put $test

 1   name="test2" owner="admin" 
     policy=ftp,reboot,read,write,policy,test,winbox,password,sniff,sensitive 
     run-count=0 source=
       :global test
       :put $test
[admin@rb750g] /system script> run 0
This is a test
[admin@rb750g] /system script> run 1
This is a test
[admin@rb750g] /system script> env pri
 # USER                      NAME                     VALUE                    
 0 admin                     test                     This is a test           
[admin@rb750g] /system script> env rem 0
[admin@rb750g] /system script> run 1

[admin@rb750g] /system script> env pri
 # USER                      NAME                     VALUE                    
[admin@rb750g] /system script>
3

I see , thank you for your vivid reply.