Description:
------------
1)block file ,don't return anyfing
-exclude $b and 



Reproduce code:
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//~~``
//~~``
//~~``
//1)//blobk file  and break exclude  file!!!!!- no return anyfing ..only loading
$b=' print index.php ';
echo `$b`;

2)
$b=' unlink index.php ';
echo `$b`;

3)
$b=' echo aaaaa ';
echo `$b - $b`;

Expected result:
----------------
loading...

Actual result:
--------------
...