CTF-PHP code audit, regular expression record

1. Global variables of PHP automation : $GLOBALS — refers to all variables available in the global scope, a global combination array containing all variables. The name of the variable is the key of the array.

flag In the variable ! <?php  

error_reporting(0);
include "flag1.php";
highlight_file(__file__);
if(isset($_GET['args'])){
    $args = $_GET['args'];
    if(!preg_match("/^\w+$/",$args)){
        die("args error!");
    }
    eval("var_dump($$args);");
}
?>

The regular expression "/^\w+$/" matches a character string, \w means character+digit+underscore {az,AZ,_,0-9 } . If it does not match, it will output ``args error!''\

Two `/``/` indicate the beginning and end of the regular expression, `^` start character, `$` end character, `+` means there can be one or more `\w`.

Variables in PHP can be used as the variable name of another variable: $$args, combined with the first sentence flag In the variable!

So construct the payload: URL?args=BLOBLAS

All args can be burst, including flag.