Disculpeeen mirenlo aqui
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title></title>
</head>
<body>
<form method="post">
<div name="header">
<h1>Ejecutar Comando</h1>
</div>
<div name="contenido">
<select name="tbLocalidad">
<option value="tC" >To</option>
<option value="tSe" >Tor</option>
</select>
Mac Adrres:<input type="text" name="tfMac" value="Aqui"/><br>
<button name="bAgregar" onclick="ejecutarComando(<?php $_POST["fname"]; ?>)">Agregar</button>
<button name="bEliminar" >Eliminar</button>
</div>
</form>
</body>
<?php
function ejecutarComando($directorio){
$comando = "mkdir ".$directorio;
exec($comando);
echo $comando;
}
?>
</html>