Barre de recherche php et affichage

<?php
		$serveur = "localhost";
		$login = "root";
		$pass = "root";

		 try{
			$connexion = new PDO("mysql:host=$serveur;dbname=cours; charset = utf8",$login,$pass);
			$connexion -> setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);
			if (isset($_POST['submit'])){
				$str = $_POST['search'];
				$requete = $connexion ->prepare("SELECT * FROM users WHERE nom='$str' ");
			$requete-> execute();
			$resultat = $requete->fetchAll(PDO::FETCH_ASSOC);
			}
			 
			print_r($resultat);
			 		}
		catch(PDOException $e){
			die('Echec de la connexion:'.$e ->getMessage());
		}
?>