$un = "";
$un .= "un";

• strtolower($String) → lowercase
• strtoupper($String) → uppercase
• ucfirst($String) → capitalize first character
• ucwords($String) → capitalize words

echo strlen("un"); // 2

Remove leadin or trailing whitespace.

echo "A" .trim(" B C D ") . "E"; // "AB C DE"

Retourne le string recherché et tout ce qui suit.

$str = "vamos a la playa";
echo strstr($str, "la"); // "la playa"
echo strstr($str, "yolo"); //  rien

$str = "vamos a la playa";
echo str_replace("la playa", "bailar la bamba", $str); // vamos a bailar la bamba

$str = "go ! ";
echo str_repeat($str, 3); // "go ! go ! go ! "

$str = "0123456789";
echo substr($str, 1,8); // "12345678";

$str = "0123456789";
echo strpos($str, "234"); // 2

$str = "0123456789";
echo strchr($str, "8"); // "89"
echo strchr($str, "a"); // rien
$str = "abba";
echo strchr($str, "a"); // "abba"
$str = "gabba";
echo strchr($str, "a"); // "abba"