Strings in PHP

//1.Removes Names.
<!DOCTYPE html>
<html>
<head>
    <title>Print Array</title>
</head>
<body>
    <form method="post">
        <label for="first">First list:</label>
        <input type="text" name="text_1" id="first">
        <br>
        <label for="second">Second list:</label>
        <input type="text" name="text_2" id="second">
        <br>
        <input type="submit" value="Go">
    </form>
    <?php
        $str_1 = $_POST['text_1'];
        $str_2 = $_POST['text_2'];
        $array_1 = explode(" ", $str_1);
        $array_2 = explode(" ", $str_2);
        $together = array_diff($array_1, $array_2);
        echo implode(" ", $together);

    ?>
</body>
</html>


//2.Count of Letters.
<!DOCTYPE html>
<html>
<head>
    <title>Count of Letters</title>
</head>
<body>
    <form method="post">
        <label for="letters">Letters:</label>
        <input type="text" name="str" id="letters">
        <br>
        <input type="submit" value="Go">
    </form>
    <?php
        $str = $_POST['str'];
        $array = explode(" ", $str);
        sort($array);
        echo '<pre>' . print_r(array_count_values($array), true) . '</pre>';
    ?>
</body>
</html>


//3.Find All Matches.
<!DOCTYPE html>
<html>
<head>
    <title>Find All Matches</title>
</head>
<body>
    <form method="post">
        <label for="text">Enter text:</label>
        <br>
        <textarea id="text" name="text" rows="10"></textarea>
        <br>
        <input type="submit" value="Go">
    </form>
    <?php
        $str = $_POST['text'];
        $str = strtolower($str);
        echo substr_count($str, 'em');
    ?>
</body>
</html>


//4.Extract all Valid URLs.
<!DOCTYPE html>
<html>
    <head>
        <title>Extract all valid URLs</title>
    </head>
    <body>
        <form method="POST">
            <label for="text">Enter text:</label>
            <input type="text" name="str" id="text">
            <input type="submit" value="Go">
        </form>
        <?php
            $str = $_POST['str'];
            $reg = "/(http|https|ftp|ftps)\:\/\/[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,3}(\/\S*)?/";
            preg_match_all($reg, $str, $url);
            echo '<pre>' . implode("\n", $url[0]) . '</pre>';
        ?>
    </body>
</html>


//6.Combine List of Letters.
<!DOCTYPE html>
<html>
<head>
    <title>Combine List of Letters</title>
</head>
<body>
    <form method="post">
        <label for="first">First list:</label>
        <input type="text" name="text_1" id="first">
        <br>
        <label for="second">Second list:</label>
        <input type="text" name="text_2" id="second">
        <br>
        <input type="submit" value="Go">
    </form>
    <?php
        $str_1 = $_POST['text_1'];
        $str_2 = $_POST['text_2'];
        $array_1 = explode(" ", $str_1);
        $array_2 = explode(" ", $str_2);
        $unique = array_diff($array_2, $array_1);
        $together = array_merge($array_1, $unique);
        echo implode(" ", $together);
    ?>
</body>
</html>