How Can I Make This 2-Page PHP Login Script Remember User Input On Page 2

Solution:

From your code, it looks like you've skipped the step from using the POST value from the first form before getting to the second.

After a form is submitted, in PHP a $_POST variable contains the values of what was in the form from the keys of the name in the form.

For example<input name="myinput"> in a form set to POST will result in$_POST['myinput'] containing the value from the submit you submit.

The simple way to achieve what you want would be to just post the value frompage1.php topage2.php, and then it looks like you handle the login on alogin.php. For example:

page1.php

<?php
    if (isset($_GET['invalidEmail'])) {
        echo "Error: Invalid email address entered.";
    }
?>
<form action="page2.php" method="post">
    <input type="email" type="email" />
    <input type="submit" value="Continue" />
</form>
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page2.php

<?php
    $email = htmlentities($_POST['email']);
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        // the email address is not valid, redirect them back to page1.php
        header('Location: page1.php?invalidEmail=true');
    }
?>
<form action="login.php" method="post">
    <input type="hidden" value="<?=$email?>" />
    <input type="password" type="password" />
    <input type="submit" value="Continue" />
</form>
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login.php

<?php
    session_start(); // before any HTML is echoed
    $email = $_POST['email'];
    $password = $_POST['password'];

    // ..do whatever you need todo to validate the email and password
    // now you can use something like $_SESSION['loggedin'] = $email which will persist across any pages 
    // you can check `if (isset($_SESSION['loggedin']))` to check if they're signed in
    // if the validation fails, redirect them back to page1.php with another error
?>
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This way you're not using$_SESSION between pages and a user must go through from entering their email on page 1, to then adding their password on page 2 and finally validating on thelogin.php file.

The above will get the basics right for you and hopefully allow you to get where you need to go. There are a few extra things you will want to consider (though without having a firm understanding of the above, the rest won't work..)

1. Validation between pages - from page1 (collecting email) to page2, I've added a line to collect and validate an email address format. You might want to do some extra validation to see if it exists in your records before asking for a password.
2. Input sanitization - you'll notice I've usedhtmlentities around the$_POST['email'] - this is to prevent users from injecting extra code on page2
3. From page2.php, if you visit it directly you're always redirected to page1.php because it requires an email address to be posted to it. You may want to consider what should happen here.
4. The flow here also means you can't skip between pages and must go through page1 => page2 => login. This is almost to be expected, but setting$_SESSION['email'] = $_POST['email'] would allow you to persist the entered data between pages.