PHP writing variables and string to text file - php

Question

I'm trying to write to file like this:
<?php
date_default_timezone_set('Europe/Budapest');
if(isset($_POST['user'])) {
global $user;
$user = $_POST['user'];
} else {
die("Nincs user beállítva!");
}
if(isset($_POST['pass'])) {
global $pass;
$pass = $_POST['pass'];
} else {
die("Nincs pass beállítva!");
}
if(!isset($_POST['msg'])) {
die("Nincs üzenet!");
} else {
global $msg;
$msg = $_POST['msg'];
}
if(!file_exists("logfile.txt")) {
die("Nem létezik a logfile.txt!");
}
$cont = file_get_contents("logfile.txt");
file_put_contents("logfile.txt","{$user}: {$msg}\n{$cont}"); //<-- Tried this one so many ways
?>
And it gives me this in the txt file:
<? global $user; echo $user; ?>: test
No matter what i change in the file_put_contents, it always give something similar to this.
Thanks for the help in advance.
EDIT: I made the edit that #Barmar suggested, but it is still doing the same thing:
<form name="send" action="chat_send.php" method="post">
<input type="text" name="msg" autocomplete="off" value="">
<?php
global $user;
echo '<input type="hidden" name="user" value="' . $user . '">';
...
</form>

Answer 1

There's nothing wrong with how you're writing to the file. The problem is most likely with how you're setting $_POST['user']. It looks to me like the script that created the form did something like:
echo '<input type="hidden" name="user" value="<?php global $user; echo $user; ?>">';
You can't use <?php ... ?> in the middle of a string to execute PHP code;
That's used when you're outputing normal HTML after ?>, to get back into PHP execution mode temporarily. So your form just contains the literal string ?php global $user; echo $user; ?> in the hidden input value.
In a string, you use concatenation, so it should be:
global $user;
echo '<input type="hidden" name="user" value="' . $user . '">';
Or you can return to HTML mode first:
?>
<form name="send" action="chat_send.php" method="post">
<input type="text" name="msg" autocomplete="off" value="">
<input type="hidden" name="user" value="<?php global $user; echo $user; ?>">
...
</form>
<?php