使用fseek在最后一行之前插入字符串

Question

I am trying to write a very basic registration module for blueimp.net's AjaxChat. I have a script that writes to the user config file.

$userfile = "lib/data/users.php";
$fh = fopen($userfile, 'a');
$addUser = "string_for_new_user";
fwrite($fh, $addUser);
fclose($fh);

But I need it to insert $addUser before the very last line, which is ?>

How would I accomplish this using fseek?

Answer 1

If you always know that the file ends with ?> and nothing more, you can:

$userfile = "lib/data/users.php";
$fh = fopen($userfile, 'r+');
$addUser = "string_for_new_user
?>";
fseek($fh, -2, SEEK_END);
fwrite($fh, $addUser);
fclose($fh);

To further enhance the answer: you're going to want to open your file in mode r+ because of the following note regarding fseek:

Note:

If you have opened the file in append (a or a+) mode, any data you write to the file will always be appended, regardless of the file position, and the result of calling fseek() will be undefined.

fseek($fh, -2, SEEK_END) will place the position at the end of the file, and then move it backwards by 2 bytes (the length of ?>)