The goal is to call the variable $url when the button is clicked. With this current bit of code, when the button is clicked nothing happens and the error says unexpected token.
<?php
$url = "edit_beginningcakephp.php?title=$title&author=$author&isbn=$isbn
&year=$year&pages=$pages&price=$price";
>?
<input type="button" value="Edit Book" onclick="window.location.href='<?= $url ?>'">
I suppose you're not correctly encoding the content of the variables (known as XSS)
You need to urlencode the content of your variables. Also, & needs to be entered as an HTML entity &.
Try:
$url = 'edit_beginningcakephp.php?title='.urlencode($title).'&author='.urlencode($author).'&isbn='.urlencode($isbn).'&year='.urlencode($year).'&pages='.urlencode($pages).'&price='.urlencode($price);
PS: >?should be ?> and make sure the URL doesn't contain any newlines.
" >? " That looks like it might be a problem, definitely throws a syntax error on my local :)
While MrTux's answer is very good and his advice should surely be followed, the actual problem with your code is the return in the URL. URLS can't contain returns!
Solution: delete the return. And the spaces. And follow MrTux's advice.