[FIXED] what does || symbol means in Preg_replace() PHP

Issue

I was reading about how to make preg_replace() act like eval() function if we put the modifier /e this is my code:

$fa= '/site'.$_GET['1st'];
$sh= $_GET['replace'];
$ka= 'admin the best over the rest';
echo preg_replace($fa,$sh,$ka);  

if the code running on site, it looks like :

www.site.com/a.php?1st=//e&replace=phpinfo();

but there is a problem that the modifier /e mustn't followed by any thing so it will work if we put || like this :

www.site.com/a.php?1st=||//e&replace=phpinfo();

so here is my question what is || here and how it works ??

im using windows 10 and php version 5.2

Solution

| separates alternatives in the regexp; e.g. /abc|def|ghi/ matches either abc, def, or ghi.

When you write 1st=||//e the resulting regexp will be /site||//e. Two of the alternatives are empty strings, which will match the empty strings before and after each character. So this will call phpinfo() for each character in $ka.

Actually, you should get an error because you have two / at the end of the regexp. It should be 1st=/e or 1st=||/e.

Answered By - Barmar

Answer Checked By - Pedro (PHPFixing Volunteer)