meaning of ?: in regular expression used for checking in php

Question

<?php
if (!preg_match("{(?:login|logout|register)\.php$}", $_SERVER["PHP_SELF"]))
{    
    if (empty($_SESSION["id"]))
    {
        redirect("login.php");
    }

 }
?>

Couldn't understand how my 1st if conditions is checking pages other than login.php, logout.php, register.php .. What ?: is doing?

This kind of duplicate is admittedly almost impossible to find, but please do try to look through some sort of documentation first. — deceze, Aug 22 '14 at 13:20
@deceze very easy if you check this [reference](http://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean) :) — HamZa, Aug 22 '14 at 13:23
@deceze Try this [query](http://stackoverflow.com/search?tab=votes&q=[regex]%20%22%3f%3a%22) :D (but I get your point) — HamZa, Aug 22 '14 at 13:28

Rahul Tripathi · Answer 1 · 2014-08-22T13:25:36.707

?: is a non capturing group ie, it matches the expression but do not capture it.

Non-capturing parentheses group the regex so you can apply regex operators, but do not capture anything.

For example:

If I dont want to capture the protocol like http then see i will use the below regex

(?:http|ftp)://([^/\r\n]+)(/[^\r\n]*)?

Now, my result looks like this:

Match "http://google.com/"
     Group 1: "google.com"
     Group 2: "/"

Match "http://google.com/ABCD/XYZ/PQR"
     Group 1: "google.com"
     Group 2: "/ABCD/XYZ/PQR"

meaning of ?: in regular expression used for checking in php

1 Answers1