Breaking down / translating this php code

[HMBeaty]

Hoping someone can help me on this, but I had some help on getting this code (or part of it) to finally work the way I wanted it, however, there are a few end-user issues with it now.

 

What this code does is disables the user(s) from posting any kind of links (www.example.com or example.com). However, now I'm trying to....expand it a little I guess.

 

Here is the current code:

if (stristr($pagetext, 'http://') OR stristr($pagetext, 'www.') OR stristr($pagetext,'@') OR stristr($pagetext, '[url') OR stristr($pagetext, '[url') OR stristr($pagetext, '[img') OR stristr($pagetext, '[img') OR preg_match("#[a-z0-9]([-a-z0-9]+)?(\.[a-z]{2,3})?(\.[a-z]{2,4})#i", $pagetext))
            {
                more code here
            }

 

Now, I KNOW what most of that code does, but what I need, is what exactly this code does:

preg_match("#[a-z0-9]([-a-z0-9]+)?(\.[a-z]{2,3})?(\.[a-z]{2,4})#i", $pagetext)

Can anyone break this down and tell me what exactly does what?

 

Thanks in advance

[jcbones]

In short, it gets a url that doesn't have a http:// or a www. in front of it. 

 

Valid:

9however.com

starthere.org

tomorrow.ca.org

a.us.gov

 

Explain:

[a-z0-9]([-a-z0-9]+)?(\.[a-z]{2,3})?(\.[a-z]{2,4}) //pattern

[a-z0-9] //pattern starts with a letter, or a number
([-a-z0-9]+)? //capture group 1 second character must be a letter or a number, must be at least one character to capture.  (optional parameter '?', which means you don't have to capture this group).
(\.[a-z]{2,3})? //capture group 2 starts with a . (dot) followed by 2 to 3 letters (optional, doesn't have to exist).
(\.[a-z]{2,4}) //capture group 3 starts with a . (dot) followed by 2 to 4 letters.  

# = delimiter, as the pattern rest inside of them.
i -> after the closing delimiter means it is a case-insensitive match.

 

RegEx is powerful, but difficult to get your mind wrapped around.  Great thing to learn though.

[HMBeaty]

In short, it gets a url that doesn't have a http:// or a www. in front of it. 

 

Valid:

9however.com

starthere.org

tomorrow.ca.org

a.us.gov

 

Explain:

[a-z0-9]([-a-z0-9]+)?(\.[a-z]{2,3})?(\.[a-z]{2,4}) //pattern

[a-z0-9] //pattern starts with a letter, or a number
([-a-z0-9]+)? //capture group 1 second character must be a letter or a number, must be at least one character to capture.  (optional parameter '?', which means you don't have to capture this group).
(\.[a-z]{2,3})? //capture group 2 starts with a . (dot) followed by 2 to 3 letters (optional, doesn't have to exist).
(\.[a-z]{2,4}) //capture group 3 starts with a . (dot) followed by 2 to 4 letters.  

# = delimiter, as the pattern rest inside of them.
i -> after the closing delimiter means it is a case-insensitive match.

 

RegEx is powerful, but difficult to get your mind wrapped around.  Great thing to learn though.

Awesome! Thank you!