Solved

html tags recognition by Regular Expression

Posted on 2002-06-25
7
371 Views
Last Modified: 2012-05-04
I program a forum on my own. I have a problem when people post html tags. So I have a variable for allowable tags:
$allowtags = "b|||A|||tAble|||tr|||TD|||i|||u";
Any other tags not in the above list will be converted "<" to "&lt;" and ">" to "&gt;". Now, I need help to build a pattern for this. The pattern must work for multi-line string. And if there is a tag like "< sCripT >", it must also match (there is space/captial letters). Please help. I'm not good at Regular Expression. Thanks.
0
Comment
Question by:quanghoc
  • 4
  • 3
7 Comments
 
LVL 6

Accepted Solution

by:
andreif earned 200 total points
ID: 7110129
try this code:

// $text  is users input, I'll define something here
$text = "<b> test</b> <textarea>";


$allowtags = "b|||A|||tAble|||tr|||TD|||i|||u";

// split them into array
$tags = explode('|||', $allowtags);

// RegExp itself
$text = preg_replace("/<(\s*(?!\/?(".join("|",$tags).")[>\s])[^>]*)>/i","&lt;\\1&gt;",$text);

// it's ready!
print $text;
0
 
LVL 1

Author Comment

by:quanghoc
ID: 7110862
Bit what if:
$text = "< B> test</b> <textarea>";  
 "< B  >" with space and capital. This one should not match.
0
 
LVL 1

Author Comment

by:quanghoc
ID: 7111068
Nope, never mind. < B > is not a valid tag. Let's me check for a couple more and the point should be granted to you qucik. Thanks.
0
Courses: Start Training Online With Pros, Today

Brush up on the basics or master the advanced techniques required to earn essential industry certifications, with Courses. Enroll in a course and start learning today. Training topics range from Android App Dev to the Xen Virtualization Platform.

 
LVL 6

Expert Comment

by:andreif
ID: 7111762
anyway, this < b > case is quite interesting, I'll try to sort this out :) Give me few hours
0
 
LVL 1

Author Comment

by:quanghoc
ID: 7112283
No, as I said above, < b> is not even a valid tag. Don't worry about this. As a matter of fact, would you please explain the pattern above? Like what '\/?(' means? and what '[>\s])[^>]*' is for?
Thanks.
0
 
LVL 6

Expert Comment

by:andreif
ID: 7112892
Okay, I'll to comment it :)

we are looking for:

< - tag begin
( - everything in this brackets will appear in \\1 value
\s* - zero ore more spaces (space and tab symbols)
(?! - zero-length negative condition
\/  - character "/" (we should use slash here to show that this is just symbol without special meaning)
? - character "/" before this sign may appear 0 or 1 times
(".join("|",$tags).") - after joining this will look like (a|b|td|i) , "|" means logical OR, () need to show borders of expression
[>\s] - one of included symbols must appear. So, after keyword "a", "b", "td" must appear either ">" or \s (space) - we need this to avoid matching "img" as valid tag if "i" is allowed, etc.
) - condition's end
[^>] - everything except > (match tag's body and properties)
* - previous can appear zero or more times (non > symbols)
) - end of grouping and the end of \\1 value
> - tag end

/i in the end shows that expression is case insensitive

Hope this helps!
0
 
LVL 1

Author Comment

by:quanghoc
ID: 7113915
Thanks a lot!
0

Featured Post

Courses: Start Training Online With Pros, Today

Brush up on the basics or master the advanced techniques required to earn essential industry certifications, with Courses. Enroll in a course and start learning today. Training topics range from Android App Dev to the Xen Virtualization Platform.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Since pre-biblical times, humans have sought ways to keep secrets, and share the secrets selectively.  This article explores the ways PHP can be used to hide and encrypt information.
Introduction This article is intended for those who are new to PHP error handling (https://www.experts-exchange.com/articles/11769/And-by-the-way-I-am-New-to-PHP.html).  It addresses one of the most common problems that plague beginning PHP develop…
The viewer will learn how to count occurrences of each item in an array.
The viewer will learn how to look for a specific file type in a local or remote server directory using PHP.

786 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question