 Need Help About Regular Expressions |
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 Aug 16 2008, 04:50 PM
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#1
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Super Member  Group: [HOSTED] Posts: 218 Joined: 12-May 08 From: Istanbul, Turkey Member No.: 62,045  |
Hi,
In my website, I don't want to allow writing links to another sites but except some sites. CODE //This is the text which is sent by the guest $variable='Some texts <a href="http://www.google.com/">Google</a><a href="http://www.microsoft.com/">Microsoft</a> '; //And the following line replaces all <a html tags to "no links allowed" text. $variable = preg_replace("!<a[^>]*(http|www|mailto)(.*)</a>!siU", "no links allowed", $variable); echo($variable); I want to allow only a few sites: google.com, trap17.com, yahoo.com, etc. I want to disallow microsoft.com, hotmail.com and any other sites. What are your suggestions? What regular expression should I use? or other opinions? This post has been edited by Erdemir: Aug 16 2008, 05:07 PM |
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Aug 16 2008, 06:32 PM
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#2
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A computer once beat me at chess, but it was no match for me at kick boxing.  Group: [MODERATOR] Posts: 4,300 Joined: 24-July 05 From: Linix, DOS and Windows…the good, the bad and the ugly Member No.: 9,787  myCENT:46.50 |
If you have a short list of acceptable links which you will allow, maybe a switch/case structure would be easier? Based on an Array of suitable values?
Regular expressions can very resource intensive on the server. |
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Aug 16 2008, 06:55 PM
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#3
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Super Member Group: [HOSTED] Posts: 218 Joined: 12-May 08 From: Istanbul, Turkey Member No.: 62,045 |
QUOTE(jlhaslip @ Aug 16 2008, 09:32 PM)  If you have a short list of acceptable links which you will allow, maybe a switch/case structure would be easier? Based on an Array of suitable values? Regular expressions can very resource intensive on the server. Ok, my allowed links array is here CODE $allowedlinks = array ("google.com", "trap17.com", "yahoo.com", "dmoz.org"); Now, how can we integrate switch/case with preg_replace or without preg_replace? Thanks... This post has been edited by Erdemir: Aug 16 2008, 06:55 PM |
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Aug 16 2008, 09:32 PM
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#4
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Define:EVIL PROGRAMMER (ē'vəl prō'grăm'ər)- n. An organism that converts caffeine into evil software. Group: [HOSTED] Posts: 1,189 Joined: 25-September 05 From: Los Angeles, California Member No.: 12,251 myCENT:39.85 |
I know I said I wasn't good at regular expressions, however I've been poking around with your problem for the past hour and found something that may work:
CODE <a href=["']?((?!((http://(www\.)?wikipedia\.org)|(http://(www\.)?google\.com)|(http://(www\.)?trap17\.com))).)+["']?>(.*?)</a> This should match all links that aren't wikipedia.org, google.com and trap17.com. |
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Aug 16 2008, 09:59 PM
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#5
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Super Member Group: [HOSTED] Posts: 218 Joined: 12-May 08 From: Istanbul, Turkey Member No.: 62,045 |
QUOTE(galexcd @ Aug 17 2008, 12:32 AM) I know I said I wasn't good at regular expressions, however I've been poking around with your problem for the past hour and found something that may work: CODE <a href=["']?((?!((http://(www\.)?wikipedia\.org)|(http://(www\.)?google\.com)|(http://(www\.)?trap17\.com))).)+["']?>(.*?)</a> This should match all links that aren't wikipedia.org, google.com and trap17.com. Sorry, I couldn't use that directly in php. But your code was too helpful. I will try to use it in preg_replace(). Thanks. Any more suggestions? |
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Aug 16 2008, 10:44 PM
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#6
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A computer once beat me at chess, but it was no match for me at kick boxing. Group: [MODERATOR] Posts: 4,300 Joined: 24-July 05 From: Linix, DOS and Windows…the good, the bad and the ugly Member No.: 9,787 myCENT:46.50 |
A small note found on the php.net manual pages for the preg_match function:
QUOTE Tip
Do not use preg_match() if you only want to check if one string is contained in another string. Use strpos() or strstr() instead as they will be faster. |
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Aug 16 2008, 10:53 PM
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#7
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Define:EVIL PROGRAMMER (ē'vəl prō'grăm'ər)- n. An organism that converts caffeine into evil software. Group: [HOSTED] Posts: 1,189 Joined: 25-September 05 From: Los Angeles, California Member No.: 12,251 myCENT:39.85 |
QUOTE(jlhaslip @ Aug 16 2008, 03:44 PM) A small note found on the php.net manual pages for the preg_match function: Interesting find... However, I believe he wishes to replace the bad links with "No Links" or something similar. I think as you said previously the regexp engine is pretty resource heavy on the server and takes a bit longer to process. Perhaps a non regular expression method would be the best way. I might see if I can whip one up for you, however until then I think we still need to hear from one of our regular expression experts... *cough* rvalkass *cough* |
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Aug 17 2008, 12:13 AM
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#8
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Ephesians 6:10-17 Group: [MODERATOR] Posts: 1,978 Joined: 22-June 05 From: somewhere... Where am i? Member No.: 8,528 myCENT:18.27 |
The following should get the results you desire:
CODE <?php $allowedlinks = array("google.com", "trap17.com", "yahoo.com", "dmoz.org"); function site_filter($matches){ global $allowedlinks; if (!preg_match("/(?:".implode("|", $allowedlinks).")\/?$/", $matches[1])){ return "Link not allowed."; } else { return $matches[0]; } } $variable='Some texts <a href="http://www.google.com/">Google</a><a href="http://www.microsoft.com/">Microsoft</a> '; $variable = preg_replace_callback("/<a href=[\"']([^<]+)[\"']>[^<]+<\/a>/", "site_filter", $variable); echo $variable; ?> Would have been easier to work with if each anchor element was on its own line. |
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Aug 17 2008, 07:01 PM
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#9
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Super Member Group: [HOSTED] Posts: 218 Joined: 12-May 08 From: Istanbul, Turkey Member No.: 62,045 |