Regex ignore URL already in HTML tags

Question

I'm having a little problem with my Regex

I've made a custom BBcode for my website, however I also want URLs to be parsed too.

I'm using preg_replace and this is the pattern used to identify URLS:

/([\w]+:\/\/[\w-?&;#~=\.\/\@]+[\w\/])/is

Which works great, however if a URL is within a [img][/img] block, the above pattern also picks it up and produces a result like this:

//[img]http://url.com/toimg.jeg[/img] will produce this result:
<img src="<a href="http://url.com/toimg.jeg" target="_blank">/>
//When it should produce:
<img src="http://url.com/toimg.jeg"/>

I tried using this:

/([^"][\w]+:\/\/[\w-?&;#~=\.\/\@]+[\w\/][^"])/is

With no luck.

Any help will be appreciated.

Edit: For solution See the 2nd comment on stema's answer.

stema · Accepted Answer · 2012-03-05 15:12:25Z

3

Try this

(?<!href=")(\b[\w]+:\/\/[\w-?&;#~=\.\/\@]+[\w\/])

See it here on Regexr

To make it more general you can simplify your lookbehind to check only for "=""

(?<!=")(\b[\w]+:\/\/[\w-?&;#~=\.\/\@]+[\w\/])

See it on Regexr

(?<!href=") is a negative lookbehind assertion, it ensures that there is no "href="" before your pattern.

\b is a word boundary that anchors the start of your link to a change from a non word to a word character. without this the lookbehind would be useless and it would match from the "ttp://..." on.

edited Mar 5, 2012 at 15:12

answered Mar 5, 2012 at 14:03

stema

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4 Comments

stema Over a year ago

@Moe Then just simplify the lookbehind to check for only "="" like this (?<!=")(\b[\w]+:\/\/[\w-?&;#~=\.\/\@]+[\w\/]) Regexr

Moe Over a year ago

That worked! I'd like to understand a bit more about the (?<!) assertion, any reading material that you'd recommend?

stema Over a year ago

@Moe regular-expressions.info is in general a good place to learn about regexes, see here the lookaround chapter

worlock Over a year ago

This doesn't run on browsers except chrome. Throws error.

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