how to fetch all the links starting with http://plus

I have a pregmatch with the following search :

   $regexp = "&l开发者_运维技巧t;a\s[^>]*href=(\"??)([^\" >]*?)\\1[^>]*>(.*)<\/a>";

now how can I reformat this to look for something like :

href="http://plus  

I dont want the entire thing to be changed , just that part for the href.

Thanks

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$regexp = "<a\s[^>]*href=(\"??)(http:\/\/plus[^\" >]*?)\\1[^>]*>(.*)<\/a>";