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<?php function tagify($str, $baseUrl = '/board/') { $regExp = '/ (?!<a[^<>]*>[^\#]*) # Dont match if there is an opening link tag and any chars after it. \#([-_\w]+\b) # Match the hashtag. (?![^<]*<\/a>) # Ignore any closing link tag including any chars before it not in hashtag. /ix'; $baseUrl = rtrim($baseUrl, '/'); return preg_replace($regExp, '<a href="'.$baseUrl.'/$1">#$1</a>', $str); } $str = <<<STR This is <a href="http://foo.com">This is #foo</a>. Simple #html-stuff text <a href="http://foobar.com#baz">#simple</a> <span class="simple">simple #simple text text</span> STR; echo tagify($str);

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