regex - Negative lookup preg_match_all in PHP for IMG tags without ALT attribute -
i'm trying find img tags don't contain alt attribute, prepare w3c validation.
i'm trying utilize negative look-around syntax:
preg_match_all('@<img[^>]*?(?!alt=)[^>]*>@', $text, $matches); which unfortunately doesn't homecoming anything, while there img tags without alt attribute sure.
i thought problem in negative lookup, illustration used:
preg_match_all('@<img[^>]+?http:\/\/(?!mysite\.com)[^>]*?>@', $text, $matches); to search images external resources , worked fine.
any ideas what's wrong first expression? thanks!
using look-ahead syntax works first one
preg_match_all('@<img[^>]*?(?=alt=)[^>]*>@', $text, $matches); $matches here contain img's alt's.
<?php $str = <<<eof <html> <body> hello <img src="withalt" alt="hi"/>asdf <img src="noalt" /> <img src="withalt2" alt="blah" /> </body> </html> eof; if (preg_match_all('@<img[^>]*?(?=alt=)[^>]*>@', $str, $matches)) { echo "matches\n"; print_r($matches); } ?> php regex html-parsing preg-match-all regex-negation
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