How to add <br> tag after <img> tag?

I want to add <br> tag after <img> tag, my code:

$string = "< div> < img src="http://example.com/a.jpg"> < /div>";
$pattern = '/< img*+开发者_JAVA技巧>+/i';
$replacement = '${1}'.'< br>';
echo preg_replace($pattern, $replacement, $string);

but it does not work.

Do you absolutely need the <br> tag added?

You could do it using CSS instead:

img { display:block; margin-bottom:10px; }

If you only wanted to affect images within a certain section, you could limit it using:

.article img { display:block; margin-bottom:10px; }

This sounds like you are trying to use <br /> when some CSS would be better.

However, if you do intend to add a br after every img element, I would strongly suggest you skip messing around with the regex and use a DOM parser.