$re = '/\<div id=\"content\"[.\s\S]*?(?=\<div id=\"footer\")/';
$str = 'hello this is some text I don\'t want
asdf
asdfasd
ff
<div id="content" class="other">
i have this other stuff
<div>More stuff</div>
<div id="footer">
hello^[^_]*_
asd;flkjasd
f;kas
dfas
df
asdf a2 5<div id="footer"><div id="content></div>';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php