$re = '/\[<a(\s+[a-zA-Z\-][a-zA-Z0-9\-]*(=("[^"]*"|\'[^\']*\'|[a-zA-Z0-9\-_]+)?)?)*\s*>([^<]|<[^a]|<a[^ >])+<\/a>\]/m';
$str = '<div>
<br/>
<div style="text-align: left;">
<p style="margin-top: 0px; margin-bottom: 0px;"> [<a id="Offer no. SGE - 100818 - 2 - Klb (24XLR - steel washing).doc" href="/apps/BIZ4TS/migration/Lists/Angebot3/Attachments/9/Offer%20no.%20SGE%20-%20%20100818%20-%20%202%20-%20Klb%20(24XLR%20-%20steel%20washing).doc">Offer no. SGE -  100818 -  2 - Klb (24XLR - steel washing).doc</a>] [<a id="_PO4501258976_EUR.pdf" href="/apps/BIZ4TS/migration/Lists/Angebot3/Attachments/9/_PO4501258976_EUR.pdf">_PO4501258976_EUR.pdf</a>] </p>
</div>
<br/>
<div style="text-align: left; color: #000000; font-family: arial, san-serif; font-size: 9pt;">
<p style="margin-top: 0px; margin-bottom: 0px;">Rechnungen im Einzelnen (lt. Linda Gölzenleuchter/Praktikantin RTB) Stand 05.05.2011</p>
</div>
<br/>
<div style="text-align: left;">
<p style="margin-top: 0px; margin-bottom: 0px;"> [<a id="2011_05.pdf" href="/apps/BIZ4TS/migration/Lists/Angebot3/Attachments/9/2011_05.pdf">2011_05.pdf</a>] [<a id="2011_01.pdf" href="/apps/BIZ4TS/migration/Lists/Angebot3/Attachments/9/2011_01.pdf">2011_01.pdf</a>] </p>
</div>
</div>
<br/>
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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