I need to update some records using a regex and others trigger them just if they are empty, when they are empty I have no problems but when it is a regular expression I always get an empty result but and I can't figure out how to

The fields look like this

[caption id="" align="alignright" width="180" caption=""]<a href="http://www.medialifemagazine.com/archives/images/collegebag.gif"><img class="size-full" title="collegebag.gif" src="http://www.medialifemagazine.com/archives/images/collegebag.gif" alt="" width="180" height="259" /></a>[/caption]

and this is my regex

Code MySQL:
^\[caption +[a-zA-Z=" 0-9\]<>:/.-]*\[\/caption\]$

Can someone help me out?