I have a huge amount of files with elements containing an id. I would like to copy the value of the id and create a new attribute with the value of the id:

<element id="some_unique.value">
    ...      
</element>

What I’m trying to achieve:

<element id="some_unique.value" new_attribute="some_unique.value">
    ...      
</element>

How can I do this using a regular expression?