# regex - where and how?

**URL:** <https://community.mp3tag.de/t/regex-where-and-how/9708>\
**Category:** Support\
**Created:** [January 15, 2010, 12:57pm UTC](https://community.mp3tag.de/t/regex-where-and-how/9708 "2010-01-15T12:57:40Z")\
**Posts on this page:** 1\
**Showing post:** 4

<div class="post-metadata">

**Author:** ![dano](https://community.mp3tag.de/user_avatar/community.mp3tag.de/dano/32/6_2.png) [@dano](https://community.mp3tag.de/u/dano)\
**Post date:** [January 15, 2010, 6:07pm UTC](https://community.mp3tag.de/t/regex-where-and-how/9708/4 "2010-01-15T18:07:23Z")

</div>

Ok it seems it is possible to add a custom extension.

Regex is availale from actions:  
[/t/967/1](https://community.mp3tag.de/t/967/1)

But also works in Convert with $regexp() function

For Convert \> filename - filename:

old mask:  
%1  
new mask:  
$regexp(%1,^(\d{2})(\d{2})(\d{4})$,$3$2$1)

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