# Filtering out differently styled track numbers in filename

**URL:** <https://community.mp3tag.de/t/filtering-out-differently-styled-track-numbers-in-filename/60077>\
**Category:** Support\
**Created:** [February 15, 2023, 3:13pm UTC](https://community.mp3tag.de/t/filtering-out-differently-styled-track-numbers-in-filename/60077 "2023-02-15T15:13:26Z")\
**Posts on this page:** 1\
**Showing post:** 11

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**Author:** ![LyricsLover](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/l/c6cbf5/32.png) [@LyricsLover](https://community.mp3tag.de/u/LyricsLover)\
**Post date:** [February 16, 2023, 2:52pm UTC](https://community.mp3tag.de/t/filtering-out-differently-styled-track-numbers-in-filename/60077/11 "2023-02-16T14:52:58Z")

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> [@ragtag](#):
>
> Could you please confirm whether parenthesis are to be used whenever an regular expression operator, such as one of the following, are deployed:

No, the parenthesis are there to "collect/remember" the matched digits or characters.  
For example, if you want to replace the matched characters with some other values, you need the parenthesis. They build groups for later use.

@ohrenkino gave you a solution for filenames, using such parenthesis:

> [@Insert text with a regular expression in the filename](https://community.mp3tag.de/t/insert-text-with-a-regular-expression-in-the-filename/60079/2):
>
> If you want to keep the number, then you have to tell MP3tag that it should remember it - which is done by enclosing the pattern in parenthesis. So for something like 101. My music file which should become 1-01. My music file Try: Search pattern: ^(\d)(.\*) Replace string: $1-$2 Further information about regular expressions can be found in the documentation:

If you want so search for parenthesis as ordinary character, you have to escape them like this `\(` for an opening bracket and `\)` for a closing bracket

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