# Debug regex help

**URL:** <https://community.mp3tag.de/t/debug-regex-help/44565>\
**Category:** Support\
**Created:** [February 16, 2019, 9:27pm UTC](https://community.mp3tag.de/t/debug-regex-help/44565 "2019-02-16T21:27:05Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Zapgok](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/z/8797f3/32.png) [@Zapgok](https://community.mp3tag.de/u/Zapgok)\
**Post date:** [February 16, 2019, 9:27pm UTC](https://community.mp3tag.de/t/debug-regex-help/44565/1 "2019-02-16T21:27:05Z")

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I'm using a couple of regular expression without being well-versed which means I can't figure out why I'm getting this result and I would really appreciate some assistance.

This is my mp3tag-action:

Replace with regular expression  
Field: Performer  
Regular expression: `([-({ _.+\x{201c}"])(\l)(?# for tags)`  
Replace matches with: `$1$upper($2)`  
Case-sensitive comparison checked

Replace with regular expression  
Field: Performer  
Regular expression: `(?<!&|:|;|-|/|!|\.|\?|\+)(\s+\b(A|And)\b)`  
Replace matches with: `$lower($1)`  
Case-sensitive comparison checked

Something in this expression causes the following error in Musicbee: [https://i.imgur.com/5MrWsEO.jpg](https://i.imgur.com/5MrWsEO.jpg)

Any insight would be greatly appreciated!

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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, 2019, 9:43pm UTC](https://community.mp3tag.de/t/debug-regex-help/44565/2 "2019-02-16T21:43:33Z")

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Again:  
Try it with some of the online regular expression checker (like [regex101.com](https://regex101.com/)) and you will see why it don't work.  
If you would tell us what your Perfomer tag contains before and after your regular expression, maybe we could help a little bit more.

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**Author:** ![Zapgok](https://community.mp3tag.de/letter_avatar_proxy/v4/letter/z/8797f3/32.png) [@Zapgok](https://community.mp3tag.de/u/Zapgok)\
**Post date:** [February 16, 2019, 11:26pm UTC](https://community.mp3tag.de/t/debug-regex-help/44565/3 "2019-02-16T23:26:44Z")

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Nevermind, it's most likely a Musicbee issue. The regex does what it supposed to do. The problem only occurs when the performer tag looks like this:

Charlie Watts (drums (drum set))

It's the double parentheses that's screwing it up.

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**Author:** ![system](https://community.mp3tag.de/uploads/default/original/2X/c/ce7035d426cb755a7916793326d23b465222a407.png) [@system](https://community.mp3tag.de/u/system)\
**Post date:** [February 9, 2026, 12:27pm UTC](https://community.mp3tag.de/t/debug-regex-help/44565/4 "2026-02-09T12:27:55Z")

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