# Quirks of Regular Expressions in Mp3tag

**URL:** https://community.mp3tag.de/t/quirks-of-regular-expressions-in-mp3tag/11650
**Category:** Support
**Created:** [February 28, 2011, 11:17pm UTC](https://community.mp3tag.de/t/quirks-of-regular-expressions-in-mp3tag/11650 "2011-02-28T23:17:46Z")
**Posts on this page:** 1
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### Author: ![Doug\_Mackie](https://community.mp3tag.de/user_avatar/community.mp3tag.de/doug_mackie/32/279_2.png) [@Doug\_Mackie](https://community.mp3tag.de/u/Doug_Mackie)
#### Post date: [February 28, 2011, 11:17pm UTC](https://community.mp3tag.de/t/quirks-of-regular-expressions-in-mp3tag/11650/1 "2011-02-28T23:17:46Z")

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Hello folks,

Could someone please help me to understand the single quote marks ( **'** ) sometimes used in regular expressions posted here? For example, here is one from Dano for extracting parenthesized years from file names:

**$regexp(%\_filename%,'^.+?\((\d{4})\)'.\*?$,$1)**

It works, but not without the single quote marks. Why? In other applications, the marks must be removed for such an expression to work. This is unfortunate because I like to use the Expresso expression builder to help construct expressions for Mp3tag. I have wasted time writing expressions that "should" work (and do work elsewhere) but fail in Mp3tag without the mysterious **'** marks.

I have not found a reference that explains when and where to use these marks and they seem to be unique to Mp3tag. Any suggestions are welcome. Perhaps a section should be added to the script help page.

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