# \[X\] $regexp(X,.\*$,YY)
**URL:** https://community.mp3tag.de/t/x-regexp-x-yy/6261
**Category:** No Bugs
**Created:** [February 15, 2008, 2:31am UTC](https://community.mp3tag.de/t/x-regexp-x-yy/6261 "2008-02-15T02:31:29Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@chrisjj](https://community.mp3tag.de/u/chrisjj)
#### Post date: [February 15, 2008, 2:31am UTC](https://community.mp3tag.de/t/x-regexp-x-yy/6261/1 "2008-02-15T02:31:29Z")
[EDITED:] ... returns YYYY rather than YY as documented.
---
### Author:  [@Florian](https://community.mp3tag.de/u/Florian)
#### Post date: [February 15, 2008, 5:46pm UTC](https://community.mp3tag.de/t/x-regexp-x-yy/6261/2 "2008-02-15T17:46:00Z")
The regular expression from the topic return YYYY because .\* matches nothing **and** the X.
This is no bug and works as intended.
---
### Author:  [@chrisjj](https://community.mp3tag.de/u/chrisjj)
#### Post date: [February 16, 2008, 5:41pm UTC](https://community.mp3tag.de/t/x-regexp-x-yy/6261/3 "2008-02-16T17:41:03Z")
> The regular expression from the topic return YYYY
(Agreed - my typo, sorry. Original report now corrected.)
> .\* matches nothing **and** the X.
Indeed, as proved by $regexp(X,(.\*)$,(\1)) -\> (X)()
I have used regexp in dozens of other tools and languages, and never seen a single wild card expression generate TWO SEPERATE replacement expressions.
> This is no bug
It is a failure to accord with the docs - \* is supposed to be greedy i.e. match everything in one hit.
Are the docs in error, then?
---
### Author:  [@Florian](https://community.mp3tag.de/u/Florian)
#### Post date: [February 16, 2008, 6:46pm UTC](https://community.mp3tag.de/t/x-regexp-x-yy/6261/4 "2008-02-16T18:46:50Z")
> [@chrisjj](#):
>
> Are the docs in error, then?
No, I don't think so.
> [@](#):
>
> The dot character "." matches any single character.
> [...]
> "\*" repeated any number of times **including zero**
---
### Author:  [@chrisjj](https://community.mp3tag.de/u/chrisjj)
#### Post date: [February 17, 2008, 12:38pm UTC](https://community.mp3tag.de/t/x-regexp-x-yy/6261/5 "2008-02-17T12:38:42Z")
> "\*" repeated any number of times including zero
That doesn't mean it isn't by default greedy. But
> Non-greedy repeats
> Non-greedy repeats are possible by appending a '?' after the repeat;
> a non-greedy repeat is one which will match the shortest possible string.
surely does.
What's your understanding Florian? Is \* (without ?) supposed to be greedy, or, not?
---
### Author:  [@Florian](https://community.mp3tag.de/u/Florian)
#### Post date: [February 17, 2008, 4:17pm UTC](https://community.mp3tag.de/t/x-regexp-x-yy/6261/6 "2008-02-17T16:17:51Z")
> [@chrisjj](#):
>
> What's your understanding Florian? Is \* (without ?) supposed to be greedy, or, not?
Sure, that's why there is an extra specifier to turn of greedyness.
---
### Author:  [@chrisjj](https://community.mp3tag.de/u/chrisjj)
#### Post date: [February 17, 2008, 4:57pm UTC](https://community.mp3tag.de/t/x-regexp-x-yy/6261/7 "2008-02-17T16:57:20Z")
> > Is \* (without ?) supposed to be greedy, or, not?
> > Sure, that's why there is an extra specifier to turn of greedyness.
I take that to mean "Sure, it is supposed to be greedy".
Well, Florian, then it is not working properly.
When .\* is greedy, $regexp(X,._$,YY) gives YY because greedy ._ matches the entire input string, and that is replaced by a single occurence of the replacement string YY. This is indeed what I get on the other regexp implemetations I just tested.
But on Mp3tag, $regexp(X,.\*$,YY) gives YYYY.
> that's why there is an extra specifier to turn of greedyness.
Actually that doesn't work either, but let's deal with one issue at a time.
PS Here's a quote from [http://en.wikipedia.org/wiki/Regular\_expressions#Syntax](http://en.wikipedia.org/wiki/Regular_expressions#Syntax) which whilst not necessarily being a spec Mp3tag aims to comply with, does define what's generally meant by 'greedy':
. The standard quantifiers in regular expressions are greedy, meaning
. they match as much as they can, only giving back as necessary to
. match the remainder of the regex.
---
### Author:  [@Florian](https://community.mp3tag.de/u/Florian)
#### Post date: [December 28, 2018, 2:22pm UTC](https://community.mp3tag.de/t/x-regexp-x-yy/6261/8 "2018-12-28T14:22:23Z")
This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.