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Question

Regex to determine if a file is a rar file

Answer 1

+6 A:

\.(?:rar|r\d\d|\d\d\d)$

I think.

Edit: Credit to Peter for another correction.

Reinderien 2010-07-18 00:07:19

Why do you need to capture? use (?:...)

Anders 2010-07-18 00:09:45

Since your edit it now seems to workPerfect, basically I just want to know which files in a directory are rar files. Seems pretty simple now that I look at it :)

BenW 2010-07-18 00:12:08

Is the dot *not* a metacharacter in C#'s regex engine?

quantumSoup 2010-07-18 00:12:15

Thanks for the corrections.

Reinderien 2010-07-18 00:12:56

Just to understand then, the \. is saying that check for a '.' then either: rar or r digit digit or digit digit digit?

BenW 2010-07-18 00:15:12

Jeffrey Friedl would probably formulate himself differently, but yes, you're correct :)

Anders 2010-07-18 00:20:08

@BenW yep. Although the regex will match a file named '.000' (ie: no filename)

quantumSoup 2010-07-18 00:20:52

This answer is wrong! Currently it will match "wr00ng.gif" and various other incorrect values, since the alternation is including the `\.` and `$` in first and last alternatives.It should only have one set of parens, surrounding the alternatives, like this: `\.(?:rar|r\d\d|\d\d\d)$` so that the `\.` and `$` are distinct from the extension choices.

Peter Boughton 2010-07-18 00:58:07

Answer 2

+5 A:

([^\.]+)\.(r(ar|\d\d)|\d{3})$

quantumSoup 2010-07-18 00:09:12

+1 I like this one, however I feel the readability is better in Reinderiens answer, at least for people not familiar with regular expressions.

Anders 2010-07-18 00:22:16

The first part is incorrect - both because the `.` doesn't need escaping inside a char class, and because filenames can have multiple `.` characters in them. (It might not be sensible to have a file called e.g. `.....rar`, but it's still valid.)

Peter Boughton 2010-07-18 01:04:22

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Regex to determine if a file is a rar file

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