Regex: how do I capture the file extension?

Question

How do I determine the file extension of a file name string?

lets say I have

I'm.a.file.name.tXt

the regex should return tXt

Many languages have built-in ways of handling filenames and extensions. What are you using? — Telemachus
– Telemachus, Commented Jul 20, 2010 at 17:18
Doesn't the language/platform you are using to run regexes have file handling routines? — Darin Dimitrov
– Darin Dimitrov, Commented Jul 20, 2010 at 17:19
I'm curious: why are you writing tXt every time, rather than txt? — Peter Boughton
– Peter Boughton, Commented Jul 20, 2010 at 18:32

Scharron · Accepted Answer · 2010-07-20 17:18:53Z

3

something like \.[^.]*$ should do it

answered Jul 20, 2010 at 17:18

Scharron

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1 Comment

Peter Boughton Over a year ago

As an extension, you possibly want make to the \. a lookbehind - so (?<=\.)[^.]*$ - to avoid potentially having to remove the . later. Though not all regex implementations support lookbehinds, and we don't know what one this is for.

Community · Accepted Answer · 2017-05-23 11:57:01Z

2

You probably don't need regex - most languages will have the equivalent to this:

ListLast(Filename,'.')

(If you do need regex for some reason, Scharron's answer is correct.)

edited May 23, 2017 at 11:57

CommunityBot

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answered Jul 20, 2010 at 17:25

Peter Boughton

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Comments

Stephen · Accepted Answer · 2010-07-20 17:20:20Z

0

What language is this in? It's quite possible you don't want to actually use a regex - assuming the name is a String you'll probably just want to do something like split it over periods and then choose the last segment. Okay, that's sort of a regex answer, but not a proper one.

answered Jul 20, 2010 at 17:20

Stephen

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Comments

Thomas O · Accepted Answer · 2010-07-20 17:18:45Z

-2

/^(.*?)\.(.*)$/

The '?' makes it greedy. Your result will be in the second group.

answered Jul 20, 2010 at 17:18

Thomas O

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4 Comments

NullVoxPopuli Over a year ago

I'm, and a.file.name.tXt not just tXt

Thomas O Over a year ago

In which case remove the greedy match at put it on the second group. You said you only wanted 'tXt'.

Peter Boughton Over a year ago

The ? makes a quantifier lazy, not greedy!

Peter Boughton Over a year ago

Based on your comment, you possibly misunderstand greedy vs lazy matching. Read more at regular-expressions.info/repeat.html but basically, if taking this approach, you want (greedy).(lazy) in order to consume as much as possible for the first group and as little as required for the second.

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