C# regex to extract string between two characters but first character has multiple occurences

Question

I'm trying to extract string between two characters. First charachter has multiple occurences and I need the last occurence of first character. I've already checked similar questions but all suggested regexes don't work in case of multiple occurences of first character.

Example:

TEST-[1111]-20190603-25_TEST17083

My code:

string input = "TEST-[1111]-20190603-25_TEST17083";
var matches = Regex.Matches(input,@"(?<=-)(.+?)(?=_)");
var match = matches.OfType<Match>().FirstOrDefault();
var value = match.Groups[0].Value;

The current result:

[1111]-20190603-25

Expected result:

Please post some code that shows what you're doing. The problem might not be with the regex but with how you're extracting the result. — Corey
– Corey, Commented Jun 3, 2019 at 10:17
(?<=-)([0-9]+)(?=_)? If we can guarantee that exepected result is a number; (?<=-)([^\-]+?)(?=_) — Dmitrii Bychenko
– Dmitrii Bychenko, Commented Jun 3, 2019 at 10:21
The point is that . matches any char. If you know there must be no other - in between - and _ use [^-] instead of the dot. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jun 3, 2019 at 10:25
The accepted answer is not accurate considering "I need the last occurrence". It will return all occurrences. — Mohammed Noureldin
– Mohammed Noureldin, Commented Jun 3, 2019 at 23:32

Wiktor Stribiżew · Accepted Answer · 2019-06-03 10:25:54Z

4

Let's try a bit different pattern:

(?<=-)([^-_]+?)(?=_)

we use [^-_] instead of .: all characters except - and _

edited Jun 3, 2019 at 10:25

Wiktor Stribiżew

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answered Jun 3, 2019 at 10:24

Dmitrii Bychenko

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1 Comment

Wiktor Stribiżew Over a year ago

- at the initial position in the character class does not have to be escaped. Actually, you do not need a non-greedy quantifier, use greedy one.

Mohammed Noureldin · Accepted Answer · 2019-06-03 10:40:14Z

2

One option to get your result (and there are many options of course) is the following pattern:

.*-([0-9]*)_

and then get the first matched group (group with Id 1).

So your code will look like this:

var input = "[1111]-20190603-25";
var pattern = @".*-([0-9]*)_";

var match = Regex.Match(input, pattern);
var value = match.Groups[1];

edited Jun 3, 2019 at 10:40

answered Jun 3, 2019 at 10:25

Mohammed Noureldin

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1 Comment

bobble bubble Over a year ago

Efficient and takes into account, that OP wants to match the last occurence which eg this regex doesn't.

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