Regex mismatch issue

Question

I am having an issue with identifying a multiple character digit in a string.

What I am attempting to do is check, from right to left, for the first digits for comparison.

My original regex:

Regex.Match(s, @"\d{3}", RegexOptions.RightToLeft);

This would match the first 3 digits it came across in any string. Eg:

hello123 - Output: 123
good234bye - Output: 234
see-you-456-tomorrow - Output: 456

No worries. However, now we're not certain of the length the number might be, so we have changed the Regex to this:

Regex.Match(s, @"\d*", RegexOptions.RightToLeft);

This looks for the first string of digits, any length, and uses that. However, it returns an empty match if the number is not on the end of the string. Eg:

hello12 - Output: 12
good-bye-1234 - Output: 1234
see-1-you-2-morrow - Output: Nothing

How can I look for the first x-length of digits in a string, from right to left and disregarding any non-digit characters, without it returning an empty match?

have you tried tu use "Global" like so: Regex.Match(s, @"\d+g", RegexOptions.RightToLeft); — Marcus Abrahão, Sep 22 '15 at 01:02
I have not. What does that check for? (I'm a bit of a newbie when it comes to regex) — Ben, Sep 22 '15 at 01:03
I'm not sure of its syntaxe in C# but the g stand for global search — Marcus Abrahão, Sep 22 '15 at 01:04
For general reference, check this post http://stackoverflow.com/questions/4736/learning-regular-expressions — Mariano, Sep 22 '15 at 01:31

Arthur Castro · Answer 1 · 2015-09-22T01:28:46.153

0

Can you try this? I'm new to Regex, but I guess it works for you!

 var s =    @"see-you-456-tomorrow";
            var r = Regex.Match(s, @"[[\d]]*\d*", RegexOptions.RightToLeft);
            Console.WriteLine(r);

You can see it working here.

edited Sep 22 '15 at 01:28

answered Sep 22 '15 at 01:13

Arthur Castro

610
6
18

That regex means: `[[\d]` a digit or a "[" **+** `]*` a "]" repeated once or more times **+** `\d*` a digit once or more times. Test against the string "`see-you-456-tomorrow[`" to see the difference – Mariano Sep 22 '15 at 01:36
The result will be 456, the first match (right to left). What you want the result to be Ben & @Mariano? – Arthur Castro Sep 22 '15 at 01:37
@ArthurCastro That's the expected result, yes. Nice job on the first try! – Ben Sep 22 '15 at 01:48

Mariano · Accepted Answer · 2015-09-22T01:24:54.527

0

Quantifiers

A digit repeated once or more times

\d+

A digit repeated from 3 times to 5 times

\d{3,5}

A digit repeated at least 5 times

\d{5,}

You can read more about quantifiers in this tutorial

As you may have realized,

              see-1-you-2-morrow
                                ^
                                |
\d* matches an empty position (here)
    between the last character and the end of string

edited Sep 22 '15 at 01:24

answered Sep 22 '15 at 01:19

Mariano

6,423
4
31
47

You're saying "repeated"... to clarify do you mean "repeated" like "111"? or just *any* digit like "456"? – Ben Sep 22 '15 at 01:37
`\d+` is what you want.. The `+` repeats the regex construct. It will match "`456`" – Mariano Sep 22 '15 at 01:38
The `\d+` gave me what I needed. Thanks! – Ben Sep 22 '15 at 01:44

Regex mismatch issue

2 Answers2

Quantifiers