Regex to match on specific string and number values

Question

I'm trying to create a regex that will allow a specific string only (Test1) for example or numeric values. How would I do this? I have tried the following but it doesn't work and won't notice the string part. What am I doing wrong with this regex?

^Test1[0-9]*$

I want to use it in an MVC model validation attribute:

  [RegularExpression("^Test1[0-9]*$", ErrorMessage = "The value must be numeric or be Test1.")]

Did you mean to write ^(Test1|[0-9]*)$? To match Test1 or zero or more digits? — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Sep 21, 2016 at 14:55
(Test1) for example or numeric values => ^(?:Test1|[0-9]+)$ — revo
– revo, Commented Sep 21, 2016 at 14:55
No unless you enclose branches in parentheses. @ThePerplexedOne — revo
– revo, Commented Sep 21, 2016 at 14:57
@revo What? OP isn't asking to capture any groups. My expression is fine. — ThePerplexedOne
– ThePerplexedOne, Commented Sep 21, 2016 at 14:58

Wiktor Stribiżew · Accepted Answer · 2016-09-21 15:16:06Z

4

Your pattern - ^Test1[0-9]*$ - matches an entire string with the following contents: Test1 followed with 0 or more digits.

If you meant to match either Test1 or zero or more digits as a whole string, you need

^(Test1|[0-9]*)$

Details:

^ - start of string
( - grouping construct start:
- Test1 - either Test1
- | - or (this is an alternation operator)
- [0-9]* - zero or more digits
) - grouping construct end (it forcesd ^ and $ anchors be applied to each of the alternatives above)
$ - end of string.

answered Sep 21, 2016 at 15:16

Wiktor Stribiżew

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3 Comments

Theomax Over a year ago

Thank you for the detailed answer - how would I modify your suggestion to specify the number of digits must be 4? I tried the following but it doesn't work: ^Test1|[0-9]{4}+$

Wiktor Stribiżew Over a year ago

Use ^(Test1|[0-9]{4})$. Do not forget the parentheses, they are crucial here. Else, you'd need to repeat the anchors in every branch: ^Test1$|^[0-9]{4}$.

Faraz Over a year ago

@WiktorStribiżew thanks for the detailed answer. It helped me solve more problems.

pawel.panasewicz · Accepted Answer · 2016-09-21 15:00:19Z

1

How about | operator between Test1 and [0-9]*?
How about replacing * with + - thanks to that empty strings won't be catched?

Regex ^Test1|[0-9]+$ should match all Test1, 123, 0, 12345 and so on.

In terms of MVC - it has nothing to do with regex.

answered Sep 21, 2016 at 15:00

pawel.panasewicz

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2 Comments

Theomax Over a year ago

Agreed it is not related to MVC just wanted to add abit more context to the question :)

Wiktor Stribiżew Over a year ago

^Test1|[0-9]+$ also finds a match in Test1$%^&^%$## and _______________________________-5.

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