Question

I shall test a date string to see if it is one of these three:
dd-mm-yyyy OR yyyy OR dd-mm-yyyy/dd-mm-yyyy

I have combine these three, but the last one makes trouble since I cannot just match a single “/” using \Q/\E.

[0-9]{2}-[0-9]{2}-[0-9]{4}                                -> dd-mm-yyyy
[0-9]{4}                                                  -> yyyy
[0-9]{2}-[0-9]{2}-[0-9]{4}\Q/\E[0-9]{2}-[0-9]{2}-[0-9]{4} -> dd-mm-yyyy/dd-mm-yyyy

Combined they will give this expression:

([0-9]{2}-[0-9]{2}-[0-9]{4}|[0-9]{4}|[0-9]{2}-[0-9]{2}-[0-9]{4}\Q/\E[0-9]{2}-[0-9]{2}-[0-9]{4})

Question 1: How to only allow a single “/” between the dates?

Question 2: What does a ^ mean in the start of a regex and $ in the end? And should
I have it in mine

Br. Anders

UPDATE: (based on answers and comments below) Thanks! Two right answer. I marked the last one right since there also was a much smoother way to write what I had tried to do.

Language is probably XSLT or C#. It is in the CMS Umbraco that I place a regex to validate a default texstring/input field.

It acts a bit funny. There is no difference if I add a ^ to the start, therefore my question about that.

This string works perfekt: ^(?:\d{4}|\d{2}-\d{2}-\d{4}(?:/\d{2}-\d{2}-\d{4})?)$

Answer 1

Since you didn’t specify a language, I’ll suggest a working Perl version:

/^(?:\d{4}|\d{2}-\d{2}-\d{4}(?:\/\d{2}-\d{2}-\d{4})?)$/

Pattern explained:

• start at the first character of the string
• look for 4 digits ( \d{4} )
• OR
• a sequence of two digits dash two digits dash four digits
• optionally a slash two digits dash two digits dash four digits
• match the end of the string to make sure there is nothing else

I quoted the literal / writing \/ as it’s the most cross-language way to do it: in Perl it would be enough to choose different pattern delimiter to avoid the need of escaping.