As is mentioned elsewhere, regular expressions almost certanily not what you want. But, having said that, if you really want a regular expression, here is how it is built:
31 day months
(0[13578]|1[02])[\/.](0[1-9]|[12][0-9]|3[01])[\/.](18|19|20)[0-9]{2}
30 day months
(0[469]|11)[\/.](0[1-9]|[12][0-9]|30)[\/.](18|19|20)[0-9]{2}
February 1-28 always valid
(02)[\/.](0[1-9]|1[0-9]|2[0-8])[\/.](18|19|20)[0-9]{2}
February 29 also valid on leap years
(02)[\/.]29[\/.](((18|19|20)(04|08|[2468][048]|[13579][26]))|2000)
which means it would be this if you put it all together:
((0[13578]|1[02])[\/.](0[1-9]|[12][0-9]|3[01])[\/.](18|19|20)[0-9]{2})|((0[469]|11)[\/.](0[1-9]|[12][0-9]|30)[\/.](18|19|20)[0-9]{2})|((02)[\/.](0[1-9]|1[0-9]|2[0-8])[\/.](18|19|20)[0-9]{2})|((02)[\/.]29[\/.](((18|19|20)(04|08|[2468][048]|[13579][26]))|2000))
This version is a little shorter, but a little harder to understand.
((0[13578]|1[02])[\/.]31[\/.](18|19|20)[0-9]{2})|((01|0[3-9]|1[1-2])[\/.](29|30)[\/.](18|19|20)[0-9]{2})|((0[1-9]|1[0-2])[\/.](0[1-9]|1[0-9]|2[0-8])[\/.](18|19|20)[0-9]{2})|((02)[\/.]29[\/.](((18|19|20)(04|08|[2468][048]|[13579][26]))|2000))
These scripts are long and unmaintainable. It should be clear that this isn’t a good idea, but it is possible.
Caveats:
- range 1800-2099 (more can be added without too much difficulty, but requires changes in 4-6 disparate places)
- requires 2 digit months and days (the strictness could be removed from the expression in ~8 places)
[\/.]
as seperators (8 places)- Hasn’t been tested (we could check it against all digit combinations and compare with the javascript date function? [proof that we’re reinventing the wheel])