How to write this regular expression?

[D H]

Peter Hansen wrote:
> could ildg wrote:
> 
>> I need a regular expression to check if a string matches it.
> 
> 
> Why do you think you need a regular expression?
> 
> If another approach that involved no regular expressions worked much 
> better, would you reject it for some reason?
> 
> -Peter

A regular expression will work fine for his problem.
Just match the digits separated by underscores using a regular 
expression, then afterward check if the values are valid.