Michael,
You will inevitably be pointed to one of a myriad of modules on
CPAN to do this. The reason being is that, generally speaking, using regexes to parse dates has the same problems as IP addresses, email addresses, HTML, XML, etc. These modules may still use regexes but they are more robust and have considered far more edge cases then the casual user trying to solve the problem for the first time.
On the other hand - if you are absolutely sure of your data then using a regex may be a fine way to go.
my $year = (split m|[/ ]|, $date)[2];