Another solution, if you want $year, $month, $day in lexical context and assign the data with $^N use a closure.

#!/usr/bin/perl
use strict;

my $foo_year = "2004-11-12 12:40:42";

test($foo_year);
test($foo_year);
test($foo_year);

{
  my ( $year, $month, $day );

  sub test {
    my ($date) = @_;
    print $date, "\n";
    $date =~ m/
    (\d+)  (?{ $year  = $^N })
    -
    (\d+)  (?{ $month = $^N })
    -
    (\d+)  (?{ $day   = $^N })
  /x;
    print "$year-$month-$day\n";
  }
}
__OUTPUT__
2004-11-12 12:40:42
2004-11-12
2004-11-12 12:40:42
2004-11-12
2004-11-12 12:40:42
2004-11-12
[download]