my %Months = (Dec => 12);
my $date = 'Dec  1 2016 18:15';
my @pcs = split " ", $date;
$date = sprintf "%02d %02d %d %s",$Months{$pcs[0]}, @pcs[1..3];
print "date: '$date'\n";
__END__
date: '12 01 2016 18:15'