use Time::Piece;

my @have = ('1/2/2003', '2/31/2014', '4/31/2015', '4/5/2006', '10/11/2012');

for my $dt (@have) {
  my $d = eval { Time::Piece->strptime($dt, '%m/%d/%Y') } or warn "Invalid date $dt\n";
  next unless $d;
  my $ymd = $d->ymd();
  print "$dt => $ymd\n";
}