use Time::Local;
my $userdate         = "Jan 12 2007";
my @months           = qw (Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec);
@monthname {@months} = 0 .. 11;
my ($m, $day, $year) = split /\s+/, $userdate;

defined $monthname {$m}  or die "no valid month\n";
my $month = $monthname {$m};
for ($day, $year) { /^\d+$/ or die "$_ invalid\n" }

my $timestamp = eval { local $SIG{__DIE__}; timelocal (0, 0, 0, $day, $month, $year) };

if ($@) {
    warn "invalid date: $@\n"
} else {
    my @ltime     = localtime ($timestamp);
    printf "date: %02d %s %04d\n", $ltime [3], $months [$ltime[4]], $ltime [5] + 1900;
}
print "done\n";
__END__