use Test::More tests => 9;
while (<DATA>) {
    chomp;
    my ($s, @d) = split;
    my @n1 = $s =~ /((?<!\d)\d{6}(?!\d))/g;
    is_deeply(\@n1, \@d, $s);
}

__DATA__
kjsadjk123456aksda      123456
kjsadjk12345aksda
kjsadjk1234567aksda
asbda123456sdjasd23456asjdk     123456
asbda123456sdjasd234567asjdk    123456 234567
asbda123456sdjasd2345678asjdk   123456
asbda1234567sdjasd23456asjdk
asbda1234567sdjasd234567asjdk   234567
asbda1234567sdjasd2345678asjdk