【正则】Perl式正则完整匹配单词的正则如何写（前瞻）

/**
 * @param $str
 *
 * @return string
 */
function getValue($str)
{
    return preg_match('/(?:\D)(\d{8})(?:\D)/', $str, $matches) ? $matches[1] : '';
}

$arrStr = [
    '10208899', //有
    '#10208899', //有
    '#test^10208899', //有
    '#ff1020889900',//无
    '#0010208899',//无
    '#1020^10208899a',//有
    '#5566880&10208899f',//有
    'test?#10208899',//有
    '#10208899.'//有
];


foreach ($arrStr as $i => $str) {
    $value = getValue($str);
    echo "$i\t{$str}\t\t=>\t{$value}\n";
}

0	10208899		=>	
1	#10208899		=>	
2	#test^10208899		=>	
3	#ff1020889900		=>	
4	#0010208899		=>	
5	#1020^10208899a		=>	10208899
6	#5566880&10208899f		=>	10208899
7	test?#10208899		=>	
8	#10208899.		=>	10208899

function getValue($str)
{
    return preg_match('/(?:^
------解决思路----------------------
\D)(\d{8})(?:\D
------解决思路----------------------
$)/', $str, $matches) ? $matches[1] : '';
}

0	10208899		=>	10208899
1	#10208899		=>	10208899
2	#test^10208899		=>	10208899
3	#ff1020889900		=>	
4	#0010208899		=>	
5	#1020^10208899a		=>	10208899
6	#5566880&10208899f		=>	10208899
7	test?#10208899		=>	10208899
8	#10208899.		=>	10208899