使用php中的preg_Match函数获取所选单词形式字符串之前的数字

$string = "Gold 5.0mm Rolo Chain 18" In";

<?php

ini_set('display_errors', 1);
$string='Gold 5.0mm Rolo Chain 18" In';
preg_match_all("/([d.]+)(?:mm|")/", $string,$matches);
print_r($matches);// its 1 index will return your desired result

<?php
ini_set('display_errors', 1);
$string='Gold 5.0mm Rolo Chain 18" In';
preg_match_all("/[d.]+(?=mm|")/", $string,$matches);
print_r($matches);