问题描述：

I want to extract 8 digit number from string using regex.

Test strings are

hi 82799162, 236232 (82342450), test data 8979

Required respective output should be

82799162, 82342450, null

I have tried following codes:

• preg_match(\'/[0-9]{8}$/\', $string, $match);
• preg_match(\'/\\d{8}$/\', $string, $match);

But it does not retrieve the number from 236232 (82342450).

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功能建议

我想使用正则表达式从字符串中提取8位数字。</ p>

测试 字符串是</ p>

hi 82799162 </ code>， 236232（82342450）</ code>， test data 8979 </ code> </ p>

</ blockquote>

所需的相应输出应为</ p>

82799162 </ code>， 82342450 </ code>， null </ code> </ p>

</ blockquote>

我试过以下代码：</ p>

• preg_match（\'/ [0-9] {8} $ /\'，$ string，$ match）; </ code> </ li>

• preg_match（\'/ \\ d {8} $ /\'，$ string，$ match）; </ code> </ li>

  </ ul>

  但它不会从 236232（82342450）中检索数字 ）</ code>。</ p>

  </ div>

  网友观点：

  The problem is with your $ sign, and it is used to indicate the end of your expression. So basically, with that expression, you are looking for a string which ends with a 8 digit number. But in your second test string; \'236232 (82342450)\', ends with a bracket, and therefore it doesn\'t match the criteria (does not end with a number).

  So remove the trailing $ and it will work.

  preg_match(\'/[0-9]{8}/\',$string,$match);
  

  Hope it helps!!

  If a regex is to capture exactly 8 digits, is must contain:

  • \\d{8} as a central part,
  • a \\\"before\\\" condition, ensuring that no digit occurs before your match,
  • an \\\"after\\\" condition, ensuring that no digit occurs after your match.

  One of possible solutions is to use negative lookbehind / lookahead:

  (?<!\\d)\\d{8}(?!\\d)
  

  Another option is word boundary assertions (at both ends):

  \\b\\d{8}\\b
  

  I think, regex like [0-9]{8} is not enough, as it captures also

  first 8 digits from a longer sequence of digits.

  Are you happy with that?

  正则表达式技巧与注意事项

  原创：打码日记（微信公众号ID：codelogs），欢迎分享，转载请保留出处。


  简介

  现如今，正则表达式几乎是程序员的必备技能了，它入手确实很容易，但如果你不仔细琢磨学习，会长期停留在正则最基本的用法层面上。
因此，本篇文章，我会介绍一些能用正则解决的场景，但这些场景如果全自己琢磨实现的话，需要花一些时间才能完成，或者就完全想不出来，另外也会介绍一些正则表达式的性能问题。

  匹配多个单词

  比如我想匹配zhangsan、lisi、wangwu这三个人名，这是一个很常见的场景，其实在正则里面也算基本功，但鉴于本人初入门时还是在网上搜索得到的答案，还是值得提一下的！
实现如下：