正则表达式（Regular Expression）是一种强大的文本处理工具，用于匹配、查找、替换和验证字符串。下面我将通过实例来讲解正则表达式的基本语法和常见用法。
1. 基本匹配
正则表达式由普通字符（例如字母、数字）和特殊字符（称为元字符）组成。最简单的正则表达式就是普通字符，例如：
-
正则表达式
hello会匹配字符串中出现的第一个"hello"。
2. 元字符
元字符是正则表达式中具有特殊意义的字符。常见的元字符包括：
-
.匹配任意单个字符（除了换行符） -
^匹配字符串的开始 -
$匹配字符串的结束 -
*匹配前面的子表达式零次或多次 -
+匹配前面的子表达式一次或多次 -
?匹配前面的子表达式零次或一次 -
{n}匹配前面的子表达式恰好n次 -
{n,}匹配前面的子表达式至少n次 -
{n,m}匹配前面的子表达式至少n次，至多m次 -
[]字符集合，匹配所包含的任意一个字符 -
或，匹配两者之一 -
()分组，将多个字符组合成一个单元，并可捕获匹配的文本
3. 转义
如果你想要匹配元字符本身，需要使用反斜杠\进行转义。例如，匹配点号.，需要使用\.。
4. 字符类
用方括号[]表示，匹配括号内的任意一个字符。
-
[abc]匹配a、b或c -
[a-z]匹配任意小写字母 -
[0-9]匹配任意数字 -
[^abc]匹配除了a、b、c之外的任意字符（在字符类中的^表示否定）
5. 预定义字符类
-
\d匹配数字，等价于[0-9] -
\D匹配非数字，等价于[^0-9] -
\w匹配字母、数字、下划线，等价于[A-Za-z0-9_] -
\W匹配非字母、数字、下划线 -
\s匹配空白字符（空格、制表符、换行符等） -
\S匹配非空白字符
6. 实例
实例1：匹配邮箱地址
假设我们要匹配一个简单的邮箱地址，格式为：用户名@域名.后缀
-
用户名：可以包含字母、数字、点、下划线、减号，且不能以点开头或结尾，不能连续两个点。
-
域名：可以包含字母、数字、减号，且不能以减号开头或结尾。
-
后缀：一般为2-5个字母。
正则表达式：^[a-zA-Z0-9]+([._-]?[a-zA-Z0-9]+)*@[a-zA-Z0-9]+(-?[a-zA-Z0-9]+)*(\.[a-zA-Z]{2,5})+$
解释：
-
^表示字符串开始 -
[a-zA-Z0-9]+至少一个字母或数字开头 -
([._-]?[a-zA-Z0-9]+)*接下来可以是零个或多个以下结构：一个可选的点、下划线或减号，然后至少一个字母或数字。注意这里我们使用了?表示前面的字符可选，这样允许中间有点、下划线或减号，但不会连续两个点。 -
@匹配字面量@ -
[a-zA-Z0-9]+域名部分以至少一个字母或数字开头 -
(-?[a-zA-Z0-9]+)*之后可以跟零个或多个：一个可选的减号然后至少一个字母或数字，这样确保域名中可以有减号但不能连续减号或开头结尾有减号。 -
(\.[a-zA-Z]{2,5})+匹配一个点后跟2到5个字母，这个整体可以出现一次或多次（例如：.com、.co.uk） -
$字符串结束
注意：这只是一个简单的示例，实际邮箱地址更复杂，此表达式可能不覆盖所有情况。
实例2：匹配URL
假设我们要匹配HTTP/HTTPS的URL。
正则表达式：^https?://[^\s/$.?#].[^\s]*$
解释：
-
^https?匹配http或https，s可选 -
://匹配字面量 -
[^\s/$.?#]匹配一个不是空白字符、不是/、$、.、?、#的字符，确保域名部分不以这些字符开头 -
[^\s]*匹配任意非空白字符，直到字符串结束
实例3：匹配日期（YYYY-MM-DD）
正则表达式：^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])$
解释：
-
^\d{4}匹配4位数字的年份 -
-匹配字面量减号 -
(0[1-9]|1[0-2])匹配月份，01-09或10-12 -
-匹配字面量减号 -
(0[1-9]|[12][0-9]|3[01])匹配日期，01-09、10-29、30-31
实例4：匹配手机号码（以中国手机为例）
中国手机号码：1开头，第二位是3-9，后面9位数字。
正则表达式：^1[3-9]\d{9}$
实例5：替换HTML标签
如果我们想移除字符串中所有的HTML标签，可以使用替换功能，将匹配到的标签替换为空字符串。
正则表达式：<[^>]+>
解释：匹配以<开头，后面跟着一个或多个不是>的字符，然后以>结尾。
基本语法
1. 字面量匹配
hello # 匹配 "hello"
test123 # 匹配 "test123"2. 特殊字符转义
<span class="token special-escape escape">\.</span> # 匹配点号字符
<span class="token special-escape escape">\\</span> # 匹配反斜杠
<span class="token special-escape escape">\$</span> # 匹配美元符号常用元字符
| 元字符 | 说明 | 示例 |
|---|---|---|
. |
匹配任意单个字符 | a.c 匹配 "abc", "a c", "a-c" |
^ |
匹配字符串开始 | ^Hello 匹配以 "Hello" 开头的字符串 |
$ |
匹配字符串结束 | end$ 匹配以 "end" 结尾的字符串 |
\d |
匹配数字 | \d\d 匹配 "12", "45" 等 |
\w |
匹配字母、数字、下划线 | \w+ 匹配单词 |
\s |
匹配空白字符 | \s+ 匹配空格、制表符等 |
量词
| 量词 | 说明 | 示例 |
|---|---|---|
* |
0次或多次 | ab*c 匹配 "ac", "abc", "abbc" |
+ |
1次或多次 | ab+c 匹配 "abc", "abbc" |
? |
0次或1次 | colou?r 匹配 "color" 或 "colour" |
{n} |
恰好n次 | a{3} 匹配 "aaa" |
{n,} |
至少n次 | a{2,} 匹配 "aa", "aaa" 等 |
{n,m} |
n到m次 | a{2,4} 匹配 "aa", "aaa", "aaaa" |
字符类
1. 自定义字符类
<span class="token char-class"><span class="token char-class-punctuation punctuation">[</span>aeiou<span class="token char-class-punctuation punctuation">]</span></span> # 匹配任意元音字母
<span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">0<span class="token range-punctuation operator">-</span>9</span><span class="token char-class-punctuation punctuation">]</span></span> # 匹配任意数字
<span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">a<span class="token range-punctuation operator">-</span>z</span><span class="token range">A<span class="token range-punctuation operator">-</span>Z</span><span class="token char-class-punctuation punctuation">]</span></span> # 匹配任意字母2. 排除字符类
<span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token char-class-negation operator">^</span>aeiou<span class="token char-class-punctuation punctuation">]</span></span> # 匹配非元音字母
<span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token char-class-negation operator">^</span><span class="token range">0<span class="token range-punctuation operator">-</span>9</span><span class="token char-class-punctuation punctuation">]</span></span> # 匹配非数字字符分组和捕获
1. 基本分组
<span class="token group punctuation">(</span>abc<span class="token group punctuation">)</span><span class="token quantifier number">+</span> # 匹配 "abc", "abcabc" 等2. 非捕获分组
<span class="token group punctuation">(?:</span>abc<span class="token group punctuation">)</span><span class="token quantifier number">+</span> # 匹配但不捕获分组3. 命名捕获组
<span class="token group punctuation">(?<<span class="token group-name variable">year</span>></span><span class="token char-set class-name">\d</span><span class="token quantifier number">{4}</span><span class="token group punctuation">)</span>-<span class="token group punctuation">(?<<span class="token group-name variable">month</span>></span><span class="token char-set class-name">\d</span><span class="token quantifier number">{2}</span><span class="token group punctuation">)</span> # 命名捕获年月实际应用示例
1. 邮箱验证
<span class="token anchor function">^</span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">a<span class="token range-punctuation operator">-</span>z</span><span class="token range">A<span class="token range-punctuation operator">-</span>Z</span><span class="token range">0<span class="token range-punctuation operator">-</span>9</span>._%+-<span class="token char-class-punctuation punctuation">]</span></span><span class="token quantifier number">+</span>@<span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">a<span class="token range-punctuation operator">-</span>z</span><span class="token range">A<span class="token range-punctuation operator">-</span>Z</span><span class="token range">0<span class="token range-punctuation operator">-</span>9</span>.-<span class="token char-class-punctuation punctuation">]</span></span><span class="token quantifier number">+</span><span class="token special-escape escape">\.</span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">a<span class="token range-punctuation operator">-</span>z</span><span class="token range">A<span class="token range-punctuation operator">-</span>Z</span><span class="token char-class-punctuation punctuation">]</span></span><span class="token quantifier number">{2,}</span><span class="token anchor function">$</span>示例匹配：
2. 手机号码验证
<span class="token anchor function">^</span>1<span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">3<span class="token range-punctuation operator">-</span>9</span><span class="token char-class-punctuation punctuation">]</span></span><span class="token char-set class-name">\d</span><span class="token quantifier number">{9}</span><span class="token anchor function">$</span>示例匹配：
-
13812345678
-
15987654321
3. URL 提取
https<span class="token quantifier number">?</span>://<span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token char-class-negation operator">^</span><span class="token char-set class-name">\s</span>/$.?#<span class="token char-class-punctuation punctuation">]</span></span><span class="token char-set class-name">.</span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token char-class-negation operator">^</span><span class="token char-set class-name">\s</span><span class="token char-class-punctuation punctuation">]</span></span><span class="token quantifier number">*</span>示例匹配：
4. 日期匹配
<span class="token char-set class-name">\d</span><span class="token quantifier number">{4}</span>-<span class="token char-set class-name">\d</span><span class="token quantifier number">{2}</span>-<span class="token char-set class-name">\d</span><span class="token quantifier number">{2}</span>示例匹配：
-
2023-12-25
-
1990-01-01
5. HTML 标签提取
<<span class="token group punctuation">(</span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">a<span class="token range-punctuation operator">-</span>z</span><span class="token char-class-punctuation punctuation">]</span></span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">a<span class="token range-punctuation operator">-</span>z</span><span class="token range">0<span class="token range-punctuation operator">-</span>9</span><span class="token char-class-punctuation punctuation">]</span></span><span class="token quantifier number">*</span><span class="token group punctuation">)</span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token char-class-negation operator">^</span>><span class="token char-class-punctuation punctuation">]</span></span><span class="token quantifier number">*</span>><span class="token group punctuation">(</span><span class="token char-set class-name">.</span><span class="token quantifier number">*?</span><span class="token group punctuation">)</span></<span class="token backreference keyword">\1</span>>示例匹配：
-
<div>内容</div> -
<p class="text">段落</p>
6. 密码强度验证
<span class="token anchor function">^</span><span class="token group punctuation">(?=</span><span class="token char-set class-name">.</span><span class="token quantifier number">*</span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">a<span class="token range-punctuation operator">-</span>z</span><span class="token char-class-punctuation punctuation">]</span></span><span class="token group punctuation">)</span><span class="token group punctuation">(?=</span><span class="token char-set class-name">.</span><span class="token quantifier number">*</span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">A<span class="token range-punctuation operator">-</span>Z</span><span class="token char-class-punctuation punctuation">]</span></span><span class="token group punctuation">)</span><span class="token group punctuation">(?=</span><span class="token char-set class-name">.</span><span class="token quantifier number">*</span><span class="token char-set class-name">\d</span><span class="token group punctuation">)</span><span class="token group punctuation">(?=</span><span class="token char-set class-name">.</span><span class="token quantifier number">*</span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span>@$!%*?&<span class="token char-class-punctuation punctuation">]</span></span><span class="token group punctuation">)</span><span class="token char-class"><span class="token char-class-punctuation punctuation">[</span><span class="token range">A<span class="token range-punctuation operator">-</span>Z</span><span class="token range">a<span class="token range-punctuation operator">-</span>z</span><span class="token char-set class-name">\d</span>@$!%*?&<span class="token char-class-punctuation punctuation">]</span></span><span class="token quantifier number">{8,}</span><span class="token anchor function">$</span>要求：
-
至少8个字符
-
包含大小写字母
-
包含数字
-
包含特殊字符
不同语言中的使用
Python 示例
<span class="token comment"># 匹配邮箱</span>
pattern <span class="token operator">=</span> <span class="token string">r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'</span>
email <span class="token operator">=</span> <span class="token string">"user@example.com"</span>
<span class="token keyword">if</span> re<span class="token punctuation">.</span><span class="token keyword">match</span><span class="token punctuation">(</span>pattern<span class="token punctuation">,</span> email<span class="token punctuation">)</span><span class="token punctuation">:</span>
<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">"邮箱格式正确"</span><span class="token punctuation">)</span>
<span class="token comment"># 提取所有数字</span>
text <span class="token operator">=</span> <span class="token string">"价格是123元，重量是45公斤"</span>
numbers <span class="token operator">=</span> re<span class="token punctuation">.</span>findall<span class="token punctuation">(</span><span class="token string">r'\d+'</span><span class="token punctuation">,</span> text<span class="token punctuation">)</span>
<span class="token keyword">print</span><span class="token punctuation">(</span>numbers<span class="token punctuation">)</span> <span class="token comment"># ['123', '45']</span>JavaScript 示例
<span class="token comment">// 验证手机号码</span>
<span class="token keyword">const</span> phonePattern <span class="token operator">=</span> <span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">^1[3-9]\d{9}$</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">;</span>
<span class="token keyword">const</span> phone <span class="token operator">=</span> <span class="token string">"13812345678"</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>phonePattern<span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span>phone<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"手机号码格式正确"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// 替换文本</span>
<span class="token keyword">const</span> text <span class="token operator">=</span> <span class="token string">"今天是2023-12-25"</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> newText <span class="token operator">=</span> text<span class="token punctuation">.</span><span class="token function">replace</span><span class="token punctuation">(</span><span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">(\d{4})-(\d{2})-(\d{2})</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">,</span> <span class="token string">"$1年$2月$3日"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>newText<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// "今天是2023年12月25日"</span>Java 示例
<span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>regex<span class="token punctuation">.</span></span><span class="token operator">*</span></span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">RegexExample</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token comment">// 验证邮箱</span>
<span class="token class-name">String</span> emailPattern <span class="token operator">=</span> <span class="token string">"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$"</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> email <span class="token operator">=</span> <span class="token string">"user@example.com"</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>email<span class="token punctuation">.</span><span class="token function">matches</span><span class="token punctuation">(</span>emailPattern<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"邮箱格式正确"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// 提取URL</span>
<span class="token class-name">String</span> text <span class="token operator">=</span> <span class="token string">"访问 https://example.com 获取更多信息"</span><span class="token punctuation">;</span>
<span class="token class-name">Pattern</span> urlPattern <span class="token operator">=</span> <span class="token class-name">Pattern</span><span class="token punctuation">.</span><span class="token function">compile</span><span class="token punctuation">(</span><span class="token string">"https?://[^\\s/$.?#].[^\\s]*"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Matcher</span> matcher <span class="token operator">=</span> urlPattern<span class="token punctuation">.</span><span class="token function">matcher</span><span class="token punctuation">(</span>text<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span>matcher<span class="token punctuation">.</span><span class="token function">find</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"找到URL: "</span> <span class="token operator">+</span> matcher<span class="token punctuation">.</span><span class="token function">group</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>实用技巧
-
使用在线测试工具：如 regex101.com 测试和调试正则表达式
-
注释复杂表达式：使用
(?#注释)或x模式添加注释 -
性能优化：避免过度使用回溯，尽量使用具体字符类
-
测试边界情况：确保正则表达式处理各种边界情况
这个教程涵盖了正则表达式的基础知识和常见应用场景。建议在实际使用中多加练习，逐步掌握这个强大的文本处理工具！
「点点赞赏，手留余香」
声明：本文为原创文章，版权归旷野小站所有，欢迎分享本文，转载请保留出处！
