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HomeBackend DevelopmentPHP TutorialPHP正则表达式入门教程[转]

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       正则表达式,大家在开发中应该是经常用到,现在很多开发语言都有正则表达式的应用,比如javascript,java,.net,php等等,我今天就把我对正则表达式的理解跟大家唠唠,不当之处,请多多指教!

需要知道的术语??下面的术语你知道多少?

Δ  定界符

Δ  字符域

Δ  修饰符

Δ  限定符

Δ  脱字符

Δ  通配符(正向预查,反向预查)

Δ  反向引用

Δ  惰性匹配

Δ  注释

Δ  零字符宽

       我们什么时候使用正则表达式呢?不是所有的字符操作都用正则就好了,php在某些方面用正则反而影响效率。当我们遇到 复杂文本数据的解析时候,用正则是比较好的选择。

      正则表达式在处理复杂字符操作的时候,可以 提高工作效率,也在一定程度 节省你的代码量。

       我们在使用正则表达式的时候,复杂的正则表达式会加大代码的 复杂度,让人很 难理解。所以我们有的时候需要在正则表达式内部添加注释。

通用模式

 ¤ 定界符,通常使用 "/"做为定界符开始和结束,也可以使用"#"。

  什么时候使用"#"呢?一般是在你的字符串中有 很多"/"字符的时候,因为正则的时候这种字符需要转义,比如uri。

     使用"/"定界符的代码如下.

$regex = '/^http:\/\/([\w.]+)\/([\w]+)\/([\w]+)\.html$/i';$str = 'http://www.youku.com/show_page/id_ABCDEFG.html';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

    preg_match中的$matches[0]将包含与整个模式匹配的字符串。 

    使用"#"定界符的代码如下.这个时候对"/"就不转义!

$regex = '#^http://([\w.]+)/([\w]+)/([\w]+)\.html$#i';$str = 'http://www.youku.com/show_page/id_ABCDEFG.html';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

  ¤ 修饰符:用于改变正则表达式的行为。

     我们看到的('/^http:\/\/([\w.]+)\/([\w]+)\/([\w]+)\.html/i')中的最后一个"i"就是修饰符,表示忽略大小写,还有一个我们经常用到的是"x"表示忽略空格。

贡献代码:

  

$regex = '/HELLO/';$str = 'hello word';$matches = array();if(preg_match($regex, $str, $matches)){    echo 'No i:Valid Successful!',"\n";}if(preg_match($regex.'i', $str, $matches)){    echo 'YES i:Valid Successful!',"\n";}

 

  ¤ 字符域:[\w]用方括号扩起来的部分就是字符域。

  ¤ 限定符:如[\w]{3,5}或者[\w]*或者[\w]+这些[\w]后面的符号都表示限定符。现介绍具体意义。

     {3,5}表示3到5个字符。{3,}超过3个字符,{,5}最多5个,{3}三个字符。

     * 表示0到多个

     + 表示1到多个。

  ¤ 脱字符号

      ^:

          > 放在字符域(如:[^\w])中表示否定(不包括的意思)??“反向选择”

          >  放在表达式之前,表示以当前这个字符开始。(/^n/i,表示以n开头)。

      注意,我们经常管"\"叫"跳脱字符"。用于转义一些特殊符号,如".","/"

 

通配符(lookarounds):断言某些字符串中某些字符的存在与否!

lookarounds分两种:lookaheads(正向预查 ?=)和lookbehinds(反向预查?

> 格式:

正向预查:(?=) 相对应的 (?!)表示否定意思

反向预查:(?

前后紧跟字符

$regex = '/(?<=c)d(?=e)/';  /* d 前面紧跟c, d 后面紧跟e*/$str = 'abcdefgk';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

否定意义:

$regex = '/(?<!c)d(?!e)/';  /* d 前面不紧跟c, d 后面不紧跟e*/$str = 'abcdefgk';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

 

>字符宽度:零

验证零字符代码

$regex = '/HE(?=L)LO/i';$str = 'HELLO';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

打印不出结果!

$regex = '/HE(?=L)LLO/i';$str = 'HELLO';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

 能打印出结果!

说明:(?=L)意思是HE后面紧跟一个L字符。但是(?=L)本身不占字符,要与(L)区分,(L)本身占一个字符。

捕获数据

没有指明类型而进行的分组,将会被获取,供以后使用。

> 指明类型指的是通配符。所以只有圆括号起始位置没有问号的才能被捕捉。

> 在同一个表达式内的引用叫做反向引用。

> 调用格式: \编号(如\1)。

$regex = '/^(Chuanshanjia)[\w\s!]+\1$/';    $str = 'Chuanshanjia thank Chuanshanjia';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

 

> 避免捕获数据

   格式:(?:pattern)

   优点:将使有效反向引用数量保持在最小,代码更加、清楚。

>命名捕获组

   格式:(?P) 调用方式 (?P=组名)

$regex = '/(?P<author>chuanshanjia)[\s]Is[\s](?P=author)/i';$str = 'author:chuanshanjia Is chuanshanjia';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

运行结果

惰性匹配(记住:会进行两部操作,请看下面的原理部分)

  格式:限定符?

     原理:"?":如果前面有限定符,会使用最小的数据。如“*”会取0个,而“+”会取1个,如过是{3,5}会取3个。

先看下面的两个代码:

代码1.

<?php$regex = '/heL*/i';$str = 'heLLLLLLLLLLLLLLLL';if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

  结果1.

 

代码2

<?php$regex = '/heL*?/i';$str = 'heLLLLLLLLLLLLLLLL';if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

  结果2

 

代码3,使用“+”

<?php$regex = '/heL+?/i';$str = 'heLLLLLLLLLLLLLLLL';if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

 结果3

代码4,使用{3,5}

<?php$regex = '/heL{3,10}?/i';$str = 'heLLLLLLLLLLLLLLLL';if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

 结果4

正则表达式的注释

格式:(?# 注释内容)

用途:主要用于复杂的注释

 贡献代码:是一个用于连接MYSQL数据库的正则表达式

$regex = '/    ^host=(?<!\.)([\d.]+)(?!\.)                 (?#主机地址)\|    ([\w!@#$%^&*()_+\-]+)                       (?#用户名)\|    ([\w!@#$%^&*()_+\-]+)                       (?#密码)(?!\|)$/ix';$str = 'host=192.168.10.221|root|123456';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

 

特殊字符

 

特殊字符 解释
* 0到多次
+ 1到多次还可以写成{1,}
? 0或1次
. 匹配除换行符外的所有单个的字符
\w [a-zA-Z0-9_]
\s 空白字符(空格,换行符,回车符)[\t\n\r]
\d [0-9]

 

原文:http://www.cnblogs.com/baochuan/archive/2012/03/12/2391135.html

 

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