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解析PHP正则表达式元字符

Jun 13, 2016 am 11:03 AM
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PHP正则表达式元字符都有什么呢?我们在使用PHP正则表达式元字符的时候需要注意什么呢?那么这里就向你详细介绍下PHP正则表达式元字符的种类以及使用的方法等等。

PHP正则表达式元字符的种类

◆大括号

◆加号

◆星号

◆问号

PHP正则表达式元字符具体的使用:

PHP正则表达式元字符在PHP正则表达式中一类有特殊意义的字符,用来描述其前导字符(即元字符前面的字符)在被匹配的对象中出现的方式。元字符本身是一个个单一的字符,但是不同或者相同的元字符组合起来可以构成大的元字符。

◆大括号:大括号用来精确指定匹配元字符出现的次数

例如"/pre{1,5}/"表示匹配的对象可以是"pre"、"pree"、"preeeee"这样在"pr"后面出现1个到5个"e"的字符串。或者"/pre{,5}/"代表pre出现0此到5次之间。

◆加号:"+"字符用来匹配元字符前的字符出现一次或者多次

例如"/ac+/"表示被匹配的对象可以是"act"、"account"、"acccc"等在"a"后面出现一个或者多个"c"的字符串。"+"相当于"{1,}"。

◆星号:"*"字符用来匹配元字符前的字符出现零次或者多次

例如"/ac*/"表示被匹配的对象可以是"app"、"acp"、"accp"等在"a"后面出现零个或者多个"c"的字符串。"*"相当于"{0,}"。

◆问号:"?"字符用来匹配元字符前的字符出现零次或者1次

例如"/ac?/"表示匹配的对象可以是"a"、"acp"、"acwp"这样在"a"后面出现零个或者1个"c"的字符串。"?"在正则表达式中还有一个非常重要的作用,即"贪婪模式"。

PHP正则表达式元字符的简单介绍就向你讲解到这里,希望对你了解和掌握PHP正则表达式元字符有所帮助。


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