php 正则 抓取网页(php正则抓取网页数据教程这些问题，什么是正则表达式？)

　　php 正则 抓取网页(php正则抓取网页数据教程这些问题，什么是正则表达式？)

　　php正则抓取网页数据教程这些问题，

　　1、什么是正则表达式？正则表达式（regularexpression）是一种表达式，它规定了一个匹配数据的范围，而不仅仅是一个文本字符串。正则表达式是用一个反斜杠\r\n表示一个匹配，而用“\0\0”表示不匹配，正则表达式很重要，因为正则表达式也可以是任意语言的语法。

　　2、正则表达式的匹配范围怎么得到？正则表达式一般用在字符串操作，比如去除某些字符，某些不想要的字符等，比如要去除“\r\n”转义符，当输入正则表达式时，就要找到正则表达式后面的\r\n，所以\r\n的正则表达式，

　　3、正则表达式常用字符列表怎么得到？想要得到正则表达式中的某个字符的正则表达式表达式，就可以通过\d匹配到\d\d这些字符，然后再跟换。匹配到\d\d\d\0就会跳过这个字符，匹配到\d\d\d\d\0就没有任何这些字符，因为\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d这些字符是完全可以表示它所匹配的数据的，例如\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\d\。