January 2021
Intermediate to advanced
505 pages
9h 45m
Chinese
Content preview from PHP编程：第4版
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正则表达式
｜
113
果你的地区有排序序列
ch
，可以使用这个字符来匹配
s
、
t
或者
ch
：
[st[.ch.]]
最后的字符类扩展是
等价类
（
equivalence class
）， 用
[=
和
=]
包含起来。等价类匹配和当
前地区相同顺序的字符，例如，本地定义
a
、
á
和
ä
字符类，它们拥有相同的排序序列，
则对于它们中的任何一个，对应的等价类是
[=a=]
。
锚
锚（
anchor
）将匹配限制在字符串中的特定位置（锚不匹配目标字符串中的实际字符）。
表
4-8
列举了正则表达式支持的锚。
表4-8：锚
锚 匹配
^
字符串开始
$
字符串结束
[[:<:]]
单词开始
[[:>:]]
单词结束
\b
单词边界（
\w
和
\W
之间或者字符串的开头、结尾）
\B
非单词边界（
\w
和
\w
之间或者
W
和
\W
之间）
\A
字符串开始
\Z
字符串结尾，或者换行符
\n
之前
\z
字符串结尾
^
一行的开头（如果
/m
标签生效，换行符
\n
后面）
$
一行的结尾（如果
/m
标签生效，换行符
\n
前面）
单词边界指在一个空白符和一个标识符（字母数字或者下画线）之间的位置 ：
preg_match("/[[:<:]]gun[[:>:]]/", "the Burgundy exploded"); //
返回
false
preg_match("/gun/", "the Burgundy exploded"); //
返回
true
注意，字符串的开头和结尾也可以作为单词边界。
量词和贪婪
正则表达式的量词通常是
贪婪
的，就是当遇到一个量词时，正则表达式引擎会尽可能地
匹配这个模式，例如 ：
preg_match("/(<.*>)/", ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.