October 2022
Beginner to intermediate
390 pages
7h 5m
Chinese
Content preview from Perl语言入门（第8版）
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152
第
8
章
用正则表达式进行匹配
在第
7
章里我们已经大致了解了正则表达式的基本概念。接下来，我们将会看到它是
如何融入
Perl
世界的。
用
m//
进行匹配
到目前为止，我们都是把正则表达式内容写在一对斜线内，比如
/fred/
。但这是简写
版本，完整写法是
m//
（模式匹配操作符），这里的
m
表示英文
match
（匹配）。和
之前看到过的
q w//
类似，你可以自行选择用于包围内容的一对字符作为定界符。所
以上面这个模式还可以改写为
m(fred)
、
m<fred>
、
m{fred}
或
m[fred]
这样使用成对
的定界符，或者像
m,fred,
、
m!fred!
、
m^fred^
这样使用不成对的定界符。
不成对定界符没有左右之分，模式两边用同样字符界定即可。
有个特例，如果选择一对斜线作为定界符，则可省略开头的
m
。
Perl
程序员不喜欢废
话，不加说明就是匹配，直接用一对斜线就行了，像
/fred/
这样。
当然，定界符要选模式中不会出现的字符。比如匹配网址时，标准写法是
/http:\/\//
，用于匹配网址的开头部分
"http://"
。但转义多了不仅令人眼花，修改
起来也容易错，因此可以改为
m%http://%
。但最常见的定界符是花括号。如果你用的
是程序员专用的文本编辑器，一般都可以从左括号跳到配对的右括号，在代码维护中
快速移动光标时就非常方便。
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