August 2018
Beginner to intermediate
382 pages
7h 14m
Chinese
Content preview from Perl语言入门
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152
｜
第
8
章
如果你不喜欢
/s
修饰符把所有
.
都修改为匹配任意字符，你可以换用自己的字符
集，比如改用
[\D\d]
或
[\S\s]
。所有数字字符以及非数字字符合起来就是任意字符
了。
用
/x
加入辅助空白字符
/x
修饰符允许我们在模式里随意加上空白字符，从而使它更易阅读、理解：
/-?[0-9]+\.?[0-9]*/ #
都挤在一起，很难看清是什么意思
/ -? [0-9]+ \.? [0-9]* /x #
加入辅助空白后好多了
由于加上
/x
后模式里可以随意插入空白，所以原来表示空格和制表符本身的空白字
符就失去了意义，
Perl
会直接忽略。但我们总可以通过转义方式变通实现，比如在空
格前面加上反斜线或者使用
\t
等等。不过最常用的还是
\s
（或者
\s*
，抑或
\s+
），
表示匹配空白字符。当然，我们也可以直接转义空格字符（印刷品上难以示例），或
者使用等效的写法
\x{20}
或
\040
。
记住，
Perl
还会把模式中出现的注释当作白字符直接忽略，所以我们可以在模式中写
上注释，帮助阅读者理解意图：
/
-? #
一个可有可无的减号
[0-9]+ #
小数点前必须出现一个或多个数字
\.? #
一个可有可无的小数点
[0-9]* #
小数点后面的数字，有没有都没关系
/x
由于井号是注释的标记，所以如果要表示井号字符本身时，就得写成
\#
，或者使用字
符集
[#]
：
/
[0-9]+ #
小数点前必须出现一个或多个数字
[#] #
井号字符本身
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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.