August 2018
Beginner to intermediate
382 pages
7h 14m
Chinese
Content preview from Perl语言入门
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178
｜
第
9
章
在这里，我们不希望
.*
一举拿下所有东西。我们只要够用的一点就好了。如果量词
后面换成
?
，就会在第一次找到合适的位置时结束：
my $text = '<b>Fred</b> and <b>Barney</b>';
my $match_count = $text =~ s|<b>(.*?)</b>|\U$1|g; #
不贪婪
print "$match_count: $text\n";
现在得到两个成功匹配并按原意将名字改为大写的：
2: FRED and BARNEY
使用非贪婪量词后，正则表达式引擎不会一次找到底再逐步回退这样去浪费时间，它
直接找最接近的符合条件的部分（参考表
9-1
）。
表
9
-
1
：使用非贪婪修饰符的正则表达式量词
元字符
意义
??
匹配零个字符（没实际用处）
*?
零个或多个，越短越好
+?
一个或多个，越短越好
{3,}?
至少
3
个，越短越好
{3,5}
至少
3
个，最多
5
个，但也是越短越好
{3}?
正好
3
个
更为别致的单词边界符
\b
转义匹配“单词”和非“单词”字符间的交替边界。我们之前在第
7
章提过，
Perl
所说的单词和我们平时说的单词的定义不同。假设我们需要把字符串中每个单词的首
字母改为大写，第一个想法是把单词边界后的字母替换为它的大写版本：
my $string = "This doesn't capitalize correctly.";
$string =~ s/\b(\w)/\U$1/g;
print "$string\n"; ...
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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.