August 2018
Beginner to intermediate
382 pages
7h 14m
Chinese
Content preview from Perl语言入门
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140
｜
第
7
章
$_ = "aa11bb";
if (/(.)\g{–1}11/) {
print "It matched!\n";
}
在这个基础上，如果再加一个捕获分组，会改变原来的分组编号，使用绝对编号书写
的模式可能需要重新确认配对顺序。而使用相对编号的反向引用则不用改动，它只关
心它左侧从近到远的分组，只要这个相对距离不变，编号就不用变。所以增加一个分
组后，原来的编号照旧：
use v5.10;
$_ = "xaa11bb";
if (/(.)(.)\g{–1}11/) {
print "It matched!\n";
}
择一匹配
模式中的竖线字符
|
，我们也叫它“或”，表示择一匹配，要么左侧部分匹配，要么
右侧部分匹配。如果左侧模式匹配失败，那就尝试右侧模式：
foreach ( qw(fred betty barney dino) ) {
if ( /fred|barney/ ) {
print "$_ matched\n";
}
}
这段程序会打印两个名字，第一次是左侧部分，第二次是右侧部分：
fred
barney
当然，我们可以提供更多选项：
foreach ( qw(fred betty barney dino) ) {
if ( /fred|barney|betty/ ) {
print "$_ matched\n";
}
}
于是打印三个名字：
fred
betty
barney
正则表达式
｜
141
竖线会把模式切成数块，有时候不是我们想要的效果。比如要寻找姓
Flintstones ...
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