Wayne
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要注意Perl系统变量值的变化
Wayne
posted @ Mon, 10 Dec 2012 10:27:55 +0000
in Experience
, 3424 readers
忘了专业点的说法怎么叫了，这里说的系统变量就是指那些 $_, $1, $# 之类的默认设置了的变量。一直以来被告诫要注意的是$_这个变量，一个while循环一个if判断什么的，有可能改变它的值。因为一直注意，倒也没遇到太大障碍。
今天栽在另一个变量上了，$1。语句是这样的：
s/$1/$hash{$1}/gi if /(\w+)/;
执行后发现总是被替换为空字符串。难道是 hash里面没值？我于是改成了：
s/$1/$hash{$1}/gi if (/(\w+)/ && defined $hash{$1} );
结果还是一样。
进行调试，把相关的值都打出来，发现各个值都取得完全没问题，唯独在 s/xxx/yyyy/gi 这步上出错了。
仔细观察了下substitution的形式特征，我想起来xxx这部分可以是regex的，比如我常用来交换位置的那种做法：
s/(xxx)(yyyy)/$2$1/g
在这样一句中，很明显 $1,$2的值由前面所决定。回到我出错的这句，估计也是这个原因了。第一个 $1，它取的if中的regex捕捉到的内容，第二个 作为hash的key的$1，它取的是xxx这个位置捕捉的内容。(话说xxx这个位置专业点的叫法是啥来着……）。做个实验验证下：
if (/(\w+)/ && defined $hash{$1} ){
$replacement = $hash{$1};
s/$1/$replacement/gi;
}
实验通过，这样果然管用。
Mon, 10 Dec 2012 13:04:36 +0000
有时候我很讨厌Perl这一点
本来觉得不需要再声明变量的，结果发现还是需要很丑陋的声明一个新的变量
Fri, 05 Jan 2024 11:48:33 +0000
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Fri, 05 Jan 2024 11:49:04 +0000
Pavzi.com is a startup by passionate webmasters and bloggers who have a passion for providing engaging content that is accurate, interesting, and worthy to read. pavzi.com We are more like a web community where you can find different information, resources, and topics on day-to-day incidents or news. We provide you with the finest web content on every topic possible with the help of the editorial and content team.
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