Perl 中的制表符扩展
刚刚遇到执行 制表符扩展 ，这里是代码：
1 while $string =~ s/\t+/' ' x (length($&) * 8 - length($`) % 8)/e;
我测试了它的工作原理，但我是一个菜鸟，无法理解这一点，有人愿意解释一下它为什么工作吗？或任何可以帮助我理解这一点的相关材料的指针将不胜感激，非常感谢。
just encountered the code for doing tab expansion in perl, here is the code:
1 while $string =~ s/\t+/' ' x (length(amp;) * 8 - length(just encountered the code for doing tab expansion in perl, here is the code:
) % 8)/e;
I tested it to be working, but I am too much a rookie to understand this, anyone care to explain a bit about why it works? or any pointer for related material that could help me understand this would be appreciated, Thanks a lot.
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Perl 允许您在正则表达式中嵌入任意代码作为替换表达式。
$&是最后一个模式匹配所匹配的字符串，在本例中是一定数量的制表符。$`是最后一个模式匹配所匹配的内容之前的字符串，这可以让您知道前一个文本的长度，以便您可以正确地将内容与列对齐。例如，针对字符串
"Something\t\t\tsomething else"运行此命令，$&为"\t\t\t"代码>，而<代码>$`是<代码>“某事”。length($&)为 3，因此最多需要 24 个空格，但length($`)%8为 1，因此要使其与列对齐每八个就增加 23 个空格。Perl lets you embed arbitrary code as replacement expressions in regexes.
$&is the string matched by the last pattern match—in this case, some number of tab characters.$`is the string preceding whatever was matched by the last pattern match—this lets you know how long the previous text was, so you can align things to columns properly.For example, running this against the string
"Something\t\t\tsomething else",$&is"\t\t\t", and$`is"Something".length($&)is 3, so there are at most 24 spaces needed, butlength($`)%8is 1, so to make it align to columns every eight it adds 23 spaces.正则表达式上的
e标志意味着将替换字符串 (' ' x (...etc...) 视为 Perl 代码，并为每个匹配解释/执行它因此，基本上查找有 1 个或多个 (+) 制表符 (\t) 的位置，然后执行小 perl 代码片段将这些制表符转换为空格。 snippet 计算匹配的制表符数量，将该数字乘以 8 以获得所需的空格数，但也会考虑匹配制表符之前可能出现的任何内容。
The
eflag on the regex means to treat the replacement string (' ' x (...etc...) as perl code and interpret/execute it for each match. So, basically look for any place there's 1 or more (+) tab characters (\t), then execute the small perl snippet to convert those tabs into spaces.The snippet calculates how many tabs were matched, multiplies that number by 8 to get the number of spaces required, but also accounts for anything which may have come before the matched tabs.