解释此perl代码，该代码在2个文件中显示公共行 [英] Explain this perl code which displays common lines in 2 files

问题描述

这两个文件共有一个perl单线显示行吗?

How does this perl one-liner display lines that 2 files have in common?

perl -ne 'print if ($seen{$_} .= @ARGV) =~ /10$/'  file1 file2

推荐答案

-n命令行选项将代码转换为等同于

The -n command line option transforms the code to something equivalent to

while ($ARGV = shift @ARGV) {
  open ARGV, $ARGV;
  LINE: while (defined($_ = <ARGV>)) {
    $seen{$_} .= @ARGV;
    print $_ if $seen{$_} =~ /10$/;
  }
}

在读取第一个文件时，scalar @ARGV是1.对于每一行，1将被附加到%seen条目.

While the first file is being read, scalar @ARGV is 1. For each line, 1 will be appended to the %seen entry.

在读取第二个文件时，scalar @ARGV是0.因此，如果一行位于文件1和文件2中，则该条目将看起来像1110000(在文件1中为3倍，在文件2中为4倍).

While the second file is being read, scalar @ARGV is 0. So if a line was in file 1 and in file2, the entry will look like 1110000 (it was 3× in file1, 4× in file2).

我们只想输出一条公共线.当在file2中首次出现一条公共行时，我们执行此操作，因此$seen{$_}为1110.这用正则表达式/10$/表示:字符串10必须出现在末尾.

We only want to output common lines exactly one time. We do this when a common line was first seen in file2, so $seen{$_} is 1110. This is expressed as the regex /10$/: The string 10 must appear at the end.

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