Question

我想对一个单词进行两次准确的匹配。输出不应显示所有匹配项。如何使用perl？

open(a,"<file.txt");
open(c,">>output.txt");
while (my $line = <a>) {
        if($line =~ m/know{2}/) { 
          print $line;
        }
}
close(a);
close(c);

示例：如果file.txt有以下几行：

I know Perl.
I know English.
I know French.
I know Dutch.

预期结果应为：

I know Perl.
I know English.

Answer 1

您似乎在询问如何查找包含know的前两行。

为此，您需要跟踪先前找到的行数。

my $count = 0;
while (<>) {
   if (/know/) {
      print;
      last if ++$count == 2;
   }
}

Answer 2

尝试使用此Perl单线版

$ perl -ne 'BEGIN {$x=2} s/(know)/$x--;$kv{$_}=1/ge; if($x==0) { print keys %kv ; exit } ' cherry2.txt
I know Perl.
I know English.
$

$ cat cherry2.txt
I know Perl.
I know English.
I know French.
I know Dutch.
$

仅匹配两次

2 个答案: