如何跳到Perl中的特定输入行?

匹配运算符默认为使用 $_ 但是 <> 操作员不存储到 美元 默认情况下,除非它在while循环中使用,否则不会在其中存储任何内容 美元 .

从 perldoc perlop :

   I/O Operators
   ...

   Ordinarily you must assign the returned value to a variable, but there
   is one situation where an automatic assignment happens.  If and only if
   the input symbol is the only thing inside the conditional of a "while"
   statement (even if disguised as a "for(;;)" loop), the value is auto‐
   matically assigned to the global variable $_, destroying whatever was
   there previously.  (This may seem like an odd thing to you, but you’ll
   use the construct in almost every Perl script you write.)  The $_ vari‐
   able is not implicitly localized.  You’ll have to put a "local $_;"
   before the loop if you want that to happen.

   The following lines are equivalent:

       while (defined($_ = )) { print; }
       while ($_ = ) { print; }
       while () { print; }
       for (;;) { print; }
       print while defined($_ = );
       print while ($_ = );
       print while ;

   This also behaves similarly, but avoids $_ :

       while (my $line = ) { print $line }

<> 是唯一的魔法 while(<>) 构建。否则它不会分配给 $_ 所以 /include/ 正则表达式没有可匹配的内容。如果你用 -w Perl会告诉你:

Use of uninitialized value in pattern match (m//) at ....

您可以使用以下方法修复此问题:

$_ = <> until /include/;

要避免警告:

while(<>)
{
    last if /include/;
}