https://blog.csdn.net/ahilll/article/details/82712694

foreach (<STDIN>){
    chomp;
    if (/gao/){
        print "$_ was matched ‘gao‘\n";
    }
}

上面使用了默认的参数变量$，它表示foreach迭代的每一行数据；上面还简写的正则匹配方式/gao/，它等价于$ =~ m/gao/。

如果要自己定义参数， 必须是$_ = "somevalue";

my $value = "value";
my $_= $value;
if (/gao/){
  print "yes"
}

perl 正则表达式