perl基础：perl中@_, 和 1,$2,...及其类似变量的含义

由于直接复制的原因，建议阅读原文：http://blog.sciencenet.cn/blog-634847-497909.html.

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1.@_含义

1)是perl中默认的数组变量

比如说你想移除数组中的一个元素赋值给一个变方法：你可以定义某个数组如 value=shift @abcd;

方法2：你没有定义任何数组
my $value=shift @_; 和上例等效
这里perl会隐式的选择@_

2）是sub子函数中的默认参数列表.

例如：
sub funct($$) {
($param1, $param2) = @_;
#Statement
}

再例如，有下面一段代码：
my max_number = &max(1,2);
print "1 and 2 ,the max number is max_number\n";
sub max{
my ( num2) = @_[0,1]; ## 取出参数列表中的元素。
........此处省略求max运算
}

在子函数中直接shift; 就可以从@_的前端弹出一个元素.

shift;
等于
shift @_;

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@_ is the list of incoming parameters to a sub. So if you write a sub, you refer to the first parameter in it as $_[0], the second parameter as $_[1] and so on. And you can refer to $#_ as the index number of the last parameter:
sub demo {
print "Called with ",#_+1," params\n";
print "First param was _[0]\n";

Note that the English module adds in the ability to refer to the special variables by other longer, but easier to remember, names such as @ARG for @_ and $. But use English; can have a detrimental performance effect if you're matching regular expressions against long incoming strings

2.$_含义

1) 为默认列表变量。在一个命令没有任何参数的时候，表示它从默认变量里读取。例如：等于 _;
2)默认模式匹配空间(pattern matching space)
s/.../.../;
等于
$_ =~ s/.../.../;

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Then any regular expression matches, chops (and lcs and many more) without a parameter, and even prints assume you want to work on     line = <FH>) {
  if ( line;
  }

Shortens to:
while (<FH>) {
  /Perl/ and
    print FHO ;
  print uc;
  }
3. 2,...等含义