隐藏的Perl特性？

在Perl中有什么真正有用但深奥的语言特性，你实际上可以用来做有用的工作？

指南：

>尝试限制对Perl核心的答案，而不是CPAN
>请给出一个例子和一个简短的描述

隐藏的功能也发现在其他语言的隐藏的功能：

(这些都是从Corion’s answer)

> C

> Duff的设备
>便携性和标准性

> C#

>引号用于空格分隔的列表和字符串
>可别名命名空间

> Java

>静电助剂

> JavaScript

>职能是头等公民
>块范围和关闭
>通过变量间接调用方法和访问器

> Ruby

>通过代码定义方法

> PHP

>全面的在线文档
>魔法方法
>符号引用

> Python

>一行值交换
>能够用您自己的功能来替换核心功能

其他隐藏功能：

运算符：

> The bool quasi-operator
> The flip-flop operator

>也用于list construction

> The ++ and unary - operators work on strings
> The repetition operator
> The spaceship operator
> The || operator (and // operator) to select from a set of choices
> The diamond operator
> Special cases of the m// operator
> The tilde-tilde “operator”

报价结构：

> The qw operator
> Letters can be used as quote delimiters in q{}-like constructs
> Quoting mechanisms

语法和名称：

> There can be a space after a sigil
> You can give subs numeric names with symbolic references
> Legal trailing commas
> Grouped Integer Literals
> hash slices
> Populating keys of a hash from an array

模块，编译指示和命令行选项：

> use strict and use warnings
> Taint checking
> Esoteric use of -n and -p
> CPAN
> overload::constant
> IO::Handle module
> Safe compartments
> Attributes

变量：

> Autovivification
> The $[ variable
> tie
> Dynamic Scoping
> Variable swapping with a single statement

循环和流量控制：

> Magic goto
> for on a single variable
> continue clause
> Desperation mode

正则表达式：

> The G anchor
> (?{}) and ‘(??{})` in regexes

其他特性：

> The debugger
> Special code blocks such as BEGIN,CHECK,and END
> The DATA block
> New Block Operations
> Source Filters
> Signal Hooks
> map(twice)
> Wrapping built-in functions
> The eof function
> The dbmopen function
> Turning warnings into errors

其他技巧和元答案：

> cat files,decompressing gzips if needed
> Perl Tips

也可以看看：

> Hidden features of C
> Hidden features of C#
> Hidden features of C++
> Hidden features of Java
> Hidden features of JavaScript
> Hidden features of Ruby
> Hidden features of PHP
> Hidden features of Python
> Hidden features of Clojure

while(<$fh>)
{
  next if 1..1; # skip first record
  ...
}