Perl包和模块

Perl的包package是用来提供命名空间的方式，一个package从package关键子开始，到文件结尾、eval结尾或者另一个 package开始时结束。默认情况下，在一个package中不能访问其他package定义的符号（变量、函数等），除非用use导入其他 package的符号表。

一个package的名字A，且文件名是A.pm，那么A就是一个Perl Module模块。

perlfaq8 What's the difference between require and use?

    1) do $file is like eval `cat $file`, except the former
    1.1: searches @INC and updates %INC.
    1.2: bequeaths an *unrelated* lexical scope on the eval'ed code.

    2) require $file is like do $file, except the former
    2.1: checks for redundant loading, skipping already loaded files.
    2.2: raises an exception on failure to find, compile, or execute $file.

    3) require Module is like require "Module.pm", except the former
    3.1: translates each "::" into your system's directory separator.
    3.2: primes the parser to disambiguate class Module as an indirect object.

    4) use Module is like require Module, except the former
    4.1: loads the module at compile time, not run-time.
    4.2: imports symbols and semantics from that package to the current one.

    5) In general, you usually want use and a proper Perl module.