Perl程序中类似setuid的权限设置

   Perl 编写了一个系统的服务程序(见文章 另类的 Linux在线文本打印和基于 Perl的 Web Service )，开机时候利用 rc.d启动，但是运行时刻都是 root权限，对于脚本程序，比起二进制的ELF文件，毕竟更怕些，嘻，因为比较容易暴露源代码…

    为了保障运行的稳定性，也让系统更稳定一些，我们需要类似 setuid之类的函数，在不需要特权的时候，以一个伪用户权限运行。

    Perl 在处理这权限，用 $< 和 $>，如下：

$< The real uid of this process. (Mnemonic: it's the uid you came
        *from*, if you're running setuid.) You can change both the real
        uid and the effective uid at the same time by using
        POSIX::setuid(). Since changes to $< require a system call,
        check $! after a change attempt to detect any possible errors.

$> The effective uid of this process. Example:

            $< = $>; # set real to effective uid

            ($<,$>) = ($>,$<); # swap real and effective uid


        You can change both the effective uid and the real uid at the
        same time by using POSIX::setuid(). Changes to $> require a
        check to $! to detect any possible errors after an attempted
        change.

        (Mnemonic: it's the uid you went *to*, if you're running
        setuid.) $< and $> can be swapped only on machines supporting
        setreuid().

    简单的 $< 用法如下：

#!/usr/bin/perl

$> = 0;
system "whoami";

$> = 1000;
system "whoami";

$> = 0;
system "whoami";




    运行效果如下：

# ./test.pl
root
dorainm
root

#