スゲい簡単なPerl入門 - 1stDay ref: http://qiita.com/items/ba7a1d337cfa586eb24d

file1.txt

$ perl test
Name "main::hoge" used only once: possible typo at test line 3.

file3.txt

$ perl test.pl
$bar is in hoge package
$bar is in hoo package
$bar is in main package

file5.txt

$ perl test.pl
$bar is in hoge package
$bar is in hoo package
$bar is in main package

test.pl

#!/usr/bin/perl

package main;

$main::bar = '$bar is in main package';

{
  package hoge;

  $hoge::bar = '$bar is in hoge package';
  print $hoge::bar,"\n";
}
{
  package hoo;

  $hoo::bar = '$bar is in hoo package';
  print $hoo::bar,"\n";
}

print $main::bar;