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.

##</code><code>##

# file foo.pl
print $var,"\n";

##</code><code>##

# requiring code
$var = 'foo';
require 'foo.pl';

##</code><code>##

# requiring code
my $var = 'foo';
require 'foo.pl';

##</code><code>##

our $var;
for $var ( qw(foo bar quux) ) {
    require 'foo.pl';
}