my $foo = "hello";
{
    # this affects the outer $foo
    $foo .= " world";
    my $foo = "something else";
    print "inner foo is $foo\n";
};
print "outer foo is $foo\n";

# produces

inner foo is something else
outer foo is hello world

##</code><code>##

my $foo = "defined";

BEGIN {
	print "foo is ", defined($foo) ? $foo : 'undef', " during BEGIN phase\n";
};

print "foo is ", defined($foo) ? $foo : undef, " at runtime\n";

# produces

foo is undef during BEGIN phase
foo is defined at runtime