Something like this? (simplified...)

#!/usr/bin/perl

use strict;
use warnings;

my $self = 'cat';
print "outside $self\n";
{
my $self = $self;
print " inside $self\n";
$self = 'dog' if not defined $ARGV[0];
print " inside $self\n";
}
print "outside $self\n";
[download]

Outputs:

outside cat
 inside cat
 inside dog
outside cat
[download]