use strict;

my $k = 1;
print "wanted: \$k = $k, got " . InvestigateValue() . "\n";

my $k = 2;
print "wanted: \$k = $k, got " . InvestigateValue() . "\n";

sub InvestigateValue
{
    return defined $k ? $k : 'undef';
}

##</code><code>##

wanted: $k = 1, got 1
wanted: $k = 2, got 2

##</code><code>##

wanted: $k = 1, got undef
wanted: $k = 2, got 2