my $foo;
{
    local $foo;
}

##</code><code>##

  Can't localize lexical variable $foo at ...

##</code><code>##

my %hash = (a => 'one', b => 'two', c => 'three' );
use Data::Dumper;
{
    local $hash{b} = 'Hello!';
    print Dumper \%hash;
}
print Dumper \%hash;