s/^\s+|\s+$//g;

##</code><code>##

%hash = map { $v = $hash{$_}; s/^\s+|\s+$//g for $v,$_; $_,$v } keys %hash;

# another way which doesn't copy the entire has, just the keys

for my $key (keys %hash) {
    my $value = delete $hash{$key};
    for ($key, $value) {
        s/^\s+|\s+$//g;
    }
    $hash{$key} = $value;
}