perl -E 'say "undefined" if ! defined($var);'

##</code><code>##

perl -E '$var = 1; say "defined" if defined($var);'

##</code><code>##

perl -E 'say "Hello" if undef == 0;'

##</code><code>##

my $var;  # Currently $var is undef
print $var + 5, "\n"; # 5
print ++$var, "\n";   # 1

##</code><code>##

my %hash;
$hash{foo} = { bar => 'baz' };

##</code><code>##

%hash = (
  foo => {        # { is an anon-hash constructor
    bar => 'baz'
  }
);

##</code><code>##

my %hash;
$hash{foo}{bar} = 'baz';