>perl -wMstrict -le
"print send_values({name => 'Joe Doe', addr => '123 4th St.'});
 print send_values({
   addr => '666 Mobil Ave.',  phone => '321-432-5432'
   });
 print send_values({
   name => 'Moe Foe', addr => '7 6th Rd.', phone => '432-543-6543'
   });
 ;;
 sub send_values {
   my ($hr_args) = @_;
   ;;
   my %defaults = (
     name => undef,  addr => undef,  phone => '(not given)',
     );
   ;;
   my %args = (%defaults, %$hr_args);
   my @bad = grep !defined($args{$_}), keys %args;
   return undef
     if @bad and warn((caller 0)[3], qq{: bad arg(s): @bad});
   ;;
   return
     sprintf qq{<n>%s</n> <a>%s</a> <p>%s</p>},
     @args{ qw(name addr phone) };
   }
"
<n>Joe Doe</n> <a>123 4th St.</a> <p>(not given)</p>
main::send_values: bad arg(s): name at -e line 1.
Use of uninitialized value in print at -e line 1.

<n>Moe Foe</n> <a>7 6th Rd.</a> <p>432-543-6543</p>