unless ( $result = my_sub() ) {
   # handle error condition
}

##</code><code>##

my $result;
unless ( my_sub(\$result) ) {
   # handle error condition
}

##</code><code>##

sub my_sub {
   my $r_result = shift;
   $$r_result = whatever();
   was_there_an_error() ? 0 : 1 ;
}