sub foo {
   trace enter;  #logs entry into the sub if loglevel is 'trace'
   eval {
      sub_that_might_die(shift @_);
   };
   if ($@) {
      debug caught; #logs catching of exception if loglevel is 'debug'
      warn $@;
      return;
   }
   trace leave; #logs departure from sub if loglevel is 'trace'
}