The key to this kind of problem is that when the line begins with a "continue-command"(plus) you want to process the rest of the line using the last "state" you were in, but when it doesnt begin with a "continue-command"(plus) you want to capture the new state, process the rest of the line with the new state, and remember that new state as the last_state for any following "continue-command"(plus) lines. Something like this

my $last_state=''; 

  while (my $line= <DATA>) { 
    chomp $line; 
    next unless ($line); 
    if (substr($line,0,1) eq '+') {
      # if line starts with a plus use last_state to process 
      process($last_state,substr($line,1));
      } 
    else { 
      # otherwise set last_state and process with it
      my @parts=split(' ',$line,2); 
      $last_state=$parts[0]; 
      process($last_state,$parts[1]);
      } 
  
    } # line 
sub process { 
  my $state=shift; 
  my $input=shift; 
  ... do stuff based on $state and $input ... 
  } # process
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