The Devel::ebug module by Léon Brocard provides an object-oriented interface to Perl’s debugger facility. It’s a work in progress, so what I say here might be different by the time you read this. The main features should still be there, though.

It comes with its own terminal-based debugger named ebug. It’s a bit of an odd name until you realize how you call it. The missing d in the name comes from Perl’s -d switch.

  $ perl -d:ebug program.pl

I don’t need to use the -d switch, though, since I can call it directly with the ebug program, but I have to call it by quoting the entire command line:^†

  $ ebug "add_numbers.pl 5 6"
  * Welcome to Devel::ebug 0.46
  main(add_numbers.pl#3):
  my $n = shift @ARGV;
  ebug: x @ARGV
  --- 5
  --- 6

  main(add_numbers.pl#3):
  my $n = shift @ARGV;
  ebug: s
  main(add_numbers.pl#4):
  my $m = $ARGV[0];
  ebug: x $n
  --- 5

The ebug program is really just a wrapper around Devel::ebug::Console, and I can call Devel::ebug in many different ways. At the core of its design is a detached process. The backend runs the program under the debugger, and the frontend communicates with it over TCP. This means, for instance, I can debug the program on a different machine than on the one it’s running.

The Devel::ebug::HTTP module uses the same Devel::ebug backend, but sets up a mini web server.^‡ I start the ebug_http the same way I did with the console version, but instead of giving me a prompt, it tells me the URL I need to access to see the debugger:^§

  $ ebug_http "add_numbers.pl 4 5"
  You can connect to your server at http://albook.local:8321

The web page shows me a bare bones debugger interface (Figure 4-4). Remember, this is basically a proof of concept, but even as that it’s very impressive and can serve as the basis for your own tailor-made programs.

Figure 4-4.  The Devel::ebug::HTTP module lets me debug a program on a remote server through my browser