Ruby Debugging

Catchpoints

• Normally, if an uncaught exception is thrown inside the debugged code, the debugger exits
• Catchpoints are the equivalent of breakpoints for exceptions
• 'catch <exception type>' will stop code when given exception type is thrown, allowing you to examine state that caused exception to be thrown
• Watch how this code causes the debugger to exit

• 
  #!/usr/local/bin/ruby
  
  class ZebraException < Exception; end 
  
  ENV['PATH'].split(/\:/).each do |path_entry|
    puts path_entry
    raise ZebraException, "crap!"
  end
  

• 
  % ruby -rdebug test-exception
  Debug.rb
  Emacs support available.
  
  test-exception:3:class ZebraException < Exception; end 
  (rdb:1) n
  test-exception:5:ENV['PATH'].split(/\:/).each do |path_entry|
  (rdb:1) n
  test-exception:6:  puts path_entry
  (rdb:1) n
  /Users/dougb/bin
  test-exception:7:  raise ZebraException, "crap!"
  (rdb:1) n
  test-exception:7: `crap!' (ZebraException)
  test-exception:7: crap! (ZebraException)
          from test-exception:5:in `each'
          from test-exception:5
  %
  

• A catchpoint is inserted and now we can stop the exit

• 
  % ruby -rdebug test-exception
  Debug.rb
  Emacs support available.
  
  test-exception:3:class ZebraException < Exception; end
  (rdb:1) catch ZebraException
  Set catchpoint ZebraException.
  (rdb:1) c
  /Users/dougb/bin
  test-exception:7: `crap!' (ZebraException)
          from test-exception:5
  test-exception:7:  raise ZebraException, "crap!"
  (rdb:1) p path_entry
  "/Users/dougb/bin"
  (rdb:1) n
  test-exception:7: crap! (ZebraException)
          from test-exception:5:in `each'
          from test-exception:5
  %