Q: How to initialize debugger's state when starting

ruby-talk
1

Quick question:

  When starting a Ruby script in debug ('-rdebug') mode, what's the
simplest way to source an *rc-type file for, say, setting breakpoints?
Is it possible to do such during the invocation of `ruby` at the
command-line?

  Thanks,
    --J J-S

2

PS:
  (What I'm looking for is something with the effect of gdb's '-x'
option.)

3

Well after looking at debug.rb and trying to hack this in, I think your best bet is to look at one of the GUI debuggers (like Mr. Guid or Emacs) that talk to rdb and write a little frontend to it that would have this capability. Unfortunately, its setup like

def do_command
      input = readline
      ...
end

instead of

def do_command(input)
    ...
end

do_command(readline)

so I gave up trying to hack in this functionality directly. Good luck, though

···

On Feb 23, 2006, at 2:48 PM, Dumaiu wrote:

PS:
  (What I'm looking for is something with the effect of gdb's '-x'
option.)

4

Thanks. I _thought_ it would be a quick question... one of those
It's-so-obvious-I-can't-see-it moments. Because I'm not much for
IDE's, I think I'll wait to see if anyone else phones in and then maybe
take a bite out of debug.rb myself.

  -J

5

A short hack.
Make a copy of debug.rb and put these lines right after the Context
class.

class Context
  alias original_readline readline
  def readline(prompt, hist)
    @rc_file ||= File.readlines("debug.rc")
    if @rc_file.empty?
      original_readline(prompt, hist)
    else
      @rc_file.shift
    end
  end
end

Now create a file debug.rc with your desired breakpoint:
b 100
b 200

Start the debugger:
ruby -r./debug myscript.rb

6

Clever. I hope if someone comes up with a clean way to do this it gets merged in. It seems like a good idea.

···

On Feb 23, 2006, at 7:53 PM, Matthias Georgi wrote:

A short hack.
Make a copy of debug.rb and put these lines right after the Context
class.

class Context
  alias original_readline readline
  def readline(prompt, hist)
    @rc_file ||= File.readlines("debug.rc")
    if @rc_file.empty?
      original_readline(prompt, hist)
    else
      @rc_file.shift
    end
  end
end

Now create a file debug.rc with your desired breakpoint:
b 100
b 200

Start the debugger:
ruby -r./debug myscript.rb

7

Cool idea! However, if you don't have a debug.rc file, this doesn't
work. I tried to change it to handle that case as follows, but it's
still not quite right. Breakpoints I set in debug.rc are listed when I
run "b", but when I run "c" to continue execution, it doesn't stop at
them. However, if I issue the same break commands in the debugger,
they work. Can you see what I'm doing wrong?

class Context
  alias original_readline readline
  def readline(prompt, history)
    # If config file exists and hasn't been read yet, read it.
    if not @rc_file and File.exists?('debug.rc')
      @rc_file = File.readlines('debug.rc')
    end

    if @rc_file and not @rc_file.empty?
      @rc_file.shift
    else
      original_readline(prompt, history)
    end
  end
end

···

On 2/23/06, Matthias Georgi <matti.georgi@gmail.com> wrote:

A short hack.
Make a copy of debug.rb and put these lines right after the Context
class.

class Context
  alias original_readline readline
  def readline(prompt, hist)
    @rc_file ||= File.readlines("debug.rc")
    if @rc_file.empty?
      original_readline(prompt, hist)
    else
      @rc_file.shift
    end
  end
end

Now create a file debug.rc with your desired breakpoint:
b 100
b 200

Start the debugger:
ruby -r./debug myscript.rb

--
R. Mark Volkmann
Partner, Object Computing, Inc.