Question

Let’s suppose I have a very simple Ruby program:

require 'rubygems'
require 'ruby-debug'
x = 1
debugger
puts x

When execution hits the ‘debugger’ command it properly halts and gives me the ‘rdb’ prompt.

Now: my goal is to have the program print 2 instead of 1. How to accomplish this? If I type ‘help’ then rdebug tells me:

ruby-debug help v0.10.4
Type 'help <command-name>' for help on a specific command

Available commands:
backtrace  delete   enable  help  method  putl     set     trace    
break      disable  eval    info  next    quit     show    undisplay
catch      display  exit    irb   p       reload   step    up       
condition  down     finish  kill  pp      restart  thread  var      
continue   edit     frame   list  ps      save     tmate   where

The ‘set’ command looks promising … but:

(rdb:1) help set
Modifies parts of the ruby-debug environment. Boolean values take
on, off, 1 or 0.
You can see these environment settings with the "show" command.

-- 
List of set subcommands:
--  
set annotate -- Set annotation level
set args -- Set argument list to give program being debugged when it is started
set autoeval -- Evaluate every unrecognized command
set autolist -- Execute 'list' command on every breakpoint
set autoirb -- Invoke IRB on every stop
set autoreload -- Reload source code when changed
set basename -- Report file basename only showing file names
set callstyle -- Set how you want call parameters displayed
set debuggertesting -- Used when testing the debugger
set forcestep -- Make sure 'next/step' commands always move to a new line
set fullpath -- Display full file names in frames
set history -- Generic command for setting command history parameters
set keep-frame-bindings -- Save frame binding on each call
set linetrace+ -- Set line execution tracing to show different lines
set linetrace -- Set line execution tracing
set listsize -- Set number of source lines to list by default
set trace -- Display stack trace when 'eval' raises exception
set width -- Number of characters the debugger thinks are in a line    

No dice. What to do?

I looked at the Official ruby-debug doc and I looked at the RailsGuides Debugging Rails Applications doc but didn’t see the answer.

Answer 1

You need to use eval or p and then finish to continue through the script. Something like:

(rdb:1) p x=2
2
(rdb:1) finish
2