--- title: Debugger --- Debugger ======== Rubinius includes a reference Ruby source-level debugger. Invoking in Code ---------------- The Rubinius debugger can be invoked from code by embedding a call to start the debugger Consider the following code in app.rb class Toast attr_accessor :setting def initialize require 'debugger' Debugger.start @setting = :brown end end p Toast.new.setting Running the code in Rubinius would produce the following: $ rbx app.rb | Breakpoint: Toast#initialize at app.rb:5 (15) | 5: Debugger.start debug> help help: Show information about debugger commands b, break, brk: Set a breakpoint at a point in a method tb, tbreak, tbrk: Set a temporary breakpoint d, delete: Delete a breakpoint n, next: Move to the next line or conditional branch s, step: Step into next method call or to next line ni, nexti: Move to the next bytecode instruction f, frame: Make a specific frame in the call stack the current frame c, cont, continue: Continue running the target thread bt, backtrace: Show the current call stack p, eval: Run code in the current context dis, disassemble: Show the bytecode for the current method i, info: Show information about things set: Set a debugger config variable show: Display the value of a variable or variables debug> bt | Backtrace: | 0 Toast#initialize at app.rb:5 (15) | 1 main.__script__ at app.rb:11 (46) | 2 Rubinius::CodeLoader#load_script(debug) at kernel/delta/codeloader.rb:67 (44) | 3 Rubinius::CodeLoader.load_script(name) at kernel/delta/codeloader.rb:91 (40) | 4 Rubinius::Loader#script at kernel/loader.rb:460 (79) | 5 Rubinius::Loader#main at kernel/loader.rb:571 (64) | 6 Rubinius::Loader.main at kernel/loader.rb:609 (33) | 7 Object#__script__ at kernel/loader.rb:621 (60) debug> n | Breakpoint: Toast#initialize at app.rb:6 (16) | 6: @setting = :brown debug> n | Breakpoint: Toast#initialize at app.rb:7 (21) | 7: @kind = :rye debug> p @setting = :light_brown $d0 = :light_brown debug> c :light_brown Help for the debugger commands is available by typing `help` when in the debugger. Invoking from the Command Line ------------------------------ The Rubinius debugger can be invoked from the command line and will present the debugger prompt just before loading the script specified on the command line. Consider the following Ruby code in bug.rb: def problem_code puts "I have a problem" a = 1 + 2 puts "a math problem" unless a == 4 end problem_code To debug this code, start the debugger from the command line with the `-Xdebug` option. $ rbx -Xdebug bug.rb | Breakpoint: Rubinius::Loader#debugger at kernel/loader.rb:424 (34) | 424: Debugger.start debug> b Object#problem_code:2 * Unable to find method 'problem_code' in Object | Would you like to defer this breakpoint to later? [y/n] y | Defered breakpoint created. debug> c | Resolved breakpoint for Object#problem_code | Set breakpoint 2: bug.rb:2 (+0) | Breakpoint: Object#problem_code at bug.rb:2 (0) | 2: puts "I have a problem" debug> n I have a problem | Breakpoint: Object#problem_code at bug.rb:3 (9) | 3: a = 1 + 2 debug> n | Breakpoint: Object#problem_code at bug.rb:4 (16) | 4: puts "a math problem" unless a == 4 debug> p a = 4 $d0 = 4 debug> n | Breakpoint: main.__script__ at bug.rb:7 (17) | 7: problem_code debug> c As you can see, executing `p a = 4` in the debugger changes the value of the local variable `a` and affects the execution of the Ruby code.