Byebug

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Debugging in Ruby 2

Byebug is a simple to use, feature rich debugger for Ruby 2. It uses the new
TracePoint API for execution control and the new Debug Inspector API for call
stack navigation, so it doesn’t depend on internal core sources. It’s developed
as a C extension, so it’s fast. And it has a full test suite so it’s reliable.

It allows you to see what is going on inside a Ruby program while it executes
and can do four main kinds of things to help you catch bugs in the act:

  • Start your program or attach to it, specifying anything that might affect its behavior.
  • Make your program stop on specified conditions.
  • Examine what has happened when your program has stopped.
  • Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.

Install

$ gem install byebug

Usage

Simply drop

byebug

wherever you want to start debugging and the execution will stop there. If you
are debugging rails, start the server and once the execution gets to your
byebug command you will get a debugging prompt.

Former debugger or
ruby-debug users, notice:

  • Some gems (rails, rspec) implement debugging flags (-d, –debugger) that early require and start the debugger. These flags are a performance penalty and Byebug doesn’t need them anymore so my recommendation is not to use them.
  • The startup configuration file is now called .byebugrc instead of .rdebugrc.

What’s different from debugger

  • Works on Ruby 2.x and it doesn’t on 1.9.x.
  • Has no MRI internal source code dependencies, just a clean API.
  • Fixes all of debugger’s open bugs in its issue tracker and provides some enhancements, such as a markdown guide or the fact that byebug can now be placed at the end of a block or method call.
  • Actively mantained.
  • Editor agnostic: no external editor built-in support.
  • Pry command is built-in. No need of external gem like debugger-pry.

Semantic Versioning

Byebug tries to follow semantic versioning. Backwards
compatibility doesn’t seem like a critic issue for a debugger because it’s not
supposed to be used permanently by any program, let alone in production
environments. However, I still like the idea of giving some meaning to version
changes.

Byebug’s public API is determined by its set of commands

Command Aliases Subcommands
backtrace bt where
break
catch
condition
continue
delete
disable breakpoints display
display
down
edit
enable breakpoints display
finish
frame
help
info args breakpoints catch display file files global_variables instance_variables line locals program stack variables
irb
kill
list
method instance iv
next
p eval
pp
pry
ps
putl
quit exit
reload
restart
save
set args autoeval autoirb autolist autoreload basename callstyle callstyle forcestep fullpath history linetrace linetrace_plus listsize post_mortem stack_on_error testing verbose width
show args autoeval autoirb autolist autoreload basename callstyle callstyle commands forcestep fullpath history linetrace linetrace_plus listsize post_mortem stack_on_error verbose width
skip
source
step
thread current list resume stop switch
trace
undisplay
up
var class constant global instance local ct

Getting Started

Read byebug’s markdown
guide to get
started. Proper documentation will be eventually written.

Related projects

Future (possible) directions

  • JRuby support.
  • Libify and test byebug’s executable.
  • Add printers support.

Credits

Everybody who has ever contributed to this forked and reforked piece of
software, specially:

  • Kent Sibilev and Mark Moseley, original authors of ruby-debug.
  • Gabriel Horner, debugger’s mantainer.
  • Koichi Sasada, author of the new C debugging API for Ruby.
  • Dennis Ushakov, author of debase, the starting point of this.
  • @kevjames3 for testing, bug reports and the interest in the project.