Byebug

Byebug is a simple to use, feature rich debugger for Ruby. It uses the TracePoint API for execution control and the 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 offers many of the traditional debugging features such as:

Stepping: Running your program one line at a time.
Breaking: Pausing the program at some event or specified instruction, to examine the current state.
Evaluating: Basic REPL functionality, although pry does a better job at that.
Tracking: Keeping track of the different values of your variables or the different lines executed by your program.

Build Status

Linux macOS Windows

Requirements

Required: MRI 2.2.0 or higher.
Recommended: MRI 2.3.0 or higher.

Install

gem install byebug

Or if you use bundler,

bundle add byebug --group "development, test"

Usage

From within the Ruby code

Simply drop

byebug

wherever you want to start debugging and the execution will stop there. If you were debugging Rails, for example, you would add byebug to your code.

def index
  byebug
  @articles = Article.find_recent
end

And then start a Rails server.

bin/rails s

Once the execution gets to your byebug command you will get a debugging prompt.

From the command line

If you want to debug a Ruby script without editing it, you can invoke byebug from the command line.

byebug myscript.rb

Byebug's commands

Command     | Aliases      | Subcommands
----------- |:------------ |:-----------
`backtrace` | `bt` `where` |
`break`     |              |
`catch`     |              |
`condition` |              |
`continue`  |              |
`delete`    |              |
`debug`     |              |
`disable`   |              | `breakpoints` `display`
`display`   |              |
`down`      |              |
`edit`      |              |
`enable`    |              | `breakpoints` `display`
`finish`    |              |
`frame`     |              |
`help`      |              |
`history`   |              |
`info`      |              | `args` `breakpoints` `catch` `display` `file` `line` `program`
`irb`       |              |
`kill`      |              |
`list`      |              |
`method`    |              | `instance`
`next`      |              |
`pry`       |              |
`quit`      |              |
`restart`   |              |
`save`      |              |
`set`       |              | `autoirb` `autolist` `autopry` `autosave` `basename` `callstyle` `fullpath` `histfile` `histsize` `linetrace` `listsize` `post_mortem` `savefile` `stack_on_error` `width`
`show`      |              | `autoirb` `autolist` `autopry` `autosave` `basename` `callstyle` `fullpath` `histfile` `histsize` `linetrace` `listsize` `post_mortem` `savefile` `stack_on_error` `width`
`source`    |              |
`step`      |              |
`thread`    |              | `current` `list` `resume` `stop` `switch`
`tracevar`  |              |
`undisplay` |              |
`up`        |              |
`var`       |              | `all` `constant` `global` `instance` `local`

Semantic Versioning

Byebug tries to follow semantic versioning and tries to bump major version only when backwards incompatible changes are released. Backwards compatibility is targeted to pry-byebug and any other plugins relying on byebug.

Getting Started

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

Related projects

pry-byebug adds next, step, finish, continue and break commands to pry using byebug.
ruby-debug-passenger adds a rake task that restarts Passenger with Byebug connected.
minitest-byebug starts a byebug session on minitest failures.
sublime_debugger provides a plugin for ruby debugging on Sublime Text.
atom-byebug provides integration with the Atom editor [EXPERIMENTAL].

Contribute

See Getting Started with Development.

You can also help byebug by leaving a small (or big) tip through Liberapay.

Credits

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

@ko1, author of the awesome TracePoint API for Ruby.
@cldwalker, debugger's maintainer.
@denofevil, author of debase, the starting point of this.
@kevjames3 for testing, bug reports and the interest in the project.
@FooBarWidget for working and helping with remote debugging.

jemmyw/byebug