Byebug

Byebug is a simple to use and feature rich debugger for Ruby. It uses the TracePoint API for execution control and the Debug Inspector API for call stack navigation. Therefore, Byebug doesn't depend on internal core sources. Byebug is also fast because it is developed as a C extension and reliable because it is supported by a full test suite.

The debugger permits the ability to understand 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.

For enterprise

Byebug for enterprise is available via the Tidelift Subscription. Learn more.

Build Status

Requirements

Required: MRI 2.5.0 or higher.
Recommended: MRI 2.6.4 or higher (MRI 2.6.0 to 2.6.3 contain a regression causing unbalanced call/return events in some cases, breaking the next command).

Install

gem install byebug

Alternatively, if you use bundler:

bundle add byebug --group "development, test"

Usage

From within the Ruby code

Simply include byebug wherever you want to start debugging and the execution will stop there. For example, if you were debugging Rails, 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 receive 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` `w` `where`
`break`	`b`
`catch`	`cat`
`condition`	`cond`
`continue`	`c` `cont`
`continue!`	`c!` `cont!`
`debug`
`delete`	`del`
`disable`	`dis`	`breakpoints` `display`
`display`	`disp`
`down`
`edit`	`ed`
`enable`	`en`	`breakpoints` `display`
`finish`	`fin`
`frame`	`f`
`help`	`h`
`history`	`hist`
`info`	`i`	`args` `breakpoints` `catch` `display` `file` `line` `program`
`interrupt`	`int`
`irb`
`kill`
`list`	`l`
`method`	`m`	`instance`
`next`	`n`
`pry`
`quit`	`q`
`quit!`	`q!`
`restart`
`save`	`sa`
`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`
`skip`	`sk`
`source`	`so`
`step`	`s`
`thread`	`th`	`current` `list` `resume` `stop` `switch`
`tracevar`	`tr`
`undisplay`	`undisp`
`untracevar`	`untr`
`up`
`var`	`v`	`all` `constant` `global` `instance` `local`

Semantic Versioning

Byebug attempts to follow semantic versioning and 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.

Funding

Subscribe to Tidelift to ensure byebug stays actively maintained, and at the same time get licensing assurances and timely security notifications for your open source dependencies.

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

Security contact information

Please use the Tidelift security contact to report a security vulnerability. Tidelift will coordinate the fix and disclosure.

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.