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. Note that byebug works only for ruby 2.0.0 or newer. For debugging ruby 1.9.3 or older, use debugger.

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.

$ gem install byebug

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. In any case, both rails and rspec have deprecated these flags in their latest versions.
• The startup configuration file is now called .byebugrc instead of .rdebugrc.

Command     | Aliases      | Subcommands
----------- |:------------ |:-----------
`backtrace` | `bt` `where` |
`break`     |              |
`catch`     |              |
`condition` |              |
`continue`  |              |
`delete`    |              |
`disable`   |              | `breakpoints` `display`
`display`   |              |
`down`      |              |
`edit`      |              |
`enable`    |              | `breakpoints` `display`
`finish`    |              |
`frame`     |              |
`help`      |              |
`history`   |              |
`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`       |              | `autoeval` `autoirb` `autolist` `autoreload` `autosave` `basename` `callstyle` `forcestep` `fullpath` `histfile` `histsize` `linetrace` `tracing_plus` `listsize` `post_mortem` `stack_on_error` `testing` `verbose` `width`
`show`      |              | `autoeval` `autoirb` `autolist` `autoreload` `autosave` `basename` `callstyle` `forcestep` `fullpath` `histfile` `histsize` `linetrace` `tracing_plus` `listsize` `post_mortem` `stack_on_error` `testing` `verbose` `width`
`skip`      |              |
`source`    |              |
`step`      |              |
`thread`    |              | `current` `list` `resume` `stop` `switch`
`tracevar`  |              |
`undisplay` |              |
`up`        |              |
`var`       |              | `class` `constant` `global` `instance` `local`

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.

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

• 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.

• Write tests for remote debugging support.
• Add printers support.
• Libify and test byebug's executable.
• Support rubies other than MRI.

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

• @ko1, author of the awesome TracePoint API for Ruby.
• @cldwalker, debugger's mantainer.
• @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.