141 lines
4.2 KiB
Markdown
141 lines
4.2 KiB
Markdown
---
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stage: none
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group: unassigned
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
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---
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# Pry debugging
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## Invoking pry debugging
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To invoke the debugger, place `binding.pry` somewhere in your
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code. When the Ruby interpreter hits that code, execution stops,
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and you can type in commands to debug the state of the program.
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When debugging code in another process like Puma or Sidekiq, you can use `binding.pry_shell`.
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You can then connect to this session by using the [pry-shell](https://github.com/meinac/pry-shell) executable.
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You can watch [this video](https://www.youtube.com/watch?v=Lzs_PL_BySo), for more information about
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how to use the `pry-shell`.
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## `byebug` vs `binding.pry`
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`byebug` has a very similar interface as `gdb`, but `byebug` does not
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use the powerful Pry REPL.
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`binding.pry` uses Pry, but lacks some of the `byebug`
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features. GitLab uses the [`pry-byebug`](https://github.com/deivid-rodriguez/pry-byebug)
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gem. This gem brings some capabilities `byebug` to `binding.pry`, so
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using that gives you the most debugging powers.
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## `byebug`
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Check out [the docs](https://github.com/deivid-rodriguez/byebug) for the full list of commands.
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You can start the Pry REPL with the `pry` command.
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## `pry`
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There are **a lot** of features present in `pry`, too much to cover in
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this document, so for the full documentation head over to the [Pry wiki](https://github.com/pry/pry/wiki).
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Below are a few features definitely worth checking out, also run
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`help` in a pry session to see what else you can do.
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### State navigation
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With the [state navigation](https://github.com/pry/pry/wiki/State-navigation)
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you can move around in the code to discover methods and such:
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```ruby
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# Change context
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[1] pry(main)> cd Pry
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[2] pry(Pry):1>
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# Print methods
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[2] pry(Pry):1> ls -m
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# Find a method
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[3] pry(Pry):1> find-method to_yaml
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```
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### Source browsing
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You [look at the source code](https://github.com/pry/pry/wiki/Source-browsing)
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from your `pry` session:
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```ruby
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[1] pry(main)> $ Array#first
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# The above is equivalent to
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[2] pry(main)> cd Array
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[3] pry(Array):1> show-source first
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```
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`$` is an alias for `show-source`.
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### Documentation browsing
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Similar to source browsing, is [Documentation browsing](https://github.com/pry/pry/wiki/Documentation-browsing).
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```ruby
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[1] pry(main)> show-doc Array#first
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```
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`?` is an alias for `show-doc`.
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### Command history
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With <kbd>Control</kbd> + <kbd>R</kbd> you can search your [command history](https://github.com/pry/pry/wiki/History).
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## Stepping
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To step through the code, you can use the following commands:
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- `break`: Manage breakpoints.
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- `step`: Step execution into the next line or method. Takes an
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optional numeric argument to step multiple times.
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- `next`: Step over to the next line within the same frame. Also takes
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an optional numeric argument to step multiple lines.
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- `finish`: Execute until current stack frame returns.
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- `continue`: Continue program execution and end the Pry session.
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## Callstack navigation
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You also can move around in the callstack with these commands:
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- `backtrace`: Shows the current stack. You can use the numbers on the
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left side with the frame command to navigate the stack.
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- `up`: Moves the stack frame up. Takes an optional numeric argument
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to move multiple frames.
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- `down`: Moves the stack frame down. Takes an optional numeric
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argument to move multiple frames.
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- `frame <n>`: Moves to a specific frame. Called without arguments
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displays the current frame.
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## Short commands
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When you use `binding.pry` instead of `byebug`, the short commands
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like `s`, `n`, `f`, and `c` do not work. To reinstall them, add this
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to `~/.pryrc`:
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```ruby
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if defined?(PryByebug)
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Pry.commands.alias_command 's', 'step'
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Pry.commands.alias_command 'n', 'next'
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Pry.commands.alias_command 'f', 'finish'
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Pry.commands.alias_command 'c', 'continue'
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end
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```
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## Repeat last command
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You can repeat the last command by just hitting the <kbd>Enter</kbd>
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key (e.g., with `step` or`next`), if you place the following snippet
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in your `~/.pryrc`:
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```ruby
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Pry::Commands.command /^$/, "repeat last command" do
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_pry_.run_command Pry.history.to_a.last
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end
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```
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`byebug` supports this out-of-the-box.
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