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Pry debugging
Invoking pry debugging
To invoke the debugger, place binding.pry somewhere in your
code. When the Ruby interpreter hits that code, execution stops,
and you can type in commands to debug the state of the program.
When debugging code in another process like Puma or Sidekiq, you can use binding.pry_shell.
You can then connect to this session by using the pry-shell executable.
You can watch this video, for more information about
how to use the pry-shell.
byebug vs binding.pry
byebug has a very similar interface as gdb, but byebug does not
use the powerful Pry REPL.
binding.pry uses Pry, but lacks some of the byebug
features. GitLab uses the pry-byebug
gem. This gem brings some capabilities byebug to binding.pry, so
using that gives you the most debugging powers.
byebug
Check out the docs for the full list of commands.
You can start the Pry REPL with the pry command.
pry
There are a lot of features present in pry, too much to cover in
this document, so for the full documentation head over to the Pry wiki.
Below are a few features definitely worth checking out, also run
help in a pry session to see what else you can do.
State navigation
With the state navigation you can move around in the code to discover methods and such:
# Change context
[1] pry(main)> cd Pry
[2] pry(Pry):1>
# Print methods
[2] pry(Pry):1> ls -m
# Find a method
[3] pry(Pry):1> find-method to_yaml
Source browsing
You look at the source code
from your pry session:
[1] pry(main)> $ Array#first
# The above is equivalent to
[2] pry(main)> cd Array
[3] pry(Array):1> show-source first
$ is an alias for show-source.
Documentation browsing
Similar to source browsing, is Documentation browsing.
[1] pry(main)> show-doc Array#first
? is an alias for show-doc.
Command history
With Control + R you can search your command history.
Stepping
To step through the code, you can use the following commands:
break: Manage breakpoints.step: Step execution into the next line or method. Takes an optional numeric argument to step multiple times.next: Step over to the next line within the same frame. Also takes an optional numeric argument to step multiple lines.finish: Execute until current stack frame returns.continue: Continue program execution and end the Pry session.
Callstack navigation
You also can move around in the callstack with these commands:
backtrace: Shows the current stack. You can use the numbers on the left side with the frame command to navigate the stack.up: Moves the stack frame up. Takes an optional numeric argument to move multiple frames.down: Moves the stack frame down. Takes an optional numeric argument to move multiple frames.frame <n>: Moves to a specific frame. Called without arguments displays the current frame.
Short commands
When you use binding.pry instead of byebug, the short commands
like s, n, f, and c do not work. To reinstall them, add this
to ~/.pryrc:
if defined?(PryByebug)
Pry.commands.alias_command 's', 'step'
Pry.commands.alias_command 'n', 'next'
Pry.commands.alias_command 'f', 'finish'
Pry.commands.alias_command 'c', 'continue'
end
Repeat last command
You can repeat the last command by just hitting the Enter
key (e.g., with step ornext), if you place the following snippet
in your ~/.pryrc:
Pry::Commands.command /^$/, "repeat last command" do
_pry_.run_command Pry.history.to_a.last
end
byebug supports this out-of-the-box.