![Alt text](http://dl.dropbox.com/u/26521875/pry_logo_shade.png) (C) John Mair (banisterfiend) 2011 _Get to the code_ Pry is a powerful alternative to the standard IRB shell for Ruby. It is written from scratch to provide a number of advanced features, some of these include: * Syntax highlighting * Navigation around state (`cd`, `ls` and friends) * Runtime invocation (use Pry as a developer console or debugger) * Command shell integration * Source code browsing (including core C source with the pry-doc gem) * Documentation browsing * Exotic object support (BasicObject instances, IClasses, ...) * A Powerful and flexible command system * Ability to view and replay history * Many convenience commands inspired by IPython and other advanced REPLs Pry is also fairly flexible and allows significant user [customization](http://rdoc.info/github/banister/pry/master/file/wiki/Customizing-pry.md). It is trivial to set it to read from any object that has a `readline` method and write to any object that has a `puts` method - many other aspects of Pry are also configurable making it a good choice for implementing custom shells. Pry comes with an executable so it can be invoked at the command line. Just enter `pry` to start. A `.pryrc` file in the user's home directory will be loaded if it exists. Type `pry --help` at the command line for more information. Try `gem install pry-doc` for additional documentation on Ruby Core methods. The additional docs are accessed through the `show-doc` and `show-method` commands. * Install the [gem](https://rubygems.org/gems/pry): `gem install pry` * Read the [documentation](http://rdoc.info/github/banister/pry/master/file/README.markdown) * See the [source code](http://github.com/banister/pry) Pry also has `rubygems-test` support; to participate, first install Pry, then: 1. Install rubygems-test: `gem install rubygems-test` 2. Run the test: `gem test pry` 3. Finally choose 'Yes' to upload the results. Example: Navigating around state --------------------------------------- Pry allows us to pop in and out of different scopes (objects) using the `cd` command. To view which variables and methods are available within a particular scope we use the versatile `ls` command. Here we will begin Pry at top-level, then pry on a class and then on an instance variable inside that class: pry(main)> class Hello pry(main)* @x = 20 pry(main)* end => 20 pry(main)> cd Hello pry(Hello):1> ls -i => [:@x] pry(Hello):1> cd @x pry(20:2)> self + 10 => 30 pry(20:2)> cd .. pry(Hello):1> cd .. pry(main)> cd .. The number after the `:` in the pry prompt indicates the nesting level. To display more information about nesting, use the `nesting` command. E.g pry("friend":3)> nesting Nesting status: 0. main (Pry top level) 1. Hello 2. 100 3. "friend" => nil We can then jump back to any of the previous nesting levels by using the `jump-to` command: pry("friend":3)> jump-to 1 Ending Pry session for "friend" Ending Pry session for 100 => 100 pry(Hello):1> Example: Runtime invocation --------------------------------------- Pry can be invoked in the middle of a running program. It opens a Pry session at the point it’s called and makes all program state at that point available. When the session ends the program continues with any modifications you made to it. This functionality can be used for such things as: debugging, implementing developer consoles and applying hot patches. code: # test.rb require 'pry' class A def hello() puts "hello world!" end end a = A.new # start a REPL session binding.pry # program resumes here (after pry session) puts "program resumes here." Pry session: pry(main)> a.hello hello world! => nil pry(main)> def a.goodbye pry(main)* puts "goodbye cruel world!" pry(main)* end => nil pry(main)> a.goodbye goodbye cruel world! => nil pry(main)> exit program resumes here. Command Shell Integration -------------------------- A line of input that begins with a '.' will be forwarded to the command shell. This enables us to navigate the file system, spawn an editor, and run git and rake directly from within Pry. Further, we can use the `shell-mode` command to incorporate the present working directory into the Pry prompt and bring in (very limited at this stage, sorry) file name completion. We can also interpolate Ruby code directly into the shell by using the normal `#{}` string interpolation syntax. In the code below we're going to switch to `shell-mode` and use the `gem-cd` command to enter the home directory for a gem and examine some of the files there: pry(main)> shell-mode pry main:/home/john/ruby/projects/pry $ .ls bin CHANGELOG examples lib LICENSE pkg Rakefile README.markdown TAGS test TODO wiki pry main:/home/john/ruby/projects/pry $ gem-cd yard pry main:/home/john/.rvm/gems/ruby-1.9.2-head/gems/yard-0.6.4 $ .ls benchmarks bin ChangeLog docs LEGAL lib LICENSE Rakefile README.md spec templates pry main:/home/john/.rvm/gems/ruby-1.9.2-head/gems/yard-0.6.4 $ .cd lib => /home/john/.rvm/gems/ruby-1.9.2-head/gems/yard-0.6.4/lib pry main:/home/john/.rvm/gems/ruby-1.9.2-head/gems/yard-0.6.4/lib $ .ls rubygems_plugin.rb yard yard.rb pry main:/home/john/.rvm/gems/ruby-1.9.2-head/gems/yard-0.6.4/lib $ .emacsclient yard.rb & We can also interpolate Ruby code into the Shell commands. In the example below we use the shell command `cat` on a random file from the current directory and count the number of lines in that file with `wc`: pry main:/home/john/.rvm/gems/ruby-1.9.2-head/gems/yard-0.6.4/lib $ .cat #{Dir['*.*'].sample} | wc -l 54 Code Browsing --------------- Features and limitations ------------------------ Pry is an irb-like clone with an emphasis on interactively examining and manipulating objects during the running of a program. Its primary utility is probably in debugging, though it may have other uses (such as implementing a quake-like console for games, for example). Here is a list of Pry's features along with some of its limitations given at the end. ###Features: * Pry can be invoked at any time and on any object in the running program. * Additional documentation and source code for Ruby Core methods are supported when the `pry-doc` gem is installed. * Pry sessions can nest arbitrarily deeply -- to go back one level of nesting type 'exit' or 'quit' or 'back' * Pry comes with syntax highlighting on by default just use the `toggle-color` command to turn it on and off. * Use `_` to recover last result. * Use `_pry_` to reference the Pry instance managing the current session. * Use `_ex_` to recover the last exception. * Pry supports tab completion. * Pry has multi-line support built in. * Use `^d` (control-d) to quickly break out of a session. * Pry has special commands not found in many other Ruby REPLs: `show-method`, `show-doc` `jump-to`, `ls`, `cd`, `cat` * Pry gives good control over nested sessions (important when exploring complicated runtime state) * Pry is not based on the IRB codebase. * Pry allows significant customizability. * Pry uses the [method_source](https://github.com/banister/method_source) gem; so this functionality is available to a Pry session. * Pry uses [RubyParser](https://github.com/seattlerb/ruby_parser) to validate expressions in 1.8, and [Ripper](http://rdoc.info/docs/ruby-core/1.9.2/Ripper) for 1.9. * Pry implements all the methods in the REPL chain separately: `Pry#r` for reading; `Pry#re` for eval; `Pry#rep` for printing; and `Pry#repl` for the loop (`Pry.start` simply wraps `Pry.new.repl`). You can invoke any of these methods directly depending on exactly what aspect of the functionality you need. ###Limitations: * Some Pry commands (e.g `show-command`) do not work in Ruby 1.8. * `method_source` functionality does not work in JRuby. * 1.9 support requires `Ripper` - some implementations may not support this. Commands ----------- ### The Pry API: * `Pry.start()` Starts a Read-Eval-Print-Loop on the object it receives as a parameter. In the case of no parameter it operates on top-level (main). It can receive any object or a `Binding` object as parameter. `Pry.start()` is implemented as `Pry.new.repl()` * `obj.pry` and `pry(obj)` may also be used as alternative syntax to `Pry.start(obj)`. However there are some differences. `obj.pry` opens a Pry session on the receiver whereas `Pry.start` (with no parameter) will start a Pry session on top-level. The other form of the `pry` method: `pry(obj)` will also start a Pry session on its parameter. The `pry` method invoked by itself, with no explict receiver and no parameter will start a Pry session on the implied receiver. It is perhaps more useful to invoke it in this form `pry(binding)` or `binding.pry` so as to get access to locals in the current context. Another difference is that `Pry.start()` accepts a second parameter that is a hash of configuration options (discussed further, below). * If, for some reason you do not want to 'loop' then use `Pry.new.rep()`; it only performs the Read-Eval-Print section of the REPL - it ends the session after just one line of input. It takes the same parameters as `Pry#repl()` * Likewise `Pry#re()` only performs the Read-Eval section of the REPL, it returns the result of the evaluation or an Exception object in case of error. It also takes the same parameters as `Pry#repl()` * Similarly `Pry#r()` only performs the Read section of the REPL, only returning the Ruby expression (as a string). It takes the same parameters as all the others. * `Pry.run_command COMMAND` enables you to invoke Pry commands outside of a session, e.g `Pry.run_command "ls -m", :context => MyObject`. See docs for more info. ### Session commands Pry supports a few commands inside the session itself. These commands are not methods and must start at the beginning of a line, with no whitespace in between. If you want to access a method of the same name, prefix the invocation by whitespace. * Typing `!` on a line by itself will clear the input buffer - useful for getting you out of a situation where the parsing process goes wrong and you get stuck in an endless read loop. * `status` shows status information about the current session. * `whereami AROUND` shows the code context of the session. Shows AROUND lines either side of the current line. * `version` Show Pry version information * `help` shows the list of session commands with brief explanations. * `toggle-color` turns on and off syntax highlighting. * `simple-prompt` toggles the simple prompt mode. * `exit` or `quit` or `back` or `^d` (control-d) will end the current Pry session and go back to the calling process or back one level of nesting (if there are nested sessions). * `ls [OPTIONS] [VAR]` returns a list of local variables, instance variables, and methods, etc. Highly flexible. See `ls --help` for more info. * `cat VAR` Calls `inspect` on `VAR` * `cd VAR` Starts a `Pry` session on the variable VAR. E.g `cd @x` (use `cd ..` to go back). * `show-method [OPTIONS] METH` Displays the sourcecode for the method `METH`. e.g `show-method hello`. See `show-method --help` for more info. * `show-doc [OPTIONS] METH` Displays comments for `METH`. See `show-doc --help` for more info. * `show-command COMMAND` Displays the sourcecode for the given Pry command. e.g: `show-command cd` * `jump-to NEST_LEVEL` Unwinds the Pry stack (nesting level) until the appropriate nesting level is reached. * `exit-all` breaks out of all Pry nesting levels and returns to the calling process. Syntax Highlighting -------------------- Syntax highlighting is on by default in Pry. You can toggle it on and off in a session by using the `toggle-color` command. Alternatively, you can turn it off permanently by putting the line `Pry.color = false` in your `~/.pryrc` file. Bindings and objects -------------------- Pry ultimately operates on `Binding` objects. If you invoke Pry with a Binding object it uses that Binding. If you invoke Pry with anything other than a `Binding`, Pry will generate a Binding for that object and use that. If you want to open a Pry session on the current context and capture the locals you should use: `binding.pry`. If you do not care about capturing the locals you can simply use `pry` (which will generate a fresh `Binding` for the receiver). Top-level is a special case; you can start a Pry session on top-level *and* capture locals by simply using: `pry`. This is because Pry automatically uses `TOPLEVEL_BINDING` for the top-level object (main). Example Programs ---------------- Pry comes bundled with a few example programs to illustrate some features, see the `examples/` directory. * `example_basic.rb` - Demonstrate basic Pry functionality * `example_input.rb` - Demonstrates how to set the `input` object. * `example_output.rb` - Demonstrates how to set the `output` object. * `example_hooks.rb` - Demonstrates how to set the `hooks` hash. * `example_print.rb` - Demonstrates how to set the `print` object. * `example_prompt.rb` - Demonstrates how to set the `prompt`. * `example_input2.rb` - An advanced `input` example. * `example_commands.rb` - Implementing a mathematical command set. * `example_commands_override.rb` - An advanced `commands` example. * `example_image_edit.rb` - A simple image editor using a Pry REPL (requires `Gosu` and `TexPlay` gems). Customizing Pry --------------- Pry allows a large degree of customization. [Read how to customize Pry here.](http://rdoc.info/github/banister/pry/master/file/wiki/Customizing-pry.md) Contact ------- Problems or questions contact me at [github](http://github.com/banister)