Pry ============= (C) John Mair (banisterfiend) 2011 _attach an irb-like session to any object at runtime_ Pry is a simple Ruby REPL (Read-Eval-Print-Loop) that specializes in the interactive manipulation of objects during the running of a program. In some sense it is the opposite of IRB in that you bring a REPL session to your code (with Pry) instead of bringing your code to a REPL session (as with IRB). It is not based on the IRB codebase, and implements some unique REPL commands such as `show-method`, `show-doc`, `ls` and `cd` 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. * 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: Interacting with an object at runtime --------------------------------------- With the `Object#pry` method we can pry (open an irb-like session) on an object. In the example below we open a Pry session for the `Test` class and execute a method and add an instance variable. The current thread is halted for the duration of the session. require 'pry' class Test def self.hello() "hello world" end end Test.pry # Pry session begins on stdin Beginning Pry session for Test pry(Test)> self => Test pry(Test)> hello => "hello world" pry(Test)> @y = 20 => 20 pry(Test)> exit Ending Pry session for Test # program resumes here If we now inspect the `Test` object we can see our changes have had effect: Test.instance_variable_get(:@y) #=> 20 ### Alternative Syntax You can also use the `Pry.start(obj)` or `pry(obj)` syntax to start a pry session on `obj`. e.g Pry.start(5) Beginning Pry session for 5 pry(5)> OR pry(6) beginning Pry session for 6 pry(6)> Example: Pry sessions can nest ----------------------------------------------- Here we will begin Pry at top-level, then pry on a class and then on an instance variable inside that class: # Pry.start() without parameters begins a Pry session on top-level (main) Pry.start Beginning Pry session for main pry(main)> class Hello pry(main)* @x = 20 pry(main)* end => 20 pry(main)> cd Hello Beginning Pry session for Hello pry(Hello):1> instance_variables => [:@x] pry(Hello):1> cd @x Beginning Pry session for 20 pry(20:2)> self + 10 => 30 pry(20:2)> exit Ending Pry session for 20 pry(Hello):1> exit Ending Pry session for Hello pry(main)> exit Ending Pry session for main 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> If we just want to go back one level of nesting we can of course use the `quit` or `exit` or `back` commands. To break out of all levels of Pry nesting and return immediately to the calling process use `exit-all`: pry("friend":3)> exit-all Ending Pry session for "friend" Ending Pry session for 100 Ending Pry session for Hello Ending Pry session for main => main # program resumes here 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. * Pry sessions can nest arbitrarily deeply -- to go back one level of nesting type 'exit' or 'quit' or 'back' * Use `_` to recover last result. * Use `_pry_` to reference the Pry instance managing the current session. * 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: * Pry does not pretend to be a replacement for `irb`, and so does not have an executable. It is designed to be used by other programs, not on its own. For a full-featured `irb` replacement see [ripl](https://github.com/cldwalker/ripl) * Pry's `show-method` and `show-doc` commands do not work in Ruby 1.8. 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. ### 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. * `version` Show Pry version information * `help` shows the list of session commands with brief explanations. * `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. * You can type `Pry.start(obj)` or `obj.pry` to nest another Pry session within the current one with `obj` as the receiver of the new session. Very useful when exploring large or complicated runtime state. 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)