(C) John Mair (banisterfiend) 2011
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[Skip to the wiki](https://github.com/pry/pry/wiki) 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: * Source code browsing (including core C source with the pry-doc gem) * Documentation browsing * Live help system * Open methods in editors (`edit-method Class#method`) * Syntax highlighting * Command shell integration (start editors, run git, and rake from within Pry) * Gist integration * Navigation around state (`cd`, `ls` and friends) * Runtime invocation (use Pry as a developer console or debugger) * Exotic object support (BasicObject instances, IClasses, ...) * A Powerful and flexible command system * Ability to view and replay history * Many convenience commands inspired by IPython, Smalltalk and other advanced REPLs Pry also aims to be more than an IRB replacement; it is an attempt to bring REPL driven programming to the Ruby language. It is currently not as powerful as tools like [SLIME](http://en.wikipedia.org/wiki/SLIME) for lisp, but that is the general direction Pry is heading. Pry is also fairly flexible and allows significant user [customization](https://github.com/pry/pry/wiki/Customization-and-configuration) 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` * Browse the comprehensive [documentation at the official Pry wiki](https://github.com/pry/pry/wiki) * Read the [YARD API documentation](http://rdoc.info/github/pry/pry/master/file/README.markdown) * See the [source code](http://github.com/pry/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. ### Commands Nearly every piece of functionality in a Pry session is implemented as a command. Commands are not methods and must start at the beginning of a line, with no whitespace in between. Commands support a flexible syntax and allow 'options' in the same way as shell commands, for example the following Pry command will show a list of all private instance methods (in scope) that begin with 'pa' pry(YARD::Parser::SourceParser):5> ls -Mp --grep ^pa [:parser_class, :parser_type=, :parser_type_for_filename] ### Navigating around state Pry allows us to pop in and out of different scopes (objects) using the `cd` command. This enables us to explore the run-time view of a program or library. To view which variables and methods are available within a particular scope we use the versatile [ls command.](https://gist.github.com/c0fc686ef923c8b87715) 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> ### 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. It can be invoked on any object using the `my_object.pry` syntax or on the current binding (or any binding) using `binding.pry`. The Pry session will then begin within the scope of the object (or binding). 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 editors, 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 (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 edit the `.pryrc` file in the home directory. We'll then cat its contents and reload the file. pry(main)> shell-mode pry main:/home/john/ruby/projects/pry $ .cd ~ pry main:/home/john $ .emacsclient .pryrc pry main:/home/john $ .cat .pryrc def hello_world puts "hello world!" end pry main:/home/john $ load ".pryrc" => true pry main:/home/john $ hello_world hello world! We can also interpolate Ruby code into the shell. 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 $ .cat #{Dir['*.*'].sample} | wc -l 44 ### Code Browsing You can browse method source code with the `show-method` command. Nearly all Ruby methods (and some C methods, with the pry-doc gem) can have their source viewed. Code that is longer than a page is sent through a pager (such as less), and all code is properly syntax highlighted (even C code). The `show-method` command accepts two syntaxes, the typical ri `Class#method` syntax and also simply the name of a method that's in scope. You can optionally pass the `-l` option to show-method to include line numbers in the output. In the following example we will enter the `Pry` class, list the instance methods beginning with 're' and display the source code for the `rep` method: pry(main)> cd Pry pry(Pry):1> ls -M --grep ^re [:re, :readline, :rep, :repl, :repl_epilogue, :repl_prologue, :retrieve_line] pry(Pry):1> show-method rep -l From: /home/john/ruby/projects/pry/lib/pry/pry_instance.rb @ line 143: Number of lines: 6 143: def rep(target=TOPLEVEL_BINDING) 144: target = Pry.binding_for(target) 145: result = re(target) 146: 147: show_result(result) if should_print? 148: end Note that we can also view C methods (from Ruby Core) using the `pry-doc` plugin; we also show off the alternate syntax for `show-method`: pry(main)> show-method Array#select From: array.c in Ruby Core (C Method): Number of lines: 15 static VALUE rb_ary_select(VALUE ary) { VALUE result; long i; RETURN_ENUMERATOR(ary, 0, 0); result = rb_ary_new2(RARRAY_LEN(ary)); for (i = 0; i < RARRAY_LEN(ary); i++) { if (RTEST(rb_yield(RARRAY_PTR(ary)[i]))) { rb_ary_push(result, rb_ary_elt(ary, i)); } } return result; } ### Documentation Browsing One use-case for Pry is to explore a program at run-time by `cd`-ing in and out of objects and viewing and invoking methods. In the course of exploring it may be useful to read the documentation for a specific method that you come across. Like `show-method` the `show-doc` command supports two syntaxes - the normal `ri` syntax as well as accepting the name of any method that is currently in scope. The Pry documentation system does not rely on pre-generated `rdoc` or `ri`, instead it grabs the comments directly above the method on demand. This results in speedier documentation retrieval and allows the Pry system to retrieve documentation for methods that would not be picked up by `rdoc`. Pry also has a basic understanding of both the rdoc and yard formats and will attempt to syntax highlight the documentation appropriately. Nonetheless The `ri` functionality is very good and has an advantage over Pry's system in that it allows documentation lookup for classes as well as methods. Pry therefore has good integration with `ri` through the `ri` command. The syntax for the command is exactly as it would be in command-line - so it is not necessary to quote strings. In our example we will enter the `Gem` class and view the documentation for the `try_activate` method: pry(main)> cd Gem pry(Gem):1> show-doc try_activate From: /Users/john/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems.rb @ line 201: Number of lines: 3 Try to activate a gem containing path. Returns true if activation succeeded or wasn't needed because it was already activated. Returns false if it can't find the path in a gem. pry(Gem):1> We can also use `ri` in the normal way: pry(main) ri Array#each ----------------------------------------------------------- Array#each array.each {|item| block } -> array ------------------------------------------------------------------------ Calls _block_ once for each element in _self_, passing that element as a parameter. a = [ "a", "b", "c" ] a.each {|x| print x, " -- " } produces: a -- b -- c -- ### Gist integration If the `gist` gem is installed then method source or documentation can be gisted to github with the `gist-method` command. The `gist-method` command accepts the same two syntaxes as `show-method`. In the example below we will gist the C source code for the `Symbol#to_proc` method to github: pry(main)> gist-method Symbol#to_proc https://gist.github.com/5332c38afc46d902ce46 pry(main)> You can see the actual gist generated here: [https://gist.github.com/5332c38afc46d902ce46](https://gist.github.com/5332c38afc46d902ce46) ### Edit methods You can use `edit-method Class#method` or `edit-method my_method` (if the method is in scope) to open a method for editing directly in your favorite editor. Pry has knowledge of a few different editors and will attempt to open the file at the line the method is defined. You can set the editor to use by assigning to the `Pry.editor` accessor. `Pry.editor` will default to `$EDITOR` or failing that will use `nano` as the backup default. The file that is edited will be automatically reloaded after exiting the editor - reloading can be suppressed by passing the `--no-reload` option to `edit-method` In the example below we will set our default editor to "emacsclient" and open the `Pry#repl` method for editing: pry(main)> Pry.editor = "emacsclient" pry(main)> edit-method Pry#repl ### Live Help System Many other commands are available in Pry; to see the full list type `help` at the prompt. A short description of each command is provided with basic instructions for use; some commands have a more extensive help that can be accessed via typing `command_name --help`. A command will typically say in its description if the `--help` option is avaiable. ### Use Pry as your Rails Console pry -r ./config/environment MyArtChannel has kindly provided a hack to replace the `rails console` command in Rails 3: [https://gist.github.com/941174](https://gist.github.com/941174) This is not recommended for code bases with multiple developers, as they may not all want to use Pry. ### Limitations: * Tab completion is currently a bit broken/limited this will have a major overhaul in a future version. ### 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. ### Future Directions Many new features are planned such as: * Increase modularity (rely more on plugin system) * Much improved tab completion (using [Bond](http://github.com/cldwalker/bond)) * Much improved documentation system, better support for YARD * Better support for code and method reloading and saving code * Extended and more sophisticated command system, allowing piping between commands and running commands in background ### Contact Problems or questions contact me at [github](http://github.com/banister) ### Contributors Pry is primarily the work of [John Mair (banisterfiend)]((http://github.com/banister)), for full list of contributors see the [CONTRIBUTORS](https://github.com/pry/pry/blob/master/CONTRIBUTORS) file.