Ruby inline documentation

In IRB, or other interactive interpreter such as pry, how can I get some inline documentation on objects and methods? For example, I can get this far:

[1] pry(main)> x = 'hello world'
=> "hello world"
[2] pry(main)> x.st
x.start_with?  x.strip        x.strip!   
[2] pry(main)> x.st

But now I want to read usage / interface / whatever rdoc has to say about those methods and their inteface. That middle line was tab-completion, by the way.

I'm looking for something similar to ipython, where ? can be appended to an attribute name to see the docstring, or even an ?? to see the source:

In [1]: x = 'potato'

In [2]: x.st
x.startswith  x.strip       

In [2]: x.strip?
Type:       builtin_function_or_method
String Form:<built-in method strip of str object at 0x15e1b10>
Docstring:
S.strip([chars]) -> string or unicode

Return a copy of the string S with leading and trailing
whitespace removed.
If chars is given and not None, remove characters in chars instead.
If chars is unicode, S will be converted to unicode before stripping

Solution

First you need to install

gem install pry-doc

Then you can get documentation with the show-doc [method] command (aliased to ? [method])

pry> x = 'potato'
=> "potato"
pry> show-doc x.strip

From: string.c (C Method):
Owner: String
Visibility: public
Signature: strip()
Number of lines: 4

Returns a copy of str with leading and trailing whitespace removed.

   "    hello    ".strip   #=> "hello"
   "\tgoodbye\r\n".strip   #=> "goodbye"

You can even look at the source code with the show-source [method] command (aliased to $ [method])

pry> show-source x.strip

From: string.c (C Method):
Owner: String
Visibility: public
Number of lines: 7

static VALUE
rb_str_strip(VALUE str)
{
    str = rb_str_dup(str);
    rb_str_strip_bang(str);
    return str;
}

This example shows C source, but it will show you the actual Ruby source if there is any. Consider this simple class:

pry> class Foo
pry*   def bar
pry*     puts 'hello'
pry*   end
pry* end
=> nil

You can look at the whole class:

pry> show-source Foo

From: (pry) @ line 2:
Class name: Foo
Number of lines: 5

class Foo
  def bar
    puts 'hello'
  end
end

But also at just a specific method:

pry> show-source Foo#bar

From: (pry) @ line 3:
Owner: Foo
Visibility: public
Number of lines: 3

def bar
  puts 'hello'
end

As @banister suggested, you may add custom commands via Pry.commands.command. This way you can define your ? and ?? commands like this in your ~/.pryrc:

Pry.commands.command /(.+) \?\z/ do |a|
  run "show-doc", a
end

Pry.commands.command /(.+) \?\?\z/ do |a|
  run "show-source", a
end

Note that we need a space between the method and the ?, because Ruby methods may end in ? (e.g. Fixnum#zero?) and those methods would break. Some examples:

pry> puts ?

From: io.c (C Method):
Owner: Kernel
Visibility: private
Signature: puts(*arg1)
Number of lines: 3

Equivalent to

    $stdout.puts(obj, ...)

pry> puts ??

From: io.c (C Method):
Owner: Kernel
Visibility: private
Number of lines: 8

static VALUE
rb_f_puts(int argc, VALUE *argv, VALUE recv)
{
    if (recv == rb_stdout) {
        return rb_io_puts(argc, argv, recv);
    }
    return rb_funcall2(rb_stdout, rb_intern("puts"), argc, argv);
}

pry> 0.zero?     # still works!
=> true

pry> 0.zero? ?

From: numeric.c (C Method):
Owner: Fixnum
Visibility: public
Signature: zero?()
Number of lines: 1

Returns true if fix is zero.