In Files

  • ruby-3.1.2/lib/pp.rb


Class/Module Index [+]



A pretty-printer for Ruby objects.

What PP Does

Standard output by p returns this:

#<PP:0x81fedf0 @genspace=#<Proc:0x81feda0>, @group_queue=#<PrettyPrint::GroupQueue:0x81fed3c @queue=[[#<PrettyPrint::Group:0x81fed78 @breakables=[], @depth=0, @break=false>], []]>, @buffer=[], @newline="\n", @group_stack=[#<PrettyPrint::Group:0x81fed78 @breakables=[], @depth=0, @break=false>], @buffer_width=0, @indent=0, @maxwidth=79, @output_width=2, @output=#<IO:0x8114ee4>>

Pretty-printed output returns this:

    [[#<PrettyPrint::Group:0x81fed78 @break=false, @breakables=[], @depth=0>],
  [#<PrettyPrint::Group:0x81fed78 @break=false, @breakables=[], @depth=0>],


pp(obj)             #=> obj
pp obj              #=> obj
pp(obj1, obj2, ...) #=> [obj1, obj2, ...]
pp()                #=> nil

Output obj(s) to $> in pretty printed format.

It returns obj(s).

Output Customization

To define a customized pretty printing function for your classes, redefine method #pretty_print(pp) in the class.

#pretty_print takes the pp argument, which is an instance of the PP class. The method uses text, breakable, nest, group and pp to print the object.

Pretty-Print JSON

To pretty-print JSON refer to JSON#pretty_generate.


Tanaka Akira <>

Public Class Methods

pp(obj, out=$>, width=width_for(out)) click to toggle source

Outputs obj to out in pretty printed format of width columns in width.

If out is omitted, $> is assumed. If width is omitted, the width of out is assumed (see width_for).

PP.pp returns out.

               # File ruby-3.1.2/lib/pp.rb, line 91
def PP.pp(obj, out=$>, width=width_for(out))
  q =, width)
  q.guard_inspect_key {q.pp obj}
  #$pp = q
  out << "\n"
sharing_detection() click to toggle source

Returns the sharing detection flag as a boolean value. It is false (nil) by default.

               # File ruby-3.1.2/lib/pp.rb, line 120
def sharing_detection
sharing_detection=(b) click to toggle source

Sets the sharing detection flag to b.

               # File ruby-3.1.2/lib/pp.rb, line 124
def sharing_detection=(b)
  Ractor.current[:pp_sharing_detection] = b
singleline_pp(obj, out=$>) click to toggle source

Outputs obj to out like PP.pp but with no indent and newline.

PP.singleline_pp returns out.

               # File ruby-3.1.2/lib/pp.rb, line 103
def PP.singleline_pp(obj, out=$>)
  q =
  q.guard_inspect_key {q.pp obj}
width_for(out) click to toggle source

Returns the usable width for out. As the width of out:

  1. If out is assigned to a tty device, its width is used.

  2. Otherwise, or it could not get the value, the COLUMN environment variable is assumed to be set to the width.

  3. If COLUMN is not set to a non-zero number, 80 is assumed.

And finally, returns the above width value - 1.

  • This -1 is for Windows command prompt, which moves the cursor to the next line if it reaches the last column.

               # File ruby-3.1.2/lib/pp.rb, line 74
def PP.width_for(out)
    require 'io/console'
    _, width = out.winsize
  rescue LoadError, NoMethodError, SystemCallError
  (width || ENV['COLUMNS']&.to_i&.nonzero? || 80) - 1