Best way to pretty print a hash

Question

require 'pp'
pp my_hash

Use pp if you need a built-in solution and just want reasonable line breaks.

Use awesome_print if you can install a gem. (Depending on your users, you may wish to use the index:false option to turn off displaying array indices.)

If you have JSON, I recommend JSON.pretty_generate(hash) because it is simpler than awesome_print, looks great in a pre tag, and allows for easy copying from a web page. (See also: How can I "pretty" format my JSON output in Ruby on Rails?)

Another solution which works better for me than pp or awesome_print:

require 'pry' # must install the gem... but you ALWAYS want pry installed anyways
Pry::ColorPrinter.pp(obj)

If you don't have any fancy gem action, but do have JSON, this CLI line will work on a hash:

puts JSON.pretty_generate(my_hash).gsub(":", " =>")

#=>
{
  :key1 => "value1",

  :key2 => "value2",

  :key3 => "value3"
}

Use the answers above if you're printing to users.

If you only want to print it for yourself in console, I suggest using the pry gem instead of irb. Besides pretty printing, pry has a lot of other features as well (check railscast below)

gem install pry

And check this railscast:

http://railscasts.com/episodes/280-pry-with-rails

Easy to do with json if you trust your keys to be sane:

JSON.pretty_generate(a: 1, 2 => 3, 3 => nil).
  gsub(": null", ": nil").
  gsub(/(^\s*)"([a-zA-Z][a-zA-Z\d_]*)":/, "\\1\\2:"). # "foo": 1 -> foo: 1
  gsub(/(^\s*)(".*?"):/, "\\1\\2 =>") # "123": 1 -> "123" => 1

{
  a: 1,
  "2" => 3,
  "3" => nil
}

In Rails

If you need

• a "pretty printed" Hash
• in e.g. the Rails.logger
• that, specifically, runs inspect on the objects in the Hash
  • which is useful if you override/define the inspect method in your objects like you're supposed to

... then this works great! (And gets better, the bigger and more nested your Hash object is.)

logger.error my_hash.pretty_inspect

For example:

class MyObject1
  def inspect
    "<#{'*' * 10} My Object 1 #{'*' * 10}>"
  end
end

class MyObject2
  def inspect
    "<#{'*' * 10} My Object 2 #{'*' * 10}>"
  end
end

my_hash = { a: 1, b: MyObject1.new, MyObject2.new => 3 }

Rails.logger.error my_hash
# {:a=>1, :b=><********** My Object 1 **********>, <********** My Object 2 **********>=>3}

# EW! ^

Rails.logger.error my_hash.pretty_inspect
# {:a=>1,
#  :b=><********** My Object 1 **********>,
#  <********** My Object 2 **********>=>3}

pretty_inspect comes from PrettyPrint, which rails includes by default. So, no gems needed and no conversion to JSON needed.

Not In Rails

If you're not in Rails or if the above fails for some reason, try using require "pp" first. For example:

require "pp"  # <-----------

class MyObject1
  def inspect
    "<#{'*' * 10} My Object 1 #{'*' * 10}>"
  end
end

class MyObject2
  def inspect
    "<#{'*' * 10} My Object 2 #{'*' * 10}>"
  end
end

my_hash = { a: 1, b: MyObject1.new, MyObject2.new => 3 }

puts my_hash
# {:a=>1, :b=><********** My Object 1 **********>, <********** My Object 2 **********>=>3}

# EW! ^

puts my_hash.pretty_inspect
# {:a=>1,
#  :b=><********** My Object 1 **********>,
#  <********** My Object 2 **********>=>3}

---

A Full Example

Big ol' pretty_inspected Hash example from my project with project-specific text from my inspected objects redacted:

{<***::******************[**:****, ************************:****]********* * ****** ******************** **** :: *********** - *** ******* *********>=>
  {:errors=>
    ["************ ************ ********** ***** ****** ******** ***** ****** ******** **** ********** **** ***** ***** ******* ******",
     "************ ************ ********** ***** ****** ******** ***** ****** ******** **** ********** is invalid",
     "************ ************ ********** ***** ****** ******** is invalid",
     "************ ************ ********** is invalid",
     "************ ************ is invalid",
     "************ is invalid"],
   :************=>
    [{<***::**********[**:****, *************:**, ******************:*, ***********************:****] :: **** **** ****>=>
       {:************=>
         [{<***::***********[**:*****, *************:****, *******************:**]******* :: *** - ******* ***** - *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: *** - *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ********* - *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ********** - ********** *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ******** - *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: **** - *******>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: *** - ********** ***** - *>=>
            {}}]}},
     {<***::**********[**:****, *************:**, ******************:*, ***********************:****] ******************** :: *** - *****>=>
       {:errors=>
         ["************ ********** ***** ****** ******** ***** ****** ******** **** ********** **** ***** ***** ******* ******",
          "************ ********** ***** ****** ******** ***** ****** ******** **** ********** is invalid",
          "************ ********** ***** ****** ******** is invalid",
          "************ ********** is invalid",
          "************ is invalid"],
        :************=>
         [{<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - ********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - ********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *******>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]*********** :: ****>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *******>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *******>=>
            {:errors=>
              ["********** ***** ****** ******** ***** ****** ******** **** ********** **** ***** ***** ******* ******",
               "********** ***** ****** ******** ***** ****** ******** **** ********** is invalid",
               "********** ***** ****** ******** is invalid",
               "********** is invalid"],
             :**********************=>
              [{<***::*******************[**:******, ************************:***]****-************ ******************** ***: * :: *** - ***** * ****** ** - ******* * **: *******>=>
                 {:errors=>
                   ["***** ****** ******** **** ********** **** ***** ***** ******* ******",
                    "***** ****** ******** **** ********** is invalid"],
                  :***************=>
                   [{<***::********************************[**:******, *************:******, ***********:******, ***********:"************ ************"]** * *** * ****-******* * ******** * ********* ******************** *********************: ***** :: "**** *" -> "">=>
                      {:errors=>["**** ***** ***** ******* ******"],
                       :**********=>
                        {<***::*****************[**:******, ****************:["****** ***", "****** ***", "****** ****", "******* ***", "******* ****", "******* ***", "****"], **:""] :: "**** *" -> "">=>
                          {:errors=>
                            ["***** ******* ******",
                             "***** ******* ******"]}}}}]}}]}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - ********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - **********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - **********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - **********>=>
            {}}]}}]}}