Tukukkk

Quick and dirty method would be

eval("{ :key_a => { :key_1a => 'value_1a', :key_2a => 'value_2a' }, :key_b => { :key_1b => 'value_1b' } }") 

But it has severe security implications.

It executes whatever it is passed, you must be 110% sure (as in, at least no user input anywhere along the way) it would contain only properly formed hashes or unexpected bugs/horrible creatures from outer space might start popping up.

For different string, you can do it without using dangerous eval method:

hash_as_string = "{"0"=>{"answer"=>"1", "value"=>"No"}, "1"=>{"answer"=>"2", "value"=>"Yes"}, "2"=>{"answer"=>"3", "value"=>"No"}, "3"=>{"answer"=>"4", "value"=>"1"}, "4"=>{"value"=>"2"}, "5"=>{"value"=>"3"}, "6"=>{"value"=>"4"}}"

JSON.parse hash_as_string.gsub('=>', ':')

This short little snippet will do it, but I can't see it working with a nested hash. I think it's pretty cute though

STRING.gsub(/[{}:]/,'').split(', ').map{|h| h1,h2 = h.split('=>'); {h1 => h2}}.reduce(:merge)

Steps
1. I eliminate the '{','}' and the ':'
2. I split upon the string wherever it finds a ','
3. I split each of the substrings that were created with the split, whenever it finds a '=>'. Then, I create a hash with the two sides of the hash I just split apart.
4. I am left with an array of hashes which I then merge together.

EXAMPLE INPUT: "{:user_id=>11, :blog_id=>2, :comment_id=>1}"
RESULT OUTPUT: {"user_id"=>"11", "blog_id"=>"2", "comment_id"=>"1"}

Maybe YAML.load ?

The solutions so far cover some cases but miss some (see below). Here's my attempt at a more thorough (safe) conversion. I know of one corner case which this solution doesn't handle which is single character symbols made up of odd, but allowed characters. For example {:> => :<} is a valid ruby hash.

I put this code up on github as well. This code starts with a test string to exercise all the conversions

require 'json'



# Example ruby hash string which exercises all of the permutations of position and type

# See http://json.org/

ruby_hash_text='{"alpha"=>{"first second > third"=>"first second > third", "after comma > foo"=>:symbolvalue, "another after comma > foo"=>10}, "bravo"=>{:symbol=>:symbolvalue, :aftercomma=>10, :anotheraftercomma=>"first second > third"}, "charlie"=>{1=>10, 2=>"first second > third", 3=>:symbolvalue}, "delta"=>["first second > third", "after comma > foo"], "echo"=>[:symbol, :aftercomma], "foxtrot"=>[1, 2]}'



puts ruby_hash_text



# Transform object string symbols to quoted strings

ruby_hash_text.gsub!(/([{,]s*):([^>s]+)s*=>/, '1"2"=>')



# Transform object string numbers to quoted strings

ruby_hash_text.gsub!(/([{,]s*)([0-9]+.?[0-9]*)s*=>/, '1"2"=>')



# Transform object value symbols to quotes strings

ruby_hash_text.gsub!(/([{,]s*)(".+?"|[0-9]+.?[0-9]*)s*=>s*:([^,}s]+s*)/, '12=>"3"')



# Transform array value symbols to quotes strings

ruby_hash_text.gsub!(/([[,]s*):([^,]s]+)/, '1"2"')



# Transform object string object value delimiter to colon delimiter

ruby_hash_text.gsub!(/([{,]s*)(".+?"|[0-9]+.?[0-9]*)s*=>/, '12:')



puts ruby_hash_text



puts JSON.parse(ruby_hash_text)

Here are some notes on the other solutions here

• 
  @Ken Bloom and @Toms Mikoss's solutions use eval which is too scary for me (as Toms rightly points out).


• 
  @zolter's solution works if your hash has no symbols or numeric keys.


• 
  @jackquack's solution works if there are no quoted strings mixed in with the symbols.


• 
  @Eugene's solution works if your symbols don't use all the allowed characters (symbol literals have a broader set of allowed characters).


• 
  @Pablo's solution works as long as you don't have a mix of symbols and quoted strings.

I had the same problem. I was storing a hash in Redis. When retrieving that hash, it was a string. I didn't want to call eval(str) because of security concerns. My solution was to save the hash as a json string instead of a ruby hash string. If you have the option, using json is easier.

  redis.set(key, ruby_hash.to_json)

  JSON.parse(redis.get(key))

TL;DR: use to_json and JSON.parse

I prefer to abuse ActiveSupport::JSON. Their approach is to convert the hash to yaml and then load it. Unfortunately the conversion to yaml isn't simple and you'd probably want to borrow it from AS if you don't have AS in your project already.

We also have to convert any symbols into regular string-keys as symbols aren't appropriate in JSON.

However, its unable to handle hashes that have a date string in them (our date strings end up not being surrounded by strings, which is where the big issue comes in):

string = '{'last_request_at' : 2011-12-28 23:00:00 UTC }'
ActiveSupport::JSON.decode(string.gsub(/:([a-zA-z])/,'\1').gsub('=>', ' : '))

Would result in an invalid JSON string error when it tries to parse the date value.

Would love any suggestions on how to handle this case

works in rails 4.1 and support symbols without quotes {:a => 'b'}

just add this to initializers folder:

class String

  def to_hash_object

    JSON.parse(self.gsub(/:([a-zA-z]+)/,'"\1"').gsub('=>', ': ')).symbolize_keys

  end

end

I built a gem hash_parser that first checks if a hash is safe or not using ruby_parser gem. Only then, it applies the eval.

You can use it as

require 'hash_parser'



# this executes successfully

a = "{ :key_a => { :key_1a => 'value_1a', :key_2a => 'value_2a' }, 

       :key_b => { :key_1b => 'value_1b' } }"

p HashParser.new.safe_load(a)



# this throws a HashParser::BadHash exception

a = "{ :key_a => system('ls') }"

p HashParser.new.safe_load(a)

The tests in https://github.com/bibstha/ruby_hash_parser/blob/master/test/test_hash_parser.rb give you more examples of the things I've tested to make sure eval is safe.

I came to this question after writing a one-liner for this purpose, so I share my code in case it helps somebody. Works for a string with only one level depth and possible empty values (but not nil), like:

"{ :key_a => 'value_a', :key_b => 'value_b', :key_c => '' }"

The code is:

the_string = '...'

the_hash = Hash.new

the_string[1..-2].split(/, /).each {|entry| entryMap=entry.split(/=>/); value_str = entryMap[1]; the_hash[entryMap[0].strip[1..-1].to_sym] = value_str.nil? ? "" : value_str.strip[1..-2]}

Please consider this solution. Library+spec:

File: lib/ext/hash/from_string.rb:

require "json"



module Ext

  module Hash

    module ClassMethods

      # Build a new object from string representation.

      #

      #   from_string('{"name"=>"Joe"}')

      #

      # @param s [String]

      # @return [Hash]

      def from_string(s)

        s.gsub!(/(?<!\)"=>nil/, '":null')

        s.gsub!(/(?<!\)"=>/, '":')

        JSON.parse(s)

      end

    end

  end

end



class Hash    #:nodoc:

  extend Ext::Hash::ClassMethods

end

File: spec/lib/ext/hash/from_string_spec.rb:

require "ext/hash/from_string"



describe "Hash.from_string" do

  it "generally works" do

    [

      # Basic cases.

      ['{"x"=>"y"}', {"x" => "y"}],

      ['{"is"=>true}', {"is" => true}],

      ['{"is"=>false}', {"is" => false}],

      ['{"is"=>nil}', {"is" => nil}],

      ['{"a"=>{"b"=>"c","ar":[1,2]}}', {"a" => {"b" => "c", "ar" => [1, 2]}}],

      ['{"id"=>34030, "users"=>[14105]}', {"id" => 34030, "users" => [14105]}],



      # Tricky cases.

      ['{"data"=>"{"x"=>"y"}"}', {"data" => "{"x"=>"y"}"}],   # Value is a `Hash#inspect` string which must be preserved.

    ].each do |input, expected|

      output = Hash.from_string(input)

      expect([input, output]).to eq [input, expected]

    end

  end # it

end