(eval):1: syntax error, unexpected end-of-input, expecting '}' {:redirect=>true ^

begin
  hash = eval(string)
rescue SyntaxError
  # It's not valid
end

def valid_hash?(string)
  eval(string).is_a?(Hash)
rescue SyntaxError
  false
end

string = "{:key=>true}"
valid_hash?(string)
#=> true
string = "I am not hash"
valid_hash?(string)
#=> false

string1 = "{:key_1=>true,key_2:false}"
string2 = "{:key=>true}"
string3 = "no hash"

def valid_hash?(string)
  begin
    string = string.gsub(/(w+):s*([^},])/, '"1":2')
    #=> "{:key_1=>true,"key_2":false}"
    string = string.gsub(/:(w+)s*=>/, '"1":')
    #=> "{"key_1":true,"key_2":false}"
    my_hash = JSON.parse(string, {symbolize_names: true})
    #=> {:key_1=>true, :key_2=>false}
    my_hash.is_a? Hash # or do whatever you want with your Hash
  rescue JSON::ParserError
    false
  end
end

valid_hash? string1
#=> true
valid_hash? string2
#=> true
valid_hash? string3
#=> false