About Error handler

Hi

I am new to ruby on rails
I need to know one thing
Is there any way to externalize all the error messages in one file and access

Do you mean the error messages from a model instance? You can just use
ruby's standard file io methods to read and write a yaml file:

File.open('errors.yml', 'w') do |out|
  out.write(my_obj.errors.full_messages.to_yaml)
end

to read it back in:
errors = YAML.load_file('errors.yml')