Variables magic and read from file

Question

Assume, i got the following file (input.txt):

name = "Peter"
age = 26
family_status = married

Mentioned lines can be stored in a random order, lie:

family_status = married
name = "Peter"
age = 26

In my program I also have variables family_status, age and name. How do I in a single cycle read those lines from file and assign correspond variables with the values?

Answer 1

You can try this. Not pretty on a single line though:

class Test
  attr_accessor :name, :age, :family_status

  def load
    File.foreach('input.txt') do |line|
      match = line.match /^(\S+)\s*=\s*"?(\S+?)"?\s*$/
      self.send("#{match[1]}=", match[2]) if match
    end
  end
end

test = Test.new
test.load

Answer 2

Setting Variables

This depends on several facts.

• What kind of variables do you have (local variables, instance variables, class variables, or global variables)
• What kind of type is family_status (String, Symbol, whatever)

I assume you are using instance variables for this:

def read_vars(io, vars)
  io.each do |line|
    # ensure the line has the right format (name = var)
    raise "wrong format" unless line=~ /^\s*(\w+)\s*=\s*"?(.*?)"?\s+$/
    var= :"@#{$1}"
    # pick the type of the data
    value= case vars[var]
    when String
      $2
    when Integer
      $2.to_i
    when Symbol
      $2.to_sym
    else
      raise "invalid var"
    end
    instance_variable_set(var, value)
  end
end

read_vars(File.read("input.txt", :@age => Integer, :@name => String, :@family_status => Symbol )

If you are not using instance variables you have to change the instacne_variable_set and var= :"@... line to you needs. This code has the following advantages:

• You control which variables can be set
• You control which types these variables have
• You can easily add new variables and/or change types of variables without changing the read code
• You can use this code to read entirely different files, without writing new code for it

reading as YAML

If your needs are not as specific as in your question I would go an entirely different approach to this.

I would write the input.txt as a yaml file. In yaml syntax it would look like this:

---
name: Peter
age: 26
family_status: :married

You can read it with:

YAML.load(File.read("input.txt")) # => {"name" => "Peter", "age" => 26, "family_status" => :married }

Be carefull if you don't control the input.txt file, you don't control which types the data will have. I would name the file input.yaml instead of input.txt. If you want to know more, about how to write yaml files have a look at: http://yaml.kwiki.org/?YamlInFiveMinutes. More infos about yaml and ruby can be found at http://www.ruby-doc.org/stdlib/libdoc/yaml/rdoc/index.html.

Answer 3

Assuming the file is really as regular as your example, you can slurp everything into a nice hash like this:

input = IO.read("input.txt")
input_hash = Hash[*input.gsub(/"/,"").split(/\s*[\n=]\s*/)]

That gives you:

=> {"name"=>"Peter", "family_status"=>"married", "age"=>"26"}

But then you're really going to need some variable-specific code to do whatever type-handling you want, particularly for whatever family_status is...