Question

Good afternoon!

I am pretty new to Ruby and want to code a basic search and replace function in Ruby.
When you call the function, you can pass parameters (search pattern, replacing word).

This works like this: multiedit(pattern1, replacement1, pattern2, replacement2, …)

Now, I want my function to read a text file, search for pattern1 and replace it with replacement2, search for pattern2 and replace it with replacement2 and so on. Finally, the altered text should be written to another text file.

I’ve tried to do this with a until loop, but all I get is that only the very first pattern is replaced while all the following patterns are ignored (in this example, only apple is replaced with fruit). I think the problem is that I always reread the original unaltered text? But I can’t figure out a solution. Can you help me? Calling the function the way I am doing it is important for me.

def multiedit(*_patterns)

  return puts "Number of search patterns does not match number of replacement strings!" if (_patterns.length % 2 > 0)

  f = File.open("1.txt", "r")  
  g = File.open("2.txt", "w")

  i = 0

  until i >= _patterns.length do
    f.each_line {|line|
      output = line.sub(_patterns[i], _patterns[i+1])
      g.puts output
    }
    i+=2  
  end

  f.close
  g.close

end

multiedit("apple", "fruit", "tomato", "veggie", "steak", "meat")

Can you help me out?

Thank you very much in advance!

Regards

Answer 1

Your loop was kind of inside-out … do this instead …

  f.each_line do |line| 
    _patterns.each_slice 2 do |a, b|
      line.sub! a, b
    end
    g.puts line
  end