The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

2.39. Expanding and Compressing Tab Characters

Occasionally we have a string with tabs in it and we want to convert them to spaces (or vice versa). The two methods shown here do these operations.

class String

  def detab(ts=8)
    str = self.dup
    while (leftmost = str.index("\t")) != nil
      space = " "*(ts-(leftmost%ts))
      str[leftmost]=space
    end
    str
  end

  def entab(ts=8)
    str = self.detab
    areas = str.length/ts
    newstr = ""
    for a in 0..areas
      temp = str[a*ts..a*ts+ts-1]
      if temp.size==ts
        if temp =~ / +/
          match=Regexp.last_match[0]
          endmatch = Regexp.new(match+"$")
          if match.length>1
            temp.sub!(endmatch,"\t")
          end
        end
      end
      newstr += temp
    end
    newstr
  end

end

foo = "This       is        only   a     test.          "

puts foo
puts foo.entab(4)
puts foo.entab(4).dump

Note that this code is not smart ...