Parse text files recursively, searching for occurrence of string

simple_search_and_replace_utf8.rb

#encoding: UTF-8
start_path = "/path/to/parent/directory/"

def change_text_file(path)
  file_contents = ""
  File.open(path,'r') do |file|
    while line = file.gets
      if line.force_encoding("ISO-8859-1").encode("utf-8", replace: nil).match "whatever"
        line = line.sub("whatever", "new whatever")
      end
      file_contents += line
    end
  end

  File.open(path,'w') do |file|
    file.print inhalt
  end
end

def build_tree(start_path)
  Dir.open(start_path).entries.each do |file_name|
    path = File.join(start_path, file_name)
    next if /^\./ =~ file_name 
    next if not /.htm/.match file_name and not File.directory?(path)
    File.directory?(path) ? build_tree(path) : change_text_file(path)
  end
end

build_tree(start_path)