readsFileInLoop.rb

#!/usr/bin/env ruby

# reads in user provided parameter for function like  ./readsFile2ReadIn.rb file2ReadIn
filename = ARGV.first

# when user forgets to provide parameter in function call like:  ./readsFile2ReadIn4.rb
while !filename                           # if !filename # wont repeat and we want to repeat
  print "file? \n"
  file_again = $stdin.gets.chomp                                                                                                     
    print "Oh you want file: #{file_again} \n"  # shows filename file2ReadIn which is not important...
   # print file_again.read
  txt_again = open(file_again)
  print txt_again.read     # finally reads/opens file
end

# when user remembers to provide parameter: ./readsFile2ReadIn4.rb file2ReadIn
while filename
  print "file is: #{filename}\n"          # shows filename file2ReadIn which is not important...
  file_again = open(filename)
  print file_again.read
    print "Do you want another file? \n"  # shows filename file2ReadIn which is not important...
  file_again = $stdin.gets.chomp          # or  # filename = gets.chomp
  txt_again = open(file_again)
  print txt_again.read
end

./data_extractor.rb test.txt
Hello!

./data_extractor.rb
Please enter a filename
test.txt
Hello!