Question

Is there a way to edit each line in a file, without involving 2 files? Say, the original file has,

test01
test02
test03

I want to edit it like

test01,a
test02,a
test03,a

Tried something as show in the code block, but it replaces some of the characters.

Writing it to a temporary file and then replace the original file works, However, I need to edit the file quite often and therefore prefer to do it within the file itself .Any pointers are appreciated.

Thank you!

File.open('mytest.csv', 'r+') do |file|
  file.each_line do |line|        
      file.seek(-line.length, IO::SEEK_CUR)
      file.puts 'a'        
  end
end

Answer 1

f = open 'mytest.csv', 'r+'
r = f.readlines.map { |e| e.strip << ',a' }
f.rewind
f.puts r
f.close # you can leave out this line if it's the last one that runs

Here is a one-liner variation, note that in this case 2 descriptors are left open until the program exits.

open(F='mytest.csv','r+').puts open(F,'r').readlines.map{|e|e.strip<<',a'}