How to correctly write lines in a text file?

Question

ruby

Good afternoon. I use Ruby 2.1.2, OS FreeBSD 9.2. It is necessary to edit the text file, but I can’t do anything so that the changes are saved.
Now I'm using this code:

f = File.open("/tmp/test.conf", "a+")

f.each_line do |line|
  puts line.gsub!(/\/(.*)/, "99999")
end

f.close

The fact that the line is located and replaced, puts shows, but it's impossible to save the changes. After closing, the file has its original state.
Please put me on the right path :).

Answer 1

Your code opens the file for writing to the end of the file,
then changes each line by subline
and closes
but does not write anything to the file

Answer 2

File.open("/tmp/test.conf", "r") do |in|
  File.open("/tmp/tmp_test.conf", "w") do |out|
    in.each_line { |line| out.puts line.gsub(/\/(.*)/, "99999") }
  end
end

In the general case, you cannot change something in the place in the file itself, you need to write the result to a new file. Rather, the replacement is possible byte to byte, and not like you have .*