How to write DOS line endings to a file from Unix

Question

My Unix Ruby program needs to write a file that will be read by SqlServer running on Windows. I need for the lines I write to this file to end in \r\n, the DOS/Windows line ending, rather than \n, the Unix line ending. I want this to happen without me having to manually add the \r to the end of each line.

The starting point

If my program writes to the file like this:

File.open("/tmp/foo", "w") do |file|
  file.puts "stuff"
end

Then the file has Unix line endings:

$ od -c foo
0000000   s   t   u   f   f  \n

That is expected, since my program is running on Unix. But I need for this file (and this file only) to have DOS line endings.

Adding the \r to each line manually

If I add the \r to each line manually:

File.open("/tmp/foo", "w") do |file|
  file.puts "stuff\r"
end

Then the file has DOS line endings:

$ od -c /tmp/foo
0000000   s   t   u   f   f  \r  \n

This works, but has to be repeated for each line I want to write.

Using String#encode

As shown by this SO answer, I can modify the string using String#encode before writing it:

File.open("/tmp/foo", "w") do |file|
  file.puts "alpha\nbeta\n".encode(crlf_newline: true)
end

This results in DOS line endings:

$ od -c /tmp/foo
0000000   a   l   p   h   a  \r  \n   b   e   t   a  \r  \n

This has the advantage that if I am writing multiple lines at once, one call to #encode will change all the line endings for that one write. However, it's verbose, and I still have to specify the line ending for every write.

How can I cause each puts to an open file in Unix to end the line in the Windows \r\n line ending rather than the Unix '\n' line ending?

I am running Ruby 2.3.1.

Answer 1

There's an option for this, the same one you're using on encode also works with File.open:

File.open('/tmp/foo', mode: 'w', crlf_newline: true) do |file|
  file.puts("alpha")
  file.puts("beta")
end

This option not only ends lines in \r\n, it also translates any explicit \n into \r\n. So this:

file.puts("alpha\nbar")

will write alpha\r\nbar\r\b