From: Xavier Noria <fxn@...>
Date: 2007-11-20T17:53:22+09:00
Subject: Re: Why does IO.readlines() keep newlines?

On Nov 20, 2007, at 12:43 AM, Daniel Brumbaugh Keeney wrote:

> I'm going to speculate that readlines does this because of operating
> system differences in line endings.
> For compatibility between most systems, it would have to remove line
> feeds (\x0A) or line-feed/carriage return combinations (\x0D\x0A).

Indeed that's not the case.

In CRLF platforms the I/O layer handles newlines in text mode so that  
the programmer *always* works with "\n", no CRLF ever goes up on  
Windows. Nor you need to print CRLFs by hand at the Ruby level. At the  
Ruby level a newline is always == "\n" and has always length 1.

The string "\n" is the logical newline in Ruby meaning it is portable  
and the I/O layer takes care of its actual representation on disk  
according to the runtime platform. In Java for example this works in a  
different way, "\n" is not portable, to write a portable newline in  
Java you invoke some println().

This article explains how newlines work in C-based languages. It is  
Perl-based but in general it applies to Ruby except that in Ruby  
there's no platform where "\n" == "\015". In Ruby "\n" == "\012"  
everywhere and that simplifies things a bit. The I/O layer in MRI is  
C's stdio instead of PerlIO, but the explained newline mangling in and  
out is analogous:

   http://www.onlamp.com/pub/a/onlamp/2006/08/17/understanding-newlines.html

I am the author but that doesn't matter.

-- fxn