\n and \r seem to work everywhere. Why is line.separator more portable?

Question

I was just perusing through questions, and I found System.getProperty(line.separator) used in place of \n with the author's comment that the code was "portable". Reading through various forums, I've seen two groups:

1. People who say there's a difference between Linux's and Windows' interpretation of newline characters, and this compensates for that (with no clear evidence).
2. People who say there's no difference by showing code and output examples, which obviously only applies to that code example and not universally.

My feeling is: it's probably non-standard OS's, like for example your company's industrial scanner's OS for example, where you'll notice a difference. When am I going to see a difference between \n and line.separator? Can you show an example, please? How did you go about discovering where the variation occurs?

Answer 1

Incorrect line endings are a frequent annoyance. For example, this is what Windows Notepad shows when writing a file with \n instead of \r\n (Windows' line.separator):

Those little boxes were supposed to be line breaks.

The other way around, when \r\n is used in place of \n (Unix' line.separator), is way worse, and breaks shell scripts and config files in weird and wonderful ways.

For example, this is what sh outputs on Debian and derived distros when trying to run a shell script that just contains ls but with \r\n line separators (it looks trashed because the carriage return causes the terminal to overwrite parts of the line):

: not foundsh: ls

There are several questions per day on StackOverflow from people being bitten by this, such as here, here and here.