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I've seen many developers use different methods to split a string by new lines, but i'm confused which is the correct: \r\n OR \n only?
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The /r stands for return or carriage return which owes it's history to the typewriter. A carriage return moved your carriage all the way to the right so you were typing at the start of the line. The /n stands for new line, again, from typewriter days you moved down to a new line.
\r and \n are digital representations of the way you would advance to the next line on a typewriter. \r is a carriage return and \n is a newline (also known as a linefeed). On a typewriter, to go to the start of the new line, you would return the carriage to the leftmost position and then feed the paper up a line.
Newline (frequently called line ending, end of line (EOL), next line (NEL) or line break) is a control character or sequence of control characters in a character encoding specification (e.g., ASCII, EBCDIC) that is used to signify the end of a line of text and the start of a new one.
The most commonly used are "\t" for TAB, "\n" for new-line, and "\\" for a (single) backslash character.
\n is used for Unix systems (including Linux, and OSX).
\r\n is mainly used on Windows.
\r is used on really old Macs.
PHP_EOL constant is used instead of these characters for portability between platforms.
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The given answer is far from complete. In fact, it is so far from complete that it tends to lead the reader to believe that this answer is OS dependent when it isn't. It also isn't something which is programming language dependent (as some commentators have suggested). I'm going to add more information in order to make this more clear. First, lets give the list of current new line variations (as in, what they've been since 1999):
\r\n is only used on Windows Notepad, the DOS command line, most of the Windows API and in some (older) Windows apps.\n is used for all other systems, applications and the Internet.You'll notice that I've put most Windows apps in the \n group which may be slightly controversial but before you disagree with this statement, please grab a UNIX formatted text file and try it in 10 web friendly Windows applications of your choice (which aren't listed in my exceptions above). What percentage of them handled it just fine? You'll find that they (practically) all implement auto detection of line endings or just use \n because, while Windows may use \r\n, the Internet uses \n. Therefore, it is best practice for applications to use \n alone if you want your output to be Internet friendly.
PHP also defines a newline character called PHP_EOL. This constant is set to the OS specific newline string for the machine PHP is running on (\r\n for Windows and \n for everything else). This constant is not very useful for webpages and should be avoided for HTML output or for writing most text to files. It becomes VERY useful when we move to command line output from PHP applications because it will allow your application to output to a terminal Window in a consistent manner across all supported OSes.
If you want your PHP applications to work from any server they are placed on, the two biggest things to remember are that you should always just use \n unless it is terminal output (in which case you use PHP_EOL) and you should also ALWAYS use / for your path separator (not \).
The even longer explanation:
An application may choose to use whatever line endings it likes regardless of the default OS line ending style. If I want my text editor to print a newline every time it encounters a period that is no harder than using the \n to represent a newline because I'm interpreting the text as I display it anyway. IOW, I'm fiddling around with measuring the width of each character so it knows where to display the next so it is very simple to add a statement saying that if the current char is a period then perform a newline action (or if it is a \n then display a period).
Aside from the null terminator, no character code is sacred and when you write a text editor or viewer you are in charge of translating the bits in your file into glyphs (or carriage returns) on the screen. The only thing that distinguishes a control character such as the newline from other characters is that most font sets don't include them (meaning they don't have a visual representation available).
That being said, if you are working at a higher level of abstraction then you probably aren't making your own textbox controls. If this is the case then you're stuck with whatever line ending that control makes available to you. Even in this case it is a simple matter to automatically detect the line ending style of any string and make the conversion before you load your text into the control and then undo it when you read from that control. Meaning, that if you're a desktop application dev and your application doesn't recognize \n as a newline then it isn't a very friendly application and you really have no excuse because it isn't hard to make it the right way. It also means that whomever wrote Notepad should be ashamed of himself because it really is very easy to do much better and so many people suffer through using it every day.
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