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CR, LF, and CRLF

One of the confusing aspects for people working across multiple platforms is the newline character. Mac OS, Windows, and Linux all use different characters for newline. Even Mac OS behaves differently between older and newer versions. In this article, we will explore the reasons behind the different newline characters used across systems.

According to the ISO 6429 standard, LF (line feed, \n) moves the cursor to the next line while maintaining the current column, and CR (carriage return, \r) moves the cursor to the beginning of the current line. To achieve the newline function, both CR and LF should be used together. This distinction was made to mimic the behavior of early printers and typewriters that separated the line-changing action from the action of moving the cursor to the beginning.

A
 B

For instance, a string "A\nB" should not result in B directly below A, but rather B should appear diagonally below A, like in the above example. However, systems using CRLF as a newline character are rare. Storage is a relatively cheap resource nowadays, but in the past, it was quite expensive. System designers of that time considered allocating two bytes for newline characters to be an excessive expense. Consequently, some system designers began using either LF or CR as the sole newline character.

Amidst this, some systems adhered to the standard. One such operating system was CP/M, which used a combination of CR and LF for newline characters. This choice was not simply due to the desire to follow the standard but was a strategic decision to maintain compatibility with earlier remote terminal devices. In other words, the costly storage expense was deemed worthwhile to secure market dominance by maintaining backward compatibility. Some subsequent operating systems also made the same choice, one of which was Microsoft's MS-DOS. This choice continues today, with Microsoft Windows using CRLF as its newline character.

Among the operating systems that chose to reduce newline characters to a single byte, there were different preferences. Some designers chose LF as the newline character, while others picked CR. Multics, an operating system that later influenced the design of Unix and BSD, chose LF. Though Multics is no longer in use, Unix-like systems, including Linux, adopted LF and move the cursor to the beginning of the next line when encountering LF.

Apple was a prominent supporter of using CR as the newline character. The Apple II, created in 1977, used CR for newline and simply ignored LF. This choice was carried over to Mac OS. However, with the creation of the POSIX.1 (Portable Operating System Interface) standard in 1988, Unix-based operating systems, including Linux, began to prioritize compatibility with one another. As a result, Apple started to change as well. Eventually, in 2001, OS X adopted LF as its newline character, making systems using CR as the newline character increasingly rare. Currently, aside from some legacy Apple programs, only LF and CRLF exist.

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