For a long time, the understanding of CRLF, CR, and LF was limited to the definition of newline characters under different operating systems. The so-called knowing the need to know why, from the learning to find fun, the memory of knowledge will be more profound.

Glossary

• CR: Carriage Return, corresponding to the ASCII escape character \r, indicating carriage return
• LF: Linefeed, corresponding to the ASCII escape character \n, indicating a newline
• CRLF: Carriage Return & Linefeed, \r\n, indicating carriage return and line feed

As we all know, the Windows operating system uses two characters for line breaks, namely CRLF; the Unix/Linux/Mac OS X operating system uses a single character LF for line breaks; in addition, the MacIntosh operating system (ie, the early Mac operating system) uses a single character CR. To make a new line.

unofficial history

Vintage mechanical typewriter (Source: Visual China)

According to historical records, in the era of mechanical typewriters a long time ago, CR and LF have different functions: LF will move the printing paper up one line, but keep the horizontal position of the current typing unchanged; CR will be "Carriage" (typewriter The upper scrolling carriage) rolls back to the far left of the printing paper, but keeps the vertical position of the current typing unchanged, that is, on the same line.

When CR and LF are used in combination, the print paper is moved up one line, and the next typing position will return to the far left of the line, which is the line feed we understand today.

Over time, mechanical typewriters gradually withdrew from the historical stage, and the original paper became the monitor of today, and the keys of typewriters evolved into today's keyboards. In the era of operating systems, limited by the lack of memory and floppy disk space, some operating system designers decided to use a single character to represent newline characters, such as Unix LF, MacIntosh CR. Their intention is to carry out a line-feeding operation, but there is no international standard (or other reasons, ghosts know), so there is such a difference in characters.

in conclusion

Many modern text editors and command line tools provide optional line break configuration, which makes it easy for users to change the form of newline characters as they wish, so we only need to know the role of CRLF, CR, and LF.

references

http://en.wikipedia.org/wiki/Newline
https://en.wikipedia.org/wiki/Control_character
https://stackoverflow.com/questions/1552749/difference-between-cr-lf-lf-and-cr-line-break-types