Line feed - Definition and Overview

In computing, line feed (LF) is a control character indicating that one line should be fed out. It has an ASCII code of 10 (0A in hexadecimal). Line feed was originally a printer command normally used in conjunction with a carriage return (a command which returned the printer carriage to the leftmost position, by analogy with typewriters; abbreviated CR). After processing a CR-LF pair, the printer head would have returned to the left margin and advanced one line down the page, ready to print a new line of text.

CRLF was eventually adopted as the standard line ending for network traffic, a decision which, in retrospect, is generally considered to be a mistake. However, this usage continued in MS-DOS and its descendant Microsoft Windows, so it will likely remain into the foreseeable future.

In Unix, a line feed is more often called a newline: in Unix-based operating systems, a line feed is interpreted as an instruction having the same effect on a computer terminal that CR-LF has on a printer. It was thought unnecessary to send printer sequences to computer displays. The C programming language, with origins in Unix, reflects this usage: in C, '\n' is an abbreviation for newline.

Apple Computer also simplified the CR-LF pair in their operating systems, choosing CR without LF. Apple Macintoshes continued to use carriage return as a line ending until the version of their operating system called Mac OS X (which was based on Unix).