Meaning of \r on linux systems

Question

I'm looking at some linux specific code which is outputting the likes of:

\r\x1b[J>

to the std io.

I understand that <ESC>[J represents deleting the contents of the screen from the current line down, but what does \r do here?

I'm also seeing the following:

>user_input\n\r>

where user_input is the text entered by the user. But what is the purpose of the \r here?

It is pronounced as *carriage return* so I think it would be easily googleable for you. — om-nom-nom, Feb 20 '13 at 08:55
@om-nom-nom I'm asking about it purpose in the context above. — Baz, Feb 20 '13 at 09:02

Some programmer dude · Accepted Answer · 2013-02-20T09:04:36.020

16

The character '\r' is carriage return. It returns the cursor to the start of the line.

It is often used in Internet protocols conjunction with newline ('\n') to mark the end of a line (most standards specifies it as "\r\n", but some allows the wrong way around). On Windows the carriage-return newline pair is also used as end-of-line. On the old Macintosh operating system (before OSX) a single carriage-return was used instead of newline as end-of-line, while UNIX and UNIX-like systems (like Linux and OSX) uses a single newline.

edited Feb 20 '13 at 09:04

answered Feb 20 '13 at 08:55

Some programmer dude

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Historically, new line meant just that: on a screen or a printer, move the cursor down one line, but leave it in the same column. And carriage return moved it to the beginning of the line, without changing the line. To go to the start of the next line, you needed both (in either order). The authors of both Unix and Mac apparently thought that they needed just a single character to go to the beginning of the next line, and chose one. – James Kanze Feb 20 '13 at 09:19

score 1 · Answer 2 · answered Feb 20 '13 at 08:55

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Control character \r moves caret (a.k.a text cursor) to the leftmost position within current line.

answered Feb 20 '13 at 08:55

Mikhail Vladimirov

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score 1 · Answer 3 · answered Feb 20 '13 at 08:56

From Wikipedia

Systems based on ASCII or a compatible character set use either LF (Line feed, '\n', 0x0A, 10 in decimal) or CR (Carriage return, '\r', 0x0D, 13 in decimal) individually, or CR followed by LF (CR+LF, '\r\n', 0x0D0A). These characters are based on printer commands: The line feed indicated that one line of paper should feed out of the printer thus instructed the printer to advance the paper one line, and a carriage return indicated that the printer carriage should return to the beginning of the current line. Some rare systems, such as QNX before version 4, used the ASCII RS (record separator, 0x1E, 30 in decimal) character as the newline character.

score 0 · Answer 4 · edited Mar 15 '13 at 13:45

0

\r is carriage return. Similarly \n is linefeed.

edited Mar 15 '13 at 13:45

answered Feb 20 '13 at 08:56

Anders R. Bystrup

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In text files, `'\n'` is more than just linefeed. A text file is a stream of lines, and '\n' is the line terminator. – James Kanze Feb 20 '13 at 09:21

score 0 · Answer 5 · answered Feb 20 '13 at 13:10

FWIW - this is a part of carriage control - from mainframe control words to Windows/UNIX/FORTRAN carriage control. Carriage control can be implemented at a language level like FORTRAN does, or system-wide like UNIX and Windows do.

\n arose from limitations of early PDP user "interfaces" - the tty terminal. Go to a museum if you want see one.

A very simple point: The difference between \n \r is explained above. But all of these explanations are really saying that carriage control is implementation dependent.

The [J is part of ANSI escape sequences and what they do on a "standards conforming tty terminal". DOS used to have ANSI.SYS to provide: colors, underline, bold using those sequences.

http://ascii-table.com/ansi-escape-sequences.php

Is a good reference for the question: what does some odd looking string in the output do?

Meaning of \r on linux systems

5 Answers5