Editing Bell character

{{Short description|Device control code used to alert operators}}
{{refimprove|date=July 2011}}
{{Distinguish|Bell code}}

A '''bell character''' (sometimes '''bell code''') is a device [[control character|control code]] originally sent to ring a small electromechanical bell on [[stock ticker|tickers]] and other [[teleprinter]]s and teletypewriters to alert operators at the other end of the line, often of an incoming message. Though tickers punched the bell codes into their tapes,<ref>{{cite web|title=Baudot |url=http://chem.ch.huji.ac.il/history/baudot.html |access-date=February 1, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20081219135647/http://chem.ch.huji.ac.il/history/baudot.html |archive-date=December 19, 2008 }}</ref> printers generally do not print a character when the bell code is received. Bell codes are usually represented by the label "<code>BEL</code>". They have been used since 1870 (initially in the [[Baudot code]]).<ref>{{cite web | last = Smith | first = Gil | title = Teletype Communication Codes | publisher = Baudot.net | year = 2001 | url = http://www.baudot.net/docs/smith--teletype-codes.pdf | access-date = 2008-07-11| archive-url= https://web.archive.org/web/20080820043949/http://www.baudot.net/docs/smith--teletype-codes.pdf| archive-date= 20 August 2008 <!--DASHBot-->|url-status = live}}</ref>

To maintain [[backward compatibility]], video display [[computer terminal|terminal]]s (VDTs) that replaced teletypewriters included speakers or buzzers to perform the same function, as did the personal computers that followed. Modern [[terminal emulator]]s often integrate the warnings to the [[desktop environment]] (e.g., the [[macOS]] [[Terminal (macOS)|Terminal]] will play the system warning sound) and also often offer a silent ''visual bell'' feature that flashes the terminal window briefly.

== Representations ==
In [[ASCII]] the bell character's value is 7 and is named "BELL" or "BEL". [[Unicode]] does not give names to control characters but has assigned it the alias "ALERT" and abbreviation "BEL." It can sometimes be typed as {{keypress|ctrl|G}} and displayed as {{mono|^G}} in [[caret notation]]. Unicode also includes characters for the visual representation of the character: {{unichar|2407|SYMBOL FOR BELL}} and {{unichar|237E|BELL SYMBOL}}.

In the 5-bit Baudot codes, BEL is represented by the number 11 (<code>0x0B</code>) when in "figures" mode.<ref>{{cite web|title=The Lorenz Cipher and how Bletchley Park broke it|url=https://www.codesandciphers.org.uk/lorenz/fish.htm|website=www.codesandciphers.org.uk|access-date=9 July 2016}}</ref> The code {{mono|0x2F}} is used in [[EBCDIC]].

In the programming language [[C (programming language)|C]] (created in 1972), and in many languages influenced by it such as [[Python (programming language)|Python]], the bell character can be placed in a string or character constant with <code>\a</code>. 'a' stands for "alert" or "audible" and was chosen because <code>\b</code> was already used for the [[backspace]] character.<ref>{{Cite web|title=2. Lexical analysis — Python 2.7.18 documentation|url=https://docs.python.org/2/reference/lexical_analysis.html#grammar-token-stringliteral|access-date=2021-02-05|website=docs.python.org}}</ref>

== Usage ==
[[File:Osborne 1 keyboard closeup.jpg|alt=photograph of the keyboard for an Osborne 1 computer showing how the word "Bell" is also printed on the key for the letter "G"|thumb|Keyboard for the [[Osborne 1]] ]]
On [[Unix-like]] systems, or on [[MS-DOS]] or [[Microsoft Windows|Windows]], a user can cause the equivalent of ringing the bell to happen by typing at the [[command line interpreter|command prompt]] the command:

 echo ^G

where the {{mono|^G}} is produced by holding down {{keypress|Ctrl}} and typing {{keypress|G}}. On Unix the user may need to type {{keypress|Ctrl}}+{{keypress|V}} first to "quote" the {{mono|^G}}.

On POSIX systems, one may also use:

 printf '\a'

and in the [[Bash (Unix shell)|Bash]] shell, one may use ANSI-C quoting:<ref>[https://www.gnu.org/software/bash/manual/bash.html#ANSI_002dC-Quoting ANSI-C quoting]</ref>

 echo $'\a'

An alternative is to use the [[tput]] command, which as a part of the [[ncurses]] library is available on most Unix/Linux operating systems:

 tput bel

A program can get the same result by printing the BEL character to a terminal.

On modern systems this may not make a noise; it may instead make a visual indication such as flashing the screen, or do nothing at all.

== See also ==
* [[C0 and C1 control codes]] ([[ISO 646]])

== References ==
{{Reflist}}
* [https://web.archive.org/web/20160303230740/http://www.atis.org/glossary/definition.aspx?id=5756 ATIS Telcom Glossary]
* [https://foldoc.org/bell Free On-Line Dictionary of Computing, 'bell']

{{DEFAULTSORT:Bell Character}}
[[Category:Control characters]]