View source for Backspace

{{Short description|Key on a keyboard}}{{redirect|ASCII 8|the eight-bit or larger encodings|Extended ASCII}}{{Distinguish|Delete key}}
[[File:Backspace.jpg|thumb|Backspace key]]
'''Backspace''' ({{keypress|Backspace}}, <code>⌫</code>) is the keyboard key that in [[typewriter]]s originally pushed the carriage one position backwards, and in modern computer systems typically moves the [[display cursor]] one position backwards,<ref group="note">The meaning of "backwards" depends on the direction of the text, and could get complicated in text involving several [[Bidirectional text|bidirectional categories]].</ref> deletes the character at that position, and shifts back any text after<ref group=note>"after" here implies on the same logical [[line of text]]</ref> that position by one character.

==Nomenclature==
[[File:Blickensderfer model 7, 1909.jpg|thumb|An early typewriter with a ''backspacer''[sic] key. ([[Blickensderfer]] Model 7)]]
Although the term "backspace" is the traditional name of the key which steps the carriage back and/or<ref group=note>in some [[correcting typewriter]]s it did both</ref> deletes the previous character, typically to the left of the cursor, the actual key may be labeled in a variety of ways, for example ''delete'',<ref>{{cite web | url=http://lowendmac.com/mail/07/0502.html | title=User Mistakes or Mac Mistakes?, Backspace vs. Delete, and It's Too Easy to Zap an Icon in the Dock | year=2007}}</ref> ''erase'',{{refn|group=note|for example in [[XO-1 (laptop)|One Laptop Per Child]]<ref>{{cite web | url=http://wiki.laptop.org/go/OLPC_Human_Interface_Guidelines/The_Sugar_Interface/Input_Systems | title=OLPC Human Interface Guidelines/The Sugar Interface/Input Systems | access-date=2008-01-15 | last=OLPC Wiki| archive-url= https://web.archive.org/web/20080118083728/http://wiki.laptop.org/go/OLPC_Human_Interface_Guidelines/The_Sugar_Interface/Input_Systems#.22Hand-held.22_Mode| archive-date= 18 January 2008 | url-status= live}}</ref>}} or with a left pointing arrow.<ref name="debian"/> A dedicated symbol for "backspace" exists as [[Miscellaneous Technical#Block|U+232B]] ⌫ but its use as a keyboard label is not universal. Some very early typewriters labeled this key the ''backspacer'' key.
[[File:Hemingway Corona number 3 typewriter.jpg|thumb|Corona #3 typewriter. Note the oddly positioned backspace key, located off the keyboard, towards the back of the machine, on the right.]]
Backspace is distinct from the [[delete key]], which in a [[teletypewriter]] would punch out all the holes in [[punched paper tape]] to strike out a character, and in modern computers deletes text at or ''following'' the cursor position. Also, the delete key often works as a generic command to remove an object (such as an image inside a document, or a file in a [[file manager]]), while backspace usually does not.<ref>{{cite web | url=https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/keys_general.mspx | title=Windows keyboard shortcuts overview | website=[[Microsoft]] | access-date=2016-02-09 }}</ref><ref>{{cite web | url=https://github.com/lxde/lxqt/issues/178 | title=Keyboard shortcuts for PCmanFM-QT [bug]/[Missing feature] | website=[[GitHub]] | access-date=2016-02-09 }}</ref> Full-size [[Mac (computer)|Mac]] keyboards have two keys labeled ''delete''; a key that functions as a backspace key, and a key that functions as a delete key. Smaller Mac keyboards, such as laptop keyboards, have only a key that functions as a backspace key.<ref>{{cite web |url=https://www.oreilly.com/library/view/switching-to-the/9781449372927/ch01s08.html |title=Keyboard Differences |work=Switching to the Mac: The Missing Manual, Mavericks Edition |first=David |last=Pogue |author-link=David Pogue}}</ref>

==Combining characters==
In some<ref group="note">Many typewriters don't advance accent characters, thus no backspace is needed where the accent is typed ahead of the letter it is to be combined with. However, even with such machines, the backspace is still used to produce certain other characters, e.g. for combining "o" with "/" to make "ø".</ref> typewriters, a typist would, for example, type a lowercase letter A with acute accent (á) by typing a lowercase letter A, backspace, and then the acute accent key. This technique (also known as [[overstrike]]) is the basis for such spacing modifiers in computer character sets such as the [[ASCII]] caret (^, for the [[circumflex]] accent). Backspace composition no longer works with typical modern digital displays or typesetting systems.<ref group="note">There is no reason why a digital display or typesetting system could not be designed to allow backspace composition, a.k.a. overstrike, if an engineer chose to do that. As most contemporary computer display and typesetting systems are raster graphics-based rather than character-based (as of 2012), they make overstrike actually quite easy to implement. However, the use of proportional-width rather than fixed-width (monospaced) fonts makes the practical implementation of overstrike more complicated, and the original physical motivation for the technique is not present in digital computer systems.</ref> It has to some degree been replaced with the [[combining diacritical mark]]s mechanism of [[Unicode]], though such characters do not work well with many fonts, and precomposed characters continue to be used. Some software like [[TeX]] or [[Microsoft Windows]] use the opposite method for diacritical marks, namely positioning the accent first, and then the base letter on its position.

==Use in computing==
===Common use===
In modern systems, the backspace key is often mapped to the delete character (0x7f in ASCII or Unicode), although the backspace key's function of deleting the character before the cursor remains.<ref name="debian">{{cite web | title=9.8 Keyboard configuration | work=Debian Policy Manual | url=http://www.debian.org/doc/debian-policy/ch-opersys.html#s9.8 | access-date=2007-07-24 | archive-url=https://web.archive.org/web/20160310144541/http://www.debian.org/doc/debian-policy/ch-opersys.html#s9.8 | archive-date=2016-03-10 | url-status=dead }}</ref> In computers, backspace can also delete a preceding [[newline]] character, something generally inapplicable to typewriters.

The backspace key is commonly used to go back a page or up one level in graphical web or file browsers.

===^H===
{{see|Caret notation}}
Pressing the backspace key on a [[computer terminal]] would generate the [[ASCII]] code 08, BS or Backspace, a [[control code]] which would delete the preceding character. That control code could also be accessed by pressing  {{keypress|[[Control key|Control]]}}+{{keypress|H}}, as [[H]] is the eighth letter of the [[Latin alphabet]]. Terminals which did not have the backspace code mapped to the function of moving the cursor backwards and deleting the preceding character would display the symbols '''^H''' ([[Caret notation|caret]], H) when the backspace key was pressed. Even if a terminal did interpret backspace by deleting the preceding character, the system receiving the text might not. Then, the sender's screen would show a message without the supposedly deleted text, while that text, and the deletion codes, would be visible to the recipient. This sequence is still used humorously for [[epanorthosis]] by computer literates, denoting the deletion of a pretended blunder, much like a [[strikethrough]]; in this case, however, the ^H symbol is faked by typing a regular '^' followed by typing a regular 'H'.

Example:
:''Be nice to this fool''^H^H^H^H''gentleman; he's visiting from corporate HQ.''<ref name="Jargon">[http://www.catb.org/~esr/jargon/html/writing-style.html Chapter 5. Hacker Writing Style], The [[Jargon File]], version 4.4.7</ref>

====Alternatives<span class="anchor" id="^W and ^U"></span>====
An alternative sometimes seen is '''^W''', which is the shortcut to delete the previous word in the Berkeley Unix terminal [[line discipline]]. This shortcut has also made it into the insert mode of the [[Vi (text editor)|Vi]] text editor and its clone [[Vim (text editor)|Vim]].<ref>{{cite web |url=https://vimdoc.sourceforge.net/vimum.html | title=VIM USER MANUAL | publisher=[[FreeBSD]] | date=November 2, 2013 | access-date=May 14, 2016}}</ref>

'''^U''' deletes a line.<ref>{{cite web |url=http://www.freebsd.org/cgi/man.cgi?query=vi | title=FreeBSD Man Pages; vi | publisher=Vimonline | date=March 9, 2002 | access-date=May 14, 2016}}</ref>

==Notes==
{{Reflist|group=note}}
{{Keyboard}}

==References==
{{Wiktionary}}
{{Commons category|Backspace}}
{{Reflist}}

{{Keyboard keys}}

[[Category:Computer keys]]
[[Category:Control characters]]