Editing Backslash (section)

===Programming languages===
In many [[programming language]]s such as [[C (programming language)|C]], [[Perl]], [[PHP]], [[Python (programming language)|Python]] and [[Unix]] scripting languages, and in many file formats such as [[JSON]], the backslash is used as an [[escape character]], to indicate that the character following it should be treated specially (if it would otherwise be treated literally), or literally (if it would otherwise be treated specially). For instance, inside a C [[string literal]] the sequence {{code|\n}} produces a [[newline]] byte instead of an 'n', and the sequence {{code|\"}} produces an actual double quote rather than the special meaning of the double quote ending the string. An actual backslash is produced by a double backslash {{code|\\}}.

[[Regular expression]] languages used it the same way, changing subsequent literal characters into [[metacharacter]]s and vice versa. For instance {{mono|\{{vbar}}{{vbar}}b}} searches for either '|'  or 'b', the first bar is escaped and searched for, the second is not escaped and acts as an "or".

{{anchor|line-continuation}}Outside quoted strings, the only common use of backslash is to ignore ("escape") a newline immediately after it. In this context it may be called a "continued line"<ref>{{cite web |url=https://gcc.gnu.org/onlinedocs/gcc-3.2.3/cpp/Initial-processing.html |title=The C Preprocessor |website=[[GNU]].org |access-date=2021-01-04 |archive-date=2021-08-03 |archive-url=https://web.archive.org/web/20210803000553/https://gcc.gnu.org/onlinedocs/gcc-3.2.3/cpp/Initial-processing.html |url-status=live }}</ref> as the current line continues into the next one. Some software replaces the backslash+newline with a space.<ref>{{cite book|chapter=3.1.1 Splitting long lines|title=GNU {{font|make|size=80%}} manual|chapter-url=https://www.gnu.org/software/make/manual/make.html#Splitting-Lines|access-date=July 28, 2019|archive-date=June 5, 2018|archive-url=https://web.archive.org/web/20180605023853/https://www.gnu.org/software/make/manual/make.html#Splitting-Lines|url-status=live}}</ref>

To support [[computers]] that lacked the backslash character, the [[C trigraph]] {{code|??/}} was added, which is equivalent to a backslash. Since this can escape the next character, which may itself be a {{code|?}}, the primary modern use may be for [[code obfuscation]]. Support for trigraphs in [[C++]] was removed in [[C++17]], and support for them in C is planned to be removed in [[C23 (C standard revision)|C23]].

In [[Visual Basic]] (and some other [[BASIC]] dialects) the backslash is used as an operator symbol to indicate [[Integer (computer science)|integer]] [[Division (mathematics)|division]].<ref>{{cite web|title=Arithmetic Operators in Visual Basic|url=http://msdn.microsoft.com/en-us/library/b6ex274z(v=vs.110).aspx|work=Visual Basic Language Features: Operators and Expressions| date=10 July 2012 |publisher=MSDN|access-date=7 October 2012|archive-date=17 September 2012|archive-url=https://web.archive.org/web/20120917100112/http://msdn.microsoft.com/en-us/library/b6ex274z(v=vs.110).aspx|url-status=live}}</ref> This rounds toward zero.

The [[ALGOL 68]] programming language uses the "\" as its [[Scientific notation|Decimal Exponent Symbol]]. ALGOL 68 has the choice of 4 Decimal Exponent Symbols: e, E, \, or <sub>10</sub>.  Examples: {{mono|6.0221415e23}}, {{mono|6.0221415E23}}, {{mono|6.0221415\23}} or {{mono|6.0221415<sub>10</sub>23}}.<ref>{{cite journal | title=Revised Report on the Algorithmic Language Algol 68 | journal=Acta Informatica | volume=5 | issue=1–3 | pages=1–236 | date=September 1973 | doi=10.1007/BF00265077 | s2cid=2490556 | url=https://ir.cwi.nl/pub/13447 | access-date=2020-02-10 | archive-date=2020-07-26 | archive-url=https://web.archive.org/web/20200726125450/https://ir.cwi.nl/pub/13447 | url-status=live }}</ref>

In [[APL (programming language)|APL]] {{mono|\}} is called ''Expand'' when used to insert fill elements into arrays, and ''Scan'' when used to produce prefix reduction (cumulative fold).

In [[PHP]] version 5.3 and higher, the backslash is used to indicate a [[namespace]].<ref>{{cite web |url=http://php.net/manual/en/language.namespaces.rationale.php |title=Namespaces overview |website=php.net |access-date=2012-10-10 |archive-date=2012-10-16 |archive-url=https://web.archive.org/web/20121016184321/http://www.php.net/manual/en/language.namespaces.rationale.php |url-status=live }}</ref>

In [[Haskell (programming language)|Haskell]], the backslash is used both to introduce special characters and to introduce [[anonymous function|lambda functions]] (since it is a reasonable approximation in ASCII of the Greek letter {{nowrap|lambda, λ)}}.<ref>O'Sullivan, Stewart, and Goerzen,  ''Real World Haskell'', ch. 4: anonymous (lambda) functions, p.99</ref>