Editing Escape sequence (section)

==Quoting escape==
===Overview===
When an [[escape character]] is needed within the quoted/escaped string, there are two strategies used within programming and scripting languages:
* doubled delimiter (e.g. <code><nowiki>'He didn''t do it.'</nowiki></code>)<ref name="IEY"/>
* secondary escape sequence

An example of the latter is in the use of the caret (<code>^</code>). E.g. this outputs "You can do so via Cut&Paste" in [[cmd.exe|CMD]]. (otherwise, the ampersand has a restricted use)<ref name="CMD.a"/>

 echo You can do so via Cut^&Paste

===In detail===
{{see|String literal#Escape sequences}}
{{see also|Escape sequences in C}}
A common use of escape sequences is in fact to remove control characters found in a binary data stream so that they will not cause their control function by mistake. In this case, the control character is replaced by a defined "escape character" (which need not be the US-ASCII escape character) and one or more other characters; after exiting the context where the control character would have caused an action, the sequence is recognized and replaced by the removed character.<ref name="CMD.a"/> To transmit the "escape character" itself, two copies are sent.<ref name="IEY"/>

In many [[programming language]]s and command line interfaces escape sequences are used in [[character literal]]s and [[string literal]]s, to express characters which are not printable or clash with the syntax of characters or strings. For example, [[control characters]] themselves might not be allowed to be placed in the program coded by the editor program, or may have undesirable side-effects if typed into a command. The end-of-quote character is also a problem for programmers that can be solved by escaping it. In most contexts the escape character is the [[backslash]] ("'''\'''").

===Samples===
For example, the single quotation mark character might be expressed as <code><nowiki>'\''</nowiki></code> since writing <code><nowiki>'''</nowiki></code> is not acceptable.

Many modern programming languages specify the doublequote character (<code><nowiki>"</nowiki></code>) as a [[delimiter]] for a string literal. The backslash escape character typically provides ways to include doublequotes inside a string literal, such as by modifying the meaning of the doublequote character embedded in the string (<code><nowiki>\"</nowiki></code>), or by modifying the meaning of a sequence of characters including the hexadecimal value of a doublequote character (<code><nowiki>\x22</nowiki></code>). Both sequences encode a literal doublequote (<code><nowiki>"</nowiki></code>).

In [[Perl]] or [[Python (programming language)|Python]] 2
<syntaxhighlight lang="perl">
print "Nancy said "Hello World!" to the crowd.";
</syntaxhighlight>
produces a syntax error, whereas:
<syntaxhighlight lang="perl">
print "Nancy said \"Hello World!\" to the crowd.";  ### example of \"
</syntaxhighlight>
produces the intended output.
Another alternative:
<syntaxhighlight lang="perl">
print "Nancy said \x22Hello World!\x22 to the crowd.";  ### example of \x22
</syntaxhighlight>
uses "\x" to indicate the following two characters are hexadecimal digits, "22" being the ASCII value for a doublequote in hexadecimal.

[[C (programming language)|C]], [[C++]], [[Java (programming language)|Java]], and [[Ruby (programming language)|Ruby]] all allow exactly the same two backslash escape styles. The [[PostScript]] language and Microsoft [[Rich Text Format]] also use backslash escapes. The [[quoted-printable]] encoding uses the [[equals sign]] as an escape character.

[[URL]] and [[URI]] use [[percent-encoding]] to quote characters with a special meaning, as for non-ASCII characters.

Another similar (and partially overlapping) syntactic trick is [[stropping (syntax)|stropping]].

Some programming languages also provide other ways to represent special characters in literals, without requiring an escape character (see e.g. [[delimiter collision]]).