Descriptions of the various uses of quoting in R.
Three types of quotes are part of the syntax of R: single and double quotation marks and the backtick (or back quote, `). In addition, backslash is used to escape the following character inside character constants.
Single and double quotes delimit character constants. They can be used interchangeably but double quotes are preferred (and character constants are printed using double quotes), so single quotes are normally only used to delimit character constants containing double quotes. Backslash is used to start an escape sequence inside character constants. Escaping a character not in the following table is an error. Single quotes need to be escaped by backslash in single-quoted strings, and double quotes in double-quoted strings.
|ASCII apostrophe '|
|ASCII quotation mark "|
|ASCII grave accent (backtick) `|
|character with given octal code (1, 2 or 3 digits)|
|character with given hex code (1 or 2 hex digits)|
|Unicode character with given code (1--4 hex digits)|
|Unicode character with given code (1--8 hex digits)|
allowEscapes = TRUE. Unicode escapes can be used to enter Unicode characters not in the current locale's charset (when the string will be stored internally in UTF-8). The parser does not allow the use of both octal/hex and Unicode escapes in a single string. These forms will also be used by
print.defaultwhen outputting non-printable characters (including backslash). Embedded nuls are not allowed in character strings, so using escapes (such as \0) for a nul will result in the string being truncated at that point (usually with a warning).
Names and Identifiers
Identifiers consist of a sequence of letters, digits, the period
.) and the underscore. They must not start with a digit nor
underscore, nor with a period followed by a digit. Reserved
words are not valid identifiers. The definition of a letter depends on the current locale, but
only ASCII digits are considered to be digits. Such identifiers are also known as syntactic names and may be used
directly in R code. Almost always, other names can be used
provided they are quoted. The preferred quote is the backtick
deparse will normally use it, but under
many circumstances single or double quotes can be used (as a character
constant will often be converted to a name). One place where
backticks may be essential is to delimit variable names in formulae:
Syntax for other aspects of the syntax.
sQuote for quoting English text.
shQuote for quoting OS commands.
The R Language Definition manual.