Quotes                 package:base                 R Documentation

Quotes

Description:

     Descriptions of the various uses of quoting in R.

Details:

     Three types of quote are part of the syntax of R: single and
     double quotation marks and the backtick (or back quote, '`').  In
     addition, backslash is used for quoting the following characters
     inside character constants.

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. Unless specified in the following table, an escaped
     character is interpreted as the character itself.  (Note that the
     parser will warn about most such uses, as they are most often
     erroneous, e.g. using '\.' where '\\.' was intended.)

     Single quotes need to be escaped by backslash in single-quoted
     strings, and double quotes in double-quoted strings.

       '\n'          newline
       '\r'          carriage return
       '\t'          tab
       '\b'          backspace
       '\a'          alert (bell)
       '\f'          form feed
       '\v'          vertical tab
       '\\'          backslash '\'
       '\nnn'        character with given octal code (1, 2 or 3 digits)
       '\xnn'        character with given hex code (1 or 2 hex digits)
       '\unnnn'      Unicode character with given code (1-4 hex digits)
       '\Unnnnnnnn'  Unicode character with given code (1-8 hex digits)

     The last two are only supported on versions of R built with MBCS
     support: they are an error on other versions.  Alternative forms
     are '\u{nnnn}' and '\U{nnnnnnnn}'.  All except the Unicode escape
     sequences are also supported when reading character strings by
     'scan' and 'read.table' if 'allowEscapes = TRUE'.

     These forms will also be used by 'print.default' when outputting
     non-printable characters (including backslash).

     Note that as from R 2.8.0 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
     ('`'), and '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: see 'formula'.

See Also:

     'Syntax' for other aspects of the syntax.

     'sQuote' for quoting English text.

     'shQuote' for quoting OS commands.

     The _R Language Definition_ manual.

