Programming Perl, 4th Edition

Pick Your Own Quotes

Although we usually think of quotes as literal values, in Perl they function more like operators, providing various kinds of interpolating and pattern-matching capabilities. Perl provides the customary quote characters for these behaviors, but it also provides a more general way for you to choose your quote character for any of them. In Table 2-7, any nonalphanumeric, nonwhitespace delimiter may be used in place of /. (The newline and space characters are no longer allowed as delimiters, although prehistoric versions of Perl once allowed this.)

Table 2-7. Quote constructs

Customary	Generic	Meaning	Interpolates
''	q//	Literal string	No
""	qq//	Literal string	Yes
``	qx//	Command execution	Yes
()	qw//	Word list	No
//	m//	Pattern match	Yes
s///	s///	Pattern substitution	Yes
tr///	y///	Character translation	No
""	qr//	Regular expression	Yes

Some of these are simply forms of “syntactic sugar” to let you avoid putting too many backslashes into quoted strings, particularly into pattern matches where your regular slashes and backslashes tend to get all tangled.

If you choose single quotes for delimiters, no variable interpolation is done even on those forms that ordinarily interpolate. If the opening delimiter is an opening parenthesis, bracket, brace, or angle bracket, the closing delimiter will be the corresponding closing character. (Embedded occurrences of the delimiters must match in pairs.) Examples:

my $single = q!I said, "You said, 'She said it.'"!; my $double = qq(Can't ...