qq//#

Build a double-quoted, interpolated string with a delimiter you pick.

qq// is the long form of the "..." string literal. It produces the same string "" would, so qq/hello $name\n/ and "hello $name\n" are interchangeable. The point of qq is the delimiter: when the content contains " (or backslash sequences that would interfere with double quotes), you pick a different delimiter and keep the string readable instead of threading \" through it.

Synopsis#

qq/STRING/
qq{STRING}
qq(STRING)
qq[STRING]
qq<STRING>
qqXSTRINGX        # any non-word, non-whitespace char works as delimiter

What you get back#

A scalar string. Variables referenced inside are interpolated at the point qq// is evaluated (not at parse time); backslash escape sequences are expanded. The result has no implicit newline - you have to write \n yourself.

Choosing a delimiter#

Any character that is not a word character (/\w/) and not whitespace may follow qq. The four bracket pairs nest:

qq(foo (bar) baz)          # "foo (bar) baz" - inner () balanced
qq{ if ($x) { 1 } else { 0 } }
qq[a[b[c]d]e]
qq<<a<b>c>>

Non-bracketing delimiters use the same character at both ends and do not nest:

qq|one|two|                # SYNTAX ERROR - first | closes
qq/a\/b/                   # "a/b" - backslash escapes the delimiter

If the delimiter is a word character, whitespace between qq and the delimiter is required:

qq XfooX                   # OK - "foo"
qqXfooX                    # WRONG - parsed as identifier qqXfooX

# as delimiter needs no space and is occasionally handy for strings containing every other punctuation mark:

qq#He said "hi" & waved.#  # "He said \"hi\" & waved."

The extra_paired_delimiters feature (5.36+) recognises a wide set of Unicode bracket pairs as nesting delimiters; enable it with use feature 'extra_paired_delimiters' when you want, say, guillemets or CJK brackets.

What gets interpolated#

Scalars: $x, $hash{key}, $array[0], $ref->{k}[2].
Arrays: @arr expands in order, elements joined by $" (default " "). Equivalent to join $", @arr.
Slices: @h{qw(a b)}, @a[1..3].
Dereferences with arrows and subscripts: $ref->{key}[0].

What is not interpolated:

Method calls: $obj->meth inside qq// interpolates $obj and leaves the literal text ->meth in the string.
Function calls: @{[ func() ]} is the usual workaround - array reference dereference runs arbitrary code and splices its result in.
Punctuation arrays other than @_, @+, @-: only interpolate when braced (@{*}). Bare @* is a literal @*.

my $obj = Some::Class->new;
qq/$obj->name/;                       # interpolates $obj, leaves "->name"
qq/@{[ $obj->name ]}/;                # calls the method, interpolates result

Escape sequences#

Available inside qq// (and anywhere else interpolation happens):

Sequence	Meaning
`\t`	tab (HT)
`\n`	newline (platform-virtual line terminator)
`\r`	carriage return (CR)
`\f`	form feed (FF)
`\b`	backspace (BS)
`\a`	alarm / bell (BEL)
`\e`	escape (ESC)
`\0`	NUL
`\\`	literal backslash
`\"`	literal double quote
`\x1b`	hex char, 0x00–0xFF
`\x{263A}`	hex char, any codepoint (braced form)
`\o{23072}`	octal char, any codepoint
`\033`	octal char, 000–777 (prefer `\o{}`)
`\cA`	control char - 64 xor’d with uppercased next char
`\N{GREEK SMALL LETTER ALPHA}`	named Unicode char (needs `use charnames`)
`\N{U+03B1}`	Unicode char by codepoint (always Unicode, even on EBCDIC)

Case and quoting modifiers apply until \E or end of string:

Sequence	Meaning
`\l`	lowercase the next character only
`\u`	titlecase (not uppercase!) the next character only
`\L`	lowercase until `\E`
`\U`	uppercase until `\E`
`\F`	foldcase until `\E`
`\Q`	quote regex metacharacters until `\E` (calls `quotemeta`)
`\E`	end the most recent `\L` / `\U` / `\F` / `\Q`

\L, \U, \F, \Q stack - each needs its own \E.

say "\u$name";                        # capitalise first letter
say "\U$name\E's account";            # uppercase $name, rest untouched
say "match $file literally: \Q$file\E";

\Q inside qq// is applied after interpolation, so qq/\Q$pat\E/ equals quotemeta($pat). (In regex quote operators qr// and m//, \Q is applied after interpolation but before regex compilation - the difference matters when $pat itself contains regex metacharacters you want to keep literal.)

Perl has no \v escape in string literals - it is a regex metacharacter. Use \x0b, \cK, or \N{VT} for a vertical tab.

Global state it touches#

$" - list separator used when interpolating arrays and slices. Default " ". Change with local $" = "," for one scope.

No other interpreter globals participate in qq// evaluation itself. Interpolated variables are of course whatever their current values are at the point qq// runs.

Examples#

Plain interpolation, identical in meaning to the "..." form:

my $name = "world";
my $s = qq/hello, $name!\n/;          # "hello, world!\n"

String that contains double quotes - qq with a different delimiter avoids backslash litter:

my $msg = qq{He said "yes" and then "maybe".};
# vs:   "He said \"yes\" and then \"maybe\"."

Multi-line HTML snippet with nested braces - the () pair nests:

my $user = "rj";
my $html = qq(
  <p>Welcome, $user.</p>
  <p>You have @{[ scalar @inbox ]} messages.</p>
);

Array interpolation with a custom separator:

my @tags = qw(perl rust docs);
local $" = ", ";
say qq/tags: @tags/;                  # "tags: perl, rust, docs"

Method-call trap - -> is literal inside qq//:

my $obj = File::Spec->new;
qq/path is $obj->rel2abs('.')/;       # "path is <stringified $obj>->rel2abs('.')"
qq/path is @{[ $obj->rel2abs('.') ]}/;
                                      # actually calls rel2abs()

Building an SQL fragment where $ident is untrusted - \Q..\E keeps embedded %, _, and backslashes literal under a LIKE clause only after you have handled proper parameterisation; for actual SQL escaping use the driver’s quoting, not \Q:

my $needle = "100% sure";
my $pat = qq/\Q$needle\E/;            # the regex-safe form
# $pat eq "100\\%\\ sure"

Stacked modifiers:

say qq/\Qfoo \ubar \Ubaz\E qux\E done/;
# "foo\ Bar\ BAZ qux done"
#  \Q quotes spaces/?; \u titlecases b; \U uppercases baz until \E;
#  outer \E ends \Q.

Edge cases#

Parse-time delimiter choice. Perl picks the closing delimiter the moment it reads the opening one. qq/.../ expects a /; there is no way to switch mid-string. If you need both kinds of braces, pick a non-bracket delimiter.
Backslash at end of string with non-bracket delimiter. qq/a\/ is a/ (backslash escapes the delimiter, string continues); to get a literal trailing backslash, change delimiter: qq{a\\}.
No nesting for non-bracket delimiters. qq|a|b| is the string a followed by the identifier b followed by | - a syntax error in most contexts. Pick bracket delimiters when the content contains the delimiter char.
# as delimiter is a special case only because of how comments interact: qq#...# is a string, but qq #...# (with whitespace) is the operator qq followed by a comment, with the string taken from the next line. This mirrors the behaviour of all q-family operators.
Empty string. qq// is the empty string, same as "".
Interpolated undef. Stringifies to the empty string and, under use warnings, triggers an uninitialized warning at the point of interpolation, not at the point $var was assigned undef.
$ or @ followed by non-identifier. Stays literal: qq/cost: \$5/ and qq/cost: $5/ both produce cost: $5 (there is no variable named $5 in the Perl 5 identifier sense - $5 is a regex capture, which does exist, so the second form interpolates capture group 5, whatever it currently is). For a literal $ or @, escape it: \$, \@.
\N{...} without charnames. Named characters require use charnames ':full' (or similar) to be loaded in scope; without it you get a compile-time error. \N{U+HEX} and the single-name forms in the :loose set work without it.
Locale-sensitive case mapping. With use locale including LC_CTYPE, \l, \u, \L, \U use the current locale’s case tables. Without it, Unicode case tables are used for codepoints above 0xFF, and ASCII rules below. \F uses Unicode foldcase regardless of locale (except under a UTF-8 locale, where it matches \L).
One level only. The result of interpolation is not re-scanned. my $v = '$x'; qq/$v/ is the four-character string $x, not the value of $x.

Differences from upstream#

Fully compatible with upstream Perl 5.44.