=over
-=item A sigil, followed solely by digits matching \p{POSIX_Digit}, like C<$0>,
-C<$1>, or C<$10000>.
-
-=item A sigil, followed by either a caret and a single POSIX uppercase letter,
-like C<$^V> or C<$^W>, or a sigil followed by a literal control character
-matching the C<\p{POSIX_Cntrl}> property.
-Due to a historical oddity, if not
-running under C<use utf8>, the 128 extra controls in the C<[0x80-0xff]> range
-may also be used in length one variables.
-
-=item Similar to the above, a sigil, followed by bareword text in brackets,
-where the first character is either a caret followed by an uppercase letter,
-or a literal control, like C<${^GLOBAL_PHASE}> or C<${\7LOBAL_PHASE}>.
-
-=item A sigil followed by a single character matching the C<\p{POSIX_Punct}>
-property, like C<$!> or C<%+>.
+=item *
+
+A sigil, followed solely by digits matching C<\p{POSIX_Digit}>, like
+C<$0>, C<$1>, or C<$10000>.
+
+=item *
+
+A sigil, followed by either a caret and a single POSIX uppercase letter,
+like C<$^V> or C<$^W>, or a sigil followed by a literal non-space,
+non-C<NUL> control character matching the C<\p{POSIX_Cntrl}> property.
+Due to a historical oddity, if not running under C<use utf8>, the 128
+characters in the C<[0x80-0xff]> range are considered to be controls,
+and may also be used in length-one variables. However, the use of
+non-graphical characters is deprecated as of v5.22, and support for them
+will be removed in a future version of perl. ASCII space characters and
+C<NUL> already aren't allowed, so this means that a single-character
+variable name with that name being any other C0 control C<[0x01-0x1F]>,
+or C<DEL> will generate a deprecated warning. Already, under C<"use
+utf8">, non-ASCII characters must match C<Perl_XIDS>. As of v5.22, when
+not under C<"use utf8"> C1 controls C<[0x80-0x9F]>, NO BREAK SPACE, and
+SOFT HYPHEN (C<SHY>)) generate a deprecated warning.
+
+=item *
+
+Similar to the above, a sigil, followed by bareword text in brackets,
+where the first character is either a caret followed by an uppercase
+letter, like C<${^GLOBAL_PHASE}> or a non-C<NUL>, non-space literal
+control like C<${\7LOBAL_PHASE}>. Like the above, when not under
+C<"use utf8">, the characters in C<[0x80-0xFF]> are considered controls, but as
+of v5.22, the use of any that are non-graphical are deprecated, and as
+of v5.20 the use of any ASCII-range literal control is deprecated.
+Support for these will be removed in a future version of perl.
+
+=item *
+
+A sigil followed by a single character matching the C<\p{POSIX_Punct}>
+property, like C<$!> or C<%+>, except the character C<"{"> doesn't work.
=back
Note that as of Perl 5.20, literal control characters in variable names
-are deprecated.
+are deprecated; and as of Perl 5.22, any other non-graphic characters
+are also deprecated.
=head2 Context
X<context> X<scalar context> X<list context>
Numeric literals are specified in any of the following floating point or
integer formats:
- 12345
- 12345.67
- .23E-10 # a very small number
- 3.14_15_92 # a very important number
- 4_294_967_296 # underscore for legibility
- 0xff # hex
- 0xdead_beef # more hex
- 0377 # octal (only numbers, begins with 0)
- 0b011011 # binary
+ 12345
+ 12345.67
+ .23E-10 # a very small number
+ 3.14_15_92 # a very important number
+ 4_294_967_296 # underscore for legibility
+ 0xff # hex
+ 0xdead_beef # more hex
+ 0377 # octal (only numbers, begins with 0)
+ 0b011011 # binary
+ 0x1.999ap-4 # hexadecimal floating point (the 'p' is required)
You are allowed to use underscores (underbars) in numeric literals
between digits for legibility (but not multiple underscores in a row:
representation. The hex() and oct() functions make these conversions
for you. See L<perlfunc/hex> and L<perlfunc/oct> for more details.
+Hexadecimal floating point can start just like a hexadecimal literal,
+and it can be followed by an optional fractional hexadecimal part,
+but it must be followed by C<p>, an optional sign, and a power of two.
+The format is useful for accurately presenting floating point values,
+avoiding conversions to or from decimal floating point, and therefore
+avoiding possible loss in precision. Notice that while most current
+platforms use the 64-bit IEEE 754 floating point, not all do. Another
+potential source of (low-order) differences are the floating point
+rounding modes, which can differ between CPUs, operating systems,
+and compilers, and which Perl doesn't control.
+
You can also embed newlines directly in your strings, i.e., they can end
on a different line than they begin. This is nice, but if you forget
your trailing quote, the error will not be reported until Perl finds
($dev, $ino, undef, undef, $uid, $gid) = stat($file);
+As of Perl 5.22, you can also use C<(undef)x2> instead of C<undef, undef>.
+(You can also do C<($x) x 2>, which is less useful, because it assigns to
+the same variable twice, clobbering the first value assigned.)
+
List assignment in scalar context returns the number of elements
produced by the expression on the right side of the assignment:
s/(\w+)/\u\L$1/g; # "titlecase" words
}
-A slice of an empty list is still an empty list. Thus:
-
- @a = ()[1,0]; # @a has no elements
- @b = (@a)[0,1]; # @b has no elements
-
-But:
-
- @a = (1)[1,0]; # @a has two elements
- @b = (1,undef)[1,0,2]; # @b has three elements
-
-More generally, a slice yields the empty list if it indexes only
-beyond the end of a list:
+As a special exception, when you slice a list (but not an array or a hash),
+if the list evaluates to empty, then taking a slice of that empty list will
+always yield the empty list in turn. Thus:
- @a = (1)[ 1,2]; # @a has no elements
- @b = (1)[0,1,2]; # @b has three elements
+ @a = ()[0,1]; # @a has no elements
+ @b = (@a)[0,1]; # @b has no elements
+ @c = (sub{}->())[0,1]; # @c has no elements
+ @d = ('a','b')[0,1]; # @d has two elements
+ @e = (@d)[0,1,8,9]; # @e has four elements
+ @f = (@d)[8,9]; # @f has two elements
This makes it easy to write loops that terminate when a null list
is returned:
- while ( ($home, $user) = (getpwent)[7,0]) {
+ while ( ($home, $user) = (getpwent)[7,0] ) {
printf "%-8s %s\n", $user, $home;
}
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