=head1 DESCRIPTION
In Perl, the operator determines what operation is performed,
-independent of the type of the operands. For example C<$a + $b>
-is always a numeric addition, and if C<$a> or C<$b> do not contain
+independent of the type of the operands. For example S<C<$x + $y>>
+is always a numeric addition, and if C<$x> or C<$y> do not contain
numbers, an attempt is made to convert them to numbers first.
This is in contrast to many other dynamic languages, where the
-operation is determined by the type of the first argument. It also
+operation is determined by the type of the first argument. It also
means that Perl has two versions of some operators, one for numeric
-and one for string comparison. For example C<$a == $b> compares
-two numbers for equality, and C<$a eq $b> compares two strings.
+and one for string comparison. For example S<C<$x == $y>> compares
+two numbers for equality, and S<C<$x eq $y>> compares two strings.
There are a few exceptions though: C<x> can be either string
repetition or list repetition, depending on the type of the left
-operand, and C<&>, C<|> and C<^> can be either string or numeric bit
+operand, and C<&>, C<|>, C<^> and C<~> can be either string or numeric bit
operations.
=head2 Operator Precedence and Associativity
they do in mathematics.
I<Operator precedence> means some operators are evaluated before
-others. For example, in C<2 + 4 * 5>, the multiplication has higher
-precedence so C<4 * 5> is evaluated first yielding C<2 + 20 ==
-22> and not C<6 * 5 == 30>.
+others. For example, in S<C<2 + 4 * 5>>, the multiplication has higher
+precedence so S<C<4 * 5>> is evaluated first yielding S<C<2 + 20 ==
+22>> and not S<C<6 * 5 == 30>>.
I<Operator associativity> defines what happens if a sequence of the
same operators is used one after another: whether the evaluator will
-evaluate the left operations first or the right. For example, in C<8
-- 4 - 2>, subtraction is left associative so Perl evaluates the
-expression left to right. C<8 - 4> is evaluated first making the
-expression C<4 - 2 == 2> and not C<8 - 2 == 6>.
+evaluate the left operations first, or the right first. For example, in
+S<C<8 - 4 - 2>>, subtraction is left associative so Perl evaluates the
+expression left to right. S<C<8 - 4>> is evaluated first making the
+expression S<C<4 - 2 == 2>> and not S<C<8 - 2 == 6>>.
Perl operators have the following associativity and precedence,
listed from highest precedence to lowest. Operators borrowed from
left and
left or xor
-In the following sections, these operators are covered in precedence order.
+In the following sections, these operators are covered in detail, in the
+same order in which they appear in the table above.
Many operators can be overloaded for objects. See L<overload>.
operators behaving as functions because you put parentheses around
the arguments. These are all documented in L<perlfunc>.
-If any list operator (print(), etc.) or any unary operator (chdir(), etc.)
+If any list operator (C<print()>, etc.) or any unary operator (C<chdir()>, etc.)
is followed by a left parenthesis as the next token, the operator and
arguments within parentheses are taken to be of highest precedence,
just like a normal function call.
@ary = (1, 3, sort 4, 2);
print @ary; # prints 1324
-the commas on the right of the sort are evaluated before the sort,
+the commas on the right of the C<sort> are evaluated before the C<sort>,
but the commas on the left are evaluated after. In other words,
list operators tend to gobble up all arguments that follow, and
then act like a simple TERM with regard to the preceding expression.
probably doesn't do what you expect at first glance. The parentheses
enclose the argument list for C<print> which is evaluated (printing
-the result of C<$foo & 255>). Then one is added to the return value
+the result of S<C<$foo & 255>>). Then one is added to the return value
of C<print> (usually 1). The result is something like this:
1 + 1, "\n"; # Obviously not what you meant.
print(($foo & 255) + 1, "\n");
-See L<Named Unary Operators> for more discussion of this.
+See L</Named Unary Operators> for more discussion of this.
-Also parsed as terms are the C<do {}> and C<eval {}> constructs, as
+Also parsed as terms are the S<C<do {}>> and S<C<eval {}>> constructs, as
well as subroutine and method calls, and the anonymous
constructors C<[]> and C<{}>.
-See also L<Quote and Quote-like Operators> toward the end of this section,
+See also L</Quote and Quote-like Operators> toward the end of this section,
as well as L</"I/O Operators">.
=head2 The Arrow Operator
or a class name (that is, a package name). See L<perlobj>.
The dereferencing cases (as opposed to method-calling cases) are
-somewhat extended by the
experimental C<postderef> feature. For the
+somewhat extended by the C<postderef> feature. For the
details of that feature, consult L<perlref/Postfix Dereference Syntax>.
=head2 Auto-increment and Auto-decrement
X<increment> X<auto-increment> X<++> X<decrement> X<auto-decrement> X<-->
-"++" and "--" work as in C. That is, if placed before a variable,
+C<"++"> and C<"--"> work as in C. That is, if placed before a variable,
they increment or decrement the variable by one before returning the
value, and if placed after, increment or decrement after returning the
value.
print ++$j; # prints 1
Note that just as in C, Perl doesn't define B<when> the variable is
-incremented or decremented. You just know it will be done sometime
-before or after the value is returned. This also means that modifying
+incremented or decremented. You just know it will be done sometime
+before or after the value is returned. This also means that modifying
a variable twice in the same statement will lead to undefined behavior.
Avoid statements like:
=head2 Exponentiation
X<**> X<exponentiation> X<power>
-Binary "**" is the exponentiation operator. It binds even more
-tightly than unary minus, so -2**4 is -(2**4), not (-2)**4. (This is
-implemented using C's pow(3) function, which actually works on doubles
+Binary C<"**"> is the exponentiation operator. It binds even more
+tightly than unary minus, so C<-2**4> is C<-(2**4)>, not C<(-2)**4>.
+(This is
+implemented using C's C<pow(3)> function, which actually works on doubles
internally.)
+Note that certain exponentiation expressions are ill-defined:
+these include C<0**0>, C<1**Inf>, and C<Inf**0>. Do not expect
+any particular results from these special cases, the results
+are platform-dependent.
+
=head2 Symbolic Unary Operators
X<unary operator> X<operator, unary>
-Unary "!" performs logical negation, that is, "not". See also C<not> for a lower
+Unary C<"!"> performs logical negation, that is, "not". See also C<not> for a lower
precedence version of this.
X<!>
-Unary "-" performs arithmetic negation if the operand is numeric,
+Unary C<"-"> performs arithmetic negation if the operand is numeric,
including any string that looks like a number. If the operand is
an identifier, a string consisting of a minus sign concatenated
with the identifier is returned. Otherwise, if the string starts
with a plus or minus, a string starting with the opposite sign is
-returned. One effect of these rules is that -bareword is equivalent
-to the string "-bareword". If, however, the string begins with a
-non-alphabetic character (excluding "+" or "-"), Perl will attempt to convert
-the string to a numeric and the arithmetic negation is performed. If the
+returned. One effect of these rules is that C<-bareword> is equivalent
+to the string C<"-bareword">. If, however, the string begins with a
+non-alphabetic character (excluding C<"+"> or C<"-">), Perl will attempt
+to convert
+the string to a numeric, and the arithmetic negation is performed. If the
string cannot be cleanly converted to a numeric, Perl will give the warning
B<Argument "the string" isn't numeric in negation (-) at ...>.
X<-> X<negation, arithmetic>
-Unary "~" performs bitwise negation, that is, 1's complement. For
-example, C<0666 & ~027> is 0640. (See also L<Integer Arithmetic> and
-L<Bitwise String Operators>.) Note that the width of the result is
-platform-dependent: ~0 is 32 bits wide on a 32-bit platform, but 64
+Unary C<"~"> performs bitwise negation, that is, 1's complement. For
+example, S<C<0666 & ~027>> is 0640. (See also L</Integer Arithmetic> and
+L</Bitwise String Operators>.) Note that the width of the result is
+platform-dependent: C<~0> is 32 bits wide on a 32-bit platform, but 64
bits wide on a 64-bit platform, so if you are expecting a certain bit
-width, remember to use the "&" operator to mask off the excess bits.
+width, remember to use the C<"&"> operator to mask off the excess bits.
X<~> X<negation, binary>
When complementing strings, if all characters have ordinal values under
architecture. So for example, C<~"\x{3B1}"> is C<"\x{FFFF_FC4E}"> on
32-bit machines and C<"\x{FFFF_FFFF_FFFF_FC4E}"> on 64-bit machines.
-Unary "+" has no effect whatsoever, even on strings. It is useful
+If the experimental "bitwise" feature is enabled via S<C<use feature
+'bitwise'>>, then unary C<"~"> always treats its argument as a number, and an
+alternate form of the operator, C<"~.">, always treats its argument as a
+string. So C<~0> and C<~"0"> will both give 2**32-1 on 32-bit platforms,
+whereas C<~.0> and C<~."0"> will both yield C<"\xff">. This feature
+produces a warning unless you use S<C<no warnings 'experimental::bitwise'>>.
+
+Unary C<"+"> has no effect whatsoever, even on strings. It is useful
syntactically for separating a function name from a parenthesized expression
that would otherwise be interpreted as the complete list of function
-arguments. (See examples above under L<Terms and List Operators (Leftward)>.)
+arguments. (See examples above under L</Terms and List Operators (Leftward)>.)
X<+>
-Unary
"\" creates a reference to whatever follows it. See L<perlreftut>
+Unary
C<"\"> creates a reference to whatever follows it. See L<perlreftut>
and L<perlref>. Do not confuse this behavior with the behavior of
backslash within a string, although both forms do convey the notion
of protecting the next thing from interpolation.
=head2 Binding Operators
X<binding> X<operator, binding> X<=~> X<!~>
-Binary "=~" binds a scalar expression to a pattern match. Certain operations
-search or modify the string $_ by default. This operator makes that kind
+Binary C<"=~"> binds a scalar expression to a pattern match. Certain operations
+search or modify the string C<$_> by default. This operator makes that kind
of operation work on some other string. The right argument is a search
pattern, substitution, or transliteration. The left argument is what is
supposed to be searched, substituted, or transliterated instead of the default
-$_. When used in scalar context, the return value generally indicates the
-success of the operation. The exceptions are substitution (s///)
-and transliteration (y///) with the C</r> (non-destructive) option,
+C<$_>. When used in scalar context, the return value generally indicates the
+success of the operation. The exceptions are substitution (C<s///>)
+and transliteration (C<y///>) with the C</r> (non-destructive) option,
which cause the B<r>eturn value to be the result of the substitution.
Behavior in list context depends on the particular operator.
See L</"Regexp Quote-Like Operators"> for details and L<perlretut> for
If the right argument is an expression rather than a search pattern,
substitution, or transliteration, it is interpreted as a search pattern at run
-time. Note that this means that its contents will be interpolated twice, so
+time. Note that this means that its
+contents will be interpolated twice, so
'\\' =~ q'\\';
is not ok, as the regex engine will end up trying to compile the
pattern C<\>, which it will consider a syntax error.
-Binary "!~" is just like "=~" except the return value is negated in
+Binary C<"!~"> is just like C<"=~"> except the return value is negated in
the logical sense.
-Binary "!~" with a non-destructive substitution (s///r) or transliteration
-(y///r) is a syntax error.
+Binary C<"!~"> with a non-destructive substitution (C<s///r>) or transliteration
+(C<y///r>) is a syntax error.
=head2 Multiplicative Operators
X<operator, multiplicative>
-Binary "*" multiplies two numbers.
+Binary C<"*"> multiplies two numbers.
X<*>
-Binary "/" divides two numbers.
+Binary C<"/"> divides two numbers.
X</> X<slash>
-Binary "%" is the modulo operator, which computes the division
+Binary C<"%"> is the modulo operator, which computes the division
remainder of its first argument with respect to its second argument.
Given integer
-operands C<$a> and C<$b>: If C<$b> is positive, then C<$a % $b> is
-C<$a> minus the largest multiple of C<$b> less than or equal to
-C<$a>. If C<$b> is negative, then C<$a % $b> is C<$a> minus the
-smallest multiple of C<$b> that is not less than C<$a> (that is, the
+operands C<$m> and C<$n>: If C<$n> is positive, then S<C<$m % $n>> is
+C<$m> minus the largest multiple of C<$n> less than or equal to
+C<$m>. If C<$n> is negative, then S<C<$m % $n>> is C<$m> minus the
+smallest multiple of C<$n> that is not less than C<$m> (that is, the
result will be less than or equal to zero). If the operands
-C<$a> and C<$b> are floating point values and the absolute value of
-C<$b> (that is C<abs($b)>) is less than C<(UV_MAX + 1)>, only
-the integer portion of C<$a> and C<$b> will be used in the operation
+C<$m> and C<$n> are floating point values and the absolute value of
+C<$n> (that is C<abs($n)>) is less than S<C<(UV_MAX + 1)>>, only
+the integer portion of C<$m> and C<$n> will be used in the operation
(Note: here C<UV_MAX> means the maximum of the unsigned integer type).
-If the absolute value of the right operand (C<abs($b)>) is greater than
-or equal to C<(UV_MAX + 1)>, "%" computes the floating-point remainder
-C<$r> in the equation C<($r = $a - $i*$b)> where C<$i> is a certain
+If the absolute value of the right operand (C<abs($n)>) is greater than
+or equal to S<C<(UV_MAX + 1)>>, C<"%"> computes the floating-point remainder
+C<$r> in the equation S<C<($r = $m - $i*$n)>> where C<$i> is a certain
integer that makes C<$r> have the same sign as the right operand
-C<$b> (B<not> as the left operand C<$a> like C function C<fmod()>)
-and the absolute value less than that of C<$b>.
-Note that when C<use integer> is in scope, "%" gives you direct access
+C<$n> (B<not> as the left operand C<$m> like C function C<fmod()>)
+and the absolute value less than that of C<$n>.
+Note that when S<C<use integer>> is in scope, C<"%"> gives you direct access
to the modulo operator as implemented by your C compiler. This
operator is not as well defined for negative operands, but it will
execute faster.
X<%> X<remainder> X<modulo> X<mod>
-Binary "x" is the repetition operator. In scalar context or if the left
+Binary C<"x"> is the repetition operator. In scalar context or if the left
operand is not enclosed in parentheses, it returns a string consisting
of the left operand repeated the number of times specified by the right
operand. In list context, if the left operand is enclosed in
-parentheses or is a list formed by C<qw/STRING/>, it repeats the list.
+parentheses or is a list formed by C<qw/I<STRING>/>, it repeats the list.
If the right operand is zero or negative (raising a warning on
negative), it returns an empty string
or an empty list, depending on the context.
=head2 Additive Operators
X<operator, additive>
-Binary C<+> returns the sum of two numbers.
+Binary C<"+"> returns the sum of two numbers.
X<+>
-Binary C<-> returns the difference of two numbers.
+Binary C<"-"> returns the difference of two numbers.
X<->
-Binary C<.> concatenates two strings.
+Binary C<"."> concatenates two strings.
X<string, concatenation> X<concatenation>
X<cat> X<concat> X<concatenate> X<.>
X<<< >> >>> X<right shift> X<left shift> X<bitwise shift>
X<shl> X<shr> X<shift, right> X<shift, left>
-Binary C<<< << >>> returns the value of its left argument shifted left by the
+Binary C<<< "<<" >>> returns the value of its left argument shifted left by the
number of bits specified by the right argument. Arguments should be
-integers. (See also L<Integer Arithmetic>.)
+integers. (See also L</Integer Arithmetic>.)
-Binary C<<< >> >>> returns the value of its left argument shifted right by
+Binary C<<< ">>" >>> returns the value of its left argument shifted right by
the number of bits specified by the right argument. Arguments should
-be integers. (See also L<Integer Arithmetic>.)
+be integers. (See also L</Integer Arithmetic>.)
+
+If S<C<use integer>> (see L</Integer Arithmetic>) is in force then
+signed C integers are used (I<arithmetic shift>), otherwise unsigned C
+integers are used (I<logical shift>), even for negative shiftees.
+In arithmetic right shift the sign bit is replicated on the left,
+in logical shift zero bits come in from the left.
+
+Either way, the implementation isn't going to generate results larger
+than the size of the integer type Perl was built with (32 bits or 64 bits).
+
+Shifting by negative number of bits means the reverse shift: left
+shift becomes right shift, right shift becomes left shift. This is
+unlike in C, where negative shift is undefined.
-Note that both C<<< << >>> and C<<< >> >>> in Perl are implemented directly using
-C<<< << >>> and C<<< >> >>> in C. If C<use integer> (see L<Integer Arithmetic>) is
-in force then signed C integers are used, else unsigned C integers are
-used. Either way, the implementation isn't going to generate results
-larger than the size of the integer type Perl was built with (32 bits
-or 64 bits).
+Shifting by more bits than the size of the integers means most of the
+time zero (all bits fall off), except that under S<C<use integer>>
+right overshifting a negative shiftee results in -1. This is unlike
+in C, where shifting by too many bits is undefined. A common C
+behavior is "shift by modulo wordbits", so that for example
-The result of overflowing the range of the integers is undefined
-because it is undefined also in C. In other words, using 32-bit
-integers, C<< 1 << 32 >> is undefined. Shifting by a negative number
-of bits is also undefined.
+ 1 >> 64 == 1 >> (64 % 64) == 1 >> 0 == 1 # Common C behavior.
+
+but that is completely accidental.
If you get tired of being subject to your platform's native integers,
-the C<use bigint> pragma neatly sidesteps the issue altogether:
+the S<C<use bigint>> pragma neatly sidesteps the issue altogether:
print 20 << 20; # 20971520
print 20 << 40; # 5120 on 32-bit machines,
The various named unary operators are treated as functions with one
argument, with optional parentheses.
-If any list operator (print(), etc.) or any unary operator (chdir(), etc.)
+If any list operator (C<print()>, etc.) or any unary operator (C<chdir()>, etc.)
is followed by a left parenthesis as the next token, the operator and
arguments within parentheses are taken to be of highest precedence,
just like a normal function call. For example,
chdir ($foo) || die; # (chdir $foo) || die
chdir +($foo) || die; # (chdir $foo) || die
-but, because * is higher precedence than named operators:
+but, because C<"*"> is higher precedence than named operators:
chdir $foo * 20; # chdir ($foo * 20)
chdir($foo) * 20; # (chdir $foo) * 20
Regarding precedence, the filetest operators, like C<-f>, C<-M>, etc. are
treated like named unary operators, but they don't follow this functional
parenthesis rule. That means, for example, that C<-f($file).".bak"> is
-equivalent to C<-f "$file.bak">.
+equivalent to S<C<-f "$file.bak">>.
X<-X> X<filetest> X<operator, filetest>
-See also L<"Terms and List Operators (Leftward)">.
+See also L</"Terms and List Operators (Leftward)">.
=head2 Relational Operators
X<relational operator> X<operator, relational>
operators in this section and the equality operators in the next
one return C<1> for true and a special version of the defined empty
string, C<"">, which counts as a zero but is exempt from warnings
-about improper numeric conversions, just as C<"0 but true"> is.
+about improper numeric conversions, just as S<C<"0 but true">> is.
-Binary "<" returns true if the left argument is numerically less than
+Binary C<< "<" >> returns true if the left argument is numerically less than
the right argument.
X<< < >>
-Binary ">" returns true if the left argument is numerically greater
+Binary C<< ">" >> returns true if the left argument is numerically greater
than the right argument.
X<< > >>
-Binary "<=" returns true if the left argument is numerically less than
+Binary C<< "<=" >> returns true if the left argument is numerically less than
or equal to the right argument.
X<< <= >>
-Binary ">=" returns true if the left argument is numerically greater
+Binary C<< ">=" >> returns true if the left argument is numerically greater
than or equal to the right argument.
X<< >= >>
-Binary "lt" returns true if the left argument is stringwise less than
+Binary C<"lt"> returns true if the left argument is stringwise less than
the right argument.
X<< lt >>
-Binary "gt" returns true if the left argument is stringwise greater
+Binary C<"gt"> returns true if the left argument is stringwise greater
than the right argument.
X<< gt >>
-Binary "le" returns true if the left argument is stringwise less than
+Binary C<"le"> returns true if the left argument is stringwise less than
or equal to the right argument.
X<< le >>
-Binary "ge" returns true if the left argument is stringwise greater
+Binary C<"ge"> returns true if the left argument is stringwise greater
than or equal to the right argument.
X<< ge >>
=head2 Equality Operators
X<equality> X<equal> X<equals> X<operator, equality>
-Binary "==" returns true if the left argument is numerically equal to
+Binary C<< "==" >> returns true if the left argument is numerically equal to
the right argument.
X<==>
-Binary "!=" returns true if the left argument is numerically not equal
+Binary C<< "!=" >> returns true if the left argument is numerically not equal
to the right argument.
X<!=>
-Binary "<=>" returns -1, 0, or 1 depending on whether the left
+Binary C<< "<=>" >> returns -1, 0, or 1 depending on whether the left
argument is numerically less than, equal to, or greater than the right
-argument. If your platform supports NaNs (not-a-numbers) as numeric
-values, using them with "<=>" returns undef. NaN is not "<", "==", ">",
-"<=" or ">=" anything (even NaN), so those 5 return false. NaN != NaN
-returns true, as does NaN != anything else. If your platform doesn't
-support NaNs then NaN is just a string with numeric value 0.
-X<< <=> >> X<spaceship>
-
- $ perl -le '$a = "NaN"; print "No NaN support here" if $a == $a'
- $ perl -le '$a = "NaN"; print "NaN support here" if $a != $a'
-
-(Note that the L<bigint>, L<bigrat>, and L<bignum> pragmas all
-support "NaN".)
-
-Binary "eq" returns true if the left argument is stringwise equal to
+argument. If your platform supports C<NaN>'s (not-a-numbers) as numeric
+values, using them with C<< "<=>" >> returns undef. C<NaN> is not
+C<< "<" >>, C<< "==" >>, C<< ">" >>, C<< "<=" >> or C<< ">=" >> anything
+(even C<NaN>), so those 5 return false. S<C<< NaN != NaN >>> returns
+true, as does S<C<NaN !=> I<anything else>>. If your platform doesn't
+support C<NaN>'s then C<NaN> is just a string with numeric value 0.
+X<< <=> >>
+X<spaceship>
+
+ $ perl -le '$x = "NaN"; print "No NaN support here" if $x == $x'
+ $ perl -le '$x = "NaN"; print "NaN support here" if $x != $x'
+
+(Note that the L<bigint>, L<bigrat>, and L<bignum> pragmas all
+support C<"NaN">.)
+
+Binary C<"eq"> returns true if the left argument is stringwise equal to
the right argument.
X<eq>
-Binary "ne" returns true if the left argument is stringwise not equal
+Binary C<"ne"> returns true if the left argument is stringwise not equal
to the right argument.
X<ne>
-Binary "cmp" returns -1, 0, or 1 depending on whether the left
+Binary C<"cmp"> returns -1, 0, or 1 depending on whether the left
argument is stringwise less than, equal to, or greater than the right
argument.
X<cmp>
-Binary "~~" does a smartmatch between its arguments. Smart matching
+Binary C<"~~"> does a smartmatch between its arguments. Smart matching
is described in the next section.
X<~~>
-"lt", "le", "ge", "gt" and "cmp" use the collation (sort) order specified
-by the current locale if a legacy C<use locale> (but not
-C<use locale ':not_characters'>) is in effect. See
-L<perllocale>. Do not mix these with Unicode, only with legacy binary
-encodings. The standard L<Unicode::Collate> and
-L<Unicode::Collate::Locale> modules offer much more powerful solutions to
-collation issues.
+C<"lt">, C<"le">, C<"ge">, C<"gt"> and C<"cmp"> use the collation (sort)
+order specified by the current C<LC_COLLATE> locale if a S<C<use
+locale>> form that includes collation is in effect. See L<perllocale>.
+Do not mix these with Unicode,
+only use them with legacy 8-bit locale encodings.
+The standard C<L<Unicode::Collate>> and
+C<L<Unicode::Collate::Locale>> modules offer much more powerful
+solutions to collation issues.
+
+For case-insensitive comparisions, look at the L<perlfunc/fc> case-folding
+function, available in Perl v5.16 or later:
+
+ if ( fc($x) eq fc($y) ) { ... }
=head2 Smartmatch Operator
}
-If you were to set C<$b[3] = 4>, then instead of reporting that "a and b
-are deep copies of each other", it now reports that "b smartmatches in a".
-That because the corresponding position in C<@a> contains an array that
+If you were to set S<C<$b[3] = 4>>, then instead of reporting that "a and b
+are deep copies of each other", it now reports that C<"b smartmatches in a">.
+That's because the corresponding position in C<@a> contains an array that
(eventually) has a 4 in it.
Smartmatching one hash against another reports whether both contain the
-same keys, no more and no less. This could be used to see whether two
+same keys, no more and no less. This could be used to see whether two
records have the same field names, without caring what values those fields
might have. For example:
...
}
-or, if other non-required fields are allowed, use ARRAY ~~ HASH:
-
- use v5.10.1;
- sub make_dogtag {
- state $REQUIRED_FIELDS = { name=>1, rank=>1, serial_num=>1 };
-
- my ($class, $init_fields) = @_;
-
- die "Must supply (at least) name, rank, and serial number"
- unless [keys %{$init_fields}] ~~ $REQUIRED_FIELDS;
-
- ...
- }
+However, this only does what you mean if C<$init_fields> is indeed a hash
+reference. The condition C<$init_fields ~~ $REQUIRED_FIELDS> also allows the
+strings C<"name">, C<"rank">, C<"serial_num"> as well as any array reference
+that contains C<"name"> or C<"rank"> or C<"serial_num"> anywhere to pass
+through.
The smartmatch operator is most often used as the implicit operator of a
C<when> clause. See the section on "Switch Statements" in L<perlsyn>.
To avoid relying on an object's underlying representation, if the
smartmatch's right operand is an object that doesn't overload C<~~>,
it raises the exception "C<Smartmatching a non-overloaded object
-breaks encapsulation>". That's because one has no business digging
-around to see whether something is "in" an object. These are all
+breaks encapsulation>". That's because one has no business digging
+around to see whether something is "in" an object. These are all
illegal on objects without a C<~~> overload:
%hash ~~ $object
"fred" ~~ $object
However, you can change the way an object is smartmatched by overloading
-the C<~~> operator. This is allowed to extend the usual smartmatch semantics.
+the C<~~> operator. This is allowed to
+extend the usual smartmatch semantics.
For objects that do have an C<~~> overload, see L<overload>.
Using an object as the left operand is allowed, although not very useful.
does I<not> invoke the overload method with C<I<X>> as an argument.
Instead the above table is consulted as normal, and based on the type of
C<I<X>>, overloading may or may not be invoked. For simple strings or
-numbers, in becomes equivalent to this:
+numbers, "in" becomes equivalent to this:
$object ~~ $number ref($object) == $number
$object ~~ $string ref($object) eq $string
=head2 Bitwise And
X<operator, bitwise, and> X<bitwise and> X<&>
-Binary "&" returns its operands ANDed together bit by bit. Although no
+Binary C<"&"> returns its operands ANDed together bit by bit. Although no
warning is currently raised, the result is not well defined when this operation
is performed on operands that aren't either numbers (see
-L<Integer Arithmetic>) or bitstrings (see L<Bitwise String Operators>).
+L</Integer Arithmetic>) nor bitstrings (see L</Bitwise String Operators>).
-Note that "&" has lower priority than relational operators, so for example
+Note that C<"&"> has lower priority than relational operators, so for example
the parentheses are essential in a test like
print "Even\n" if ($x & 1) == 0;
+If the experimental "bitwise" feature is enabled via S<C<use feature
+'bitwise'>>, then this operator always treats its operand as numbers. This
+feature produces a warning unless you also use C<S<no warnings
+'experimental::bitwise'>>.
+
=head2 Bitwise Or and Exclusive Or
X<operator, bitwise, or> X<bitwise or> X<|> X<operator, bitwise, xor>
X<bitwise xor> X<^>
-Binary "|" returns its operands ORed together bit by bit.
+Binary C<"|"> returns its operands ORed together bit by bit.
-Binary "^" returns its operands XORed together bit by bit.
+Binary C<"^"> returns its operands XORed together bit by bit.
Although no warning is currently raised, the results are not well
defined when these operations are performed on operands that aren't either
-numbers (see L<Integer Arithmetic>) or bitstrings (see L<Bitwise String
+numbers (see L</Integer Arithmetic>) nor bitstrings (see L</Bitwise String
Operators>).
-Note that "|" and "^" have lower priority than relational operators, so
-for example the brackets are essential in a test like
+Note that C<"|"> and C<"^"> have lower priority than relational operators, so
+for example the parentheses are essential in a test like
print "false\n" if (8 | 2) != 10;
+If the experimental "bitwise" feature is enabled via S<C<use feature
+'bitwise'>>, then this operator always treats its operand as numbers. This
+feature produces a warning unless you also use S<C<no warnings
+'experimental::bitwise'>>.
+
=head2 C-style Logical And
X<&&> X<logical and> X<operator, logical, and>
-Binary "&&" performs a short-circuit logical AND operation. That is,
+Binary C<"&&"> performs a short-circuit logical AND operation. That is,
if the left operand is false, the right operand is not even evaluated.
Scalar or list context propagates down to the right operand if it
is evaluated.
=head2 C-style Logical Or
X<||> X<operator, logical, or>
-Binary "||" performs a short-circuit logical OR operation. That is,
+Binary C<"||"> performs a short-circuit logical OR operation. That is,
if the left operand is true, the right operand is not even evaluated.
Scalar or list context propagates down to the right operand if it
is evaluated.
X<//> X<operator, logical, defined-or>
Although it has no direct equivalent in C, Perl's C<//> operator is related
-to its C-style or. In fact, it's exactly the same as C<||>, except that it
+to its C-style "or". In fact, it's exactly the same as C<||>, except that it
tests the left hand side's definedness instead of its truth. Thus,
-C<< EXPR1 // EXPR2 >> returns the value of C<< EXPR1 >> if it's defined,
-otherwise, the value of C<< EXPR2 >> is returned. (C<< EXPR1 >> is evaluated
-in scalar context, C<< EXPR2 >> in the context of C<< // >> itself). Usually,
-this is the same result as C<< defined(EXPR1) ? EXPR1 : EXPR2 >> (except that
-the ternary-operator form can be used as a lvalue, while C<< EXPR1 // EXPR2 >>
-cannot). This is very useful for
+S<C<< EXPR1 // EXPR2 >>> returns the value of C<< EXPR1 >> if it's defined,
+otherwise, the value of C<< EXPR2 >> is returned.
+(C<< EXPR1 >> is evaluated in scalar context, C<< EXPR2 >>
+in the context of C<< // >> itself). Usually,
+this is the same result as S<C<< defined(EXPR1) ? EXPR1 : EXPR2 >>> (except that
+the ternary-operator form can be used as a lvalue, while S<C<< EXPR1 // EXPR2 >>>
+cannot). This is very useful for
providing default values for variables. If you actually want to test if
-at least one of C<$a> and C<$b> is defined, use C<defined($a // $b)>.
+at least one of C<$x> and C<$y> is defined, use S<C<defined($x // $y)>>.
The C<||>, C<//> and C<&&> operators return the last value evaluated
-(unlike C's C<||> and C<&&>, which return 0 or 1). Thus, a reasonably
+(unlike C's C<||> and C<&&>, which return 0 or 1). Thus, a reasonably
portable way to find out the home directory might be:
$home = $ENV{HOME}
In particular, this means that you shouldn't use this
for selecting between two aggregates for assignment:
- @a = @b || @c; # this is wrong
- @a = scalar(@b) || @c; # really meant this
- @a = @b ? @b : @c; # this works fine, though
+ @a = @b || @c; # This doesn't do the right thing
+ @a = scalar(@b) || @c; # because it really means this.
+ @a = @b ? @b : @c; # This works fine, though.
As alternatives to C<&&> and C<||> when used for
control flow, Perl provides the C<and> and C<or> operators (see below).
-The short-circuit behavior is identical. The precedence of "and"
-and "or" is much lower, however, so that you can safely use them after a
+The short-circuit behavior is identical. The precedence of C<"and">
+and C<"or"> is much lower, however, so that you can safely use them after a
list operator without the need for parentheses:
unlink "alpha", "beta", "gamma"
next LINE;
}
-Using "or" for assignment is unlikely to do what you want; see below.
+Using C<"or"> for assignment is unlikely to do what you want; see below.
=head2 Range Operators
X<operator, range> X<range> X<..> X<...>
-Binary ".." is the range operator, which is really two different
+Binary C<".."> is the range operator, which is really two different
operators depending on the context. In list context, it returns a
list of values counting (up by ones) from the left value to the right
value. If the left value is greater than the right value then it
returns the empty list. The range operator is useful for writing
-C<foreach (1..10)> loops and for doing slice operations on arrays. In
+S<C<foreach (1..10)>> loops and for doing slice operations on arrays. In
the current implementation, no temporary array is created when the
range operator is used as the expression in C<foreach> loops, but older
versions of Perl might burn a lot of memory when you write something
The range operator also works on strings, using the magical
auto-increment, see below.
-In scalar context, ".." returns a boolean value. The operator is
+In scalar context, C<".."> returns a boolean value. The operator is
bistable, like a flip-flop, and emulates the line-range (comma)
-operator of B<sed>, B<awk>, and various editors. Each ".." operator
+operator of B<sed>, B<awk>, and various editors. Each C<".."> operator
maintains its own boolean state, even across calls to a subroutine
-that contains it. It is false as long as its left operand is false.
+that contains it. It is false as long as its left operand is false.
Once the left operand is true, the range operator stays true until the
right operand is true, I<AFTER> which the range operator becomes false
again. It doesn't become false till the next time the range operator
is evaluated. It can test the right operand and become false on the
same evaluation it became true (as in B<awk>), but it still returns
-true once. If you don't want it to test the right operand until the
-next evaluation, as in B<sed>, just use three dots ("...") instead of
-two. In all other regards, "..." behaves just like ".." does.
+true once. If you don't want it to test the right operand until the
+next evaluation, as in B<sed>, just use three dots (C<"...">) instead of
+two. In all other regards, C<"..."> behaves just like C<".."> does.
The right operand is not evaluated while the operator is in the
"false" state, and the left operand is not evaluated while the
than || and &&. The value returned is either the empty string for
false, or a sequence number (beginning with 1) for true. The sequence
number is reset for each range encountered. The final sequence number
-in a range has the string "E0" appended to it, which doesn't affect
+in a range has the string C<"E0"> appended to it, which doesn't affect
its numeric value, but gives you something to search for if you want
to exclude the endpoint. You can exclude the beginning point by
waiting for the sequence number to be greater than 1.
-If either operand of scalar ".." is a constant expression,
+If either operand of scalar C<".."> is a constant expression,
that operand is considered true if it is equal (C<==>) to the current
input line number (the C<$.> variable).
-To be pedantic, the comparison is actually C<int(EXPR) == int(EXPR)>,
+To be pedantic, the comparison is actually S<C<int(EXPR) == int(EXPR)>>,
but that is only an issue if you use a floating point expression; when
implicitly using C<$.> as described in the previous paragraph, the
-comparison is C<int(EXPR) == int($.)> which is only an issue when C<$.>
+comparison is S<C<int(EXPR) == int($.)>> which is only an issue when C<$.>
is set to a floating point value and you are not reading from a file.
-Furthermore, C<"span" .. "spat"> or C<2.18 .. 3.14> will not do what
+Furthermore, S<C<"span" .. "spat">> or S<C<2.18 .. 3.14>> will not do what
you want in scalar context because each of the operands are evaluated
using their integer representation.
}
}
-This program will print only the line containing "Bar". If
+This program will print only the line containing "Bar". If
the range operator is changed to C<...>, it will also print the
"Baz" line.
increment would produce, the sequence goes until the next value would
be longer than the final value specified.
+As of Perl 5.26, the list-context range operator on strings works as expected
+in the scope of L<< S<C<"use feature 'unicode_strings">>|feature/The
+'unicode_strings' feature >>. In previous versions, and outside the scope of
+that feature, it exhibits L<perlunicode/The "Unicode Bug">: its behavior
+depends on the internal encoding of the range endpoint.
+
If the initial value specified isn't part of a magical increment
sequence (that is, a non-empty string matching C</^[a-zA-Z]*[0-9]*\z/>),
only the initial value will be returned. So the following will only
L<experimental feature|perlrecharclass/Extended Bracketed Character
Classes> C<S</(?[ \p{Greek} & \p{Lower} ])+/>>).
-Because each operand is evaluated in integer form, C<2.18 .. 3.14> will
+Because each operand is evaluated in integer form, S<C<2.18 .. 3.14>> will
return two elements in list context.
@list = (2.18 .. 3.14); # same as @list = (2 .. 3);
=head2 Conditional Operator
X<operator, conditional> X<operator, ternary> X<ternary> X<?:>
-Ternary "?:" is the conditional operator, just as in C. It works much
-like an if-then-else. If the argument before the ? is true, the
-argument before the : is returned, otherwise the argument after the :
-is returned. For example:
+Ternary C<"?:"> is the conditional operator, just as in C. It works much
+like an if-then-else. If the argument before the C<?> is true, the
+argument before the C<:> is returned, otherwise the argument after the
+C<:> is returned. For example:
printf "I have %d dog%s.\n", $n,
($n == 1) ? "" : "s";
Scalar or list context propagates downward into the 2nd
or 3rd argument, whichever is selected.
- $a = $ok ? $b : $c; # get a scalar
- @a = $ok ? @b : @c; # get an array
- $a = $ok ? @b : @c; # oops, that's just a count!
+ $x = $ok ? $y : $z; # get a scalar
+ @x = $ok ? @y : @z; # get an array
+ $x = $ok ? @y : @z; # oops, that's just a count!
The operator may be assigned to if both the 2nd and 3rd arguments are
legal lvalues (meaning that you can assign to them):
- ($a_or_b ? $a : $b) = $c;
+ ($x_or_y ? $x : $y) = $z;
Because this operator produces an assignable result, using assignments
without parentheses will get you in trouble. For example, this:
- $a % 2 ? $a += 10 : $a += 2
+ $x % 2 ? $x += 10 : $x += 2
Really means this:
- (($a % 2) ? ($a += 10) : $a) += 2
+ (($x % 2) ? ($x += 10) : $x) += 2
Rather than this:
- ($a % 2) ? ($a += 10) : ($a += 2)
+ ($x % 2) ? ($x += 10) : ($x += 2)
That should probably be written more simply as:
- $a += ($a % 2) ? 10 : 2;
+ $x += ($x % 2) ? 10 : 2;
=head2 Assignment Operators
X<assignment> X<operator, assignment> X<=> X<**=> X<+=> X<*=> X<&=>
X<<< <<= >>> X<&&=> X<-=> X</=> X<|=> X<<< >>= >>> X<||=> X<//=> X<.=>
-X<%=> X<^=> X<x=>
+X<%=> X<^=> X<x=> X<&.=> X<|.=> X<^.=>
-"=" is the ordinary assignment operator.
+C<"="> is the ordinary assignment operator.
Assignment operators work as in C. That is,
- $a += 2;
+ $x += 2;
is equivalent to
- $a = $a + 2;
+ $x = $x + 2;
although without duplicating any side effects that dereferencing the lvalue
-might trigger, such as from tie(). Other assignment operators work similarly.
+might trigger, such as from C<tie()>. Other assignment operators work similarly.
The following are recognized:
- **= += *= &= <<= &&=
- -= /= |= >>= ||=
- .= %= ^= //=
+ **= += *= &= &.= <<= &&=
+ -= /= |= |.= >>= ||=
+ .= %= ^= ^.= //=
x=
Although these are grouped by family, they all have the precedence
-of assignment.
+of assignment. These combined assignment operators can only operate on
+scalars, whereas the ordinary assignment operator can assign to arrays,
+hashes, lists and even references. (See L<"Context"|perldata/Context>
+and L<perldata/List value constructors>, and L<perlref/Assigning to
+References>.)
Unlike in C, the scalar assignment operator produces a valid lvalue.
Modifying an assignment is equivalent to doing the assignment and
Likewise,
- ($a += 2) *= 3;
+ ($x += 2) *= 3;
is equivalent to
- $a += 2;
- $a *= 3;
+ $x += 2;
+ $x *= 3;
Similarly, a list assignment in list context produces the list of
lvalues assigned to, and a list assignment in scalar context returns
the number of elements produced by the expression on the right hand
side of the assignment.
+The three dotted bitwise assignment operators (C<&.=> C<|.=> C<^.=>) are new in
+Perl 5.22 and experimental. See L</Bitwise String Operators>.
+
=head2 Comma Operator
X<comma> X<operator, comma> X<,>
-Binary "," is the comma operator. In scalar context it evaluates
+Binary C<","> is the comma operator. In scalar context it evaluates
its left argument, throws that value away, then evaluates its right
argument and returns that value. This is just like C's comma operator.
both its arguments into the list. These arguments are also evaluated
from left to right.
-The C<< => >> operator is a synonym for the comma except that it causes a
+The C<< => >> operator (sometimes pronounced "fat comma") is a synonym
+for the comma except that it causes a
word on its left to be interpreted as a string if it begins with a letter
or underscore and is composed only of letters, digits and underscores.
This includes operands that might otherwise be interpreted as operators,
-constants, single number v-strings or function calls. If in doubt about
+constants, single number v-strings or function calls. If in doubt about
this behavior, the left operand can be quoted explicitly.
Otherwise, the C<< => >> operator behaves exactly as the comma operator
print time.shift => "bbb";
-That example prints something like "1314363215shiftbbb", because the
+That example prints something like C<"1314363215shiftbbb">, because the
C<< => >> implicitly quotes the C<shift> immediately on its left, ignoring
the fact that C<time.shift> is the entire left operand.
On the right side of a list operator, the comma has very low precedence,
such that it controls all comma-separated expressions found there.
The only operators with lower precedence are the logical operators
-"and", "or", and "not", which may be used to evaluate calls to list
+C<"and">, C<"or">, and C<"not">, which may be used to evaluate calls to list
operators without the need for parentheses:
open HANDLE, "< :utf8", "filename" or die "Can't open: $!\n";
open(HANDLE, "< :utf8", "filename") or die "Can't open: $!\n";
-in which case you might as well just use the more customary "||" operator:
+in which case you might as well just use the more customary C<"||"> operator:
open(HANDLE, "< :utf8", "filename") || die "Can't open: $!\n";
-See also discussion of list operators in L<Terms and List Operators (Leftward)>.
+See also discussion of list operators in L</Terms and List Operators (Leftward)>.
=head2 Logical Not
X<operator, logical, not> X<not>
-Unary "not" returns the logical negation of the expression to its right.
-It's the equivalent of "!" except for the very low precedence.
+Unary C<"not"> returns the logical negation of the expression to its right.
+It's the equivalent of C<"!"> except for the very low precedence.
=head2 Logical And
X<operator, logical, and> X<and>
-Binary "and" returns the logical conjunction of the two surrounding
+Binary C<"and"> returns the logical conjunction of the two surrounding
expressions. It's equivalent to C<&&> except for the very low
precedence. This means that it short-circuits: the right
expression is evaluated only if the left expression is true.
X<operator, logical, exclusive or>
X<or> X<xor>
-Binary "or" returns the logical disjunction of the two surrounding
+Binary C<"or"> returns the logical disjunction of the two surrounding
expressions. It's equivalent to C<||> except for the very low precedence.
This makes it useful for control flow:
be careful to avoid using it as replacement for the C<||> operator.
It usually works out better for flow control than in assignments:
- $a = $b or $c; # bug: this is wrong
- ($a = $b) or $c; # really means this
- $a = $b || $c; # better written this way
+ $x = $y or $z; # bug: this is wrong
+ ($x = $y) or $z; # really means this
+ $x = $y || $z; # better written this way
However, when it's a list-context assignment and you're trying to use
-C<||> for control flow, you probably need "or" so that the assignment
+C<||> for control flow, you probably need C<"or"> so that the assignment
takes higher precedence.
@info = stat($file) || die; # oops, scalar sense of stat!
Then again, you could always use parentheses.
-Binary C<xor> returns the exclusive-OR of the two surrounding expressions.
+Binary C<"xor"> returns the exclusive-OR of the two surrounding expressions.
It cannot short-circuit (of course).
There is no low precedence operator for defined-OR.
=item unary &
-Address-of operator. (But see the "\" operator for taking a reference.)
+Address-of operator. (But see the C<"\"> operator for taking a reference.)
=item unary *
-Dereference-address operator. (Perl's prefix dereferencing
-operators are typed: $, @, %, and &.)
+Dereference-address operator. (Perl's prefix dereferencing
+operators are typed: C<$>, C<@>, C<%>, and C<&>.)
=item (TYPE)
Note, however, that this does not always work for quoting Perl code:
- $s = q{ if($a eq "}") ... }; # WRONG
+ $s = q{ if($x eq "}") ... }; # WRONG
-is a syntax error. The C<Text::Balanced> module (standard as of v5.8,
+is a syntax error. The C<L<Text::Balanced>> module (standard as of v5.8,
and from CPAN before then) is able to do this properly.
-There can be whitespace between the operator and the quoting
+There can (and in some cases, must) be whitespace between the operator
+and the quoting
characters, except when C<#> is being used as the quoting character.
-C<q#foo#> is parsed as the string C<foo>, while C<q #foo#> is the
+C<q#foo#> is parsed as the string C<foo>, while S<C<q #foo#>> is the
operator C<q> followed by a comment. Its argument will be taken
from the next line. This allows you to write:
s {foo} # Replace foo
{bar} # with bar.
+The cases where whitespace must be used are when the quoting character
+is a word character (meaning it matches C</\w/>):
+
+ q XfooX # Works: means the string 'foo'
+ qXfooX # WRONG!
+
The following escape sequences are available in constructs that interpolate,
and in transliterations:
X<\t> X<\n> X<\r> X<\f> X<\b> X<\a> X<\e> X<\x> X<\0> X<\c> X<\N> X<\N{}>
The result is the character specified by the hexadecimal number between
the braces. See L</[8]> below for details on which character.
-Only hexadecimal digits are valid between the braces. If an invalid
+Only hexadecimal digits are valid between the braces. If an invalid
character is encountered, a warning will be issued and the invalid
character and all subsequent characters (valid or invalid) within the
braces will be discarded.
Only hexadecimal digits are valid following C<\x>. When C<\x> is followed
by fewer than two valid digits, any valid digits will be zero-padded. This
-means that C<\x7> will be interpreted as C<\x07>, and a lone <\x> will be
+means that C<\x7> will be interpreted as C<\x07>, and a lone C<"\x"> will be
interpreted as C<\x00>. Except at the end of a string, having fewer than
two valid digits will result in a warning. Note that although the warning
says the illegal character is ignored, it is only ignored as part of the
=item [4]
-C<\N{U+I<hexadecimal number>}> means the Unicode character whose Unicode code
+S<C<\N{U+I<hexadecimal number>}>> means the Unicode character whose Unicode code
point is I<hexadecimal number>.
=item [5]
\cZ chr(26)
\cz chr(26)
\c[ chr(27)
+ # See below for chr(28)
\c] chr(29)
\c^ chr(30)
\c_ chr(31)
- \c? chr(127) # (on ASCII platforms)
+ \c? chr(127) # (on ASCII platforms; see below for link to
+ # EBCDIC discussion)
In other words, it's the character whose code point has had 64 xor'd with
its uppercase. C<\c?> is DELETE on ASCII platforms because
S<C<ord("?") ^ 64>> is 127, and
-C<\c@> is NULL because the ord of "@" is 64, so xor'ing 64 itself produces 0.
+C<\c@> is NULL because the ord of C<"@"> is 64, so xor'ing 64 itself produces 0.
-Also, C<\c\I<X>> yields C< chr(28) . "I<X>"> for any I<X>, but cannot come at the
+Also, C<\c\I<X>> yields S<C< chr(28) . "I<X>">> for any I<X>, but cannot come at the
end of a string, because the backslash would be parsed as escaping the end
quote.
use C<\o{}> instead, which avoids all these problems. Otherwise, it is best to
use this construct only for ordinals C<\077> and below, remembering to pad to
the left with zeros to make three digits. For larger ordinals, either use
-C<\o{}>, or convert to something else, such as to hex and use C<\x{}>
-instead.
+C<\o{}>, or convert to something else, such as to hex and use C<\N{U+}>
+(which is portable between platforms with different character sets) or
+C<\x{}> instead.
=item [8]
character. For example C<\x{50}> and C<\o{120}> both are the number 80 in
decimal, which is less than 256, so the number is interpreted in the native
character set encoding. In ASCII the character in the 80th position (indexed
-from 0) is the letter "P", and in EBCDIC it is the ampersand symbol "&".
+from 0) is the letter C<"P">, and in EBCDIC it is the ampersand symbol C<"&">.
C<\x{100}> and C<\o{400}> are both 256 in decimal, so the number is interpreted
as a Unicode code point no matter what the native encoding is. The name of the
character in the 256th position (indexed by 0) in Unicode is
C<LATIN CAPITAL LETTER A WITH MACRON>.
-There are a couple of exceptions to the above rule. S<C<\N{U+I<hex number>}>> is
-always interpreted as a Unicode code point, so that C<\N{U+0050}> is "P" even
-on EBCDIC platforms. And if L<C<S<use encoding>>|encoding> is in effect, the
-number is considered to be in that encoding, and is translated from that into
-the platform's native encoding if there is a corresponding native character;
-otherwise to Unicode.
+An exception to the above rule is that S<C<\N{U+I<hex number>}>> is
+always interpreted as a Unicode code point, so that C<\N{U+0050}> is C<"P"> even
+on EBCDIC platforms.
=back
B<NOTE>: Unlike C and other languages, Perl has no C<\v> escape sequence for
the vertical tab (VT, which is 11 in both ASCII and EBCDIC), but you may
-use C<\ck> or
-C<\x0b>. (C<\v>
+use C<\N{VT}>, C<\ck>, C<\N{U+0b}>, or C<\x0b>. (C<\v>
does have meaning in regular expression patterns in Perl, see L<perlre>.)
The following escape sequences are available in constructs that interpolate,
say"This \Qquoting \ubusiness \Uhere isn't quite\E done yet,\E is it?";
This quoting\ Business\ HERE\ ISN\'T\ QUITE\ done\ yet\, is it?
-If C<use locale> is in effect (but not C<use locale ':not_characters'>),
-the case map used by C<\l>, C<\L>,
-C<\u>, and C<\U> is taken from the current locale. See L<perllocale>.
-If Unicode (for example, C<\N{}> or code points of 0x100 or
-beyond) is being used, the case map used by C<\l>, C<\L>, C<\u>, and
-C<\U> is as defined by Unicode. That means that case-mapping
-a single character can sometimes produce several characters.
-Under C<use locale>, C<\F> produces the same results as C<\L>
+If a S<C<use locale>> form that includes C<LC_CTYPE> is in effect (see
+L<perllocale>), the case map used by C<\l>, C<\L>, C<\u>, and C<\U> is
+taken from the current locale. If Unicode (for example, C<\N{}> or code
+points of 0x100 or beyond) is being used, the case map used by C<\l>,
+C<\L>, C<\u>, and C<\U> is as defined by Unicode. That means that
+case-mapping a single character can sometimes produce a sequence of
+several characters.
+Under S<C<use locale>>, C<\F> produces the same results as C<\L>
for all locales but a UTF-8 one, where it instead uses the Unicode
definition.
device drivers, C libraries, and Perl all conspire to preserve. Not all
systems read C<"\r"> as ASCII CR and C<"\n"> as ASCII LF. For example,
on the ancient Macs (pre-MacOS X) of yesteryear, these used to be reversed,
-and on systems without line terminator,
+and on systems without a line terminator,
printing C<"\n"> might emit no actual data. In general, use C<"\n"> when
you mean a "newline" for your system, but use the literal ASCII when you
need an exact character. For example, most networking protocols expect
Interpolating an array or slice interpolates the elements in order,
separated by the value of C<$">, so is equivalent to interpolating
-C<join $", @array>. "Punctuation" arrays such as C<@*> are usually
+S<C<join $", @array>>. "Punctuation" arrays such as C<@*> are usually
interpolated only if the name is enclosed in braces C<@{*}>, but the
arrays C<@_>, C<@+>, and C<@-> are interpolated even without braces.
For the pattern of regex operators (C<qr//>, C<m//> and C<s///>),
the quoting from C<\Q> is applied after interpolation is processed,
-but before escapes are processed. This allows the pattern to match
-literally (except for C<$> and C<@>). For example, the following matches:
+but before escapes are processed. This allows the pattern to match
+literally (except for C<$> and C<@>). For example, the following matches:
'\s\t' =~ /\Q\s\t/
=over 8
-=item qr/STRING/msixpodual
+=item C<qr/I<STRING>/msixpodualn>
X<qr> X</i> X</m> X</o> X</s> X</x> X</p>
This operator quotes (and possibly compiles) its I<STRING> as a regular
expression. I<STRING> is interpolated the same way as I<PATTERN>
-in C<m/PATTERN/>. If "'" is used as the delimiter, no interpolation
-is done. Returns a Perl value which may be used instead of the
-corresponding C</STRING/msixpodual> expression. The returned value is a
-normalized version of the original pattern. It magically differs from
+in C<m/I<PATTERN>/>. If C<"'"> is used as the delimiter, no variable
+interpolation is done. Returns a Perl value which may be used instead of the
+corresponding C</I<STRING>/msixpodualn> expression. The returned value is a
+normalized version of the original pattern. It magically differs from
a string containing the same characters: C<ref(qr/x/)> returns "Regexp";
however, dereferencing it is not well defined (you currently get the
normalized version of the original pattern, but this may change).
$string =~ $re; # or used standalone
$string =~ /$re/; # or this way
-Since Perl may compile the pattern at the moment of execution of the qr()
-operator, using qr() may have speed advantages in some situations,
-notably if the result of qr() is used standalone:
+Since Perl may compile the pattern at the moment of execution of the C<qr()>
+operator, using C<qr()> may have speed advantages in some situations,
+notably if the result of C<qr()> is used standalone:
sub match {
my $patterns = shift;
}
Precompilation of the pattern into an internal representation at
-the moment of qr() avoids a need to recompile the pattern every
+the moment of C<qr()> avoids the need to recompile the pattern every
time a match C</$pat/> is attempted. (Perl has many other internal
optimizations, but none would be triggered in the above example if
-we did not use qr() operator.)
+we did not use C<qr()> operator.)
Options (specified by the following modifiers) are:
m Treat string as multiple lines.
s Treat string as single line. (Make . match a newline)
i Do case-insensitive pattern matching.
- x Use extended regular expressions.
+ x Use extended regular expressions; specifying two
+ x's means \t and the SPACE character are ignored within
+ square-bracketed character classes
p When matching preserve a copy of the matched string so
that ${^PREMATCH}, ${^MATCH}, ${^POSTMATCH} will be
- defined.
+ defined (ignored starting in v5.20) as these are always
+ defined starting in that relese
o Compile pattern only once.
a ASCII-restrict: Use ASCII for \d, \s, \w; specifying two
- a's further restricts /i matching so that no ASCII
- character will match a non-ASCII one.
- l Use the locale.
+ a's further restricts things to that that no ASCII
+ character will match a non-ASCII one under /i.
+ l Use the current run-time locale's rules.
u Use Unicode rules.
d Use Unicode or native charset, as in 5.12 and earlier.
+ n Non-capture mode. Don't let () fill in $1, $2, etc...
If a precompiled pattern is embedded in a larger pattern then the effect
-of "msixpluad" will be propagated appropriately. The effect the "o"
-modifier has is not propagated, being restricted to those patterns
+of C<"msixpluadn"> will be propagated appropriately. The effect that the
+C</o> modifier has is not propagated, being restricted to those patterns
explicitly using it.
The last four modifiers listed above, added in Perl 5.14,
to want to specify explicitly; the other three are selected
automatically by various pragmas.
-See L<perlre> for additional information on valid syntax for STRING, and
+See L<perlre> for additional information on valid syntax for I<STRING>, and
for a detailed look at the semantics of regular expressions. In
particular, all modifiers except the largely obsolete C</o> are further
explained in L<perlre/Modifiers>. C</o> is described in the next section.
-=item m/PATTERN/msixpodualgc
+=item C<m/I<PATTERN>/msixpodualngc>
X<m> X<operator, match>
X<regexp, options> X<regexp> X<regex, options> X<regex>
X</m> X</s> X</i> X</x> X</p> X</o> X</g> X</c>
-=item /PATTERN/msixpodualgc
+=item C</I<PATTERN>/msixpodualngc>
Searches a string for a pattern match, and in scalar context returns
true if it succeeds, false if it fails. If no string is specified
-via the C<=~> or C<!~> operator, the $_ string is searched. (The
+via the C<=~> or C<!~> operator, the C<$_> string is searched. (The
string specified with C<=~> need not be an lvalue--it may be the
result of an expression evaluation, but remember the C<=~> binds
rather tightly.) See also L<perlre>.
c Do not reset search position on a failed match when /g is
in effect.
-If "/" is the delimiter then the initial C<m> is optional. With the C<m>
+If C<"/"> is the delimiter then the initial C<m> is optional. With the C<m>
you can use any pair of non-whitespace (ASCII) characters
as delimiters. This is particularly useful for matching path names
-that contain "/", to avoid LTS (leaning toothpick syndrome). If "?" is
+that contain C<"/">, to avoid LTS (leaning toothpick syndrome). If C<"?"> is
the delimiter, then a match-only-once rule applies,
-described in C<m?PATTERN?> below. If "'" (single quote) is the delimiter,
-no interpolation is performed on the PATTERN.
-When using a character valid in an identifier, whitespace is required
+described in C<m?I<PATTERN>?> below. If C<"'"> (single quote) is the delimiter,
+no variable interpolation is performed on the I<PATTERN>.
+When using a delimiter character valid in an identifier, whitespace is required
after the C<m>.
-PATTERN may contain variables, which will be interpolated
+I<PATTERN> may contain variables, which will be interpolated
every time the pattern search is evaluated, except
for when the delimiter is a single quote. (Note that C<$(>, C<$)>, and
C<$|> are not interpolated because they look like end-of-string tests.)
The bottom line is that using C</o> is almost never a good idea.
-=item The empty pattern //
+=item The empty pattern C<//>
-If the PATTERN evaluates to the empty string, the last
-I<successfully> matched regular expression is used instead. In this
+If the I<PATTERN> evaluates to the empty string, the last
+I<successfully> matched regular expression is used instead. In this
case, only the C<g> and C<c> flags on the empty pattern are honored;
-the other flags are taken from the original pattern. If no match has
+the other flags are taken from the original pattern. If no match has
previously succeeded, this will (silently) act instead as a genuine
empty pattern (which will always match).
Note that it's possible to confuse Perl into thinking C<//> (the empty
regex) is really C<//> (the defined-or operator). Perl is usually pretty
good about this, but some pathological cases might trigger this, such as
-C<$a///> (is that C<($a) / (//)> or C<$a // />?) and C<print $fh //>
-(C<print $fh(//> or C<print($fh //>?). In all of these examples, Perl
+C<$x///> (is that S<C<($x) / (//)>> or S<C<$x // />>?) and S<C<print $fh //>>
+(S<C<print $fh(//>> or S<C<print($fh //>>?). In all of these examples, Perl
will assume you meant defined-or. If you meant the empty regex, just
use parentheses or spaces to disambiguate, or even prefix the empty
regex with an C<m> (so C<//> becomes C<m//>).
if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))
-This last example splits $foo into the first two words and the
-remainder of the line, and assigns those three fields to $F1, $F2, and
-$Etc. The conditional is true if any variables were assigned; that is,
+This last example splits C<$foo> into the first two words and the
+remainder of the line, and assigns those three fields to C<$F1>, C<$F2>, and
+C<$Etc>. The conditional is true if any variables were assigned; that is,
if the pattern matched.
The C</g> modifier specifies global pattern matching--that is,
-matching as many times as possible within the string. How it behaves
-depends on the context. In list context, it returns a list of the
+matching as many times as possible within the string. How it behaves
+depends on the context. In list context, it returns a list of the
substrings matched by any capturing parentheses in the regular
-expression. If there are no parentheses, it returns a list of all
+expression. If there are no parentheses, it returns a list of all
the matched strings, as if there were parentheses around the whole
pattern.
In scalar context, each execution of C<m//g> finds the next match,
returning true if it matches, and false if there is no further match.
The position after the last match can be read or set using the C<pos()>
-function; see L<perlfunc/pos>. A failed match normally resets the
+function; see L<perlfunc/pos>. A failed match normally resets the
search position to the beginning of the string, but you can avoid that
-by adding the C</c> modifier (for example, C<m//gc>). Modifying the target
+by adding the C</c> modifier (for example, C<m//gc>). Modifying the target
string also resets the search position.
-=item \G assertion
+=item C<\G I<assertion>>
You can intermix C<m//g> matches with C<m/\G.../g>, where C<\G> is a
zero-width assertion that matches the exact position where the
-previous C<m//g>, if any, left off. Without the C</g> modifier, the
+previous C<m//g>, if any, left off. Without the C</g> modifier, the
C<\G> assertion still anchors at C<pos()> as it was at the start of
the operation (see L<perlfunc/pos>), but the match is of course only
-attempted once. Using C<\G> without C</g> on a target string that has
+attempted once. Using C<\G> without C</g> on a target string that has
not previously had a C</g> match applied to it is the same as using
the C<\A> assertion to match the beginning of the string. Note also
that, currently, C<\G> is only properly supported when anchored at the
Final: 'q', pos=8
Notice that the final match matched C<q> instead of C<p>, which a match
-without the C<\G> anchor would have done. Also note that the final match
-did not update C<pos>. C<pos> is only updated on a C</g> match. If the
+without the C<\G> anchor would have done. Also note that the final match
+did not update C<pos>. C<pos> is only updated on a C</g> match. If the
final match did indeed match C<p>, it's a good bet that you're running a
very old (pre-5.6.0) version of Perl.
lowercase line-noise lowercase lowercase line-noise lowercase
lowercase line-noise MiXeD line-noise. That's all!
-=item m?PATTERN?msixpodualgc
+=item C<m?I<PATTERN>?msixpodualngc>
X<?> X<operator, match-once>
-=item ?PATTERN?msixpodualgc
+=item C<?I<PATTERN>?msixpodualngc>
-This is just like the C<m/PATTERN/> search, except that it matches
-only once between calls to the reset() operator. This is a useful
+This is just like the C<m/I<PATTERN>/> search, except that it matches
+only once between calls to the C<reset()> operator. This is a useful
optimization when you want to see only the first occurrence of
something in each file of a set of files, for instance. Only C<m??>
patterns local to the current package are reset.
s//utf8/ if m? ^ =encoding \h+ \K latin1 ?x;
The match-once behavior is controlled by the match delimiter being
-C<?>; with any other delimiter this is the normal C<m//> operator.
+C<?>; with any other delimiter this is the normal C<m//> operator.
-For historical reasons, the leading C<m> in C<m?PATTERN?> is optional,
-but the resulting C<?PATTERN?> syntax is deprecated, will warn on
-usage and might be removed from a future stable release of Perl (without
-further notice!).
+In the past, the leading C<m> in C<m?I<PATTERN>?> was optional, but omitting it
+would produce a deprecation warning. As of v5.22.0, omitting it produces a
+syntax error. If you encounter this construct in older code, you can just add
+C<m>.
-=item s/PATTERN/REPLACEMENT/msixpodualgcer
+=item C<s/I<PATTERN>/I<REPLACEMENT>/msixpodualngcer>
X<substitute> X<substitution> X<replace> X<regexp, replace>
X<regexp, substitute> X</m> X</s> X</i> X</x> X</p> X</o> X</g> X</c> X</e> X</r>
hash element, or an assignment to one of those; that is, some sort of
scalar lvalue.
-If the delimiter chosen is a single quote, no interpolation is
-done on either the PATTERN or the REPLACEMENT. Otherwise, if the
-PATTERN contains a $ that looks like a variable rather than an
+If the delimiter chosen is a single quote, no variable interpolation is
+done on either the I<PATTERN> or the I<REPLACEMENT>. Otherwise, if the
+I<PATTERN> contains a C<$> that looks like a variable rather than an
end-of-string test, the variable will be interpolated into the pattern
at run-time. If you want the pattern compiled only once the first time
the variable is interpolated, use the C</o> option. If the pattern
evaluates to the empty string, the last successfully executed regular
expression is used instead. See L<perlre> for further explanation on these.
-Options are as with m// with the addition of the following replacement
+Options are as with C<m//> with the addition of the following replacement
specific options:
e Evaluate the right side as an expression.
are used, no interpretation is done on the replacement string (the C</e>
modifier overrides this, however). Note that Perl treats backticks
as normal delimiters; the replacement text is not evaluated as a command.
-If the PATTERN is delimited by bracketing quotes, the REPLACEMENT has
+If the I<PATTERN> is delimited by bracketing quotes, the I<REPLACEMENT> has
its own pair of quotes, which may or may not be bracketing quotes, for example,
C<s(foo)(bar)> or C<< s<foo>/bar/ >>. A C</e> will cause the
replacement portion to be treated as a full-fledged Perl expression
and evaluated right then and there. It is, however, syntax checked at
-compile-time. A second C<e> modifier will cause the replacement portion
+compile-time. A second C<e> modifier will cause the replacement portion
to be C<eval>ed before being run as a Perl expression.
Examples:
s/^=(\w+)/pod($1)/ge; # use function call
$_ = 'abc123xyz';
- $a = s/abc/def/r; # $a is 'def123xyz' and
+ $x = s/abc/def/r; # $x is 'def123xyz' and
# $_ remains 'abc123xyz'.
# expand variables in $_, but dynamics only, using
s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields
-Note the use of $ instead of \ in the last example. Unlike
-B<sed>, we use the \<I<digit>> form in only the left hand side.
+Note the use of C<$> instead of C<\> in the last example. Unlike
+B<sed>, we use the \<I<digit>> form only in the left hand side.
Anywhere else it's $<I<digit>>.
Occasionally, you can't use just a C</g> to get all the changes
=over 4
-=item q/STRING/
+=item C<q/I<STRING>/>
X<q> X<quote, single> X<'> X<''>
-=item 'STRING'
+=item C<'I<STRING>'>
A single-quoted, literal string. A backslash represents a backslash
unless followed by the delimiter or another backslash, in which case
$bar = q('This is it.');
$baz = '\n'; # a two-character string
-=item qq/STRING/
+=item C<qq/I<STRING>/>
X<qq> X<quote, double> X<"> X<"">
-=item "STRING"
+=item "I<STRING>"
A double-quoted, interpolated string.
if /\b(tcl|java|python)\b/i; # :-)
$baz = "\n"; # a one-character string
-=item qx/STRING/
+=item C<qx/I<STRING>/>
X<qx> X<`> X<``> X<backtick>
-=item `STRING`
+=item C<`I<STRING>`>
A string which is (possibly) interpolated and then executed as a
system command with F</bin/sh> or its equivalent. Shell wildcards,
pipes, and redirections will be honored. The collected standard
output of the command is returned; standard error is unaffected. In
scalar context, it comes back as a single (potentially multi-line)
-string, or undef if the command failed. In list context, returns a
-list of lines (however you've defined lines with $/ or
-$INPUT_RECORD_SEPARATOR), or an empty list if the command failed.
+string, or C<undef> if the command failed. In list context, returns a
+list of lines (however you've defined lines with C<$/> or
+C<$INPUT_RECORD_SEPARATOR>), or an empty list if the command failed.
Because backticks do not affect standard error, use shell file descriptor
syntax (assuming the shell supports this) if you care to address this.
interpreter on your system. On most platforms, you will have to protect
shell metacharacters if you want them treated literally. This is in
practice difficult to do, as it's unclear how to escape which characters.
-See L<perlsec> for a clean and safe example of a manual fork() and exec()
+See L<perlsec> for a clean and safe example of a manual C<fork()> and C<exec()>
to emulate backticks safely.
On some platforms (notably DOS-like ones), the shell may not be
Perl will attempt to flush all files opened for
output before starting the child process, but this may not be supported
on some platforms (see L<perlport>). To be safe, you may need to set
-C<$|> (
$AUTOFLUSH in English) or call the C<autoflush()> method of
-C<IO::Handle> on any open handles.
+C<$|> (
C<$AUTOFLUSH> in C<L<English>>) or call the C<autoflush()> method of
+C<L<IO::Handle>> on any open handles.
Beware that some command shells may place restrictions on the length
of the command line. You must ensure your strings don't exceed this
a glue language, and one of the things it glues together is commands.
Just understand what you're getting yourself into.
+Like C<system>, backticks put the child process exit code in C<$?>.
+If you'd like to manually inspect failure, you can check all possible
+failure modes by inspecting C<$?> like this:
+
+ if ($? == -1) {
+ print "failed to execute: $!\n";
+ }
+ elsif ($? & 127) {
+ printf "child died with signal %d, %s coredump\n",
+ ($? & 127), ($? & 128) ? 'with' : 'without';
+ }
+ else {
+ printf "child exited with value %d\n", $? >> 8;
+ }
+
+Use the L<open> pragma to control the I/O layers used when reading the
+output of the command, for example:
+
+ use open IN => ":encoding(UTF-8)";
+ my $x = `cmd-producing-utf-8`;
+
See L</"I/O Operators"> for more discussion.
-=item qw/STRING/
+=item C<qw/I<STRING>/>
X<qw> X<quote, list> X<quote, words>
-Evaluates to a list of the words extracted out of STRING, using embedded
+Evaluates to a list of the words extracted out of I<STRING>, using embedded
whitespace as the word delimiters. It can be understood as being roughly
equivalent to:
use POSIX qw( setlocale localeconv )
@EXPORT = qw( foo bar baz );
-A common mistake is to try to separate the words with comma or to
+A common mistake is to try to separate the words with commas or to
put comments into a multi-line C<qw>-string. For this reason, the
-C<use warnings> pragma and the B<-w> switch (that is, the C<$^W> variable)
-produces warnings if the STRING contains the "," or the "#" character.
+S<C<use warnings>> pragma and the B<-w> switch (that is, the C<$^W> variable)
+produces warnings if the I<STRING> contains the C<","> or the C<"#"> character.
-=item tr/SEARCHLIST/REPLACEMENTLIST/cdsr
+=item C<tr/I<SEARCHLIST>/I<REPLACEMENTLIST>/cdsr>
X<tr> X<y> X<transliterate> X</c> X</d> X</s>
-=item y/SEARCHLIST/REPLACEMENTLIST/cdsr
+=item C<y/I<SEARCHLIST>/I<REPLACEMENTLIST>/cdsr>
Transliterates all occurrences of the characters found in the search list
with the corresponding character in the replacement list. It returns
the number of characters replaced or deleted. If no string is
-specified via the C<=~> or C<!~> operator, the $_ string is transliterated.
+specified via the C<=~> or C<!~> operator, the C<$_> string is transliterated.
If the C</r> (non-destructive) option is present, a new copy of the string
is made and its characters transliterated, and this copy is returned no
A character range may be specified with a hyphen, so C<tr/A-J/0-9/>
does the same replacement as C<tr/ACEGIBDFHJ/0246813579/>.
For B<sed> devotees, C<y> is provided as a synonym for C<tr>. If the
-SEARCHLIST is delimited by bracketing quotes, the REPLACEMENTLIST has
-its own pair of quotes, which may or may not be bracketing quotes;
-for example, C<tr[aeiouy][yuoiea]> or C<tr(+\-*/)/ABCD/>.
+I<SEARCHLIST> is delimited by bracketing quotes, the I<REPLACEMENTLIST>
+must have its own pair of quotes, which may or may not be bracketing
+quotes; for example, C<tr[aeiouy][yuoiea]> or C<tr(+\-*/)/ABCD/>.
+
+Characters may be literals or any of the escape sequences accepted in
+double-quoted strings. But there is no variable interpolation, so C<"$">
+and C<"@"> are treated as literals. A hyphen at the beginning or end, or
+preceded by a backslash is considered a literal. Escape sequence
+details are in L<the table near the beginning of this section|/Quote and
+Quote-like Operators>.
Note that C<tr> does B<not> do regular expression character classes such as
-C<\d> or C<\pL>. The C<tr> operator is not equivalent to the tr(1)
-utility. If you want to map strings between lower/upper cases, see
-L<perlfunc/lc> and L<perlfunc/uc>, and in general consider using the C<s>
-operator if you need regular expressions. The C<\U>, C<\u>, C<\L>, and
-C<\l> string-interpolation escapes on the right side of a substitution
-operator will perform correct case-mappings, but C<tr[a-z][A-Z]> will not
-(except sometimes on legacy 7-bit data).
-
-Note also that the whole range idea is rather unportable between
-character sets--and even within character sets they may cause results
-you probably didn't expect. A sound principle is to use only ranges
-that begin from and end at either alphabets of equal case (a-e, A-E),
-or digits (0-4). Anything else is unsafe. If in doubt, spell out the
+C<\d> or C<\pL>. The C<tr> operator is not equivalent to the C<L<tr(1)>>
+utility. C<tr[a-z][A-Z]> will uppercase the 26 letters "a" through "z",
+but for case changing not confined to ASCII, use
+L<C<lc>|perlfunc/lc>, L<C<uc>|perlfunc/uc>,
+L<C<lcfirst>|perlfunc/lcfirst>, L<C<ucfirst>|perlfunc/ucfirst>
+(all documented in L<perlfunc>), or the
+L<substitution operator C<sE<sol>I<PATTERN>E<sol>I<REPLACEMENT>E<sol>>|/sE<sol>PATTERNE<sol>REPLACEMENTE<sol>msixpodualngcer>
+(with C<\U>, C<\u>, C<\L>, and C<\l> string-interpolation escapes in the
+I<REPLACEMENT> portion).
+
+Most ranges are unportable between character sets, but certain ones
+signal Perl to do special handling to make them portable. There are two
+classes of portable ranges. The first are any subsets of the ranges
+C<A-Z>, C<a-z>, and C<0-9>, when expressed as literal characters.
+
+ tr/h-k/H-K/
+
+capitalizes the letters C<"h">, C<"i">, C<"j">, and C<"k"> and nothing
+else, no matter what the platform's character set is. In contrast, all
+of
+
+ tr/\x68-\x6B/\x48-\x4B/
+ tr/h-\x6B/H-\x4B/
+ tr/\x68-k/\x48-K/
+
+do the same capitalizations as the previous example when run on ASCII
+platforms, but something completely different on EBCDIC ones.
+
+The second class of portable ranges is invoked when one or both of the
+range's end points are expressed as C<\N{...}>
+
+ $string =~ tr/\N{U+20}-\N{U+7E}//d;
+
+removes from C<$string> all the platform's characters which are
+equivalent to any of Unicode U+0020, U+0021, ... U+007D, U+007E. This
+is a portable range, and has the same effect on every platform it is
+run on. It turns out that in this example, these are the ASCII
+printable characters. So after this is run, C<$string> has only
+controls and characters which have no ASCII equivalents.
+
+But, even for portable ranges, it is not generally obvious what is
+included without having to look things up. A sound principle is to use
+only ranges that begin from and end at either ASCII alphabetics of equal
+case (C<b-e>, C<B-E>), or digits (C<1-4>). Anything else is unclear
+(and unportable unless C<\N{...}> is used). If in doubt, spell out the
character sets in full.
Options:
r Return the modified string and leave the original string
untouched.
-If the C</c> modifier is specified, the SEARCHLIST character set
+If the C</c> modifier is specified, the I<SEARCHLIST> character set
is complemented. If the C</d> modifier is specified, any characters
-specified by SEARCHLIST not found in REPLACEMENTLIST are deleted.
+specified by I<SEARCHLIST> not found in I<REPLACEMENTLIST> are deleted.
(Note that this is slightly more flexible than the behavior of some
-B<tr> programs, which delete anything they find in the SEARCHLIST,
-period.) If the C</s> modifier is specified, sequences of characters
+B<tr> programs, which delete anything they find in the I<SEARCHLIST>,
+period.) If the C</s> modifier is specified, sequences of characters
that were transliterated to the same character are squashed down
to a single instance of the character.
-If the C</d> modifier is used, the REPLACEMENTLIST is always interpreted
-exactly as specified. Otherwise, if the REPLACEMENTLIST is shorter
-than the SEARCHLIST, the final character is replicated till it is long
-enough. If the REPLACEMENTLIST is empty, the SEARCHLIST is replicated.
+If the C</d> modifier is used, the I<REPLACEMENTLIST> is always interpreted
+exactly as specified. Otherwise, if the I<REPLACEMENTLIST> is shorter
+than the I<SEARCHLIST>, the final character is replicated till it is long
+enough. If the I<REPLACEMENTLIST> is empty, the I<SEARCHLIST> is replicated.
This latter is useful for counting characters in a class or for
squashing character sequences in a class.
will transliterate any A to X.
Because the transliteration table is built at compile time, neither
-the SEARCHLIST nor the REPLACEMENTLIST are subjected to double quote
+the I<SEARCHLIST> nor the I<REPLACEMENTLIST> are subjected to double quote
interpolation. That means that if you want to use variables, you
-must use an eval():
+must use an C<eval()>:
eval "tr/$oldlist/$newlist/";
die $@ if $@;
eval "tr/$oldlist/$newlist/, 1" or die $@;
-=item <<EOF
+=item C<< <<I<EOF> >>
X<here-doc> X<heredoc> X<here-document> X<<< << >>>
A line-oriented form of quoting is based on the shell "here-document"
the quoted material, and all lines following the current line down to
the terminating string are the value of the item.
+Prefixing the terminating string with a C<~> specifies that you
+want to use L</Indented Here-docs> (see below).
+
The terminating string may be either an identifier (a word), or some
quoted text. An unquoted identifier works like double quotes.
There may not be a space between the C<< << >> and the identifier,
=item Single Quotes
Single quotes indicate the text is to be treated literally with no
-interpolation of its content. This is similar to single quoted
+interpolation of its content. This is similar to single quoted
strings except that backslashes have no special meaning, with C<\\>
being treated as two backslashes and not one as they would in every
other quoting construct.
=item Backticks
The content of the here doc is treated just as it would be if the
-string were embedded in backticks. Thus the content is interpolated
+string were embedded in backticks. Thus the content is interpolated
as though it were double quoted and then executed via the shell, with
the results of the execution returned.
=back
+=over 4
+
+=item Indented Here-docs
+
+The here-doc modifier C<~> allows you to indent your here-docs to make
+the code more readable:
+
+ if ($some_var) {
+ print <<~EOF;
+ This is a here-doc
+ EOF
+ }
+
+This will print...
+
+ This is a here-doc
+
+...with no leading whitespace.
+
+The delimiter is used to determine the B<exact> whitespace to
+remove from the beginning of each line. All lines B<must> have
+at least the same starting whitespace (except lines only
+containing a newline) or perl will croak. Tabs and spaces can
+be mixed, but are matched exactly. One tab will not be equal to
+8 spaces!
+
+Additional beginning whitespace (beyond what preceded the
+delimiter) will be preserved:
+
+ print <<~EOF;
+ This text is not indented
+ This text is indented with two spaces
+ This text is indented with two tabs
+ EOF
+
+Finally, the modifier may be used with all of the forms
+mentioned above:
+
+ <<~\EOF;
+ <<~'EOF'
+ <<~"EOF"
+ <<~`EOF`
+
+And whitespace may be used between the C<~> and quoted delimiters:
+
+ <<~ 'EOF'; # ... "EOF", `EOF`
+
+=back
+
It is possible to stack multiple here-docs in a row:
print <<"foo", <<"bar"; # you can stack them
outside of string evals.
Additionally, quoting rules for the end-of-string identifier are
-unrelated to Perl's quoting rules. C<q()>, C<qq()>, and the like are not
+unrelated to Perl's quoting rules. C<q()>, C<qq()>, and the like are not
supported in place of C<''> and C<"">, and the only interpolation is for
backslashing the quoting character:
=item Finding the end
-The first pass is finding the end of the quoted construct, where
-the information about the delimiters is used in parsing.
-During this search, text between the starting and ending delimiters
-is copied to a safe location. The text copied gets delimiter-independent.
+The first pass is finding the end of the quoted construct. This results
+in saving to a safe location a copy of the text (between the starting
+and ending delimiters), normalized as necessary to avoid needing to know
+what the original delimiters were.
If the construct is a here-doc, the ending delimiter is a line
-that has a terminating string as the content. Therefore C<<<EOF> is
+that has a terminating string as the content. Therefore C<<<EOF> is
terminated by C<EOF> immediately followed by C<"\n"> and starting
from the first column of the terminating line.
When searching for the terminating line of a here-doc, nothing
-is skipped. In other words, lines after the here-doc syntax
+is skipped. In other words, lines after the here-doc syntax
are compared with the terminating string line by line.
For the constructs except here-docs, single characters are used as starting
-and ending delimiters. If the starting delimiter is an opening punctuation
+and ending delimiters. If the starting delimiter is an opening punctuation
(that is C<(>, C<[>, C<{>, or C<< < >>), the ending delimiter is the
corresponding closing punctuation (that is C<)>, C<]>, C<}>, or C<< > >>).
If the starting delimiter is an unpaired character like C</> or a closing
-punctuation, the ending delimiter is same as the starting delimiter.
+punctuation, the ending delimiter is the same as the starting delimiter.
Therefore a C</> terminates a C<qq//> construct, while a C<]> terminates
both C<qq[]> and C<qq]]> constructs.
and C<\\> are skipped. For example, while searching for terminating C</>,
combinations of C<\\> and C<\/> are skipped. If the delimiters are
bracketing, nested pairs are also skipped. For example, while searching
-for closing C<]> paired with the opening C<[>, combinations of C<\\>, C<\]>,
+for a closing C<]> paired with the opening C<[>, combinations of C<\\>, C<\]>,
and C<\[> are all skipped, and nested C<[> and C<]> are skipped as well.
However, when backslashes are used as the delimiters (like C<qq\\> and
C<tr\\\>), nothing is skipped.
For constructs with three-part delimiters (C<s///>, C<y///>, and
C<tr///>), the search is repeated once more.
If the first delimiter is not an opening punctuation, the three delimiters must
-be same such as C<s!!!> and C<tr)))>, in which case the second delimiter
+be the same, such as C<s!!!> and C<tr)))>,
+in which case the second delimiter
terminates the left part and starts the right part at once.
If the left part is delimited by bracketing punctuation (that is C<()>,
C<[]>, C<{}>, or C<< <> >>), the right part needs another pair of
delimiters such as C<s(){}> and C<tr[]//>. In these cases, whitespace
-and comments are allowed between the two parts, though the comment must follow
+and comments are allowed between the two parts, although the comment must follow
at least one whitespace character; otherwise a character expected as the
start of the comment may be regarded as the starting delimiter of the right part.
modifier. So the embedded C<#> is interpreted as a literal C<#>.
Also no attention is paid to C<\c\> (multichar control char syntax) during
-this search. Thus the second C<\> in C<qq/\c\/> is interpreted as a part
+this search. Thus the second C<\> in C<qq/\c\/> is interpreted as a part
of C<\/>, and the following C</> is not recognized as a delimiter.
Instead, use C<\034> or C<\x1c> at the end of quoted constructs.
=item C<''>, C<q//>, C<tr'''>, C<y'''>, the replacement of C<s'''>
The only interpolation is removal of C<\> from pairs of C<\\>.
-Therefore C<-> in C<tr'''> and C<y'''> is treated literally
+Therefore C<"-"> in C<tr'''> and C<y'''> is treated literally
as a hyphen and no character range is available.
C<\1> in the replacement of C<s'''> does not work as C<$1>.
case and quoting such as C<\Q>, C<\U>, and C<\E> are not recognized.
The other escape sequences such as C<\200> and C<\t> and backslashed
characters such as C<\\> and C<\-> are converted to appropriate literals.
-The character C<-> is treated specially and therefore C<\-> is treated
-as a literal C<->.
+The character C<"-"> is treated specially and therefore C<\-> is treated
+as a literal C<"-">.
=item C<"">, C<``>, C<qq//>, C<qx//>, C<< <file*glob> >>, C<<<"EOF">
C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, C<\F> (possibly paired with C<\E>) are
converted to corresponding Perl constructs. Thus, C<"$foo\Qbaz$bar">
-is converted to C<$foo . (quotemeta("baz" . $bar))> internally.
+is converted to S<C<$foo . (quotemeta("baz" . $bar))>> internally.
The other escape sequences such as C<\200> and C<\t> and backslashed
characters such as C<\\> and C<\-> are replaced with appropriate
expansions.
may be closer to the conjectural I<intention> of the writer of C<"\Q\t\E">.
Interpolated scalars and arrays are converted internally to the C<join> and
-C<.> catenation operations. Thus, C<"$foo XXX '@arr'"> becomes:
+C<"."> catenation operations. Thus, S<C<"$foo XXX '@arr'">> becomes:
$foo . " XXX '" . (join $", @arr) . "'";
All operations above are performed simultaneously, left to right.
-Because the result of C<"\Q STRING \E"> has all metacharacters
+Because the result of S<C<"\Q I<STRING> \E">> has all metacharacters
quoted, there is no way to insert a literal C<$> or C<@> inside a
-C<\Q\E> pair. If protected by C<\>, C<$> will be quoted to became
+C<\Q\E> pair. If protected by C<\>, C<$> will be quoted to become
C<"\\\$">; if not, it is interpreted as the start of an interpolated
scalar.
Note also that the interpolation code needs to make a decision on
where the interpolated scalar ends. For instance, whether
-C<< "a $b -> {c}" >> really means:
+S<C<< "a $x -> {c}" >>> really means:
- "a " . $b . " -> {c}";
+ "a " . $x . " -> {c}";
or:
- "a " . $b -> {c};
+ "a " . $x -> {c};
Most of the time, the longest possible text that does not include
spaces between components and which contains matching braces or
It is at this step that C<\1> is begrudgingly converted to C<$1> in
the replacement text of C<s///>, in order to correct the incorrigible
I<sed> hackers who haven't picked up the saner idiom yet. A warning
-is emitted if the C<use warnings> pragma or the B<-w> command-line flag
+is emitted if the S<C<use warnings>> pragma or the B<-w> command-line flag
(that is, the C<$^W> variable) was set.
=item C<RE> in C<?RE?>, C</RE/>, C<m/RE/>, C<s/RE/foo/>,
back to the perl parser, in a similar way that an interpolated array
subscript expression such as C<"foo$array[1+f("[xyz")]bar"> would be.
-Moreover, inside C<(?{BLOCK})>, C<(?# comment )>, and
-a C<#>-comment in a C<//x>-regular expression, no processing is
+Moreover, inside C<(?{BLOCK})>, S<C<(?# comment )>>, and
+a C<#>-comment in a C</x>-regular expression, no processing is
performed whatsoever. This is the first step at which the presence
-of the C<//x> modifier is relevant.
+of the C</x> modifier is relevant.
Interpolation in patterns has several quirks: C<$|>, C<$(>, C<$)>, C<@+>
and C<@-> are not interpolated, and constructs C<$var[SOMETHING]> are
In the RE above, which is intentionally obfuscated for illustration, the
delimiter is C<m>, the modifier is C<mx>, and after delimiter-removal the
-RE is the same as for C<m/ ^ a \s* b /mx>. There's more than one
+RE is the same as for S<C<m/ ^ a \s* b /mx>>. There's more than one
reason you're encouraged to restrict your delimiters to non-alphanumeric,
non-whitespace choices.
Whatever happens in the RE engine might be better discussed in L<perlre>,
but for the sake of continuity, we shall do so here.
-This is another step where the presence of the C<//x> modifier is
+This is another step where the presence of the C</x> modifier is
relevant. The RE engine scans the string from left to right and
-converts it to a finite automaton.
+converts it into a finite automaton.
Backslashed characters are either replaced with corresponding
literal strings (as with C<\{>), or else they generate special nodes
RE engine (such as C<|>) generate corresponding nodes or groups of
nodes. C<(?#...)> comments are ignored. All the rest is either
converted to literal strings to match, or else is ignored (as is
-whitespace and C<#>-style comments if C<//x> is present).
+whitespace and C<#>-style comments if C</x> is present).
Parsing of the bracketed character class construct, C<[...]>, is
rather different than the rule used for the rest of the pattern.
It is possible to inspect both the string given to RE engine and the
resulting finite automaton. See the arguments C<debug>/C<debugcolor>
-in the C<use L<re>> pragma, as well as Perl's B<-Dr> command-line
+in the S<C<use L<re>>> pragma, as well as Perl's B<-Dr> command-line
switch documented in L<perlrun/"Command Switches">.
=item Optimization of regular expressions
=head2 I/O Operators
X<operator, i/o> X<operator, io> X<io> X<while> X<filehandle>
-X<< <> >> X<@ARGV>
+X<< <> >> X<< <<>> >> X<@ARGV>
There are several I/O operators you should know about.
there is one situation where an automatic assignment happens. If
and only if the input symbol is the only thing inside the conditional
of a C<while> statement (even if disguised as a C<for(;;)> loop),
-the value is automatically assigned to the global variable $_,
+the value is automatically assigned to the global variable C<$_>,
destroying whatever was there previously. (This may seem like an
odd thing to you, but you'll use the construct in almost every Perl
-script you write.) The $_ variable is not implicitly localized.
-You'll have to put a C<local $_;> before the loop if you want that
+script you write.) The C<$_> variable is not implicitly localized.
+You'll have to put a S<C<local $_;>> before the loop if you want that
to happen.
The following lines are equivalent:
is automatic or explicit) is then tested to see whether it is
defined. The defined test avoids problems where the line has a string
value that would be treated as false by Perl; for example a "" or
-a "0" with no trailing newline. If you really mean for such values
+a C<"0"> with no trailing newline. If you really mean for such values
to terminate the loop, they should be tested for explicitly:
while (($_ = <STDIN>) ne '0') { ... }
while (<STDIN>) { last unless $_; ... }
-In other boolean contexts, C<< <FILEHANDLE> >> without an
+In other boolean contexts, C<< <I<FILEHANDLE>> >> without an
explicit C<defined> test or comparison elicits a warning if the
-C<use warnings> pragma or the B<-w>
+S<C<use warnings>> pragma or the B<-w>
command-line switch (the C<$^W> variable) is in effect.
The filehandles STDIN, STDOUT, and STDERR are predefined. (The
filehandles C<stdin>, C<stdout>, and C<stderr> will also work except
in packages, where they would be interpreted as local identifiers
rather than global.) Additional filehandles may be created with
-the
open() function, amongst others. See L<perlopentut> and
+the
C<open()> function, amongst others. See L<perlopentut> and
L<perlfunc/open> for details on this.
X<stdin> X<stdout> X<sterr>
-If a <FILEHANDLE> is used in a context that is looking for
+If a C<< <I<FILEHANDLE>> >> is used in a context that is looking for
a list, a list comprising all input lines is returned, one line per
list element. It's easy to grow to a rather large data space this
way, so use with care.
-<FILEHANDLE> may also be spelled C<readline(*FILEHANDLE)>.
+C<< <I<FILEHANDLE>> >> may also be spelled C<readline(*I<FILEHANDLE>)>.
See L<perlfunc/readline>.
-The null filehandle <> is special: it can be used to emulate the
+The null filehandle C<< <> >> is special: it can be used to emulate the
behavior of B<sed> and B<awk>, and any other Unix filter program
that takes a list of filenames, doing the same to each line
-of input from all of them. Input from <> comes either from
+of input from all of them. Input from C<< <> >> comes either from
standard input, or from each file listed on the command line. Here's
-how it works: the first time <> is evaluated, the @ARGV array is
-checked, and if it is empty, C<$ARGV[0]> is set to "-", which when opened
-gives you standard input. The @ARGV array is then processed as a list
+how it works: the first time C<< <> >> is evaluated, the C<@ARGV> array is
+checked, and if it is empty, C<$ARGV[0]> is set to C<"-">, which when opened
+gives you standard input. The C<@ARGV> array is then processed as a list
of filenames. The loop
while (<>) {
}
except that it isn't so cumbersome to say, and will actually work.
-It really does shift the @ARGV array and put the current filename
-into the
$ARGV variable. It also uses filehandle I<ARGV>
-internally. <> is just a synonym for <ARGV>, which
+It really does shift the C<@ARGV> array and put the current filename
+into the
C<$ARGV> variable. It also uses filehandle I<ARGV>
+internally. C<< <> >> is just a synonym for C<< <ARGV> >>, which
is magical. (The pseudo code above doesn't work because it treats
-<ARGV> as non-magical.)
+C<< <ARGV> >> as non-magical.)
Since the null filehandle uses the two argument form of L<perlfunc/open>
it interprets special characters, so if you have a script like this:
print;
}
-and call it with C<perl dangerous.pl 'rm -rfv *|'>, it actually opens a
+and call it with S<C<perl dangerous.pl 'rm -rfv *|'>>, it actually opens a
pipe, executes the C<rm> command and reads C<rm>'s output from that pipe.
If you want all items in C<@ARGV> to be interpreted as file names, you
-can use the module C<ARGV::readonly> from CPAN.
+can use the module C<ARGV::readonly> from CPAN, or use the double bracket:
-You can modify @ARGV before the first <> as long as the array ends up
+ while (<<>>) {
+ print;
+ }
+
+Using double angle brackets inside of a while causes the open to use the
+three argument form (with the second argument being C<< < >>), so all
+arguments in C<ARGV> are treated as literal filenames (including C<"-">).
+(Note that for convenience, if you use C<< <<>> >> and if C<@ARGV> is
+empty, it will still read from the standard input.)
+
+You can modify C<@ARGV> before the first C<< <> >> as long as the array ends up
containing the list of filenames you really want. Line numbers (C<$.>)
continue as though the input were one big happy file. See the example
in L<perlfunc/eof> for how to reset line numbers on each file.
-If you want to set @ARGV to your own list of files, go right ahead.
-This sets @ARGV to all plain text files if no @ARGV was given:
+If you want to set C<@ARGV> to your own list of files, go right ahead.
+This sets C<@ARGV> to all plain text files if no C<@ARGV> was given:
@ARGV = grep { -f && -T } glob('*') unless @ARGV;
@ARGV = map { /\.(gz|Z)$/ ? "gzip -dc < $_ |" : $_ } @ARGV;
If you want to pass switches into your script, you can use one of the
-Getopts modules or put a loop on the front like this:
+C<Getopts> modules or put a loop on the front like this:
while ($_ = $ARGV[0], /^-/) {
shift;
# ... # code for each line
}
-The <> symbol will return C<undef> for end-of-file only once.
+The C<< <> >> symbol will return C<undef> for end-of-file only once.
If you call it again after this, it will assume you are processing another
-@ARGV list, and if you haven't set @ARGV, will read input from STDIN.
+C<@ARGV> list, and if you haven't set C<@ARGV>, will read input from STDIN.
If what the angle brackets contain is a simple scalar variable (for example,
-<$foo>), then that variable contains the name of the
+C<$foo>), then that variable contains the name of the
filehandle to input from, or its typeglob, or a reference to the
same. For example:
reference, it is interpreted as a filename pattern to be globbed, and
either a list of filenames or the next filename in the list is returned,
depending on context. This distinction is determined on syntactic
-grounds alone. That means C<< <$x> >> is always a readline() from
-an indirect handle, but C<< <$hash{key}> >> is always a glob().
-That's because $x is a simple scalar variable, but C<$hash{key}> is
+grounds alone. That means C<< <$x> >> is always a C<readline()> from
+an indirect handle, but C<< <$hash{key}> >> is always a C<glob()>.
+That's because C<$x> is a simple scalar variable, but C<$hash{key}> is
not--it's a hash element. Even C<< <$x > >> (note the extra space)
is treated as C<glob("$x ")>, not C<readline($x)>.
}
except that the globbing is actually done internally using the standard
-C<File::Glob> extension. Of course, the shortest way to do the above is:
+C<L<File::Glob>> extension. Of course, the shortest way to do the above is:
chmod 0644, <*.c>;
returning false.
If you're trying to do variable interpolation, it's definitely better
-to use the glob() function, because the older notation can cause people
+to use the C<glob()> function, because the older notation can cause people
to become confused with the indirect filehandle notation.
@files = glob("$dir/*.[ch]");
1 while foo();
=head2 Bitwise String Operators
-X<operator, bitwise, string>
+X<operator, bitwise, string> X<&.> X<|.> X<^.> X<~.>
Bitstrings of any size may be manipulated by the bitwise operators
(C<~ | & ^>).
$baz = 0+$foo & 0+$bar; # both ops explicitly numeric
$biz = "$foo" ^ "$bar"; # both ops explicitly stringy
+This somewhat unpredictable behavior can be avoided with the experimental
+"bitwise" feature, new in Perl 5.22. You can enable it via S<C<use feature
+'bitwise'>>. By default, it will warn unless the C<"experimental::bitwise">
+warnings category has been disabled. (S<C<use experimental 'bitwise'>> will
+enable the feature and disable the warning.) Under this feature, the four
+standard bitwise operators (C<~ | & ^>) are always numeric. Adding a dot
+after each operator (C<~. |. &. ^.>) forces it to treat its operands as
+strings:
+
+ use experimental "bitwise";
+ $foo = 150 | 105; # yields 255 (0x96 | 0x69 is 0xFF)
+ $foo = '150' | 105; # yields 255
+ $foo = 150 | '105'; # yields 255
+ $foo = '150' | '105'; # yields 255
+ $foo = 150 |. 105; # yields string '155'
+ $foo = '150' |. 105; # yields string '155'
+ $foo = 150 |.'105'; # yields string '155'
+ $foo = '150' |.'105'; # yields string '155'
+
+ $baz = $foo & $bar; # both operands numeric
+ $biz = $foo ^. $bar; # both operands stringy
+
+The assignment variants of these operators (C<&= |= ^= &.= |.= ^.=>)
+behave likewise under the feature.
+
+The behavior of these operators is problematic (and subject to change)
+if either or both of the strings are encoded in UTF-8 (see
+L<perlunicode/Byte and Character Semantics>.
+
See L<perlfunc/vec> for information on how to manipulate individual bits
in a bit vector.
which lasts until the end of that BLOCK. Note that this doesn't
mean everything is an integer, merely that Perl will use integer
operations for arithmetic, comparison, and bitwise operators. For
-example, even under C<use integer>, if you take the C<sqrt(2)>, you'll
+example, even under S<C<use integer>>, if you take the C<sqrt(2)>, you'll
still get C<1.4142135623731> or so.
-Used on numbers, the bitwise operators ("&", "|", "^", "~", "<<",
-and ">>") always produce integral results. (But see also
-L<Bitwise String Operators>.) However, C<use integer> still has meaning for
+Used on numbers, the bitwise operators (C<&> C<|> C<^> C<~> C<< << >>
+C<< >> >>) always produce integral results. (But see also
+L</Bitwise String Operators>.) However, S<C<use integer>> still has meaning for
them. By default, their results are interpreted as unsigned integers, but
-if C<use integer> is in effect, their results are interpreted
+if S<C<use integer>> is in effect, their results are interpreted
as signed integers. For example, C<~0> usually evaluates to a large
-integral value. However, C<use integer; ~0> is C<-1> on two's-complement
+integral value. However, S<C<use integer; ~0>> is C<-1> on two's-complement
machines.
=head2 Floating-point Arithmetic
X<floating-point> X<floating point> X<float> X<real>
-While C<use integer> provides integer-only arithmetic, there is no
+While S<C<use integer>> provides integer-only arithmetic, there is no
analogous mechanism to provide automatic rounding or truncation to a
certain number of decimal places. For rounding to a certain number
-of digits, sprintf() or printf() is usually the easiest route.
+of digits, C<sprintf()> or C<printf()> is usually the easiest route.
See L<perlfaq4>.
Floating-point numbers are only approximations to what a mathematician
}
The POSIX module (part of the standard perl distribution) implements
-ceil(), floor(), and other mathematical and trigonometric functions.
-The Math::Complex module (part of the standard perl distribution)
+C<ceil()>, C<floor()>, and other mathematical and trigonometric functions.
+The C<L<Math::Complex>> module (part of the standard perl distribution)
defines mathematical functions that work on both the reals and the
-imaginary numbers. Math::Complex not as efficient as POSIX, but
+imaginary numbers. C<Math::Complex> is not as efficient as POSIX, but
POSIX can't work with complex numbers.
Rounding in financial applications can have serious implications, and
=head2 Bigger Numbers
X<number, arbitrary precision>
-The standard C<Math::BigInt>, C<Math::BigRat>, and C<Math::BigFloat> modules,
+The standard C<L<Math::BigInt>>, C<L<Math::BigRat>>, and
+C<L<Math::BigFloat>> modules,
along with the C<bignum>, C<bigint>, and C<bigrat> pragmas, provide
variable-precision arithmetic and overloaded operators, although
-they're currently pretty slow. At the cost of some space and
+they're currently pretty slow. At the cost of some space and
considerable speed, they avoid the normal pitfalls associated with
limited-precision representations.
Or with rationals:
- use 5.010;
- use bigrat;
- $a = 3/22;
- $b = 4/6;
- say "a/b is ", $a/$b;
- say "a*b is ", $a*$b;
- a/b is 9/44
- a*b is 1/11
-
-Several modules let you calculate with (bound only by memory and CPU time)
-unlimited or fixed precision. There are also some non-standard modules that
+ use 5.010;
+ use bigrat;
+ $x = 3/22;
+ $y = 4/6;
+ say "x/y is ", $x/$y;
+ say "x*y is ", $x*$y;
+ x/y is 9/44
+ x*y is 1/11
+
+Several modules let you calculate with unlimited or fixed precision
+(bound only by memory and CPU time). There
+are also some non-standard modules that
provide faster implementations via external C libraries.
Here is a short, but incomplete summary:
https://perl5.git.perl.org / perl5.git / blobdiff