X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/3ff8ecf9096ea21482e9ec57e735cc8af89aa9ce..fb5f378b17e3b41db03064c19b9205db64a3354c:/pod/perlop.pod diff --git a/pod/perlop.pod b/pod/perlop.pod index 508853a..d6adbd1 100644 --- a/pod/perlop.pod +++ b/pod/perlop.pod @@ -5,23 +5,59 @@ perlop - Perl operators and precedence =head1 DESCRIPTION +In Perl, the operator determines what operation is performed, +independent of the type of the operands. For example S> +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 +means that Perl has two versions of some operators, one for numeric +and one for string comparison. For example S> compares +two numbers for equality, and S> compares two strings. + +There are a few exceptions though: C can be either string +repetition or list repetition, depending on the type of the left +operand, and C<&>, C<|>, C<^> and C<~> can be either string or numeric bit +operations. + =head2 Operator Precedence and Associativity X X X Operator precedence and associativity work in Perl more or less like they do in mathematics. -I 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>. - -I 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>. +I means some operators group more tightly than others. +For example, in C<2 + 4 * 5>, the multiplication has higher precedence, so C<4 +* 5> is grouped together as the right-hand operand of the addition, rather +than C<2 + 4> being grouped together as the left-hand operand of the +multiplication. It is as if the expression were written C<2 + (4 * 5)>, not +C<(2 + 4) * 5>. So the expression yields C<2 + 20 == 22>, rather than +C<6 * 5 == 30>. + +I defines what happens if a sequence of the same +operators is used one after another: whether they will be grouped at the left +or the right. For example, in C<9 - 3 - 2>, subtraction is left associative, +so C<9 - 3> is grouped together as the left-hand operand of the second +subtraction, rather than C<3 - 2> being grouped together as the right-hand +operand of the first subtraction. It is as if the expression were written +C<(9 - 3) - 2>, not C<9 - (3 - 2)>. So the expression yields C<6 - 2 == 4>, +rather than C<9 - 1 == 8>. + +For simple operators that evaluate all their operands and then combine the +values in some way, precedence and associativity (and parentheses) imply some +ordering requirements on those combining operations. For example, in C<2 + 4 * +5>, the grouping implied by precedence means that the multiplication of 4 and +5 must be performed before the addition of 2 and 20, simply because the result +of that multiplication is required as one of the operands of the addition. But +the order of operations is not fully determined by this: in C<2 * 2 + 4 * 5> +both multiplications must be performed before the addition, but the grouping +does not say anything about the order in which the two multiplications are +performed. In fact Perl has a general rule that the operands of an operator +are evaluated in left-to-right order. A few operators such as C<&&=> have +special evaluation rules that can result in an operand not being evaluated at +all; in general, the top-level operator in an expression has control of +operand evaluation. Perl operators have the following associativity and precedence, listed from highest precedence to lowest. Operators borrowed from @@ -48,14 +84,15 @@ values only, not array values. left || // nonassoc .. ... right ?: - right = += -= *= etc. + right = += -= *= etc. goto last next redo dump left , => nonassoc list operators (rightward) right not 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. @@ -69,7 +106,7 @@ aren't really functions in this sense, just list operators and unary operators behaving as functions because you put parentheses around the arguments. These are all documented in L. -If any list operator (print(), etc.) or any unary operator (chdir(), etc.) +If any list operator (C, etc.) or any unary operator (C, 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. @@ -82,7 +119,7 @@ For example, in @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 are evaluated before the C, 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. @@ -103,7 +140,7 @@ Also note that probably doesn't do what you expect at first glance. The parentheses enclose the argument list for C which is evaluated (printing -the result of C<$foo & 255>). Then one is added to the return value +the result of S>). Then one is added to the return value of C (usually 1). The result is something like this: 1 + 1, "\n"; # Obviously not what you meant. @@ -112,13 +149,13 @@ To do what you meant properly, you must write: print(($foo & 255) + 1, "\n"); -See L for more discussion of this. +See L for more discussion of this. -Also parsed as terms are the C and C constructs, as +Also parsed as terms are the S> and S> constructs, as well as subroutine and method calls, and the anonymous constructors C<[]> and C<{}>. -See also L toward the end of this section, +See also L toward the end of this section, as well as L. =head2 The Arrow Operator @@ -137,10 +174,14 @@ variable containing either the method name or a subroutine reference, and the left side must be either an object (a blessed reference) or a class name (that is, a package name). See L. +The dereferencing cases (as opposed to method-calling cases) are +somewhat extended by the C feature. For the +details of that feature, consult L. + =head2 Auto-increment and Auto-decrement X X X<++> X X 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. @@ -150,8 +191,8 @@ value. print ++$j; # prints 1 Note that just as in C, Perl doesn't define B 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: @@ -182,52 +223,69 @@ The auto-decrement operator is not magical. =head2 Exponentiation X<**> X X -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 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. Do not expect +any particular results from these special cases, the results +are platform-dependent. + =head2 Symbolic Unary Operators X X -Unary "!" performs logical negation, that is, "not". See also C for a lower -precedence version of this. +Unary C<"!"> performs logical negation, that is, "not". See also +L|/Logical 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. X<-> X -Unary "~" performs bitwise negation, that is, 1's complement. For -example, C<0666 & ~027> is 0640. (See also L and -L.) 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> is 0640. (See also L and +L.) 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 -When complementing strings, if all characters have ordinal values under -256, then their complements will, also. But if they do not, all -characters will be in either 32- or 64-bit complements, depending on your -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. +Starting in Perl 5.28, it is a fatal error to try to complement a string +containing a character with an ordinal value above 255. + +If the "bitwise" feature is enabled via S> or C, 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">. Until Perl 5.28, +this feature produced a warning in the C<"experimental::bitwise"> category. -Unary "+" has no effect whatsoever, even on strings. It is useful +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.) +arguments. (See examples above under L.) X<+> -Unary "\" creates a reference to whatever follows it. See L +Unary C<"\"> creates references. If its operand is a single sigilled +thing, it creates a reference to that object. If its operand is a +parenthesised list, then it creates references to the things mentioned +in the list. Otherwise it puts its operand in list context, and creates +a list of references to the scalars in the list provided by the operand. +See L and L. 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. @@ -236,14 +294,14 @@ X<\> X X =head2 Binding Operators X X 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 -$_. When used in scalar context, the return value generally indicates the -success of the operation. The exceptions are substitution (s///) -and transliteration (y///) with the C (non-destructive) option, +C<$_>. When used in scalar context, the return value generally indicates the +success of the operation. The exceptions are substitution (C) +and transliteration (C) with the C (non-destructive) option, which cause the Beturn value to be the result of the substitution. Behavior in list context depends on the particular operator. See L for details and L for @@ -251,58 +309,65 @@ examples using these operators. 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) or transliteration +(C) is a syntax error. =head2 Multiplicative Operators X -Binary "*" multiplies two numbers. +Binary C<"*"> multiplies two numbers. X<*> -Binary "/" divides two numbers. +Binary C<"/"> divides two numbers. X X -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<$n> is positive, then S> is +C<$m> minus the largest multiple of C<$n> less than or equal to +C<$m>. If C<$n> is negative, then S> is C<$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<$b> (that is C) is less than C<(UV_MAX + 1)>, only -the integer portion of C<$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) is less than S>, only +the integer portion of C<$m> and C<$n> will be used in the operation (Note: here C means the maximum of the unsigned integer type). -If the absolute value of the right operand (C) 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<$i> is a certain +If the absolute value of the right operand (C) is greater than +or equal to S>, C<"%"> computes the floating-point remainder +C<$r> in the equation S> where C<$i> is a certain integer that makes C<$r> have the same sign as the right operand -C<$b> (B as the left operand C<$a> like C function C) -and the absolute value less than that of C<$b>. -Note that when C is in scope, "%" gives you direct access +C<$n> (B as the left operand C<$m> like C function C) +and the absolute value less than that of C<$n>. +Note that when S> 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 X X -Binary "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, it repeats the list. -If the right operand is zero or negative, it returns an empty string +Binary C is the repetition operator. In scalar context, or if the +left operand is neither enclosed in parentheses nor a C list, +it performs a string repetition. In that case it supplies scalar +context to the left operand, and returns a string consisting of the +left operand string repeated the number of times specified by the right +operand. If the C is in list context, and the left operand is either +enclosed in parentheses or a C list, it performs a list repetition. +In that case it supplies list context to the left operand, and returns +a list consisting of the left operand list repeated the number of times +specified by the right operand. +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. X @@ -317,13 +382,13 @@ X =head2 Additive Operators X -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 X X X X X<.> @@ -332,31 +397,42 @@ X X X<<< << >>> X<<< >> >>> X X X X X X X -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.) +integers. (See also L.) -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.) +be integers. (See also L.) + +If S> (see L) is in force then +signed C integers are used (I), otherwise unsigned C +integers are used (I), 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. -Note that both C<<< << >>> and C<<< >> >>> in Perl are implemented directly using -C<<< << >>> and C<<< >> >>> in C. If C (see L) 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). +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). -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. +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. + +Shifting by more bits than the size of the integers means most of the +time zero (all bits fall off), except that under S> +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 + + 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 pragma neatly sidesteps the issue altogether: +the S> pragma neatly sidesteps the issue altogether: print 20 << 20; # 20971520 - print 20 << 40; # 5120 on 32-bit machines, + print 20 << 40; # 5120 on 32-bit machines, # 21990232555520 on 64-bit machines use bigint; print 20 << 100; # 25353012004564588029934064107520 @@ -367,7 +443,7 @@ X 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, etc.) or any unary operator (C, 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, @@ -378,7 +454,7 @@ because named unary operators are higher precedence than C<||>: 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 $foo) * 20 @@ -393,103 +469,111 @@ but, because * is higher precedence than named operators: Regarding precedence, the filetest operators, like C<-f>, C<-M>, etc. are treated like named unary operators, but they don't follow this functional parenthesis rule. That means, for example, that C<-f($file).".bak"> is -equivalent to C<-f "$file.bak">. +equivalent to S>. X<-X> X X -See also L<"Terms and List Operators (Leftward)">. +See also L. =head2 Relational Operators X X -Perl operators that return true or false generally return values +Perl operators that return true or false generally return values that can be safely used as numbers. For example, the 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> 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 X X X -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 - - $ 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, L, and L pragmas all -support "NaN".) - -Binary "eq" returns true if the left argument is stringwise equal to +argument. If your platform supports C's (not-a-numbers) as numeric +values, using them with C<< "<=>" >> returns undef. C is not +C<< "<" >>, C<< "==" >>, C<< ">" >>, C<< "<=" >> or C<< ">=" >> anything +(even C), so those 5 return false. S>> returns +true, as does S I>. If your platform doesn't +support C's then C is just a string with numeric value 0. +X<< <=> >> +X + + $ perl -le '$x = "NaN"; print "No NaN support here" if $x == $x' + $ perl -le '$x = "NaN"; print "NaN support here" if $x != $x' + +(Note that the L, L, and L pragmas all +support C<"NaN">.) + +Binary C<"eq"> returns true if the left argument is stringwise equal to the right argument. X -Binary "ne" returns true if the left argument is stringwise not equal +Binary C<"ne"> returns true if the left argument is stringwise not equal to the right argument. X -Binary "cmp" returns -1, 0, or 1 depending on whether the left +Binary C<"cmp"> returns -1, 0, or 1 depending on whether the left argument is stringwise less than, equal to, or greater than the right argument. X -Binary "~~" does a smartmatch between its arguments. Smart matching +Binary C<"~~"> does a smartmatch between its arguments. Smart matching is described in the next section. X<~~> -"lt", "le", "ge", "gt" and "cmp" use the collation (sort) order specified -by the current locale if a legacy C (but not -C) is in effect. See -L. Do not mix these with Unicode, only with legacy binary -encodings. The standard L and -L modules offer much more powerful solutions to -collation issues. +C<"lt">, C<"le">, C<"ge">, C<"gt"> and C<"cmp"> use the collation (sort) +order specified by the current C locale if a S> form that includes collation is in effect. See L. +Do not mix these with Unicode, +only use them with legacy 8-bit locale encodings. +The standard C> and +C> modules offer much more powerful +solutions to collation issues. + +For case-insensitive comparisons, look at the L case-folding +function, available in Perl v5.16 or later: + + if ( fc($x) eq fc($y) ) { ... } =head2 Smartmatch Operator @@ -497,7 +581,9 @@ First available in Perl 5.10.1 (the 5.10.0 version behaved differently), binary C<~~> does a "smartmatch" between its arguments. This is mostly used implicitly in the C construct described in L, although not all C clauses call the smartmatch operator. Unique among all of -Perl's operators, the smartmatch operator can recurse. +Perl's operators, the smartmatch operator can recurse. The smartmatch +operator is L and its behavior is +subject to change. It is also unique in that all other Perl operators impose a context (usually string or numeric context) on their operands, autoconverting @@ -521,81 +607,81 @@ whose types apply determines the smartmatch behavior. Because what actually happens is mostly determined by the type of the second operand, the table is sorted on the right operand instead of on the left. - Left Right Description and pseudocode + Left Right Description and pseudocode =============================================================== - Any undef check whether Any is undefined + Any undef check whether Any is undefined like: !defined Any Any Object invoke ~~ overloading on Object, or die Right operand is an ARRAY: - Left Right Description and pseudocode + Left Right Description and pseudocode =============================================================== ARRAY1 ARRAY2 recurse on paired elements of ARRAY1 and ARRAY2[2] like: (ARRAY1[0] ~~ ARRAY2[0]) && (ARRAY1[1] ~~ ARRAY2[1]) && ... - HASH ARRAY any ARRAY elements exist as HASH keys + HASH ARRAY any ARRAY elements exist as HASH keys like: grep { exists HASH->{$_} } ARRAY Regexp ARRAY any ARRAY elements pattern match Regexp like: grep { /Regexp/ } ARRAY - undef ARRAY undef in ARRAY + undef ARRAY undef in ARRAY like: grep { !defined } ARRAY - Any ARRAY smartmatch each ARRAY element[3] + Any ARRAY smartmatch each ARRAY element[3] like: grep { Any ~~ $_ } ARRAY Right operand is a HASH: - Left Right Description and pseudocode + Left Right Description and pseudocode =============================================================== - HASH1 HASH2 all same keys in both HASHes + HASH1 HASH2 all same keys in both HASHes like: keys HASH1 == grep { exists HASH2->{$_} } keys HASH1 - ARRAY HASH any ARRAY elements exist as HASH keys + ARRAY HASH any ARRAY elements exist as HASH keys like: grep { exists HASH->{$_} } ARRAY - Regexp HASH any HASH keys pattern match Regexp + Regexp HASH any HASH keys pattern match Regexp like: grep { /Regexp/ } keys HASH - undef HASH always false (undef can't be a key) + undef HASH always false (undef can't be a key) like: 0 == 1 - Any HASH HASH key existence + Any HASH HASH key existence like: exists HASH->{Any} Right operand is CODE: - - Left Right Description and pseudocode + + Left Right Description and pseudocode =============================================================== ARRAY CODE sub returns true on all ARRAY elements[1] like: !grep { !CODE->($_) } ARRAY HASH CODE sub returns true on all HASH keys[1] like: !grep { !CODE->($_) } keys HASH - Any CODE sub passed Any returns true + Any CODE sub passed Any returns true like: CODE->(Any) Right operand is a Regexp: - Left Right Description and pseudocode + Left Right Description and pseudocode =============================================================== - ARRAY Regexp any ARRAY elements match Regexp + ARRAY Regexp any ARRAY elements match Regexp like: grep { /Regexp/ } ARRAY - HASH Regexp any HASH keys match Regexp + HASH Regexp any HASH keys match Regexp like: grep { /Regexp/ } keys HASH - Any Regexp pattern match + Any Regexp pattern match like: Any =~ /Regexp/ Other: - Left Right Description and pseudocode + Left Right Description and pseudocode =============================================================== Object Any invoke ~~ overloading on Object, or fall back to... - Any Num numeric equality + Any Num numeric equality like: Any == Num Num nummy[4] numeric equality like: Num == nummy undef Any check whether undefined like: !defined(Any) - Any Any string equality + Any Any string equality like: Any eq Any @@ -604,13 +690,13 @@ Notes: =over =item 1. -Empty hashes or arrays match. +Empty hashes or arrays match. =item 2. That is, each element smartmatches the element of the same index in the other array.[3] =item 3. -If a circular reference is found, fall back to referential equality. +If a circular reference is found, fall back to referential equality. =item 4. Either an actual number, or a string that looks like one. @@ -665,7 +751,7 @@ recursively. my @bigger = ("red", "blue", [ "orange", "green" ] ); if (@little ~~ @bigger) { # true! say "little is contained in bigger"; - } + } Because the smartmatch operator recurses on nested arrays, this will still report that "red" is in the array. @@ -679,30 +765,30 @@ If two arrays smartmatch each other, then they are deep copies of each others' values, as this example reports: use v5.12.0; - my @a = (0, 1, 2, [3, [4, 5], 6], 7); - my @b = (0, 1, 2, [3, [4, 5], 6], 7); + my @a = (0, 1, 2, [3, [4, 5], 6], 7); + my @b = (0, 1, 2, [3, [4, 5], 6], 7); if (@a ~~ @b && @b ~~ @a) { say "a and b are deep copies of each other"; - } + } elsif (@a ~~ @b) { say "a smartmatches in b"; - } + } elsif (@b ~~ @a) { say "b smartmatches in a"; - } + } else { say "a and b don't smartmatch each other at all"; - } + } -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>, 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: @@ -718,19 +804,11 @@ 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 clause. See the section on "Switch Statements" in L. @@ -740,8 +818,8 @@ C clause. See the section on "Switch Statements" in L. 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". 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 @@ -749,7 +827,8 @@ illegal on objects without a C<~~> overload: "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. Using an object as the left operand is allowed, although not very useful. @@ -764,10 +843,10 @@ means that does I invoke the overload method with C> as an argument. Instead the above table is consulted as normal, and based on the type of C>, 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 + $object ~~ $string ref($object) eq $string For example, this reports that the handle smells IOish (but please don't really do this!): @@ -776,7 +855,7 @@ For example, this reports that the handle smells IOish my $fh = IO::Handle->new(); if ($fh ~~ /\bIO\b/) { say "handle smells IOish"; - } + } That's because it treats C<$fh> as a string like C<"IO::Handle=GLOB(0x8039e0)">, then pattern matches against that. @@ -784,33 +863,48 @@ C<"IO::Handle=GLOB(0x8039e0)">, then pattern matches against that. =head2 Bitwise And X X X<&> -Binary "&" returns its operands ANDed together bit by bit. -(See also L and L.) +Binary C<"&"> returns its operands ANDed together bit by bit. Although no +warning is currently raised, the result is not well defined when this operation +is performed on operands that aren't either numbers (see +L) nor bitstrings (see L). -Note that "&" has lower priority than relational operators, so for example +Note that C<"&"> has lower priority than relational operators, so for example the parentheses are essential in a test like print "Even\n" if ($x & 1) == 0; +If the "bitwise" feature is enabled via S> or +C, then this operator always treats its operands as numbers. +Before Perl 5.28 this feature produced a warning in the +C<"experimental::bitwise"> category. + =head2 Bitwise Or and Exclusive Or X X X<|> X X X<^> -Binary "|" returns its operands ORed together bit by bit. -(See also L and L.) +Binary C<"|"> returns its operands ORed together bit by bit. -Binary "^" returns its operands XORed together bit by bit. -(See also L and L.) +Binary C<"^"> returns its operands XORed together bit by bit. -Note that "|" and "^" have lower priority than relational operators, so -for example the brackets are essential in a test like +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) nor bitstrings (see L). + +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 "bitwise" feature is enabled via S> or +C, then this operator always treats its operands as numbers. +Before Perl 5.28. this feature produced a warning in the +C<"experimental::bitwise"> category. + =head2 C-style Logical And X<&&> X X -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. @@ -818,7 +912,7 @@ is evaluated. =head2 C-style Logical Or X<||> X -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. @@ -827,19 +921,20 @@ is evaluated. X X 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>> 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>> (except that +the ternary-operator form can be used as a lvalue, while S>> +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. +at least one of C<$x> and C<$y> is defined, use S>. 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} @@ -850,14 +945,14 @@ portable way to find out the home directory might be: 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 C 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" @@ -873,19 +968,19 @@ It would be even more readable to write that this way: unless(unlink("alpha", "beta", "gamma")) { gripe(); 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 X 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 loops and for doing slice operations on arrays. In +S> 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 loops, but older versions of Perl might burn a lot of memory when you write something @@ -898,19 +993,19 @@ like this: 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, B, and various editors. Each ".." operator +operator of B, B, 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 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), but it still returns -true once. If you don't want it to test the right operand until the -next evaluation, as in B, 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, 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 @@ -918,21 +1013,21 @@ operator is in the "true" state. The precedence is a little lower 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, +To be pedantic, the comparison is actually S>, but that is only an issue if you use a floating point expression; when implicitly using C<$.> as described in the previous paragraph, the -comparison is C which is only an issue when C<$.> +comparison is S> 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> or S> will not do what you want in scalar context because each of the operands are evaluated using their integer representation. @@ -976,7 +1071,7 @@ the two range operators: } } -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. @@ -1007,6 +1102,12 @@ If the final value specified is not in the sequence that the magical 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>|feature/The +'unicode_strings' feature >>. In previous versions, and outside the scope of +that feature, it exhibits L: 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), only the initial value will be returned. So the following will only @@ -1019,16 +1120,18 @@ To get the 25 traditional lowercase Greek letters, including both sigmas, you could use this instead: use charnames "greek"; - my @greek_small = map { chr } ( ord("\N{alpha}") + my @greek_small = map { chr } ( ord("\N{alpha}") .. - ord("\N{omega}") + ord("\N{omega}") ); However, because there are I other lowercase Greek characters than just those, to match lowercase Greek characters in a regular expression, -you would use the pattern C. +you could use the pattern C (or the +L C>). -Because each operand is evaluated in integer form, C<2.18 .. 3.14> will +Because each operand is evaluated in integer form, S> will return two elements in list context. @list = (2.18 .. 3.14); # same as @list = (2 .. 3); @@ -1036,10 +1139,10 @@ return two elements in list context. =head2 Conditional Operator X X X 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"; @@ -1047,58 +1150,62 @@ is returned. For example: 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 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 = $x + 2; although without duplicating any side effects that dereferencing the lvalue -might trigger, such as from tie(). Other assignment operators work similarly. +might trigger, such as from C. Other assignment operators work similarly. The following are recognized: - **= += *= &= <<= &&= - -= /= |= >>= ||= - .= %= ^= //= + **= += *= &= &.= <<= &&= + -= /= |= |.= >>= ||= + .= %= ^= ^.= //= x= Although these are grouped by family, they all have the precedence -of assignment. +of assignment. These combined assignment operators can only operate on +scalars, whereas the ordinary assignment operator can assign to arrays, +hashes, lists and even references. (See L<"Context"|perldata/Context> +and L, and L.) Unlike in C, the scalar assignment operator produces a valid lvalue. Modifying an assignment is equivalent to doing the assignment and @@ -1114,22 +1221,25 @@ Although as of 5.14, that can be also be accomplished this way: Likewise, - ($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. See L. + =head2 Comma Operator X X 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. @@ -1137,11 +1247,12 @@ In list context, it's just the list argument separator, and inserts 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 @@ -1172,7 +1283,7 @@ I of the left operand: 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 immediately on its left, ignoring the fact that C is the entire left operand. @@ -1182,32 +1293,35 @@ X X 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, "< :encoding(UTF-8)", "filename" + or die "Can't open: $!\n"; However, some people find that code harder to read than writing it with parentheses: - open(HANDLE, "< :utf8", "filename") or die "Can't open: $!\n"; + open(HANDLE, "< :encoding(UTF-8)", "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"; + open(HANDLE, "< :encoding(UTF-8)", "filename") + || die "Can't open: $!\n"; -See also discussion of list operators in L. +See also discussion of list operators in L. =head2 Logical Not X X -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 X -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. @@ -1217,7 +1331,7 @@ X X X X X -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: @@ -1228,12 +1342,12 @@ only if the left expression is false. Due to its precedence, you must 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! @@ -1241,7 +1355,7 @@ takes higher precedence. Then again, you could always use parentheses. -Binary C 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. @@ -1256,12 +1370,12 @@ Here is what C has that Perl doesn't: =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) @@ -1307,22 +1421,29 @@ is the same as 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 module (standard as of v5.8, +is a syntax error. The C> 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 is parsed as the string C, while C is the +C is parsed as the string C, while S> is the operator C 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): + + q XfooX # Works: means the string 'foo' + qXfooX # WRONG! + The following escape sequences are available in constructs that interpolate, -and in transliterations: +and in transliterations whose delimiters aren't single quotes (C<"'">). X<\t> X<\n> X<\r> X<\f> X<\b> X<\a> X<\e> X<\x> X<\0> X<\c> X<\N> X<\N{}> X<\o{}> @@ -1349,7 +1470,7 @@ X<\o{}> The result is the character specified by the hexadecimal number between the braces. See L 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. @@ -1365,7 +1486,7 @@ The result is the character specified by the hexadecimal number in the range 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 @@ -1385,7 +1506,7 @@ See L. =item [4] -C<\N{U+I}> means the Unicode character whose Unicode code +S}>> means the Unicode character whose Unicode code point is I. =item [5] @@ -1403,28 +1524,33 @@ table: \cZ chr(26) \cz chr(26) \c[ chr(27) + # See below for chr(28) \c] chr(29) \c^ chr(30) - \c? chr(127) + \c_ chr(31) + \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 because C is 127, and -C<\c@> is NULL because the ord of "@" is 64, so xor'ing 64 itself produces 0. +its uppercase. C<\c?> is DELETE on ASCII platforms because +S> is 127, and +C<\c@> is NULL because the ord of C<"@"> is 64, so xor'ing 64 itself produces 0. -Also, C<\c\I> yields C< chr(28) . "I"> for any I, but cannot come at the +Also, C<\c\I> yields S">> for any I, but cannot come at the end of a string, because the backslash would be parsed as escaping the end quote. On ASCII platforms, the resulting characters from the list above are the complete set of ASCII controls. This isn't the case on EBCDIC platforms; see -L for the complete list of what these -sequences mean on both ASCII and EBCDIC platforms. +L for a full discussion of the +differences between these for ASCII versus EBCDIC platforms. -Use of any other character following the "c" besides those listed above is -discouraged, and some are deprecated with the intention of removing -those in a later Perl version. What happens for any of these -other characters currently though, is that the value is derived by xor'ing -with the seventh bit, which is 64. +Use of any other character following the C<"c"> besides those listed above is +discouraged, and as of Perl v5.20, the only characters actually allowed +are the printable ASCII ones, minus the left brace C<"{">. What happens +for any of the allowed other characters is that the value is derived by +xor'ing with the seventh bit, which is 64, and a warning raised if +enabled. Using the non-allowed characters generates a fatal error. To get platform independent controls, you can use C<\N{...}>. @@ -1451,14 +1577,9 @@ see L.) Starting in Perl 5.14, you may 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. - -Having fewer than 3 digits may lead to a misleading warning message that says -that what follows is ignored. For example, C<"\128"> in the ASCII character set -is equivalent to the two characters C<"\n8">, but the warning C will be thrown. If C<"\n8"> is what you want, you can -avoid this warning by padding your octal number with C<0>'s: C<"\0128">. +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] @@ -1473,23 +1594,21 @@ it as a Unicode code point and the result is the corresponding Unicode 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. -There are a couple of exceptions to the above rule. S}>> is -always interpreted as a Unicode code point, so that C<\N{U+0050}> is "P" even -on EBCDIC platforms. And if L>|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}>> is +always interpreted as a Unicode code point, so that C<\N{U+0050}> is C<"P"> even +on EBCDIC platforms. =back B: Unlike C and other languages, Perl has no C<\v> escape sequence for -the vertical tab (VT - ASCII 11), but you may use C<\ck> or C<\x0b>. (C<\v> +the vertical tab (VT, which is 11 in both ASCII and EBCDIC), but you may +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.) The following escape sequences are available in constructs that interpolate, @@ -1515,14 +1634,16 @@ C<\E> for each. For example: 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 is in effect (but not C), -the case map used by C<\l>, C<\L>, -C<\u>, and C<\U> is taken from the current locale. See L. -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, C<\F> produces the same results as C<\L>. +If a S> form that includes C is in effect (see +L), 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<\F> produces the same results as C<\L> +for all locales but a UTF-8 one, where it instead uses the Unicode +definition. All systems use the virtual C<"\n"> to represent a line terminator, called a "newline". There is no such thing as an unvarying, physical @@ -1530,7 +1651,7 @@ newline character. It is only an illusion that the operating system, 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 @@ -1548,7 +1669,7 @@ But method calls such as C<< $obj->meth >> are not. Interpolating an array or slice interpolates the elements in order, separated by the value of C<$">, so is equivalent to interpolating -C. "Punctuation" arrays such as C<@*> are usually +S>. "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. @@ -1563,8 +1684,8 @@ is equivalent to For the pattern of regex operators (C, C and C), 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/ @@ -1591,17 +1712,17 @@ matching and related activities. =over 8 -=item qr/STRING/msixpodual +=item C/msixpodualn> X X X X X X X

This operator quotes (and possibly compiles) its I as a regular expression. I is interpolated the same way as I -in C. If "'" is used as the delimiter, no interpolation -is done. Returns a Perl value which may be used instead of the -corresponding C expression. The returned value is a -normalized version of the original pattern. It magically differs from +in C/>. 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/msixpodualn> expression. The returned value is a +normalized version of the original pattern. It magically differs from a string containing the same characters: C returns "Regexp"; -however, dereferencing it is not well defined (you currently get the +however, dereferencing it is not well defined (you currently get the normalized version of the original pattern, but this may change). @@ -1623,9 +1744,9 @@ The result may be used as a subpattern in a match: $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 +operator, using C may have speed advantages in some situations, +notably if the result of C is used standalone: sub match { my $patterns = shift; @@ -1640,53 +1761,58 @@ notably if the result of qr() is used standalone: } 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 avoids the need to recompile the pattern every time a match C 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 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 release 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 - u Use Unicode rules - d Use Unicode or native charset, as in 5.12 and earlier + a ASCII-restrict: Use ASCII for \d, \s, \w and [[:posix:]] + character classes; specifying two a's adds the further + restriction 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 modifier has is not propagated, being restricted to those patterns explicitly using it. -The last four modifiers listed above, added in Perl 5.14, -control the character set semantics, but C is the only one you are likely +The C, C, C, and C modifiers (added in Perl 5.14) +control the character set rules, but C is the only one you are likely to want to specify explicitly; the other three are selected automatically by various pragmas. -See L for additional information on valid syntax for STRING, and +See L for additional information on valid syntax for I, and for a detailed look at the semantics of regular expressions. In particular, all modifiers except the largely obsolete C are further explained in L. C is described in the next section. -=item m/PATTERN/msixpodualgc +=item C/msixpodualngc> X X X X X X X X X X X

X X X -=item /PATTERN/msixpodualgc +=item C/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. @@ -1698,17 +1824,17 @@ process modifiers are available: c Do not reset search position on a failed match when /g is in effect. -If "/" is the delimiter then the initial C is optional. With the C +If C<"/"> is the delimiter then the initial C is optional. With the C 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 below. -If "'" is the delimiter, no interpolation is performed on the PATTERN. -When using a character valid in an identifier, whitespace is required +described in C?> below. If C<"'"> (single quote) is the delimiter, +no variable interpolation is performed on the I. +When using a delimiter character valid in an identifier, whitespace is required after the C. -PATTERN may contain variables, which will be interpolated +I 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<$|> are not interpolated because they look like end-of-string tests.) @@ -1718,7 +1844,7 @@ test and never recompile by adding a C (which stands for "once") after the trailing delimiter. Once upon a time, Perl would recompile regular expressions unnecessarily, and this modifier was useful to tell it not to do so, in the -interests of speed. But now, the only reasons to use C are either: +interests of speed. But now, the only reasons to use C are one of: =over @@ -1753,20 +1879,20 @@ Use C if you want to avoid this. The bottom line is that using C is almost never a good idea. -=item The empty pattern // +=item The empty pattern C -If the PATTERN evaluates to the empty string, the last -I matched regular expression is used instead. In this +If the I evaluates to the empty string, the last +I matched regular expression is used instead. In this case, only the C and C flags on the empty pattern are honored; -the other flags are taken from the original pattern. If no match has +the other flags are taken from the original pattern. If no match has previously succeeded, this will (silently) act instead as a genuine empty pattern (which will always match). Note that it's possible to confuse Perl into thinking C (the empty regex) is really C (the defined-or operator). Perl is usually pretty good about this, but some pathological cases might trigger this, such as -C<$a///> (is that C<($a) / (//)> or C<$a // />?) and C -(C or C?). In all of these examples, Perl +C<$x///> (is that S> or S>?) and S> +(S> or S>?). 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 (so C becomes C). @@ -1777,7 +1903,7 @@ If the C option is not used, C in list context returns a list consisting of the subexpressions matched by the parentheses in the pattern, that is, (C<$1>, C<$2>, C<$3>...) (Note that here C<$1> etc. are also set). When there are no parentheses in the pattern, the return -value is the list C<(1)> for success. +value is the list C<(1)> for success. With or without parentheses, an empty list is returned upon failure. Examples: @@ -1799,35 +1925,35 @@ Examples: if (($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 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 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 -function; see L. A failed match normally resets the +function; see L. A failed match normally resets the search position to the beginning of the string, but you can avoid that -by adding the C modifier (for example, C). Modifying the target +by adding the C modifier (for example, C). Modifying the target string also resets the search position. -=item \G assertion +=item C<\G I> You can intermix C matches with C, where C<\G> is a zero-width assertion that matches the exact position where the -previous C, if any, left off. Without the C modifier, the +previous C, if any, left off. Without the C modifier, the C<\G> assertion still anchors at C as it was at the start of the operation (see L), but the match is of course only -attempted once. Using C<\G> without C on a target string that has +attempted once. Using C<\G> without C on a target string that has not previously had a C 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 @@ -1898,10 +2024,10 @@ The last example should print: Final: 'q', pos=8 Notice that the final match matched C instead of C

, which a match -without the C<\G> anchor would have done. Also note that the final match -did not update C. C is only updated on a C match. If the -final match did indeed match C

, it's a good bet that you're running a -very old (pre-5.6.0) version of Perl. +without the C<\G> anchor would have done. Also note that the final match +did not update C. C is only updated on a C match. If the +final match did indeed match C

, it's a good bet that you're running an +ancient (pre-5.6.0) version of Perl. A useful idiom for C-like scanners is C. You can combine several regexps like this to process a string part-by-part, @@ -1935,13 +2061,11 @@ Here is the output (split into several lines): lowercase line-noise lowercase lowercase line-noise lowercase lowercase line-noise MiXeD line-noise. That's all! -=item m?PATTERN?msixpodualgc +=item C?msixpodualngc> X X -=item ?PATTERN?msixpodualgc - -This is just like the C search, except that it matches -only once between calls to the reset() operator. This is a useful +This is just like the C/> search, except that it matches +only once between calls to the C 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 patterns local to the current package are reset. @@ -1960,20 +2084,21 @@ to "utf8" in a pod file: 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 operator. +C; with any other delimiter this is the normal C operator. -For historical reasons, the leading C in C is optional, -but the resulting C 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 in C?> 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. -=item s/PATTERN/REPLACEMENT/msixpodualgcer -X X X X +=item C/I/msixpodualngcer> +X X X X X X X X X X X

X X X X X Searches a string for a pattern, and if found, replaces that pattern with the replacement text and returns the number of substitutions -made. Otherwise it returns false (specifically, the empty string). +made. Otherwise it returns false (a value that is both an empty string (C<"">) +and numeric zero (C<0>) as described in L). If the C (non-destructive) option is used then it runs the substitution on a copy of the string and instead of returning the @@ -1988,16 +2113,16 @@ the string specified must be a scalar variable, an array element, a 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 or the I. Otherwise, if the +I 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 option. If the pattern evaluates to the empty string, the last successfully executed regular expression is used instead. See L for further explanation on these. -Options are as with m// with the addition of the following replacement +Options are as with C with the addition of the following replacement specific options: e Evaluate the right side as an expression. @@ -2011,12 +2136,12 @@ the C when using a character allowed in identifiers. If single quotes are used, no interpretation is done on the replacement string (the C 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 is delimited by bracketing quotes, the I has its own pair of quotes, which may or may not be bracketing quotes, for example, C or C<< s/bar/ >>. A C 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 modifier will cause the replacement portion +compile-time. A second C modifier will cause the replacement portion to be Ced before being run as a Perl expression. Examples: @@ -2050,7 +2175,7 @@ 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 @@ -2086,8 +2211,8 @@ Examples: s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields -Note the use of $ instead of \ in the last example. Unlike -B, we use the \> form in only the left hand side. +Note the use of C<$> instead of C<\> in the last example. Unlike +B, we use the \> form only in the left hand side. Anywhere else it's $>. Occasionally, you can't use just a C to get all the changes @@ -2106,10 +2231,10 @@ X =over 4 -=item q/STRING/ +=item C/> X X X<'> X<''> -=item 'STRING' +=item C<'I'> A single-quoted, literal string. A backslash represents a backslash unless followed by the delimiter or another backslash, in which case @@ -2119,10 +2244,10 @@ the delimiter or backslash is interpolated. $bar = q('This is it.'); $baz = '\n'; # a two-character string -=item qq/STRING/ +=item C/> X X X<"> X<""> -=item "STRING" +=item "I" A double-quoted, interpolated string. @@ -2131,19 +2256,19 @@ A double-quoted, interpolated string. if /\b(tcl|java|python)\b/i; # :-) $baz = "\n"; # a one-character string -=item qx/STRING/ +=item C/> X X<`> X<``> X -=item `STRING` +=item C<`I`> A string which is (possibly) interpolated and then executed as a -system command with C or its equivalent. Shell wildcards, +system command with F 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 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. @@ -2190,21 +2315,21 @@ How that string gets evaluated is entirely subject to the command 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 for a clean and safe example of a manual fork() and exec() +See L for a clean and safe example of a manual C and C to emulate backticks safely. On some platforms (notably DOS-like ones), the shell may not be capable of dealing with multiline commands, so putting newlines in the string may not get you what you want. You may be able to evaluate multiple commands in a single line by separating them with the command -separator character, if your shell supports that (for example, C<;> on +separator character, if your shell supports that (for example, C<;> on many Unix shells and C<&> on the Windows NT C shell). 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). To be safe, you may need to set -C<$|> ($AUTOFLUSH in English) or call the C method of -C on any open handles. +C<$|> (C<$AUTOFLUSH> in C>) or call the C method of +C> 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 @@ -2220,18 +2345,40 @@ when they're the right way to get something done. Perl was made to be a glue language, and one of the things it glues together is commands. Just understand what you're getting yourself into. +Like C, 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 pragma to control the I/O layers used when reading the +output of the command, for example: + + use open IN => ":encoding(UTF-8)"; + my $x = `cmd-producing-utf-8`; + See L for more discussion. -=item qw/STRING/ +=item C/> X X X -Evaluates to a list of the words extracted out of STRING, using embedded +Evaluates to a list of the words extracted out of I, using embedded whitespace as the word delimiters. It can be understood as being roughly equivalent to: split(" ", q/STRING/); -the differences being that it generates a real list at compile time, and +the differences being that it only splits on ASCII whitespace, +generates a real list at compile time, and in scalar context it returns the last element in the list. So this expression: @@ -2246,20 +2393,20 @@ Some frequently seen examples: use POSIX qw( setlocale localeconv ) @EXPORT = qw( foo bar baz ); -A common mistake is to try to separate the words with comma or to +A common mistake is to try to separate the words with commas or to put comments into a multi-line C-string. For this reason, the -C pragma and the B<-w> switch (that is, the C<$^W> variable) -produces warnings if the STRING contains the "," or the "#" character. +S> pragma and the B<-w> switch (that is, the C<$^W> variable) +produces warnings if the I contains the C<","> or the C<"#"> character. -=item tr/SEARCHLIST/REPLACEMENTLIST/cdsr +=item C/I/cdsr> X X X X X X -=item y/SEARCHLIST/REPLACEMENTLIST/cdsr +=item C/I/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 (non-destructive) option is present, a new copy of the string is made and its characters transliterated, and this copy is returned no @@ -2271,28 +2418,76 @@ Unless the C option is used, the string specified with C<=~> must be a scalar variable, an array element, a hash element, or an assignment to one of those; in other words, an lvalue. -A character range may be specified with a hyphen, so C -does the same replacement as C. -For B devotees, C is provided as a synonym for C. 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 or C. +If the characters delimiting I and I +are single quotes (C'I'>), the only +interpolation is removal of C<\> from pairs of C<\\>. + +Otherwise, a character range may be specified with a hyphen, so +C does the same replacement as +C. + +For B devotees, C is provided as a synonym for C. + +If the I is delimited by bracketing quotes, the +I must have its own pair of quotes, which may or may +not be bracketing quotes; for example, C or +C. + +Characters may be literals or (if the delimiters aren't single quotes) +any of the escape sequences accepted in double-quoted strings. But +there is never any 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. Note that C does B do regular expression character classes such as -C<\d> or C<\pL>. The C operator is not equivalent to the tr(1) -utility. If you want to map strings between lower/upper cases, see -L and L, and in general consider using the C -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 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 -character sets in full. +C<\d> or C<\pL>. The C operator is not equivalent to the C> +utility. C will uppercase the 26 letters "a" through "z", +but for case changing not confined to ASCII, use +L|perlfunc/lc>, L|perlfunc/uc>, +L|perlfunc/lcfirst>, L|perlfunc/ucfirst> +(all documented in L), or the +LIEIE>|/sEPATTERNEREPLACEMENTEmsixpodualngcer> +(with C<\U>, C<\u>, C<\L>, and C<\l> string-interpolation escapes in the +I 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, C, 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 both begin from and end at either ASCII alphabetics of +equal case (C, C), 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: @@ -2302,23 +2497,37 @@ Options: r Return the modified string and leave the original string untouched. -If the C modifier is specified, the SEARCHLIST character set -is complemented. If the C modifier is specified, any characters -specified by SEARCHLIST not found in REPLACEMENTLIST are deleted. +If the C modifier is specified, the I character set +is complemented. So for example these two are equivalent (the exact +maximum number will depend on your platform): + + tr/\x00-\xfd/ABCD/c + tr/\xfe-\x{7fffffff}/ABCD/ + +If the C modifier is specified, any characters +specified by I not found in I are deleted. (Note that this is slightly more flexible than the behavior of some -B programs, which delete anything they find in the SEARCHLIST, -period.) If the C 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 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. +B programs, which delete anything they find in the I, +period.) + +If the C modifier is specified, runs of the same character in the +result, where each those characters were substituted by the +transliteration, are squashed down to a single instance of the character. + +If the C modifier is used, the I is always interpreted +exactly as specified. Otherwise, if the I is shorter +than the I, the final character is replicated till it is long +enough. If the I is empty, the I is replicated. This latter is useful for counting characters in a class or for -squashing character sequences in a class. +squashing character sequences in a class. For example, each of these pairs +are equivalent: -Examples: + tr/abcd// tr/abcd/abcd/ + tr/abcd/AB/ tr/abcd/ABBB/ + tr/abcd//d s/[abcd]//g + tr/abcd/AB/d (tr/ab/AB/ + s/[cd]//g) - but run together + +Some examples: $ARGV[1] =~ tr/A-Z/a-z/; # canonicalize to lower case ASCII @@ -2352,16 +2561,16 @@ first one is used: will transliterate any A to X. Because the transliteration table is built at compile time, neither -the SEARCHLIST nor the REPLACEMENTLIST are subjected to double quote +the I nor the I are subjected to double quote interpolation. That means that if you want to use variables, you -must use an eval(): +must use an C: eval "tr/$oldlist/$newlist/"; die $@ if $@; eval "tr/$oldlist/$newlist/, 1" or die $@; -=item < >> X X X X<<< << >>> A line-oriented form of quoting is based on the shell "here-document" @@ -2369,13 +2578,15 @@ syntax. Following a C<< << >> you specify a string to terminate 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 (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, -unless the identifier is explicitly quoted. (If you put a space it -will be treated as a null identifier, which is valid, and matches the -first empty line.) The terminating string must appear by itself -(unquoted and with no surrounding whitespace) on the terminating line. +unless the identifier is explicitly quoted. The terminating string +must appear by itself (unquoted and with no surrounding whitespace) +on the terminating line. If the terminating string is quoted, the type of quotes used determine the treatment of the text. @@ -2399,7 +2610,7 @@ the same rules as normal double quoted strings. =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. @@ -2422,7 +2633,7 @@ can and do make good use of. =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. @@ -2432,6 +2643,55 @@ 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 whitespace to +remove from the beginning of each line. All lines B 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 @@ -2464,35 +2724,35 @@ use C. END If you want your here-docs to be indented with the rest of the code, -you'll need to remove leading whitespace from each line manually: +use the C<<< <<~FOO >>> construct described under L: - ($quote = <<'FINIS') =~ s/^\s+//gm; + $quote = <<~'FINIS'; The Road goes ever on and on, down from the door where it began. - FINIS + FINIS If you use a here-doc within a delimited construct, such as in C, -the quoted material must come on the lines following the final delimiter. -So instead of +the quoted material must still come on the line following the +C<<< <>> marker, which means it may be inside the delimited +construct: s/this/<. +outside of string evals. Additionally, quoting rules for the end-of-string identifier are -unrelated to Perl's quoting rules. C, C, and the like are not +unrelated to Perl's quoting rules. C, C, and the like are not supported in place of C<''> and C<"">, and the only interpolation is for backslashing the quoting character: @@ -2537,33 +2797,33 @@ one to four, but these passes are always performed in the same order. =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<< is +that has a terminating string as the content. Therefore C<< is terminated by C 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 construct, while a C<]> terminates -C and C constructs. +both C and C constructs. When searching for single-character delimiters, escaped delimiters 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 and C), nothing is skipped. @@ -2573,14 +2833,15 @@ safe location). For constructs with three-part delimiters (C, C, and C), the search is repeated once more. -If the first delimiter is not an opening punctuation, three delimiters must -be same such as C and C, in which case the second delimiter +If the first delimiter is not an opening punctuation, the three delimiters must +be the same, such as C and C, +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 and C. In these cases, whitespace -and comments are allowed between both parts, though the comment must follow -at least one whitespace character; otherwise a character expected as the +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. During this search no attention is paid to the semantics of the construct. @@ -2601,7 +2862,7 @@ the example above is not C, but rather C with no C 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 is interpreted as a part +this search. Thus the second C<\> in 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. @@ -2628,7 +2889,7 @@ to L. =item C<''>, C, C, C, the replacement of C The only interpolation is removal of C<\> from pairs of C<\\>. -Therefore C<-> in C and C is treated literally +Therefore C<"-"> in C and C is treated literally as a hyphen and no character range is available. C<\1> in the replacement of C does not work as C<$1>. @@ -2638,21 +2899,21 @@ No variable interpolation occurs. String modifying combinations for case and quoting such as C<\Q>, C<\U>, and C<\E> are not recognized. The other escape sequences such as C<\200> and C<\t> and backslashed characters such as C<\\> and C<\-> are converted to appropriate literals. -The character C<-> is treated specially and therefore C<\-> is treated -as a literal C<->. +The character C<"-"> is treated specially and therefore C<\-> is treated +as a literal C<"-">. =item C<"">, C<``>, C, C, C<< >>, C<<<"EOF"> C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, C<\F> (possibly paired with C<\E>) are converted to corresponding Perl constructs. Thus, C<"$foo\Qbaz$bar"> -is converted to C<$foo . (quotemeta("baz" . $bar))> internally. +is converted to S> internally. The other escape sequences such as C<\200> and C<\t> and backslashed characters such as C<\\> and C<\-> are replaced with appropriate expansions. Let it be stressed that I and C<\E>> is interpolated in the usual way. Something like C<"\Q\\E"> has -no C<\E> inside. instead, it has C<\Q>, C<\\>, and C, so the +no C<\E> inside. Instead, it has C<\Q>, C<\\>, and C, so the result is the same as for C<"\\\\E">. As a general rule, backslashes between C<\Q> and C<\E> may lead to counterintuitive results. So, C<"\Q\t\E"> is converted to C, which is the same @@ -2664,27 +2925,27 @@ as C<"\\\t"> (since TAB is not alphanumeric). Note also that: may be closer to the conjectural I of the writer of C<"\Q\t\E">. Interpolated scalars and arrays are converted internally to the C and -C<.> catenation operations. Thus, C<"$foo XXX '@arr'"> becomes: +C<"."> catenation operations. Thus, S> becomes: $foo . " XXX '" . (join $", @arr) . "'"; All operations above are performed simultaneously, left to right. -Because the result of C<"\Q STRING \E"> has all metacharacters +Because the result of S \E">> has all metacharacters quoted, there is no way to insert a literal C<$> 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}" >>> 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 @@ -2700,10 +2961,10 @@ happens as with C constructs. It is at this step that C<\1> is begrudgingly converted to C<$1> in the replacement text of C, in order to correct the incorrigible I hackers who haven't picked up the saner idiom yet. A warning -is emitted if the C pragma or the B<-w> command-line flag +is emitted if the S> pragma or the B<-w> command-line flag (that is, the C<$^W> variable) was set. -=item C in C, C, C, C, +=item C in C, C, C, C, Processing of C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, C<\F>, C<\E>, and interpolation happens (almost) as with C constructs. @@ -2724,10 +2985,10 @@ Code blocks such as C<(?{BLOCK})> are handled by temporarily passing control back to the perl parser, in a similar way that an interpolated array subscript expression such as C<"foo$array[1+f("[xyz")]bar"> would be. -Moreover, inside C<(?{BLOCK})>, C<(?# comment )>, and -a C<#>-comment in a C-regular expression, no processing is +Moreover, inside C<(?{BLOCK})>, S>, and +a C<#>-comment in a C-regular expression, no processing is performed whatsoever. This is the first step at which the presence -of the C modifier is relevant. +of the C modifier is relevant. Interpolation in patterns has several quirks: C<$|>, C<$(>, C<$)>, C<@+> and C<@-> are not interpolated, and constructs C<$var[SOMETHING]> are @@ -2746,14 +3007,14 @@ finish the regular expression, C<\/> will be stripped to C on the previous step, and C<\\/> will be left as is. Because C is equivalent to C<\/> inside a regular expression, this does not matter unless the delimiter happens to be character special to the -RE engine, such as in C, C, or C; or an +RE engine, such as in C, C, or C; or an alphanumeric char, as in: m m ^ a \s* b mmx; In the RE above, which is intentionally obfuscated for illustration, the delimiter is C, the modifier is C, and after delimiter-removal the -RE is the same as for C. There's more than one +RE is the same as for S>. There's more than one reason you're encouraged to restrict your delimiters to non-alphanumeric, non-whitespace choices. @@ -2775,9 +3036,9 @@ resulting I is passed to the RE engine for compilation. Whatever happens in the RE engine might be better discussed in L, but for the sake of continuity, we shall do so here. -This is another step where the presence of the C modifier is +This is another step where the presence of the C 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 @@ -2785,7 +3046,7 @@ in the finite automaton (as with C<\b>). Characters special to the 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 is present). +whitespace and C<#>-style comments if C is present). Parsing of the bracketed character class construct, C<[...]>, is rather different than the rule used for the rest of the pattern. @@ -2800,7 +3061,7 @@ logically balancing terminating C<}> is found. It is possible to inspect both the string given to RE engine and the resulting finite automaton. See the arguments C/C -in the C> pragma, as well as Perl's B<-Dr> command-line +in the S>> pragma, as well as Perl's B<-Dr> command-line switch documented in L. =item Optimization of regular expressions @@ -2818,7 +3079,7 @@ mean C. =head2 I/O Operators X X X X X -X<< <> >> X<@ARGV> +X<< <> >> X<< <<>> >> X<@ARGV> There are several I/O operators you should know about. @@ -2850,14 +3111,17 @@ Ordinarily you must assign the returned value to a variable, but 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 statement (even if disguised as a C 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 $_ variable is not implicitly localized. -You'll have to put a C before the loop if you want that -to happen. +script you write.) The C<$_> variable is not implicitly localized. +You'll have to put a S> before the loop if you want that +to happen. Furthermore, if the input symbol or an explicit assignment +of the input symbol to a scalar is used as a C/C condition, +then the condition actually tests for definedness of the expression's +value, not for its regular truth value. -The following lines are equivalent: +Thus the following lines are equivalent: while (defined($_ = )) { print; } while ($_ = ) { print; } @@ -2867,7 +3131,7 @@ The following lines are equivalent: print while ($_ = ); print while ; -This also behaves similarly, but assigns to a lexical variable +This also behaves similarly, but assigns to a lexical variable instead of to C<$_>: while (my $line = ) { print $line } @@ -2876,41 +3140,41 @@ In these loop constructs, the assigned value (whether assignment is automatic or explicit) is then tested to see whether it is defined. The defined test avoids problems where the line has a string value that would be treated as false by Perl; for example a "" or -a "0" with no trailing newline. If you really mean for such values +a C<"0"> with no trailing newline. If you really mean for such values to terminate the loop, they should be tested for explicitly: while (($_ = ) ne '0') { ... } while () { last unless $_; ... } -In other boolean contexts, C<< >> without an +In other boolean contexts, C<< > >> without an explicit C test or comparison elicits a warning if the -C pragma or the B<-w> +S> pragma or the B<-w> command-line switch (the C<$^W> variable) is in effect. The filehandles STDIN, STDOUT, and STDERR are predefined. (The filehandles C, C, and C 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 and +the C function, amongst others. See L and L for details on this. X X X -If a is used in a context that is looking for +If a C<< > >> 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. - may also be spelled C. +C<< > >> may also be spelled C)>. See L. -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 and B, 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 (<>) { @@ -2928,11 +3192,11 @@ is equivalent to the following Perl-like pseudo code: } 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 $ARGV variable. It also uses filehandle I -internally. <> is just a synonym for , which +It really does shift the C<@ARGV> array and put the current filename +into the C<$ARGV> variable. It also uses filehandle I +internally. C<< <> >> is just a synonym for C<< >>, which is magical. (The pseudo code above doesn't work because it treats - as non-magical.) +C<< >> as non-magical.) Since the null filehandle uses the two argument form of L it interprets special characters, so if you have a script like this: @@ -2941,18 +3205,28 @@ it interprets special characters, so if you have a script like this: print; } -and call it with C, it actually opens a +and call it with S>, it actually opens a pipe, executes the C command and reads C'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 from CPAN. +can use the module C from CPAN, or use the double bracket: + + while (<<>>) { + print; + } -You can modify @ARGV before the first <> as long as the array ends up +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 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<$.>) continue as though the input were one big happy file. See the example in L for how to reset line numbers on each file. -If you want to set @ARGV to your own list of files, go right ahead. -This sets @ARGV to all plain text files if no @ARGV was given: +If you want to set C<@ARGV> to your own list of files, go right ahead. +This sets C<@ARGV> to all plain text files if no C<@ARGV> was given: @ARGV = grep { -f && -T } glob('*') unless @ARGV; @@ -2962,7 +3236,7 @@ filters compressed arguments through B: @ARGV = map { /\.(gz|Z)$/ ? "gzip -dc < $_ |" : $_ } @ARGV; If you want to pass switches into your script, you can use one of the -Getopts modules or put a loop on the front like this: +C modules or put a loop on the front like this: while ($_ = $ARGV[0], /^-/) { shift; @@ -2976,12 +3250,12 @@ Getopts modules or put a loop on the front like this: # ... # code for each line } -The <> symbol will return C for end-of-file only once. +The C<< <> >> symbol will return C for end-of-file only once. If you call it again after this, it will assume you are processing another -@ARGV list, and if you haven't set @ARGV, will read input from STDIN. +C<@ARGV> list, and if you haven't set C<@ARGV>, will read input from STDIN. If what the angle brackets contain is a simple scalar variable (for example, -<$foo>), then that variable contains the name of the +C<$foo>), then that variable contains the name of the filehandle to input from, or its typeglob, or a reference to the same. For example: @@ -2993,9 +3267,9 @@ scalar variable containing a filehandle name, typeglob, or typeglob reference, it is interpreted as a filename pattern to be globbed, and either a list of filenames or the next filename in the list is returned, depending on context. This distinction is determined on syntactic -grounds alone. That means C<< <$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<< <$x> >> is always a C from +an indirect handle, but C<< <$hash{key}> >> is always a C. +That's because C<$x> is a simple scalar variable, but C<$hash{key}> is not--it's a hash element. Even C<< <$x > >> (note the extra space) is treated as C, not C. @@ -3020,7 +3294,7 @@ is roughly equivalent to: } except that the globbing is actually done internally using the standard -C extension. Of course, the shortest way to do the above is: +C> extension. Of course, the shortest way to do the above is: chmod 0644, <*.c>; @@ -3047,12 +3321,19 @@ because the latter will alternate between returning a filename and returning false. If you're trying to do variable interpolation, it's definitely better -to use the glob() function, because the older notation can cause people +to use the C function, because the older notation can cause people to become confused with the indirect filehandle notation. @files = glob("$dir/*.[ch]"); @files = glob($files[$i]); +If an angle-bracket-based globbing expression is used as the condition of +a C or C loop, then it will be implicitly assigned to C<$_>. +If either a globbing expression or an explicit assignment of a globbing +expression to a scalar is used as a C/C condition, then +the condition actually tests for definedness of the expression's value, +not for its regular truth value. + =head2 Constant Folding X X @@ -3064,7 +3345,7 @@ variable substitution. Backslash interpolation also happens at compile time. You can say 'Now is the time for all' - . "\n" + . "\n" . 'good men to come to.' and this all reduces to one string internally. Likewise, if @@ -3087,7 +3368,7 @@ context, so you can for example safely do 1 while foo(); =head2 Bitwise String Operators -X +X X<&.> X<|.> X<^.> X<~.> Bitstrings of any size may be manipulated by the bitwise operators (C<~ | & ^>). @@ -3118,6 +3399,35 @@ operation you intend by using C<""> or C<0+>, as in the examples below. $baz = 0+$foo & 0+$bar; # both ops explicitly numeric $biz = "$foo" ^ "$bar"; # both ops explicitly stringy +This somewhat unpredictable behavior can be avoided with the "bitwise" +feature, new in Perl 5.22. You can enable it via S> or C. Before Perl 5.28, it used to emit a warning +in the C<"experimental::bitwise"> category. 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 feature "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. + +It is a fatal error if an operand contains a character whose ordinal +value is above 0xFF, and hence not expressible except in UTF-8. The +operation is performed on a non-UTF-8 copy for other operands encoded in +UTF-8. See L. + See L for information on how to manipulate individual bits in a bit vector. @@ -3138,26 +3448,26 @@ the enclosing BLOCK. An inner BLOCK may countermand this by saying 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, if you take the C, you'll +example, even under S>, if you take the C, you'll still get C<1.4142135623731> or so. -Used on numbers, the bitwise operators ("&", "|", "^", "~", "<<", -and ">>") always produce integral results. (But see also -L.) However, C still has meaning for +Used on numbers, the bitwise operators (C<&> C<|> C<^> C<~> C<< << >> +C<< >> >>) always produce integral results. (But see also +L.) However, S> still has meaning for them. By default, their results are interpreted as unsigned integers, but -if C is in effect, their results are interpreted +if S> is in effect, their results are interpreted as signed integers. For example, C<~0> usually evaluates to a large -integral value. However, C is C<-1> on two's-complement +integral value. However, S> is C<-1> on two's-complement machines. =head2 Floating-point Arithmetic X X X X -While C provides integer-only arithmetic, there is no +While S> 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 or C is usually the easiest route. See L. Floating-point numbers are only approximations to what a mathematician @@ -3182,10 +3492,10 @@ this topic. } 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, C, and other mathematical and trigonometric functions. +The C> 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 is not as efficient as POSIX, but POSIX can't work with complex numbers. Rounding in financial applications can have serious implications, and @@ -3197,10 +3507,11 @@ need yourself. =head2 Bigger Numbers X -The standard C, C, and C modules, +The standard C>, C>, and +C> modules, along with the C, C, and C 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. @@ -3212,32 +3523,35 @@ 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: - Math::Fraction big, unlimited fractions like 9973 / 12967 Math::String treat string sequences like numbers Math::FixedPrecision calculate with a fixed precision Math::Currency for currency calculations Bit::Vector manipulate bit vectors fast (uses C) Math::BigIntFast Bit::Vector wrapper for big numbers Math::Pari provides access to the Pari C library - Math::BigInteger uses an external C library - Math::Cephes uses external Cephes C library (no big numbers) + Math::Cephes uses the external Cephes C library (no + big numbers) Math::Cephes::Fraction fractions via the Cephes library Math::GMP another one using an external C library + Math::GMPz an alternative interface to libgmp's big ints + Math::GMPq an interface to libgmp's fraction numbers + Math::GMPf an interface to libgmp's floating point numbers Choose wisely.