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PERLOP(1) Perl Programmers Reference Guide PERLOP(1) NAME perlop - Perl expressions: operators, precedence, string literals DESCRIPTION In Perl, the operator determines what operation is performed, independent of the type of the operands. For example "$x + $y" is always a numeric ad- dition, and if $x or $y do not contain numbers, an attempt is made to con- vert them to numbers first. This is in contrast to many other dynamic languages, where the operation is determined by the type of the first argument. It also means that Perl has two versions of some operators, one for numeric and one for string compari- son. For example "$x == $y" compares two numbers for equality, and "$x eq $y" compares two strings. There are a few exceptions though: The operator "x" can be either string repetition or list repetition, depending on the type of the left operand, and "&", "|", "^" and "~" can be either string or numeric bit operations (unless "use v5.28" or later, or "The 'bitwise' feature" in feature is in effect, in which case a different version of each operator exists for ma- nipulating strings). Operator Precedence and Associativity Operator precedence and associativity work in Perl more or less like they do in mathematics. Operator precedence means some operators group more tightly than others. For example, in "2 + 4 * 5", the multiplication has higher precedence, so "4 * 5" is grouped together as the right-hand operand of the addition, rather than "2 + 4" being grouped together as the left-hand operand of the multiplication. It is as if the expression were written "2 + (4 * 5)", not "(2 + 4) * 5". So the expression yields "2 + 20 == 22", rather than "6 * 5 == 30". Operator associativity defines what happens if a sequence of the same oper- ators is used one after another: usually that they will be grouped at the left or the right. For example, in "9 - 3 - 2", subtraction is left asso- ciative, so "9 - 3" is grouped together as the left-hand operand of the second subtraction, rather than "3 - 2" being grouped together as the right-hand operand of the first subtraction. It is as if the expression were written "(9 - 3) - 2", not "9 - (3 - 2)". So the expression yields "6 - 2 == 4", rather than "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 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 be- cause 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 "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 op- erators such as "&&=" 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. Some comparison operators, as their associativity, chain with some opera- tors of the same precedence (but never with operators of different prece- dence). This chaining means that each comparison is performed on the two arguments surrounding it, with each interior argument taking part in two comparisons, and the comparison results are implicitly ANDed. Thus "$x < $y <= $z" behaves exactly like "$x < $y && $y <= $z", assuming that "$y" is as simple a scalar as it looks. The ANDing short-circuits just like "&&" does, stopping the sequence of comparisons as soon as one yields false. In a chained comparison, each argument expression is evaluated at most once, even if it takes part in two comparisons, but the result of the eval- uation is fetched for each comparison. (It is not evaluated at all if the short-circuiting means that it's not required for any comparisons.) This matters if the computation of an interior argument is expensive or non-de- terministic. For example, if ($x < expensive_sub() <= $z) { ... is not entirely like if ($x < expensive_sub() && expensive_sub() <= $z) { ... but instead closer to my $tmp = expensive_sub(); if ($x < $tmp && $tmp <= $z) { ... in that the subroutine is only called once. However, it's not exactly like this latter code either, because the chained comparison doesn't actually involve any temporary variable (named or otherwise): there is no assign- ment. This doesn't make much difference where the expression is a call to an ordinary subroutine, but matters more with an lvalue subroutine, or if the argument expression yields some unusual kind of scalar by other means. For example, if the argument expression yields a tied scalar, then the ex- pression is evaluated to produce that scalar at most once, but the value of that scalar may be fetched up to twice, once for each comparison in which it is actually used. In this example, the expression is evaluated only once, and the tied scalar (the result of the expression) is fetched for each comparison that uses it. if ($x < $tied_scalar < $z) { ... In the next example, the expression is evaluated only once, and the tied scalar is fetched once as part of the operation within the expression. The result of that operation is fetched for each comparison, which normally doesn't matter unless that expression result is also magical due to opera- tor overloading. if ($x < $tied_scalar + 42 < $z) { ... Some operators are instead non-associative, meaning that it is a syntax er- ror to use a sequence of those operators of the same precedence. For exam- ple, "$x .. $y .. $z" is an error. Perl operators have the following associativity and precedence, listed from highest precedence to lowest. Operators borrowed from C keep the same precedence relationship with each other, even where C's precedence is slightly screwy. (This makes learning Perl easier for C folks.) With very few exceptions, these all operate on scalar values only, not array values. left terms and list operators (leftward) left -> nonassoc ++ -- right ** right ! ~ ~. \ and unary + and - left =~ !~ left * / % x left + - . left << >> nonassoc named unary operators nonassoc isa chained < > <= >= lt gt le ge chain/na == != eq ne <=> cmp ~~ left & &. left | |. ^ ^. left && left || ^^ // nonassoc .. ... right ?: right = += -= *= etc. goto last next redo dump left , => nonassoc list operators (rightward) right not left and left or xor The following sections cover these operators in detail. Each section cov- ers all the operators for a single precedence level. The sections are or- dered highest precedence first, same as in the table above. Many operators can be overloaded for objects. See overload. Terms and List Operators (Leftward) A TERM has the highest precedence in Perl. They include variables, quote and quote-like operators, any expression in parentheses, and any function whose arguments are parenthesized. Actually, there aren't really functions in this sense, just list operators and unary operators behaving as func- tions because you put parentheses around the arguments. These are all doc- umented in perlfunc. If any list operator (print(), etc.) or any unary operator (chdir(), etc.) is followed by a left parenthesis as the next token, the operator and argu- ments within parentheses are taken to be of highest precedence, just like a normal function call. In the absence of parentheses, the precedence of list operators such as "print", "sort", or "chmod" is either very high or very low depending on whether you are looking at the left side or the right side of the operator. 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", 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. Be careful with parentheses: # These evaluate exit before doing the print: print($foo, exit); # Obviously not what you want. print $foo, exit; # Nor is this. # These do the print before evaluating exit: (print $foo), exit; # This is what you want. print($foo), exit; # Or this. print ($foo), exit; # Or even this. Also note that print ($foo & 255) + 1, "\n"; probably doesn't do what you expect at first glance. The parentheses en- close the argument list for "print" which is evaluated (printing the result of "$foo & 255"). Then one is added to the return value of "print" (usu- ally 1). The result is something like this: 1 + 1, "\n"; # Obviously not what you meant. To do what you meant properly, you must write: print(($foo & 255) + 1, "\n"); See "Named Unary Operators" for more discussion of this. Also parsed as terms are the "do {}" and "eval {}" constructs, as well as subroutine and method calls, and the anonymous constructors "[]" and "{}". See also "Quote and Quote-like Operators" below, as well as "I/O Opera- tors". The Arrow Operator ""->"" is an infix dereference operator, just as it is in C and C++. If the right side is one of a "[...]", "{...}", or a "(...)" subscript, then the left side must be either a hard or symbolic reference to an array, a hash, or a subroutine respectively. (Or technically speaking, a location capable of holding a hard reference, if it's an array or hash reference be- ing used for assignment.) See perlreftut and perlref. Otherwise, the right side is a method name or a simple scalar variable con- taining either the method name or a subroutine reference, and (if it is a method name) the left side must be either an object (a blessed reference) or a class name (that is, a package name). See perlobj. The right side may also be the name of a subroutine, prefixed with the "&" sigil. This creates what looks like a lexical method invocation, where the method subroutine is resolved lexically instead of by name by a search within the packages of the object's class. This resolution happens en- tirely at compile-time, and performs the same as a regular subroutine call at runtime. The dereferencing cases (as opposed to method-calling cases) are somewhat extended by the "postderef" feature. For the details of that feature, con- sult "Postfix Dereference Syntax" in perlref. Auto-increment and Auto-decrement "++" and "--" work as in C. That is, if placed before a variable, they in- crement or decrement the variable by one before returning the value, and if placed after, increment or decrement after returning the value. $i = 0; $j = 0; print $i++; # prints 0 print ++$j; # prints 1 Note that just as in C, Perl doesn't define when the variable is incre- mented 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 state- ments like: $i = $i ++; print ++ $i + $i ++; Perl will not guarantee what the result of the above statements is. The auto-increment operator has a little extra builtin magic to it. If you increment a variable that is numeric, or that has ever been used in a nu- meric context, you get a normal increment. If, however, the variable has been used in only string contexts since it was set, and has a value that is not the empty string and matches the pattern "/^[a-zA-Z]*[0-9]*\z/", the increment is done as a string, preserving each character within its range, with carry: print ++($foo = "99"); # prints "100" print ++($foo = "a0"); # prints "a1" print ++($foo = "Az"); # prints "Ba" print ++($foo = "zz"); # prints "aaa" "undef" is always treated as numeric, and in particular is changed to 0 be- fore incrementing (so that a post-increment of an undef value will return 0 rather than "undef"). The auto-decrement operator is not magical. Exponentiation Binary "**" is the exponentiation operator. It binds even more tightly than unary minus, so "-2**4" is "-(2**4)", not "(-2)**4". (This is imple- mented using C's pow(3) function, which actually works on doubles inter- nally.) Note that certain exponentiation expressions are ill-defined: these include "0**0", "1**Inf", and "Inf**0". Do not expect any particular results from these special cases, the results are platform-dependent. Symbolic Unary Operators Unary "!" performs logical negation, that is, "not". See also "not" for a lower precedence version of this. Unary "-" 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 re- turned. 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 nega- tion is performed. If the string cannot be cleanly converted to a numeric, Perl will give the warning Argument "the string" isn't numeric in negation (-) at .... Unary "~" performs bitwise negation, that is, 1's complement. For example, "0666 & ~027" is 0640. (See also "Integer Arithmetic" and "Bitwise String Operators".) Note that the width of the result is platform-dependent: "~0" is 32 bits wide on a 32-bit platform, but 64 bits wide on a 64-bit plat- form, so if you are expecting a certain bit width, remember to use the "&" operator to mask off the excess bits. 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 "use feature 'bitwise'" or "use v5.28", then unary "~" always treats its argument as a number, and an al- ternate form of the operator, "~.", always treats its argument as a string. So "~0" and "~"0"" will both give 2**32-1 on 32-bit platforms, whereas "~.0" and "~."0"" will both yield "\xff". Until Perl 5.28, this feature produced a warning in the "experimental::bitwise" category. Unary "+" has no effect whatsoever, even on strings. It is useful syntac- tically 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 "Terms and List Operators (Leftward)".) Unary "\" 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. Oth- erwise it puts its operand in list context, and creates a list of refer- ences to the scalars in the list provided by the operand. See perlreftut and perlref. Do not confuse this behavior with the behavior of backslash within a string, although both forms do convey the notion of protecting the next thing from interpolation. Binding Operators Binary "=~" binds a scalar expression to a pattern match. Certain opera- tions search or modify the string $_ 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 "/r" (non-destructive) op- tion, which cause the return value to be the result of the substitution. Behavior in list context depends on the particular operator. See "Regexp Quote-Like Operators" for details and perlretut for examples using these operators. If the right argument is an expression rather than a search pattern, sub- stitution, or transliteration, it is interpreted as a search pattern at run 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 "\", which it will consider a syntax error. Binary "!~" is just like "=~" except the return value is negated in the logical sense. Binary "!~" with a non-destructive substitution ("s///r") or translitera- tion ("y///r") is a syntax error. Multiplicative Operators Binary "*" multiplies two numbers. Binary "/" divides two numbers. Binary "%" is the modulo operator, which computes the division remainder of its first argument with respect to its second argument. Given integer operands $m and $n: If $n is positive, then "$m % $n" is $m minus the largest multiple of $n less than or equal to $m. If $n is negative, then "$m % $n" is $m minus the smallest multiple of $n that is not less than $m (that is, the result will be less than or equal to zero). If the operands $m and $n are floating point values and the absolute value of $n (that is abs($n)) is less than "(UV_MAX + 1)", only the integer portion of $m and $n will be used in the operation (Note: here "UV_MAX" means the maximum of the unsigned integer type). If the absolute value of the right operand (abs($n)) is greater than or equal to "(UV_MAX + 1)", "%" computes the floating-point remainder $r in the equation "($r = $m - $i*$n)" where $i is a certain integer that makes $r have the same sign as the right operand $n (not as the left operand $m like C function fmod()) and the absolute value less than that of $n. Note that when "use integer" is in scope, "%" gives you direct access to the modulo operator as implemented by your C compiler. This operator is not as well defined for negative operands, but it will ex- ecute faster. Binary "x" is the repetition operator. In scalar context, or if the left operand is neither enclosed in parentheses nor a "qw//" list, it performs a string repetition. In that case it supplies scalar context to the left operand, and returns a string consisting of the left operand string re- peated the number of times specified by the right operand. If the "x" is in list context, and the left operand is either enclosed in parentheses or a "qw//" list, it performs a list repetition. In that case it supplies list context to the left operand, and returns a list consisting of the left operand list repeated the number of times specified by the right operand. If the right operand is zero or negative (raising a warning on negative), it returns an empty string or an empty list, depending on the context. print '-' x 80; # print row of dashes print "\t" x ($tab/8), ' ' x ($tab%8); # tab over @ones = (1) x 80; # a list of 80 1's @ones = (5) x @ones; # set all elements to 5 Additive Operators Binary "+" returns the sum of two numbers. Binary "-" returns the difference of two numbers. Binary "." concatenates two strings. Shift Operators Binary "<<" returns the value of its left argument shifted left by the num- ber of bits specified by the right argument. Arguments should be integers. (See also "Integer Arithmetic".) Binary ">>" returns the value of its left argument shifted right by the number of bits specified by the right argument. Arguments should be inte- gers. (See also "Integer Arithmetic".) If "use integer" (see "Integer Arithmetic") is in force then signed C inte- gers are used (arithmetic shift), otherwise unsigned C integers are used (logical shift), even for negative shiftees. In arithmetic right shift the sign bit is replicated on the left, in logical shift zero bits come in from the left. Either way, the implementation isn't going to generate results larger than the size of the integer type Perl was built with (32 bits or 64 bits). Shifting by a 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 a value greater than or equal to integer size (in bits) results in zero (all bits fall off), except that under "use integer" right shifting a negative value by such an amount results in -1. This is unlike in C, where shifting by too many bits is undefined. If you get tired of being subject to your platform's native integers, the "use bigint" pragma neatly sidesteps the issue altogether: print 20 << 20; # 20971520 print 20 << 32; # 0 with 32-bit integer, # 85899345920 with 64-bit integer use bigint; print 20 << 100; # 25353012004564588029934064107520 Named Unary Operators The various named unary operators are treated as functions with one argu- ment, with optional parentheses. If any list operator (print(), etc.) or any unary operator (chdir(), etc.) is followed by a left parenthesis as the next token, the operator and argu- ments within parentheses are taken to be of highest precedence, just like a normal function call. For example, because named unary operators are higher precedence than "||": chdir $foo || die; # (chdir $foo) || die chdir($foo) || die; # (chdir $foo) || die chdir ($foo) || die; # (chdir $foo) || die chdir +($foo) || die; # (chdir $foo) || die but, because "*" is higher precedence than named operators: chdir $foo * 20; # chdir ($foo * 20) chdir($foo) * 20; # (chdir $foo) * 20 chdir ($foo) * 20; # (chdir $foo) * 20 chdir +($foo) * 20; # chdir ($foo * 20) rand 10 * 20; # rand (10 * 20) rand(10) * 20; # (rand 10) * 20 rand (10) * 20; # (rand 10) * 20 rand +(10) * 20; # rand (10 * 20) Regarding precedence, the filetest operators, like "-f", "-M", etc. are treated like named unary operators, but they don't follow this functional parenthesis rule. That means, for example, that "-f($file).".bak"" is equivalent to "-f "$file.bak"". See also "Terms and List Operators (Leftward)". Class Instance Operator Binary "isa" evaluates to true when the left argument is an object instance of the class (or a subclass derived from that class) given by the right ar- gument. If the left argument is not defined, not a blessed object in- stance, and does not derive from the class given by the right argument, the operator evaluates as false. The right argument may give the class either as a bareword or a scalar expression that yields a string class name: if ( $obj isa Some::Class ) { ... } if ( $obj isa "Different::Class" ) { ... } if ( $obj isa $name_of_class ) { ... } This feature is available from Perl 5.31.6 onwards when enabled by "use feature 'isa'". This feature is enabled automatically by a "use v5.36" (or higher) declaration in the current scope. Relational Operators Perl operators that return true or false generally return values that can be safely used as numbers. For example, the relational operators in this section and the equality operators in the next one return 1 for true and a special version of the defined empty string, "", which counts as a zero but is exempt from warnings about improper numeric conversions, just as "0 but true" is. Binary "<" returns true if the left argument is numerically less than the right argument. Binary ">" returns true if the left argument is numerically greater than the right argument. Binary "<=" returns true if the left argument is numerically less than or equal to the right argument. Binary ">=" returns true if the left argument is numerically greater than or equal to the right argument. Binary "lt" returns true if the left argument is stringwise less than the right argument. Binary "gt" returns true if the left argument is stringwise greater than the right argument. Binary "le" returns true if the left argument is stringwise less than or equal to the right argument. Binary "ge" returns true if the left argument is stringwise greater than or equal to the right argument. A sequence of relational operators, such as "$x < $y <= $z", performs chained comparisons, in the manner described above in the section "Operator Precedence and Associativity". Beware that they do not chain with equality operators, which have lower precedence. "lt", "le", "ge", "gt", and "cmp" (this last is described in the next sec- tion) use the collation (sort) order specified by the current "LC_COLLATE" locale if a "use locale" form that includes collation is in effect. See perllocale. Depending on the capabilities of the platform, these can give reasonable results with Unicode, but the standard "Unicode::Collate" and "Unicode::Collate::Locale" modules offer much more powerful solutions to collation issues. For case-insensitive comparisons, look at the "fc" in perlfunc case-folding function, available in Perl v5.16 or later: if ( fc($x) eq fc($y) ) { ... } Equality Operators Binary "==" returns true if the left argument is numerically equal to the right argument. Binary "!=" returns true if the left argument is numerically not equal to the right argument. Binary "eq" returns true if the left argument is stringwise equal to the right argument. Binary "ne" returns true if the left argument is stringwise not equal to the right argument. A sequence of the above equality operators, such as "$x == $y == $z", per- forms chained comparisons, in the manner described above in the section "Operator Precedence and Associativity". Beware that they do not chain with relational operators, which have higher precedence. Binary "<=>" 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 "NaN"'s (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 "NaN"'s then "NaN" is just a string with numeric value 0. $ 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 bigint, bigrat, and bignum pragmas all support "NaN".) Binary "cmp" returns -1, 0, or 1 depending on whether the left argument is stringwise less than, equal to, or greater than the right argument. Here we can see the difference between "<=>" and "cmp", print 10 <=> 2 #prints 1 print 10 cmp 2 #prints -1 (likewise between the relational operators that were described in the pre- vious section: "gt" and ">", "lt" and "<", etc.) Binary "~~" does a smartmatch between its arguments. Smart matching is complicated enough to warrant two subsections, starting just below. The two-sided ordering operators "<=>" and "cmp", and the smartmatch opera- tor "~~", are non-associative with respect to each other and with respect to the equality operators of the same precedence. Smartmatch Operator The "smartmatch" feature is discouraged for new code and retained for back- ward compatibility. The smartmatch operator was introduced in 5.10.0 had significant changes in 5.10.1. It is enabled by default and in all feature bundles up to 5.40. To use smartmatch with a later feature bundle you will need enable it ex- plicitly: use v5.42; use feature "smartmatch"; Binary "~~" does a "smartmatch" between its arguments. This is mostly used implicitly in the "when" construct described in perlsyn, although not all "when" clauses call the smartmatch operator. Unique among all of Perl's operators, the smartmatch operator can recurse. It is also unique in that all other Perl operators impose a context (usu- ally string or numeric context) on their operands, autoconverting those operands to those imposed contexts. In contrast, smartmatch infers con- texts from the actual types of its operands and uses that type information to select a suitable comparison mechanism. The "~~" operator compares its operands "polymorphically", determining how to compare them according to their actual types (numeric, string, array, hash, etc.). Like the equality operators with which it shares the same precedence, "~~" returns 1 for true and "" for false. It is often best read aloud as "in", "inside of", or "is contained in", because the left operand is often looked for inside the right operand. That makes the order of the operands to the smartmatch operand often opposite that of the regu- lar match operator. In other words, the "smaller" thing is usually placed in the left operand and the larger one in the right. The behavior of a smartmatch depends on what type of things its arguments are, as determined by the following table. The first row of the table whose types apply determines the smartmatch behavior. Because what actu- ally 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 =============================================================== 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 =============================================================== 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 like: grep { exists HASH->{$_} } ARRAY Regexp ARRAY any ARRAY elements pattern match Regexp like: grep { /Regexp/ } ARRAY undef ARRAY undef in ARRAY like: grep { !defined } ARRAY Any ARRAY smartmatch each ARRAY element[3] like: grep { Any ~~ $_ } ARRAY Right operand is a HASH: Left Right Description and pseudocode =============================================================== HASH1 HASH2 all same keys in both HASHes like: keys HASH1 == grep { exists HASH2->{$_} } keys HASH1 ARRAY HASH any ARRAY elements exist as HASH keys like: grep { exists HASH->{$_} } ARRAY Regexp HASH any HASH keys pattern match Regexp like: grep { /Regexp/ } keys HASH undef HASH always false (undef cannot be a key) like: 0 == 1 Any HASH HASH key existence like: exists HASH->{Any} Right operand is CODE: Left Right Description and pseudocode =============================================================== ARRAY CODE sub returns true on all ARRAY elements[1] like: !grep { !CODE->($_) } ARRAY HASH CODE sub returns true on all HASH keys[1] like: !grep { !CODE->($_) } keys HASH Any CODE sub passed Any returns true like: CODE->(Any) Right operand is a Regexp: Left Right Description and pseudocode =============================================================== ARRAY Regexp any ARRAY elements match Regexp like: grep { /Regexp/ } ARRAY HASH Regexp any HASH keys match Regexp like: grep { /Regexp/ } keys HASH Any Regexp pattern match like: Any =~ /Regexp/ Other: Left Right Description and pseudocode =============================================================== Object Any invoke ~~ overloading on Object, or fall back to... 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 like: Any eq Any Notes: 1. Empty hashes or arrays match. 2. That is, each element smartmatches the element of the same index in the other array.[3] 3. If a circular reference is found, fall back to referential equality. 4. Either an actual number, or a string that looks like one. The smartmatch implicitly dereferences any non-blessed hash or array refer- ence, so the "HASH" and "ARRAY" entries apply in those cases. For blessed references, the "Object" entries apply. Smartmatches involving hashes only consider hash keys, never hash values. The "like" code entry is not always an exact rendition. For example, the smartmatch operator short-circuits whenever possible, but "grep" does not. Also, "grep" in scalar context returns the number of matches, but "~~" re- turns only true or false. Unlike most operators, the smartmatch operator knows to treat "undef" spe- cially: use v5.10.1; @array = (1, 2, 3, undef, 4, 5); say "some elements undefined" if undef ~~ @array; Each operand is considered in a modified scalar context, the modification being that array and hash variables are passed by reference to the opera- tor, which implicitly dereferences them. Both elements of each pair are the same: use v5.10.1; my %hash = (red => 1, blue => 2, green => 3, orange => 4, yellow => 5, purple => 6, black => 7, grey => 8, white => 9); my @array = qw(red blue green); say "some array elements in hash keys" if @array ~~ %hash; say "some array elements in hash keys" if \@array ~~ \%hash; say "red in array" if "red" ~~ @array; say "red in array" if "red" ~~ \@array; say "some keys end in e" if /e$/ ~~ %hash; say "some keys end in e" if /e$/ ~~ \%hash; Two arrays smartmatch if each element in the first array smartmatches (that is, is "in") the corresponding element in the second array, recursively. use v5.10.1; my @little = qw(red blue green); 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. use v5.10.1; my @array = qw(red blue green); my $nested_array = [[[[[[[ @array ]]]]]]]; say "red in array" if "red" ~~ $nested_array; If two arrays smartmatch each other, then they are deep copies of each oth- ers' values, as this example reports: use v5.12.0; my @a = (0, 1, 2, [3, [4, 5], 6], 7); my @b = (0, 1, 2, [3, [4, 5], 6], 7); if (@a ~~ @b && @b ~~ @a) { say "a and b are deep copies of each other"; } elsif (@a ~~ @b) { say "a smartmatches in b"; } elsif (@b ~~ @a) { say "b smartmatches in a"; } else { say "a and b don't smartmatch each other at all"; } If you were to set "$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's because the corresponding position in @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 records have the same field names, without caring what values those fields might have. For example: use v5.10.1; sub make_dogtag { state $REQUIRED_FIELDS = { name=>1, rank=>1, serial_num=>1 }; my ($class, $init_fields) = @_; die "Must supply (only) name, rank, and serial number" unless $init_fields ~~ $REQUIRED_FIELDS; ... } However, this only does what you mean if $init_fields is indeed a hash ref- erence. The condition "$init_fields ~~ $REQUIRED_FIELDS" also allows the strings "name", "rank", "serial_num" as well as any array reference that contains "name" or "rank" or "serial_num" anywhere to pass through. The smartmatch operator is most often used as the implicit operator of a "when" clause. See the section on "Switch Statements" in perlsyn. Smartmatching of Objects To avoid relying on an object's underlying representation, if the smart- match's right operand is an object that doesn't overload "~~", it raises the exception ""Smartmatching a non-overloaded object breaks encapsula- tion"". 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 "~~" overload: %hash ~~ $object 42 ~~ $object "fred" ~~ $object However, you can change the way an object is smartmatched by overloading the "~~" operator. This is allowed to extend the usual smartmatch seman- tics. For objects that do have an "~~" overload, see overload. Using an object as the left operand is allowed, although not very useful. Smartmatching rules take precedence over overloading, so even if the object in the left operand has smartmatch overloading, this will be ignored. A left operand that is a non-overloaded object falls back on a string or nu- meric comparison of whatever the "ref" operator returns. That means that $object ~~ X does not invoke the overload method with "X" as an argument. Instead the above table is consulted as normal, and based on the type of "X", overload- ing may or may not be invoked. For simple strings or numbers, "in" becomes equivalent to this: $object ~~ $number ref($object) == $number $object ~~ $string ref($object) eq $string For example, this reports that the handle smells IOish (but please don't really do this!): use IO::Handle; my $fh = IO::Handle->new(); if ($fh ~~ /\bIO\b/) { say "handle smells IOish"; } That's because it treats $fh as a string like "IO::Handle=GLOB(0x8039e0)", then pattern matches against that. Bitwise And Binary "&" returns its operands ANDed together bit by bit. Although no warning is currently raised, the result is not well defined when this oper- ation is performed on operands that aren't either numbers (see "Integer Arithmetic") nor bitstrings (see "Bitwise String Operators"). Note that "&" has lower priority than relational operators, so for example the parentheses are essential in a test like print "Even\n" if ($x & 1) == 0; If the "bitwise" feature is enabled via "use feature 'bitwise'" or "use v5.28", then this operator always treats its operands as numbers. Before Perl 5.28 this feature produced a warning in the "experimental::bitwise" category. Bitwise Or and Exclusive Or Binary "|" returns its operands ORed together bit by bit. If both corre- sponding bits are 0, the resulting bit is 0; if either is 1, the result is 1. Binary "^" returns its operands XORed together bit by bit. If both corre- sponding bits are 0 or both are 1, the resulting bit is 0; if just one is 1, the result is 1. 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 "Integer Arithmetic") nor bitstrings (see "Bitwise String Operators"). Note that "|" and "^" 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 "use feature 'bitwise'" or "use v5.28", then this operator always treats its operands as numbers. Before Perl 5.28. this feature produced a warning in the "experimental::bitwise" category. C-style Logical And Binary "&&" 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. "&&" returns the last value evaluated (unlike C's "&&", which returns 0 or 1). As an alternative to "&&" when used for control flow, Perl provides the "and" operator (see below). The short-circuit behavior is identical. The precedence of "and" is much lower, however, so that you can safely use it after a list operator without the need for parentheses. C-style Logical Or, Xor, and Defined Or Binary "||" 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 does get evaluated. As an alternative to "||" when used for control flow, Perl provides the "or" operator (see below). The short-circuit behavior is identical. The precedence of "or" is much lower, however, so that you can safely use it after a list operator without the need for parentheses: unlink "alpha", "beta", "gamma" or gripe(), next LINE; With the C-style operator that would have been written like this: unlink("alpha", "beta", "gamma") || (gripe(), next LINE); 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. Binary "^^" performs a logical XOR operation. Both operands are evaluated and the result is true only if exactly one of the operands is true. Scalar or list context propagates down to the right operand. Although it has no direct equivalent in C, Perl's "//" operator is related to its C-style "or". In fact, it's exactly the same as "||", except that it tests the left hand side's definedness instead of its truth. Thus, "EXPR1 // EXPR2" returns the value of "EXPR1" if it's defined, otherwise, the value of "EXPR2" is returned. ("EXPR1" is evaluated in scalar context, "EXPR2" in the context of "//" itself). Usually, this is the same result as "defined(EXPR1) ? EXPR1 : EXPR2" (except that the ternary-operator form can be used as a lvalue, while "EXPR1 // EXPR2" cannot). This is very use- ful for providing default values for variables. If you actually want to test if at least one of $x and $y is defined, use "defined($x // $y)". The "||" and "//" operators return the last value evaluated (unlike C's "||" which returns 0 or 1). Thus, a reasonably portable way to find out the home directory might be: $home = $ENV{HOME} // $ENV{LOGDIR} // (getpwuid($<))[7] // die "You're homeless!\n"; In particular, this means that you shouldn't use this for selecting between two aggregates for assignment: @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. Range Operators Binary ".." 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 "foreach (1..10)" loops and for doing slice operations on arrays. No temporary array is created when the range operator is used as the expression in "foreach" loops. The range operator also works on strings, using the magical auto-increment, see below. In scalar context, ".." returns a boolean value. The operator is bistable, like a flip-flop, and emulates the line-range (comma) operator of sed, awk, and various editors. Each ".." 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. Once the left operand is true, the range opera- tor stays true until the right operand is true, AFTER which the range oper- ator 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 awk), but it still re- turns true once. If you don't want it to test the right operand until the next evaluation, as in sed, just use three dots ("...") instead of two. In all other regards, "..." behaves just like ".." does. The right operand is not evaluated while the operator is in the "false" state, and the left operand is not evaluated while the 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 (begin- ning with 1) for true. The sequence number is reset for each range encoun- tered. The final sequence number in a range has the string "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 begin- ning point by waiting for the sequence number to be greater than 1. If either operand of scalar ".." is a constant expression, that operand is considered true if it is equal ("==") to the current input line number (the $. variable). To be pedantic, the comparison is actually "int(EXPR) == int(EXPR)", but that is only an issue if you use a floating point expression; when implic- itly using $. as described in the previous paragraph, the comparison is "int(EXPR) == int($.)" which is only an issue when $. is set to a floating point value and you are not reading from a file. Furthermore, "span" .. "spat" or "2.18 .. 3.14" will not do what you want in scalar con- text because each of the operands are evaluated using their integer repre- sentation. Examples: As a scalar operator: if (101 .. 200) { print; } # print 2nd hundred lines, short for # if ($. == 101 .. $. == 200) { print; } next LINE if 1 .. /^$/; # skip header lines, short for # next LINE if $. == 1 .. /^$/; # (typically in a loop labeled LINE) s/^/> / if /^$/ .. eof(); # quote body # parse mail messages while (<>) { $in_header = 1 .. /^$/; $in_body = /^$/ .. eof; if ($in_header) { # do something } else { # in body # do something else } } continue { close ARGV if eof; # reset $. each file } Here's a simple example to illustrate the difference between the two range operators: @lines = (" - Foo", "01 - Bar", "1 - Baz", " - Quux"); foreach (@lines) { if (/0/ .. /1/) { print "$_\n"; } } This program will print only the line containing "Bar". If the range oper- ator is changed to "...", it will also print the "Baz" line. And now some examples as a list operator: for (101 .. 200) { print } # print $_ 100 times @foo = @foo[0 .. $#foo]; # an expensive no-op @foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items Because each operand is evaluated in integer form, "2.18 .. 3.14" will re- turn two elements in list context. @list = (2.18 .. 3.14); # same as @list = (2 .. 3); The range operator in list context can make use of the magical auto-incre- ment algorithm if both operands are strings, subject to the following rules: * With one exception (below), if both strings look like numbers to Perl, the magic increment will not be applied, and the strings will be treated as numbers (more specifically, integers) instead. For example, "-2".."2" is the same as -2..2, and "2.18".."3.14" pro- duces "2, 3". * The exception to the above rule is when the left-hand string begins with 0 and is longer than one character, in this case the magic incre- ment will be applied, even though strings like "01" would normally look like a number to Perl. For example, "01".."04" produces "01", "02", "03", "04", and "00".."-1" produces "00" through "99" - this may seem surprising, but see the fol- lowing rules for why it works this way. To get dates with leading ze- ros, you can say: @z2 = ("01" .. "31"); print $z2[$mday]; If you want to force strings to be interpreted as numbers, you could say @numbers = ( 0+$first .. 0+$last ); Note: In Perl versions 5.30 and below, any string on the left-hand side beginning with "0", including the string "0" itself, would cause the magic string increment behavior. This means that on these Perl ver- sions, "0".."-1" would produce "0" through "99", which was inconsistent with "0..-1", which produces the empty list. This also means that "0".."9" now produces a list of integers instead of a list of strings. * If the initial value specified isn't part of a magical increment se- quence (that is, a non-empty string matching "/^[a-zA-Z]*[0-9]*\z/"), only the initial value will be returned. For example, "ax".."az" produces "ax", "ay", "az", but "*x".."az" pro- duces only "*x". * For other initial values that are strings that do follow the rules of the magical increment, the corresponding sequence will be returned. For example, you can say @alphabet = ("A" .. "Z"); to get all normal letters of the English alphabet, or $hexdigit = (0 .. 9, "a" .. "f")[$num & 15]; to get a hexadecimal digit. * 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. If the length of the final string is shorter than the first, the empty list is returned. For example, "a".."--" is the same as "a".."zz", "0".."xx" produces "0" through "99", and "aaa".."--" returns the empty list. As of Perl 5.26, the list-context range operator on strings works as ex- pected in the scope of "use feature 'unicode_strings'". In previous ver- sions, and outside the scope of that feature, it exhibits "The "Unicode Bug"" in perlunicode: its behavior depends on the internal encoding of the range endpoint. Because the magical increment only works on non-empty strings matching "/^[a-zA-Z]*[0-9]*\z/", the following will only return an alpha: use charnames "greek"; my @greek_small = ("\N{alpha}" .. "\N{omega}"); 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}") .. ord("\N{omega}") ); However, because there are many other lowercase Greek characters than just those, to match lowercase Greek characters in a regular expression, you could use the pattern "/(?:(?=\p{Greek})\p{Lower})+/" (or the experimental feature "/(?[ \p{Greek} & \p{Lower} ])+/"). Conditional Operator 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 be- fore the ":" is returned, otherwise the argument after the ":" is returned. For example: printf "I have %d dog%s.\n", $n, ($n == 1) ? "" : "s"; Scalar or list context propagates downward into the 2nd or 3rd argument, whichever is selected. $x = $ok ? $y : $z; # get a scalar @x = $ok ? @y : @z; # get an array $x = $ok ? @y : @z; # oops, that's just a count! The operator may be assigned to if both the 2nd and 3rd arguments are legal lvalues (meaning that you can assign to them): ($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: $x % 2 ? $x += 10 : $x += 2 Really means this: (($x % 2) ? ($x += 10) : $x) += 2 Rather than this: ($x % 2) ? ($x += 10) : ($x += 2) That should probably be written more simply as: $x += ($x % 2) ? 10 : 2; Assignment Operators "=" is the ordinary assignment operator. Assignment operators work as in C. That is, $x += 2; is equivalent to $x = $x + 2; although without duplicating any side effects that dereferencing the lvalue might trigger, such as from tie(). Other assignment operators work simi- larly. The following are recognized: **= += *= &= &.= <<= &&= -= /= |= |.= >>= ||= .= %= ^= ^.= //= x= ^^= Although these are grouped by family, they all have the precedence of as- signment. These combined assignment operators can only operate on scalars, whereas the ordinary assignment operator can assign to arrays, hashes, lists and even references. (See "Context" and "List value constructors" in perldata, and "Assigning to References" in perlref.) The scalar assignment operator returns its left operand, i.e. the scalar assigned to. Unlike in C, it produces a valid lvalue. Modifying an as- signment is equivalent to doing the assignment and then modifying the vari- able that was assigned to. This is useful for modifying a copy of some- thing, like this: ($tmp = $global) =~ tr/13579/24680/; Although as of 5.14, that can be also be accomplished this way: use v5.14; $tmp = ($global =~ tr/13579/24680/r); Likewise, ($x += 2) *= 3; is equivalent to $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 assign- ment. The three dotted bitwise assignment operators ("&.=" "|.=" "^.=") are new in Perl 5.22. See "Bitwise String Operators". Comma Operator Binary "," is the comma operator. In scalar context it evaluates its left argument, throws that value away, then evaluates its right argument and re- turns that value. This is just like C's comma operator. 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 "=>" 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 other- wise be interpreted as operators, constants, single number v-strings or function calls. If in doubt about this behavior, the left operand can be quoted explicitly. Otherwise, the "=>" operator behaves exactly as the comma operator or list argument separator, according to context. For example: use constant FOO => "something"; my %h = ( FOO => 23 ); is equivalent to: my %h = ("FOO", 23); It is NOT: my %h = ("something", 23); The "=>" operator is helpful in documenting the correspondence between keys and values in hashes, and other paired elements in lists. %hash = ( $key => $value ); login( $username => $password ); The special quoting behavior ignores precedence, and hence may apply to part of the left operand: print time.shift => "bbb"; That example prints something like "1314363215shiftbbb", because the "=>" implicitly quotes the "shift" immediately on its left, ignoring the fact that "time.shift" is the entire left operand. List Operators (Rightward) 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 operators without the need for parentheses: 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, "< :encoding(UTF-8)", "filename") or die "Can't open: $!\n"; in which case you might as well just use the more customary "||" operator: open(HANDLE, "< :encoding(UTF-8)", "filename") || die "Can't open: $!\n"; See also discussion of list operators in "Terms and List Operators (Left- ward)". Logical Not Unary "not" returns the logical negation of the expression to its right. It's the equivalent of "!" except for the very low precedence. Logical And Binary "and" returns the logical conjunction of the two surrounding expres- sions. It's equivalent to "&&" except for the very low precedence. This means that it short-circuits: the right expression is evaluated only if the left expression is true. Logical or and Exclusive Or There is no low precedence operator for defined-OR. Binary "or" returns the logical inclusive disjunction of the two surround- ing expressions. It's equivalent to "||" except for it having very low precedence. This makes it useful for control flow: print FH $data or die "Can't write to FH: $!"; This means that it short-circuits: the right expression is evaluated only if the left expression is false. Due to its precedence, you must be care- ful to avoid using it as replacement for the "||" operator. It usually works out better for flow control than in assignments: $x = $y or $z; # bug: this is wrong ($x = $y) or $z; # really means this $x = $y || $z; # better written this way However, when it's a list-context assignment and you're trying to use "||" for control flow, you probably need "or" so that the assignment takes higher precedence. @info = stat($file) || die; # oops, scalar sense of stat! @info = stat($file) or die; # better, now @info gets its due Then again, you could always use parentheses. Binary "xor" returns the logical exclusive disjunction of the two surround- ing expressions. That means it returns "true" if either, but not both, are true. It's equivalent to "^^" except for it having very low precedence. It cannot short-circuit (of course). It tends to be used to verify that two mutually-exclusive conditions are actually mutually exclusive. For ex- ample, in Perl's test suite, we might want to test that a regular expres- sion pattern can't both match and not match, for otherwise it would be a bug in our pattern matching code. ($x =~ qr/$pat/ xor $x !~ qr/$pat/) or die; C Operators Missing From Perl Here is what C has that Perl doesn't: unary & Address-of operator. (But see the "\" operator for taking a refer- ence.) unary * Dereference-address operator. (Perl's prefix dereferencing opera- tors are typed: "$", "@", "%", and "&".) (TYPE) Type-casting operator. Quote and Quote-like Operators While we usually think of quotes as literal values, in Perl they function as operators, providing various kinds of interpolating and pattern matching capabilities. Perl provides customary quote characters for these behav- iors, but also provides a way for you to choose your quote character for any of them. In the following table, a "{}" represents any pair of delim- iters you choose. Customary Generic Meaning Interpolates '' q{} Literal no "" qq{} Literal yes `` qx{} Command yes* qw{} Word list no // m{} Pattern match yes* qr{} Pattern yes* s{}{} Substitution yes* tr{}{} Transliteration no (but see below) y{}{} Transliteration no (but see below) <<EOF here-doc yes* * unless the delimiter is ''. Non-bracketing delimiters use the same character fore and aft, but the four sorts of ASCII brackets (round, angle, square, curly) all nest, which means that q{foo{bar}baz} is the same as 'foo{bar}baz' Note, however, that this does not always work for quoting Perl code: $s = q{ if ($x eq "}") ... }; # WRONG is a syntax error. The "Text::Balanced" module (standard as of v5.8, and from CPAN before then) is able to do this properly. If the "extra_paired_delimiters" feature is enabled, then Perl will addi- tionally recognise a variety of Unicode characters as being paired. For a full list, see the "List of Extra Paired Delimiters" at the end of this document. There can (and in some cases, must) be whitespace between the operator and the quoting characters, except when "#" is being used as the quoting char- acter. "q#foo#" is parsed as the string "foo", while "q #foo#" is the op- erator "q" followed by a comment. Its argument will be taken from the next line. This allows you to write: s {foo} # Replace foo {bar} # with bar. The cases where whitespace must be used are when the quoting character is a word character (meaning it matches "/\w/"): q XfooX # Works: means the string 'foo' qXfooX # WRONG! The following escape sequences are available in constructs that interpo- late, and in transliterations whose delimiters aren't single quotes ("'"). In all the ones with braces, any number of blanks and/or tabs adjoining and within the braces are allowed (and ignored). Sequence Note Description \t tab (HT, TAB) \n newline (NL) \r return (CR) \f form feed (FF) \b backspace (BS) \a alarm (bell) (BEL) \e escape (ESC) \x{263A} [1,8] hex char (example shown: SMILEY) \x{ 263A } Same, but shows optional blanks inside and adjoining the braces \x1b [2,8] restricted range hex char (example: ESC) \N{name} [3] named Unicode character or character sequence \N{U+263D} [4,8] Unicode character (example: FIRST QUARTER MOON) \c[ [5] control char (example: chr(27)) \o{23072} [6,8] octal char (example: SMILEY) \033 [7,8] restricted range octal char (example: ESC) Note that any escape sequence using braces inside interpolated constructs may have optional blanks (tab or space characters) adjoining with and in- side of the braces, as illustrated above by the second "\x{ }" example. [1] The result is the character specified by the hexadecimal number between the braces. See "[8]" below for details on which character. Blanks (tab or space characters) may separate the number from either or both of the braces. Otherwise, only hexadecimal digits are valid between the braces. If an invalid character is encountered, a warning will be issued and the in- valid character and all subsequent characters (valid or invalid) within the braces will be discarded. If there are no valid digits between the braces, the generated charac- ter is the NULL character ("\x{00}"). However, an explicit empty brace ("\x{}") will not cause a warning (currently). [2] The result is the character specified by the hexadecimal number in the range 0x00 to 0xFF. See "[8]" below for details on which character. Only hexadecimal digits are valid following "\x". When "\x" is fol- lowed by fewer than two valid digits, any valid digits will be zero-padded. This means that "\x7" will be interpreted as "\x07", and a lone "\x" will be interpreted as "\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 escape and will still be used as the subsequent character in the string. For example: Original Result Warns? "\x7" "\x07" no "\x" "\x00" no "\x7q" "\x07q" yes "\xq" "\x00q" yes [3] The result is the Unicode character or character sequence given by name. See charnames. [4] "\N{U+hexadecimal number}" means the Unicode character whose Unicode code point is hexadecimal number. [5] The character following "\c" is mapped to some other character as shown in the table: Sequence Value \c@ chr(0) \cA chr(1) \ca chr(1) \cB chr(2) \cb chr(2) ... \cZ chr(26) \cz chr(26) \c[ chr(27) # See below for chr(28) \c] chr(29) \c^ chr(30) \c_ chr(31) \c? chr(127) # (on ASCII platforms; 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?" is DELETE on ASCII platforms because "ord("?") ^ 64" is 127, and "\c@" is NULL because the ord of "@" is 64, so xor'ing 64 itself produces 0. Also, "\c\X" yields " chr(28) . "X"" for any X, 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 "OPERATOR DIFFERENCES" in perlebcdic for a full discus- sion of the differences between these for ASCII versus EBCDIC plat- forms. Use of any other character following the "c" besides those listed above is discouraged, and as of Perl v5.20, the only characters actually al- lowed are the printable ASCII ones, minus the left brace "{". 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 "\N{...}". [6] The result is the character specified by the octal number between the braces. See "[8]" below for details on which character. Blanks (tab or space characters) may separate the number from either or both of the braces. Otherwise, if a character that isn't an octal digit is encountered, a warning is raised, and the value is based on the octal digits before it, discarding it and all following characters up to the closing brace. It is a fatal error if there are no octal digits at all. [7] The result is the character specified by the three-digit octal number in the range 000 to 777 (but best to not use above 077, see next para- graph). See "[8]" below for details on which character. Some contexts allow 2 or even 1 digit, but any usage without exactly three digits, the first being a zero, may give unintended results. (For example, in a regular expression it may be confused with a back- reference; see "Octal escapes" in perlrebackslash.) Starting in Perl 5.14, you may use "\o{}" instead, which avoids all these problems. Otherwise, it is best to use this construct only for ordinals "\077" and below, remembering to pad to the left with zeros to make three dig- its. For larger ordinals, either use "\o{}", or convert to something else, such as to hex and use "\N{U+}" (which is portable between plat- forms with different character sets) or "\x{}" instead. [8] Several constructs above specify a character by a number. That number gives the character's position in the character set encoding (indexed from 0). This is called synonymously its ordinal, code position, or code point. Perl works on platforms that have a native encoding cur- rently of either ASCII/Latin1 or EBCDIC, each of which allow specifica- tion of 256 characters. In general, if the number is 255 (0xFF, 0377) or below, Perl interprets this in the platform's native encoding. If the number is 256 (0x100, 0400) or above, Perl interprets it as a Uni- code code point and the result is the corresponding Unicode character. For example "\x{50}" and "\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 "&". "\x{100}" and "\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 "LATIN CAPITAL LETTER A WITH MACRON". An exception to the above rule is that "\N{U+hex number}" is always in- terpreted as a Unicode code point, so that "\N{U+0050}" is "P" even on EBCDIC platforms. NOTE: Unlike C and other languages, Perl has no "\v" escape sequence for the vertical tab (VT, which is 11 in both ASCII and EBCDIC), but you may use "\N{VT}", "\ck", "\N{U+0b}", or "\x0b". ("\v" does have meaning in regular expression patterns in Perl, see perlre.) The following escape sequences are available in constructs that interpo- late, but not in transliterations. \l lowercase next character only \u titlecase (not uppercase!) next character only \L lowercase all characters till \E or end of string \U uppercase all characters till \E or end of string \F foldcase all characters till \E or end of string \Q quote (disable) pattern metacharacters till \E or end of string \E end either case modification or quoted section (whichever was last seen) See "quotemeta" in perlfunc for the exact definition of characters that are quoted by "\Q". "\L", "\U", "\F", and "\Q" can stack, in which case you need one "\E" for each. For example: say "This \Qquoting \ubusiness \Uhere isn't\E done yet,\E is it?"; This quoting Business HERE ISN'T done yet, is it? If a "use locale" form that includes "LC_CTYPE" is in effect (see perllo- cale), the case map used by "\l", "\L", "\u", and "\U" is taken from the current locale. If Unicode (for example, "\N{}" or code points of 0x100 or beyond) is being used, the case map used by "\l", "\L", "\u", and "\U" is as defined by Unicode. That means that case-mapping a single character can sometimes produce a sequence of several characters. Under "use locale", "\F" produces the same results as "\L" for all locales but a UTF-8 one, where it instead uses the Unicode definition. All systems use the virtual "\n" to represent a line terminator, called a "newline". There is no such thing as an unvarying, physical newline char- acter. It is only an illusion that the operating system, device drivers, C libraries, and Perl all conspire to preserve. Not all systems read "\r" as ASCII CR and "\n" as ASCII LF. For example, on the ancient Macs (pre-MacOS X) of yesteryear, these used to be reversed, and on systems without a line terminator, printing "\n" might emit no actual data. In general, use "\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 and prefer a CR+LF ("\015\012" or "\cM\cJ") for line terminators, and al- though they often accept just "\012", they seldom tolerate just "\015". If you get in the habit of using "\n" for networking, you may be burned some day. For constructs that do interpolate, variables beginning with ""$"" or ""@"" are interpolated. Subscripted variables such as $a[3] or "$href->{key}[0]" are also interpolated, as are array and hash slices. But method calls such as "$obj->meth" are not. Interpolating an array or slice interpolates the elements in order, sepa- rated by the value of $", so is equivalent to interpolating "join $", @ar- ray". "Punctuation" arrays such as "@*" are usually interpolated only if the name is enclosed in braces "@{*}", but the arrays @_, "@+", and "@-" are interpolated even without braces. For double-quoted strings, the quoting from "\Q" is applied after interpo- lation and escapes are processed. "abc\Qfoo\tbar$s\Exyz" is equivalent to "abc" . quotemeta("foo\tbar$s") . "xyz" For the pattern of regex operators ("qr//", "m//" and "s///"), the quoting from "\Q" is applied after interpolation is processed, but before escapes are processed. This allows the pattern to match literally (except for "$" and "@"). For example, the following matches: '\s\t' =~ /\Q\s\t/ Because "$" or "@" trigger interpolation, you'll need to use something like "/\Quser\E\@\Qhost/" to match them literally. Patterns are subject to an additional level of interpretation as a regular expression. This is done as a second pass, after variables are interpo- lated, so that regular expressions may be incorporated into the pattern from the variables. If this is not what you want, use "\Q" to interpolate a variable literally. Apart from the behavior described above, Perl does not expand multiple lev- els of interpolation. In particular, contrary to the expectations of shell programmers, back-quotes do NOT interpolate within double quotes, nor do single quotes impede evaluation of variables when used within double quotes. Simpler Quote-Like Operators "q/STRING/" 'STRING' A single-quoted, literal string. A backslash represents a backslash unless followed by the delimiter or another backslash, in which case the delimiter or backslash is interpolated. $foo = q!I said, "You said, 'She said it.'"!; $bar = q('This is it.'); $baz = '\n'; # a two-character string "qq/STRING/" "STRING" A double-quoted, interpolated string. $_ .= qq (*** The previous line contains the naughty word "$1".\n) if /\b(tcl|java|python)\b/i; # :-) $baz = "\n"; # a one-character string "qx/STRING/" `STRING` A string which is (possibly) interpolated and then executed as a system command, via /bin/sh or its equivalent if required. Shell wildcards, pipes, and redirections will be honored. Similarly to "system", if the string contains no shell metacharacters then it will be executed di- rectly. 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 shell (or command) could not be started. In list context, returns a list of lines (however you've defined lines with $/ or $INPUT_RECORD_SEPARA- TOR), or an empty list if the shell (or command) could not be started. print qx/date/; # prints "Sun Jan 28 06:16:19 CST 2024" Because backticks do not affect standard error, use shell file descrip- tor syntax (assuming the shell supports this) if you care to address this. To capture a command's STDERR and STDOUT together: $output = `cmd 2>&1`; To capture a command's STDOUT but discard its STDERR: $output = `cmd 2>/dev/null`; To capture a command's STDERR but discard its STDOUT (ordering is im- portant here): $output = `cmd 2>&1 1>/dev/null`; To exchange a command's STDOUT and STDERR in order to capture the STDERR but leave its STDOUT to come out the old STDERR: $output = `cmd 3>&1 1>&2 2>&3 3>&-`; To read both a command's STDOUT and its STDERR separately, it's easiest to redirect them separately to files, and then read from those files when the program is done: system("program args 1>program.stdout 2>program.stderr"); The STDIN filehandle used by the command is inherited from Perl's STDIN. For example: open(SPLAT, "stuff") || die "can't open stuff: $!"; open(STDIN, "<&SPLAT") || die "can't dupe SPLAT: $!"; print STDOUT `sort`; will print the sorted contents of the file named "stuff". Using single-quote as a delimiter protects the command from Perl's dou- ble-quote interpolation, passing it on to the shell instead: $perl_info = qx(ps $$); # that's Perl's $$ $shell_info = qx'ps $$'; # that's the new shell's $$ How that string gets evaluated is entirely subject to the command in- terpreter 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 charac- ters. See perlsec for a clean and safe example of a manual fork() and exec() 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, ";" on many Unix shells and "&" on the Windows NT "cmd" 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 perlport). To be safe, you may need to set $| ($AUTOFLUSH in "Eng- lish") or call the autoflush() method of "IO::Handle" on any open han- dles. Beware that some command shells may place restrictions on the length of the command line. You must ensure your strings don't exceed this limit after any necessary interpolations. See the platform-specific release notes for more details about your particular environment. Using this operator can lead to programs that are difficult to port, because the shell commands called vary between systems, and may in fact not be present at all. As one example, the "type" command under the POSIX shell is very different from the "type" command under DOS. That doesn't mean you should go out of your way to avoid backticks 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 "system", backticks put the child process exit code in $?. If you'd like to manually inspect failure, you can check all possible failure modes by inspecting $? like this: if ($? == -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 open pragma to control the I/O layers used when reading the output of the command, for example: use open IN => ":encoding(UTF-8)"; my $x = `cmd-producing-utf-8`; "qx//" can also be called like a function with "readpipe" in perlfunc. See "I/O Operators" for more discussion. "qw/STRING/" Evaluates to a list of the words extracted out of STRING, using embed- ded whitespace as the word delimiters. It can be understood as being roughly equivalent to: split(" ", q/STRING/); the differences being that it only splits on ASCII whitespace, gener- ates a real list at compile time, and in scalar context it returns the last element in the list. So this expression: qw(foo bar baz) is semantically equivalent to the list: "foo", "bar", "baz" Some frequently seen examples: use POSIX qw( setlocale localeconv ) @EXPORT = qw( foo bar baz ); Common mistakes are trying to separate the words with commas, trying to put comments into a multi-line "qw"-string, or trying to "\"-escape the space between words. For this reason, the "use warnings" pragma and the -w switch (that is, the $^W variable) produce warnings if the STRING contains the ",", "#", or "\" characters. Regexp Quote-Like Operators Here are the quote-like operators that apply to pattern matching and re- lated activities. "qr/STRING/msixpodualn" This operator quotes (and possibly compiles) its STRING as a regu- lar expression. STRING is interpolated the same way as PATTERN in "m/PATTERN/". If "'" is used as the delimiter, no variable inter- polation is done. Returns a Perl value which may be used instead of the corresponding "/STRING/msixpodualn" expression. The re- turned value is a normalized version of the original pattern. It magically differs from a string containing the same characters: ref(qr/x/) returns "Regexp"; however, dereferencing it is not well defined (you currently get the normalized version of the original pattern, but this may change). For example, $rex = qr/my.STRING/is; print $rex; # prints (?si-xm:my.STRING) s/$rex/foo/; is equivalent to s/my.STRING/foo/is; The result may be used as a subpattern in a match: $re = qr/$pattern/; $string =~ /foo${re}bar/; # can be interpolated in other # patterns $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: sub match { my $patterns = shift; my @compiled = map qr/$_/i, @$patterns; grep { my $success = 0; foreach my $pat (@compiled) { $success = 1, last if /$pat/; } $success; } @_; } Precompilation of the pattern into an internal representation at the moment of qr() avoids the need to recompile the pattern every time a match "/$pat/" is attempted. (Perl has many other internal optimizations, but none would be triggered in the above example if we did not use qr() operator.) 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; 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 (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 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 "msixpluadn" will be propagated appropriately. The ef- fect that the "/o" modifier has is not propagated, being restricted to those patterns explicitly using it. The "/a", "/d", "/l", and "/u" modifiers (added in Perl 5.14) con- trol the character set rules, but "/a" is the only one you are likely to want to specify explicitly; the other three are selected automatically by various pragmas. See perlre for additional information on valid syntax for STRING, and for a detailed look at the semantics of regular expressions. In particular, all modifiers except the largely obsolete "/o" are further explained in "Modifiers" in perlre. "/o" is described in the next section. "m/PATTERN/msixpodualngc" "/PATTERN/msixpodualngc" Searches a string for a pattern match, and in scalar context re- turns true if it succeeds, false if it fails. If no string is specified via the "=~" or "!~" operator, the $_ string is searched. (The string specified with "=~" need not be an lvalue--it may be the result of an expression evaluation, but remember the "=~" binds rather tightly.) See also perlre. Options are as described in "qr//" above; in addition, the follow- ing match process modifiers are available: g Match globally, i.e., find all occurrences. c Do not reset search position on a failed match when /g is in effect. If "/" is the delimiter then the initial "m" is optional. With the "m" you can use any pair of non-whitespace (ASCII) characters as delimiters. This is particularly useful for matching path names that contain "/", to avoid LTS (leaning toothpick syndrome). If "?" is the delimiter, then a match-only-once rule applies, de- scribed in "m?PATTERN?" below. If "'" (single quote) is the delim- iter, no variable interpolation is performed on the PATTERN. When using a delimiter character valid in an identifier, whitespace is required after the "m". PATTERN may contain variables, which will be interpolated every time the pattern search is evaluated, except for when the delimiter is a single quote. (Note that $(, $), and $| are not interpolated because they look like end-of-string tests.) Perl will not recom- pile the pattern unless an interpolated variable that it contains changes. You can force Perl to skip the test and never recompile by adding a "/o" (which stands for "once") after the trailing de- limiter. Once upon a time, Perl would recompile regular expres- sions 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 "/o" are one of: 1. The variables are thousands of characters long and you know that they don't change, and you need to wring out the last lit- tle bit of speed by having Perl skip testing for that. (There is a maintenance penalty for doing this, as mentioning "/o" constitutes a promise that you won't change the variables in the pattern. If you do change them, Perl won't even notice.) 2. you want the pattern to use the initial values of the variables regardless of whether they change or not. (But there are saner ways of accomplishing this than using "/o".) 3. If the pattern contains embedded code, such as use re 'eval'; $code = 'foo(?{ $x })'; /$code/ then perl will recompile each time, even though the pattern string hasn't changed, to ensure that the current value of $x is seen each time. Use "/o" if you want to avoid this. The bottom line is that using "/o" is almost never a good idea. The empty pattern "//" (This subsection applies to "//", "m//", and "s///", but not to "qr//".) If the PATTERN evaluates to the empty string, the last successfully matched regular expression in the current dynamic scope is used in- stead (see also "Scoping Rules of Regex Variables" in perlvar). In this case, only the "g" and "c" flags on the empty pattern are hon- ored; the other flags are taken from the original pattern. If no match has previously succeeded, this will (silently) act instead as a genuine empty pattern (which will always match). Using a user supplied string as a pattern has the risk that if the string is empty that it triggers the "last successful match" behavior, which can be very confusing. In such cases you are recommended to replace "m/$pattern/" with "m/(?:$pattern)/" to avoid this behavior. The last successful pattern may be accessed as a variable via "${^LAST_SUCCESSFUL_PATTERN}". Matching against it, or the empty pattern should have the same effect, with the exception that when there is no last successful pattern the empty pattern will silently match, whereas using the "${^LAST_SUCCESSFUL_PATTERN}" variable will produce undefined warnings (if warnings are enabled). You can check defined(${^LAST_SUCCESSFUL_PATTERN}) to test if there is a "last successful match" in the current scope. Note that it's possible to confuse Perl into thinking "//" (the empty regex) is really "//" (the defined-or operator). Perl is usually pretty good about this, but some pathological cases might trigger this, such as "$x///" (is that "($x) / (//)" or "$x // /"?) and "print $fh //" ("print $fh(//" or "print($fh //"?). In all of these examples, Perl will assume you meant defined-or. If you meant the empty regex, just use parentheses or spaces to disam- biguate, or even prefix the empty regex with an "m" (so "//" be- comes "m//"). Matching in list context If the "/g" option is not used, "m//" in list context returns a list consisting of the subexpressions matched by the parentheses in the pattern, that is, ($1, $2, $3...) (Note that here $1 etc. are also set). When there are no parentheses in the pattern, the re- turn value is the list "(1)" for success. With or without paren- theses, an empty list is returned upon failure. Examples: open(TTY, "+</dev/tty") || die "can't access /dev/tty: $!"; <TTY> =~ /^y/i && foo(); # do foo if desired if (/Version: *([0-9.]*)/) { $version = $1; } next if m#^/usr/spool/uucp#; # poor man's grep $arg = shift; while (<>) { print if /$arg/; } if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/)) This last example splits $foo into the first two words and the re- mainder of the line, and assigns those three fields to $F1, $F2, and $Etc. The conditional is true if any variables were assigned; that is, if the pattern matched. The "/g" modifier specifies global pattern matching--that is, matching as many times as possible within the string. How it be- haves depends on the context. In list context, it returns a list of the substrings matched by any capturing parentheses in the regu- lar expression. If there are no parentheses, it returns a list of all the matched strings, as if there were parentheses around the whole pattern. In scalar context, each execution of "m//g" finds the next match, returning true if it matches, and false if there is no further match. The position after the last match can be read or set using the pos() function; see "pos" in perlfunc. A failed match normally resets the search position to the beginning of the string, but you can avoid that by adding the "/c" modifier (for example, "m//gc"). Modifying the target string also resets the search position. "\G assertion" You can intermix "m//g" matches with "m/\G.../g", where "\G" is a zero-width assertion that matches the exact position where the pre- vious "m//g", if any, left off. Without the "/g" modifier, the "\G" assertion still anchors at pos() as it was at the start of the operation (see "pos" in perlfunc), but the match is of course only attempted once. Using "\G" without "/g" on a target string that has not previously had a "/g" match applied to it is the same as using the "\A" assertion to match the beginning of the string. Note also that, currently, "\G" is only properly supported when an- chored at the very beginning of the pattern. Examples: # list context ($one,$five,$fifteen) = (`uptime` =~ /(\d+\.\d+)/g); # scalar context local $/ = ""; while ($paragraph = <>) { while ($paragraph =~ /\p{Ll}['")]*[.!?]+['")]*\s/g) { $sentences++; } } say $sentences; Here's another way to check for sentences in a paragraph: my $sentence_rx = qr{ (?: (?<= ^ ) | (?<= \s ) ) # after start-of-string or # whitespace \p{Lu} # capital letter .*? # a bunch of anything (?<= \S ) # that ends in non- # whitespace (?<! \b [DMS]r ) # but isn't a common abbr. (?<! \b Mrs ) (?<! \b Sra ) (?<! \b St ) [.?!] # followed by a sentence # ender (?= $ | \s ) # in front of end-of-string # or whitespace }sx; local $/ = ""; while (my $paragraph = <>) { say "NEW PARAGRAPH"; my $count = 0; while ($paragraph =~ /($sentence_rx)/g) { printf "\tgot sentence %d: <%s>\n", ++$count, $1; } } Here's how to use "m//gc" with "\G": $_ = "ppooqppqq"; while ($i++ < 2) { print "1: '"; print $1 while /(o)/gc; print "', pos=", pos, "\n"; print "2: '"; print $1 if /\G(q)/gc; print "', pos=", pos, "\n"; print "3: '"; print $1 while /(p)/gc; print "', pos=", pos, "\n"; } print "Final: '$1', pos=",pos,"\n" if /\G(.)/; The last example should print: 1: 'oo', pos=4 2: 'q', pos=5 3: 'pp', pos=7 1: '', pos=7 2: 'q', pos=8 3: '', pos=8 Final: 'q', pos=8 Notice that the final match matched "q" instead of "p", which a match without the "\G" anchor would have done. Also note that the final match did not update "pos". "pos" is only updated on a "/g" match. If the final match did indeed match "p", it's a good bet that you're running an ancient (pre-5.6.0) version of Perl. A useful idiom for "lex"-like scanners is "/\G.../gc". You can combine several regexps like this to process a string part-by-part, doing different actions depending on which regexp matched. Each regexp tries to match where the previous one leaves off. $_ = <<'EOL'; $url = URI::URL->new( "http://example.com/" ); die if $url eq "xXx"; EOL LOOP: { print(" digits"), redo LOOP if /\G\d+\b[,.;]?\s*/gc; print(" lowercase"), redo LOOP if /\G\p{Ll}+\b[,.;]?\s*/gc; print(" UPPERCASE"), redo LOOP if /\G\p{Lu}+\b[,.;]?\s*/gc; print(" Capitalized"), redo LOOP if /\G\p{Lu}\p{Ll}+\b[,.;]?\s*/gc; print(" MiXeD"), redo LOOP if /\G\pL+\b[,.;]?\s*/gc; print(" alphanumeric"), redo LOOP if /\G[\p{Alpha}\pN]+\b[,.;]?\s*/gc; print(" line-noise"), redo LOOP if /\G\W+/gc; print ". That's all!\n"; } Here is the output (split into several lines): line-noise lowercase line-noise UPPERCASE line-noise UPPERCASE line-noise lowercase line-noise lowercase line-noise lowercase lowercase line-noise lowercase lowercase line-noise lowercase lowercase line-noise MiXeD line-noise. That's all! "m?PATTERN?msixpodualngc" This is just like the "m/PATTERN/" search, except that it matches only once between calls to the reset() operator. This is a useful optimization when you want to see only the first occurrence of something in each file of a set of files, for instance. Only "m??" patterns local to the current package are reset. while (<>) { if (m?^$?) { # blank line between header and body } } continue { reset if eof; # clear m?? status for next file } Another example switched the first "latin1" encoding it finds 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 "?"; with any other delimiter this is the normal "m//" operator. In the past, the leading "m" in "m?PATTERN?" was optional, but omitting it would produce a deprecation warning. As of v5.22.0, omitting it produces a syntax error. If you encounter this con- struct in older code, you can just add "m". "s/PATTERN/REPLACEMENT/msixpodualngcer" Searches a string for a pattern, and if found, replaces that pat- tern with the replacement text and returns the number of substitu- tions made. Otherwise it returns false (a value that is both an empty string ("") and numeric zero (0) as described in "Relational Operators"). If the "/r" (non-destructive) option is used then it runs the sub- stitution on a copy of the string and instead of returning the num- ber of substitutions, it returns the copy whether or not a substi- tution occurred. The original string is never changed when "/r" is used. The copy will always be a plain string, even if the input is an object or a tied variable. If no string is specified via the "=~" or "!~" operator, the $_ variable is searched and modified. Unless the "/r" option is used, the string specified must be a scalar variable, an array element, a hash element, or an assignment to one of those; that is, some sort of scalar lvalue. If the delimiter chosen is a single quote, no variable interpola- tion is done on either the PATTERN or the REPLACEMENT. Otherwise, if the PATTERN contains a "$" 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 "/o" op- tion. If the pattern evaluates to the empty string, the last suc- cessfully executed regular expression is used instead. See perlre for further explanation on these. Options are as with "m//" with the addition of the following re- placement specific options: e Evaluate the right side as a block of code. ee Evaluate the right side as a block of code, then eval() the resulting string. r Return substitution and leave the original string untouched. Any non-whitespace delimiter may replace the slashes. Add space after the "s" when using a character allowed in identifiers. If single quotes are used, no interpretation is done on the replace- ment string (the "/e" modifier overrides this, however). Note that Perl treats backticks as normal delimiters; the replacement text is not evaluated as a command. If the PATTERN is delimited by brack- eting quotes, the REPLACEMENT has its own pair of quotes, which may or may not be bracketing quotes, for example, "s(foo)(bar)" or "s<foo>/bar/". A "/e" will cause the replacement portion to be treated as a full-fledged block of Perl code and evaluated right then and there. It is, however, syntax checked at compile-time. A second "e" modifier will cause the result of the block of code to be "eval"ed. That is, "s/FOO/BAR/e" will compute the replacement string at match time as if it had been written as "do { BAR }" (see "do BLOCK" in perlfunc). Each additional "e" modifier wraps a call to "eval" around the result: "s/FOO/BAR/ee" will compute the replacement string like "eval(do { BAR })", "s/FOO/BAR/eee" like "eval(eval(do { BAR }))", etc. Examples: s/\bgreen\b/mauve/g; # don't change wintergreen $path =~ s|/usr/bin|/usr/local/bin|; s/Login: $foo/Login: $bar/; # run-time pattern ($foo = $bar) =~ s/this/that/; # copy first, then # change ($foo = "$bar") =~ s/this/that/; # convert to string, # copy, then change $foo = $bar =~ s/this/that/r; # Same as above using /r $foo = $bar =~ s/this/that/r =~ s/that/the other/r; # Chained substitutes # using /r @foo = map { s/this/that/r } @bar # /r is very useful in # maps $count = ($paragraph =~ s/Mister\b/Mr./g); # get change-cnt $_ = 'abc123xyz'; s/\d+/$&*2/e; # yields 'abc246xyz' s/\d+/sprintf("%5d",$&)/e; # yields 'abc 246xyz' s/\w/$& x 2/eg; # yields 'aabbcc 224466xxyyzz' s/%(.)/$percent{$1}/g; # change percent escapes; no /e s/%(.)/$percent{$1} || $&/ge; # expr now, so /e s/^=(\w+)/pod($1)/ge; # use function call $_ = 'abc123xyz'; $x = s/abc/def/r; # $x is 'def123xyz' and # $_ remains 'abc123xyz'. # expand variables in $_, but dynamics only, using # symbolic dereferencing s/\$(\w+)/${$1}/g; # Add one to the value of any numbers in the string s/(\d+)/1 + $1/eg; # Titlecase words in the last 30 characters only (presuming # that the substring doesn't start in the middle of a word) substr($str, -30) =~ s/\b(\p{Alpha})(\p{Alpha}*)\b/\u$1\L$2/g; # This will expand any embedded scalar variable # (including lexicals) in $_ : First $1 is interpolated # to the variable name, and then evaluated s/(\$\w+)/$1/eeg; # Same as above, but perhaps clearer s/(\$\w+)/eval($1)/eg; # Delete (most) C comments. $program =~ s { /\* # Match the opening delimiter. .*? # Match a minimal number of characters. \*/ # Match the closing delimiter. } []gsx; s/^\s*(.*?)\s*$/$1/; # trim whitespace in $_, # expensively for ($variable) { # trim whitespace in $variable, # cheap s/^\s+//; s/\s+$//; } s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields $foo !~ s/A/a/g; # Lowercase all A's in $foo; return # 0 if any were found and changed; # otherwise return 1 Note the use of "$" instead of "\" in the last example. Unlike sed, we use the \<digit> form only in the left hand side. Anywhere else it's $<digit>. Occasionally, you can't use just a "/g" to get all the changes to occur that you might want. Here are two common cases: # put commas in the right places in an integer 1 while s/(\d)(\d\d\d)(?!\d)/$1,$2/g; # expand tabs to 8-column spacing 1 while s/\t+/' ' x (length($&)*8 - length($`)%8)/e; While "s///" accepts the "/c" flag, it has no effect beyond produc- ing a warning if warnings are enabled. Transliteration Quote-Like Operators "tr/SEARCHLIST/REPLACEMENTLIST/cdsr" "y/SEARCHLIST/REPLACEMENTLIST/cdsr" These transliterate all occurrences of the characters found (or not found if the "/c" modifier is specified) in the search list with the positionally corresponding character in the replacement list, possibly deleting some, depending on the modifiers specified. Unless the "/r" flag is specified, they return the number of characters replaced or deleted. If no string is specified via the "=~" or "!~" operator, the $_ string is transliterated. For sed devotees, "y" is provided as a synonym for "tr". If the "/r" (non-destructive) option is present, a new copy of the string is made and its characters transliterated, and this copy is re- turned, instead of a count, no matter whether it was modified or not: the original string is always left unchanged. The new copy is always a plain string, even if the input string is an object or a tied variable. Unless the "/r" option is used, the string specified with "=~" must be a scalar variable, an array element, a hash element, or an assignment to one of those; in other words, an lvalue. The characters delimiting SEARCHLIST and REPLACEMENTLIST can be any printable character, not just forward slashes. If they are single quotes ("tr'SEARCHLIST'REPLACEMENTLIST'"), the only interpolation is removal of "\" from pairs of "\\"; so hyphens are interpreted literally rather than specifying a character range. Otherwise, a character range may be specified with a hyphen, so "tr/A-J/0-9/" does the same replacement as "tr/ACEGIBDFHJ/0246813579/". If the SEARCHLIST is delimited by bracketing quotes, the REPLACE- MENTLIST must have its own pair of quotes, which may or may not be bracketing quotes; for example, "tr(aeiouy)(yuoiea)" or "tr[+\-*/]"ABCD"". This final example shows a way to visually clarify what is going on for people who are more familiar with regular expres- sion patterns than with "tr", and who may think forward slash delim- iters imply that "tr" is more like a regular expression pattern than it actually is. (Another option might be to use "tr[...][...]".) "tr" isn't fully like bracketed character classes, just (significantly) more like them than it is to full patterns. For example, characters appearing more than once in either list behave differently here than in patterns, and "tr" lists do not allow backslashed character classes such as "\d" or "\pL", nor variable interpolation, so "$" and "@" are always treated as literals. The allowed elements are literals plus "\'" (meaning a single quote). If the delimiters aren't single quotes, also allowed are any of the es- cape sequences accepted in double-quoted strings. Escape sequence de- tails are in the table near the beginning of this section. A hyphen at the beginning or end, or preceded by a backslash is also always considered a literal. Precede a delimiter character with a backslash to allow it. The "tr" operator is not equivalent to the "tr(1)" utility. "tr[a-z][A-Z]" will uppercase the 26 letters "a" through "z", but for case changing not confined to ASCII, use "lc", "uc", "lcfirst", "uc- first" (all documented in perlfunc), or the substitution operator "s/PATTERN/REPLACEMENT/" (with "\U", "\u", "\L", and "\l" string-inter- polation escapes in the REPLACEMENT portion). Most ranges are unportable between character sets, but certain ones signal Perl to do special handling to make them portable. There are two classes of portable ranges. The first are any subsets of the ranges "A-Z", "a-z", and "0-9", when expressed as literal characters. tr/h-k/H-K/ capitalizes the letters "h", "i", "j", and "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 "\N{...}" $string =~ tr/\N{U+20}-\N{U+7E}//d; removes from $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. In this example, these are the ASCII printable characters. So after this is run, $string has only controls and characters which have no ASCII equivalents. But, even for portable ranges, it is not generally obvious what is in- cluded without having to look things up in the manual. A sound princi- ple is to use only ranges that both begin from, and end at, either ASCII alphabetics of equal case ("b-e", "B-E"), or digits ("1-4"). Anything else is unclear (and unportable unless "\N{...}" is used). If in doubt, spell out the character sets in full. Options: c Complement the SEARCHLIST. d Delete found but unreplaced characters. r Return the modified string instead of a count, and leave the original string untouched. s Squash duplicate replaced characters. If the "/d" modifier is specified, any characters specified by SEARCH- LIST not found in REPLACEMENTLIST are deleted. (Note that this is slightly more flexible than the behavior of some tr programs, which delete anything they find in the SEARCHLIST, period.) If the "/s" modifier is specified, sequences of characters, all in a row, that were transliterated to the same character are squashed down to a single instance of that character. my $x = "aaabbbca"; $x =~ tr/ab/dd/s; # $x now is "dcd" If the "/d" modifier is used, the REPLACEMENTLIST is always interpreted exactly as specified. Otherwise, if the REPLACEMENTLIST is shorter than the SEARCHLIST, the final character, if any, is replicated until it is long enough. There won't be a final character if and only if the REPLACEMENTLIST is empty, in which case REPLACEMENTLIST is copied from SEARCHLIST. An empty REPLACEMENTLIST is useful for counting charac- ters in a class, or for squashing character sequences in a class. 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 If the "/c" modifier is specified, the characters to be transliterated are the ones NOT in SEARCHLIST, that is, it is complemented. If "/d" and/or "/s" are also specified, they apply to the complemented SEARCH- LIST. Recall, that if REPLACEMENTLIST is empty (except under "/d") a copy of SEARCHLIST is used instead. That copy is made after comple- menting under "/c". SEARCHLIST is sorted by code point order after complementing, and any REPLACEMENTLIST is applied to that sorted re- sult. This means that under "/c", the order of the characters speci- fied in SEARCHLIST is irrelevant. This can lead to different results on EBCDIC systems if REPLACEMENTLIST contains more than one character, hence it is generally non-portable to use "/c" with such a REPLACE- MENTLIST. Another way of describing the operation is this: If "/c" is specified, the SEARCHLIST is sorted by code point order, then complemented. If REPLACEMENTLIST is empty and "/d" is not specified, REPLACEMENTLIST is replaced by a copy of SEARCHLIST (as modified under "/c"), and these potentially modified lists are used as the basis for what follows. Any character in the target string that isn't in SEARCHLIST is passed through unchanged. Every other character in the target string is re- placed by the character in REPLACEMENTLIST that positionally corre- sponds to its mate in SEARCHLIST, except that under "/s", the 2nd and following characters are squeezed out in a sequence of characters in a row that all translate to the same character. If SEARCHLIST is longer than REPLACEMENTLIST, characters in the target string that match a character in SEARCHLIST that doesn't have a correspondence in REPLACE- MENTLIST are either deleted from the target string if "/d" is speci- fied; or replaced by the final character in REPLACEMENTLIST if "/d" isn't specified. Some examples: $ARGV[1] =~ tr/A-Z/a-z/; # canonicalize to lower case ASCII $cnt = tr/*/*/; # count the stars in $_ $cnt = tr/*//; # same thing $cnt = $sky =~ tr/*/*/; # count the stars in $sky $cnt = $sky =~ tr/*//; # same thing $cnt = $sky =~ tr/*//c; # count all the non-stars in $sky $cnt = $sky =~ tr/*/*/c; # same, but transliterate each non-star # into a star, leaving the already-stars # alone. Afterwards, everything in # $sky is a star. $cnt = tr/0-9//; # count the ASCII digits in $_ tr/a-zA-Z//s; # bookkeeper -> bokeper tr/o/o/s; # bookkeeper -> bokkeeper tr/oe/oe/s; # bookkeeper -> bokkeper tr/oe//s; # bookkeeper -> bokkeper tr/oe/o/s; # bookkeeper -> bokkopor ($HOST = $host) =~ tr/a-z/A-Z/; $HOST = $host =~ tr/a-z/A-Z/r; # same thing $HOST = $host =~ tr/a-z/A-Z/r # chained with s///r =~ s/:/ -p/r; tr/a-zA-Z/ /cs; # change non-alphas to single space @stripped = map tr/a-zA-Z/ /csr, @original; # /r with map tr [\200-\377] [\000-\177]; # wickedly delete 8th bit $foo !~ tr/A/a/ # transliterate all the A's in $foo to 'a', # return 0 if any were found and changed. # Otherwise return 1 Transliterated characters are not rescanned for further translitera- tion, even if a character in the REPLACEMENTLIST appears elsewhere in the SEARCHLIST: tr/ox/xo/; # oxxo -> xoox If multiple transliterations are given for a character, only the first one is used: tr/AAA/XYZ/ will transliterate any A to X. Because the transliteration table is built at compile time, neither the SEARCHLIST nor the REPLACEMENTLIST are subjected to double quote inter- polation. That means that if you want to use variables, you must use an eval(): eval "tr/$oldlist/$newlist/"; die $@ if $@; eval "tr/$oldlist/$newlist/, 1" or die $@; Here-docs "<<EOT" "<<~EOT" A line-oriented form of quoting is based on the shell "here-document" syntax. Following a "<<" you specify a string to terminate the quoted material, and all lines following the current line down to the termi- nating string are the value of the item. An example is my $endng = <<WHIMPER; This is the way the text ends. This is the way the text ends. Not with a bang, but with a WHIMPER In this case, the terminator is an identifier, the word "WHIMPER". Most usually, people capitalize the identifier, just so it stands out, but this is just a convention that isn't necessary. The terminator may be enclosed in quotes, as detailed below, but with- out them, the text of the here-doc acts exactly as if it were dou- ble-quoted. my $person = 'John'; print uc <<EOT; Hello, $person! And the text goes on. EOT This yields: HELLO, JOHN! AND THE TEXT GOES ON. The parentheses in the "uc" function call don't have to be omitted: print uc(<<EOT); Hello, $person! And the text goes on. EOT HELLO, JOHN! AND THE TEXT GOES ON. And you can intermix a here-document with other things: print <<EOT, "Followed by the next argument\n"; Hello, $person! And the text goes on. EOT Hello, John! And the text goes on. Followed by the next argument And you can have multiple here-documents: print <<EOT1, <<EOT2; Hello, $person! And the text goes on. EOT1 Followed by the next argument EOT2 Hello, John! And the text goes on. Followed by the next argument The terminator doesn't have to be a single word; it may also be some quoted text: my $pagliaci = << "La Commedia e finita!"; A troupe comes to town to perform a play, a comedy. The lead actress and lead actor are in an unhappy marriage. On stage, he stabs her for real; then he stabs her lover who has rushed from the audience to defend her. Both die. La Commedia e finita! There may not be a space between the "<<" and the identifier unless the terminator is quoted, as demonstrated in the example just above. Quot- ing rules for the terminator are unrelated to Perl's quoting rules. Only "", '', and `` can be used to quote it, NOT q(), qq(), and the like. The only interpolation is for backslashing the quoting charac- ter: print << "abc\"def"; testing... abc"def The terminating string must appear by itself (unquoted and with no sur- rounding whitespace) on the terminating line. Also, it cannot span multiple lines. The general rule is that the identifier must be a string literal. Stick with that, and you should be safe. Don't forget that you have to put a semicolon on the end to finish the statement, as Perl doesn't know you're not going to try to do this: print <<ABC 10 ABC + 20; which prints 30 and no line terminator. If you want your here-doc to not have a line terminator on the final line, use chomp(). chomp($string = <<'END'); This is the first line. This second line won't end in a \n. END If you use a here-doc within a delimited construct, such as in "s///eg", the quoted material must still come on the line following the "<<TERMINATOR" marker, which means it may be inside the delimited con- struct: s/this/<<E . 'that' the other E . 'more '/eg; (It works this way as of Perl 5.18. Historically, it was inconsistent, and you would have to write s/this/<<E . 'that' . 'more '/eg; the other E outside of string evals.) A problem with the Here-doc syntax given so far is that it must be at the left margin of your program, messing up the indentation. Starting in Perl v5.26, the tilde "~" modifier 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 line containing the delimiter that marks the end of the here-doc determines the indentation template for the whole thing. Compilation croaks if any non-empty line inside the here-doc does not begin with the precise indentation of the terminating line. (An empty line con- sists of the single character "\n".) For example, suppose the termi- nating line begins with a tab character followed by 4 space characters. Every non-empty line in the here-doc must begin with a tab followed by 4 spaces. They are stripped from each line, and any leading white space remaining on a line serves as the indentation for that line. Currently, only the TAB and SPACE characters are treated as whitespace for this purpose. Tabs and spaces may be mixed, but are matched ex- actly; tabs remain tabs and are not expanded. 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 line is indented with two tabs, though those may have been converted to spaces by various filters by the time you read this. EOF Quoting the delimiter As mentioned above, the terminating string may be quoted. There are three types of quoting possible. The type used determines the treatment of the text. Double Quotes Double quotes surrounding the terminating word or string behave as if no quotes were there, namely the text will be interpolated using ex- actly the same rules as normal double quoted strings, as in all the ex- amples above. So my $person = 'John'; print uc << "EOT"; Hello, $person! And the text goes on. EOT yields: HELLO, JOHN! AND THE TEXT GOES ON. which is the same result as without quotes. Single Quotes If instead, single quotes are used, the text is treated literally, with no interpolation of its content. my $person = 'John'; print uc <<'EOT'; Hello, $person! And the text goes on. EOT HELLO, $PERSON! AND THE TEXT GOES ON. The difference between a single-quoted here-doc and a single-quoted string is that backslashes have no special meaning in a here-doc, with "\\" being treated as two backslashes and not one as they would in every other quoting construct. Just as in the shell, a backslashed bareword following the "<<" means the same thing as a single-quoted string does: $cost = <<'VISTA'; # hasta la ... That'll be $10 please, ma'am. VISTA $cost = <<\VISTA; # Same thing! That'll be $10 please, ma'am. VISTA These two forms are the only ways of quoting in Perl where there is no need to worry about escaping content, something that code generators can and do make good use of. Backticks Finally, if instead backticks are used to quote the terminating string, the content of the here doc is treated just as it would be if it were a string 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. print << `EOC`; # execute command and get results echo hi there EOC Gory details of parsing quoted constructs When presented with something that might have several different interpreta- tions, Perl uses the DWIM (that's "Do What I Mean") principle to pick the most probable interpretation. This strategy is so successful that Perl programmers often do not suspect the ambiguity of what they write. But from time to time, Perl's notions differ substantially from what the author honestly meant. This section hopes to clarify how Perl handles quoted constructs. Although the most common reason to learn this is to unravel labyrinthine regular ex- pressions, because the initial steps of parsing are the same for all quot- ing operators, they are all discussed together. The most important Perl parsing rule is the first one discussed below: when processing a quoted construct, Perl first finds the end of that construct, then interprets its contents. If you understand this rule, you may skip the rest of this section on the first reading. The other rules are likely to contradict the user's expectations much less frequently than this first one. Some passes discussed below are performed concurrently, but because their results are the same, we consider them individually. For different quoting constructs, Perl performs different numbers of passes, from one to four, but these passes are always performed in the same order. Finding the end The first pass is finding the end of the quoted construct. This re- sults in saving to a safe location a copy of the text (between the starting and ending delimiters), normalized as necessary to avoid need- ing 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 "<<EOF" is terminated by "EOF" immediately followed by "\n" and starting from the first col- umn 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 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 open- ing punctuation (that is "(", "[", "{", or "<"), the ending delimiter is the corresponding closing punctuation (that is ")", "]", "}", or ">"). If the starting delimiter is an unpaired character like "/" or a closing punctuation, the ending delimiter is the same as the starting delimiter. Therefore a "/" terminates a "qq//" construct, while a "]" terminates both "qq[]" and "qq]]" constructs. When searching for single-character delimiters, escaped delimiters and "\\" are skipped. For example, while searching for terminating "/", combinations of "\\" and "\/" are skipped. If the delimiters are bracketing, nested pairs are also skipped. For example, while search- ing for a closing "]" paired with the opening "[", combinations of "\\", "\]", and "\[" are all skipped, and nested "[" and "]" are skipped as well. However, when backslashes are used as the delimiters (like "qq\\" and "tr\\\"), nothing is skipped. During the search for the end, backslashes that escape delimiters or other backslashes are removed (exactly speaking, they are not copied to the safe location). For constructs with three-part delimiters ("s///", "y///", and "tr///"), the search is repeated once more. If the first delimiter is not an opening punctuation, the three delimiters must be the same, such as "s!!!" and "tr)))", in which case the second delimiter terminates the left part and starts the right part at once. If the left part is delimited by bracketing punctuation (that is "()", "[]", "{}", or "<>"), the right part needs another pair of delimiters such as "s(){}" and "tr[]//". In these cases, whitespace and comments are allowed be- tween 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 con- struct. Thus: "$hash{"$foo/$bar"}" or: m/ bar # NOT a comment, this slash / terminated m//! /x do not form legal quoted expressions. The quoted part ends on the first """ and "/", and the rest happens to be a syntax error. Because the slash that terminated "m//" was followed by a "SPACE", the example above is not "m//x", but rather "m//" with no "/x" modifier. So the embedded "#" is interpreted as a literal "#". Also no attention is paid to "\c\" (multichar control char syntax) dur- ing this search. Thus the second "\" in "qq/\c\/" is interpreted as a part of "\/", and the following "/" is not recognized as a delimiter. Instead, use "\034" or "\x1c" at the end of quoted constructs. Interpolation The next step is interpolation in the text obtained, which is now de- limiter-independent. There are multiple cases. "<<'EOF'" No interpolation is performed. Note that the combination "\\" is left intact, since escaped delimiters are not available for here-docs. "m''", the pattern of "s'''" No interpolation is performed at this stage. Any backslashed se- quences including "\\" are treated at the stage of "Parsing regular expressions". '', "q//", "tr'''", "y'''", the replacement of "s'''" The only interpolation is removal of "\" from pairs of "\\". Therefore "-" in "tr'''" and "y'''" is treated literally as a hy- phen and no character range is available. "\1" in the replacement of "s'''" does not work as $1. "tr///", "y///" No variable interpolation occurs. String modifying combinations for case and quoting such as "\Q", "\U", and "\E" are not recog- nized. The other escape sequences such as "\200" and "\t" and backslashed characters such as "\\" and "\-" are converted to ap- propriate literals. The character "-" is treated specially and therefore "\-" is treated as a literal "-". "", ``, "qq//", "qx//", "<file*glob>", "<<"EOF"" "\Q", "\U", "\u", "\L", "\l", "\F" (possibly paired with "\E") are converted to corresponding Perl constructs. Thus, "$foo\Qbaz$bar" is converted to "$foo . (quotemeta("baz" . $bar))" internally. The other escape sequences such as "\200" and "\t" and backslashed characters such as "\\" and "\-" are replaced with appropriate ex- pansions. Let it be stressed that whatever falls between "\Q" and "\E" is in- terpolated in the usual way. Something like "\Q\\E" has no "\E" inside. Instead, it has "\Q", "\\", and "E", so the result is the same as for "\\\\E". As a general rule, backslashes between "\Q" and "\E" may lead to counterintuitive results. So, "\Q\t\E" is converted to quotemeta("\t"), which is the same as "\\\t" (since TAB is not alphanumeric). Note also that: $str = '\t'; return "\Q$str"; may be closer to the conjectural intention of the writer of "\Q\t\E". Interpolated scalars and arrays are converted internally to the "join" and "." catenation operations. Thus, "$foo XXX '@arr'" be- comes: $foo . " XXX '" . (join $", @arr) . "'"; All operations above are performed simultaneously, left to right. Because the result of "\Q STRING \E" has all metacharacters quoted, there is no way to insert a literal "$" or "@" inside a "\Q\E" pair. If protected by "\", "$" will be quoted to become "\\\$"; 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 "a $x -> {c}" really means: "a " . $x . " -> {c}"; or: "a " . $x -> {c}; Most of the time, the longest possible text that does not include spaces between components and which contains matching braces or brackets. because the outcome may be determined by voting based on heuristic estimators, the result is not strictly predictable. For- tunately, it's usually correct for ambiguous cases. The replacement of "s///" Processing of "\Q", "\U", "\u", "\L", "\l", "\F" and interpolation happens as with "qq//" constructs. It is at this step that "\1" is begrudgingly converted to $1 in the replacement text of "s///", in order to correct the incorrigible sed hackers who haven't picked up the saner idiom yet. A warning is emitted if the "use warnings" pragma or the -w command-line flag (that is, the $^W variable) was set. "RE" in "m?RE?", "/RE/", "m/RE/", "s/RE/foo/", Processing of "\Q", "\U", "\u", "\L", "\l", "\F", "\E", and inter- polation happens (almost) as with "qq//" constructs. Processing of "\N{...}" is also done here, and compiled into an in- termediate form for the regex compiler. (This is because, as men- tioned below, the regex compilation may be done at execution time, and "\N{...}" is a compile-time construct.) However any other combinations of "\" followed by a character are not substituted but only skipped, in order to parse them as regular expressions at the following step. As "\c" is skipped at this step, "@" of "\c@" in RE is possibly treated as an array symbol (for example @foo), even though the same text in "qq//" gives in- terpolation of "\c@". Code blocks such as "(?{BLOCK})" are handled by temporarily passing control back to the perl parser, in a similar way that an interpo- lated array subscript expression such as "foo$ar- ray[1+f("[xyz")]bar" would be. Moreover, inside "(?{BLOCK})", "(?# comment )", and a "#"-comment in a "/x"-regular expression, no processing is performed whatso- ever. This is the first step at which the presence of the "/x" modifier is relevant. Interpolation in patterns has several quirks: $|, $(, $), "@+" and "@-" are not interpolated, and constructs $var[SOMETHING] are voted (by several different estimators) to be either an array element or $var followed by an RE alternative. This is where the notation "${arr[$bar]}" comes handy: "/${arr[0-9]}/" is interpreted as array element -9, not as a regular expression from the variable $arr fol- lowed by a digit, which would be the interpretation of "/$arr[0-9]/". Since voting among different estimators may occur, the result is not predictable. The lack of processing of "\\" creates specific restrictions on the post-processed text. If the delimiter is "/", one cannot get the combination "\/" into the result of this step. "/" will finish the regular expression, "\/" will be stripped to "/" on the previous step, and "\\/" will be left as is. Because "/" is equivalent to "\/" inside a regular expression, this does not matter unless the delimiter happens to be character special to the RE engine, such as in "s*foo*bar*", "m[foo]", or "m?foo?"; or an alphanumeric char, as in: m m ^ a \s* b mmx; In the RE above, which is intentionally obfuscated for illustra- tion, the delimiter is "m", the modifier is "mx", and after delim- iter-removal the RE is the same as for "m/ ^ a \s* b /mx". There's more than one reason you're encouraged to restrict your delimiters to non-alphanumeric, non-whitespace choices. This step is the last one for all constructs except regular expres- sions, which are processed further. Parsing regular expressions Previous steps were performed during the compilation of Perl code, but this one happens at run time, although it may be optimized to be calcu- lated at compile time if appropriate. After preprocessing described above, and possibly after evaluation if concatenation, joining, casing translation, or metaquoting are involved, the resulting string is passed to the RE engine for compilation. Whatever happens in the RE engine might be better discussed in perlre, but for the sake of continuity, we shall do so here. This is another step where the presence of the "/x" modifier is rele- vant. The RE engine scans the string from left to right and converts it into a finite automaton. Backslashed characters are either replaced with corresponding literal strings (as with "\{"), or else they generate special nodes in the fi- nite automaton (as with "\b"). Characters special to the RE engine (such as "|") generate corresponding nodes or groups of nodes. "(?#...)" comments are ignored. All the rest is either converted to literal strings to match, or else is ignored (as is whitespace and "#"-style comments if "/x" is present). Parsing of the bracketed character class construct, "[...]", is rather different than the rule used for the rest of the pattern. The termina- tor of this construct is found using the same rules as for finding the terminator of a "{}"-delimited construct, the only exception being that "]" immediately following "[" is treated as though preceded by a back- slash. The terminator of runtime "(?{...})" is found by temporarily switching control to the perl parser, which should stop at the point where the logically balancing terminating "}" is found. It is possible to inspect both the string given to RE engine and the resulting finite automaton. See the arguments "debug"/"debugcolor" in the "use re" pragma, as well as Perl's -Dr command-line switch docu- mented in "Command Switches" in perlrun. Optimization of regular expressions This step is listed for completeness only. Since it does not change semantics, details of this step are not documented and are subject to change without notice. This step is performed over the finite automa- ton that was generated during the previous pass. It is at this stage that split() silently optimizes "/^/" to mean "/^/m". I/O Operators There are several I/O operators you should know about. A string enclosed by backticks (grave accents) first undergoes double-quote interpolation. It is then interpreted as an external command, and the out- put of that command is the value of the backtick string, like in a shell. In scalar context, a single string consisting of all output is returned. In list context, a list of values is returned, one per line of output. (You can set $/ to use a different line terminator.) The command is exe- cuted each time the pseudo-literal is evaluated. The status value of the command is returned in $? (see perlvar for the interpretation of $?). Un- like in csh, no translation is done on the return data--newlines remain newlines. Unlike in any of the shells, single quotes do not hide variable names in the command from interpretation. To pass a literal dollar-sign through to the shell you need to hide it with a backslash. The generalized form of backticks is "qx//", or you can call the "readpipe" in perlfunc function. (Because backticks always undergo shell expansion as well, see perlsec for security concerns.) In scalar context, evaluating a filehandle in angle brackets yields the next line from that file (the newline, if any, included), or "undef" at end-of-file or on error. When $/ is set to "undef" (sometimes known as file-slurp mode) and the file is empty, it returns '' the first time, fol- lowed by "undef" subsequently. 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 "while" state- ment (even if disguised as a for(;;) loop), the value is automatically as- signed to the global variable $_, 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 lo- calized. You'll have to put a "local $_;" before the loop if you want that to happen. Furthermore, if the input symbol or an explicit assignment of the input symbol to a scalar is used as a "while"/"for" condition, then the condition actually tests for definedness of the expression's value, not for its regular truth value. Thus the following lines are equivalent: while (defined($_ = <STDIN>)) { print; } while ($_ = <STDIN>) { print; } while (<STDIN>) { print; } for (;<STDIN>;) { print; } print while defined($_ = <STDIN>); print while ($_ = <STDIN>); print while <STDIN>; This also behaves similarly, but assigns to a lexical variable instead of to $_: while (my $line = <STDIN>) { print $line } In these loop constructs, the assigned value (whether assignment is auto- matic or explicit) is then tested to see whether it is defined. The de- fined test avoids problems where the line has a string value that would be treated as false by Perl; for example a "" or a "0" with no trailing new- line. If you really mean for such values to terminate the loop, they should be tested for explicitly: while (($_ = <STDIN>) ne '0') { ... } while (<STDIN>) { last unless $_; ... } In other boolean contexts, "<FILEHANDLE>" without an explicit "defined" test or comparison elicits a warning if the "use warnings" pragma or the -w command-line switch (the $^W variable) is in effect. The filehandles STDIN, STDOUT, and STDERR are predefined. (The filehandles "stdin", "stdout", and "stderr" will also work except in packages, where they would be interpreted as local identifiers rather than global.) Addi- tional filehandles may be created with the open() function, amongst others. See perlopentut and "open" in perlfunc for details on this. If a "<FILEHANDLE>" is used in a context that is looking for a list, a list comprising all input lines is returned, one line per list element. It's easy to grow to a rather large data space this way, so use with care. "<FILEHANDLE>" may also be spelled readline(*FILEHANDLE). See "readline" in perlfunc. The null filehandle "<>" (sometimes called the diamond operator) is spe- cial: it can be used to emulate the behavior of sed and awk, and any other Unix filter program that takes a list of filenames, doing the same to each line of input from all of them. Input from "<>" comes either from 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, $ARGV[0] is set to "-", which when opened gives you standard input. The @ARGV array is then processed as a list of filenames. The loop while (<>) { ... # code for each line } is equivalent to the following Perl-like pseudo code: unshift(@ARGV, '-') unless @ARGV; while ($ARGV = shift) { open(ARGV, $ARGV); while (<ARGV>) { ... # code for each line } } except that it isn't so cumbersome to say, and will actually work. It re- ally does shift the @ARGV array and put the current filename into the $ARGV variable. It also uses filehandle ARGV internally. "<>" is just a synonym for "<ARGV>", which is magical. (The pseudo code above doesn't work be- cause it treats "<ARGV>" as non-magical.) Since the null filehandle uses the two argument form of "open" in perlfunc it interprets special characters, so if you have a script like this: while (<>) { print; } and call it with "perl dangerous.pl 'rm -rfv *|'", it actually opens a pipe, executes the "rm" command and reads "rm"'s output from that pipe. If you want all items in @ARGV to be interpreted as file names, you can use the module "ARGV::readonly" from CPAN, or use the double diamond operator: while (<<>>) { print; } Using double angle brackets inside of a while causes the open to use the three argument form (with the second argument being "<"), so all arguments in "ARGV" are treated as literal filenames (including "-"). (Note that for convenience, if you use "<<>>" and if @ARGV is empty, it will still read from the standard input.) You can modify @ARGV before the first "<>" as long as the array ends up containing the list of filenames you really want. Line numbers ($.) con- tinue as though the input were one big happy file. See the example in "eof" in perlfunc 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: @ARGV = grep { -f && -T } glob('*') unless @ARGV; You can even set them to pipe commands. For example, this automatically filters compressed arguments through gzip: @ARGV = map { /\.(gz|Z)$/ ? "gzip -dc < $_ |" : $_ } @ARGV; If you want to pass switches into your script, you can use one of the "Getopts" modules or put a loop on the front like this: while ($_ = $ARGV[0], /^-/) { shift; last if /^--$/; if (/^-D(.*)/) { $debug = $1 } if (/^-v/) { $verbose++ } # ... # other switches } while (<>) { # ... # code for each line } The "<>" symbol will return "undef" for end-of-file only once. If you call it again after this, it will assume you are processing another @ARGV list, and if you haven't set @ARGV, will read input from STDIN. If what the angle brackets contain is a simple scalar variable (for exam- ple, $foo), then that variable contains the name of the filehandle to input from, or its typeglob, or a reference to the same. For example: $fh = \*STDIN; $line = <$fh>; If what's within the angle brackets is neither a filehandle nor a simple scalar variable containing a filehandle name, typeglob, or typeglob refer- ence, 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 "<$x>" is always a readline() from an indirect handle, but "<$hash{key}>" is always a glob(). That's because $x is a simple scalar variable, but $hash{key} is not--it's a hash element. Even "<$x >" (note the extra space) is treated as "glob("$x ")", not readline($x). One level of double-quote interpretation is done first, but you can't say "<$foo>" because that's an indirect filehandle as explained in the previous paragraph. (In older versions of Perl, programmers would insert curly brackets to force interpretation as a filename glob: "<${foo}>". These days, it's considered cleaner to call the internal function directly as glob($foo), which is probably the right way to have done it in the first place.) For example: while (<*.c>) { chmod 0644, $_; } is roughly equivalent to: open(FOO, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|"); while (<FOO>) { chomp; chmod 0644, $_; } except that the globbing is actually done internally using the standard "File::Glob" extension. Of course, the shortest way to do the above is: chmod 0644, <*.c>; A (file)glob evaluates its (embedded) argument only when it is starting a new list. All values must be read before it will start over. In list con- text, this isn't important because you automatically get them all anyway. However, in scalar context the operator returns the next value each time it's called, or "undef" when the list has run out. As with filehandle reads, an automatic "defined" is generated when the glob occurs in the test part of a "while", because legal glob returns (for example, a file called 0) would otherwise terminate the loop. Again, "undef" is returned only once. So if you're expecting a single value from a glob, it is much better to say ($file) = <blurch*>; than $file = <blurch*>; because the latter will alternate between returning a filename and return- ing false. If you're trying to do variable interpolation, it's definitely better to use the glob() function, because the older notation can cause people to be- come confused with the indirect filehandle notation. @files = glob("$dir/*.[ch]"); @files = glob($files[$i]); If an angle-bracket-based globbing expression is used as the condition of a "while" or "for" loop, then it will be implicitly assigned to $_. If ei- ther a globbing expression or an explicit assignment of a globbing expres- sion to a scalar is used as a "while"/"for" condition, then the condition actually tests for definedness of the expression's value, not for its regu- lar truth value. Constant Folding Like C, Perl does a certain amount of expression evaluation at compile time whenever it determines that all arguments to an operator are static and have no side effects. In particular, string concatenation happens at com- pile time between literals that don't do variable substitution. Backslash interpolation also happens at compile time. You can say 'Now is the time for all' . "\n" . 'good men to come to.' and this all reduces to one string internally. Likewise, if you say foreach $file (@filenames) { if (-s $file > 5 + 100 * 2**16) { } } the compiler precomputes the number which that expression represents so that the interpreter won't have to. No-ops Perl doesn't officially have a no-op operator, but the bare constants 0 and 1 are special-cased not to produce a warning in void context, so you can for example safely do 1 while foo(); Bitwise String Operators Bitstrings of any size may be manipulated by the bitwise operators ("~ | & ^"). If the operands to a binary bitwise op are strings of different sizes, | and ^ ops act as though the shorter operand had additional zero bits on the right, while the & op acts as though the longer operand was truncated to the length of the shorter. The granularity for such extension or trunca- tion is one or more bytes. # ASCII-based examples print "j p \n" ^ " a h"; # prints "JAPH\n" print "JA" | " ph\n"; # prints "japh\n" print "japh\nJunk" & '_____'; # prints "JAPH\n"; print 'p N$' ^ " E<H\n"; # prints "Perl\n"; If you are intending to manipulate bitstrings, be certain that you're sup- plying bitstrings: If an operand is a number, that will imply a numeric bitwise operation. You may explicitly show which type of operation you in- tend by using "" or "0+", as in the examples below. $foo = 150 | 105; # yields 255 (0x96 | 0x69 is 0xFF) $foo = '150' | 105; # yields 255 $foo = 150 | '105'; # yields 255 $foo = '150' | '105'; # yields string '155' (under ASCII) $baz = 0+$foo & 0+$bar; # both ops explicitly numeric $biz = "$foo" ^ "$bar"; # both ops explicitly stringy This somewhat unpredictable behavior can be avoided with the "bitwise" fea- ture, new in Perl 5.22. You can enable it via use feature 'bitwise' or "use v5.28". Before Perl 5.28, it used to emit a warning in the "experi- mental::bitwise" category. Under this feature, the four standard bitwise operators ("~ | & ^") are always numeric. Adding a dot after each operator ("~. |. &. ^.") 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 ("&= |= ^= &.= |.= ^.=") 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 "Byte and Character Semantics" in perlunicode. See "vec" in perlfunc for information on how to manipulate individual bits in a bit vector. Integer Arithmetic By default, Perl assumes that it must do most of its arithmetic in floating point. But by saying use integer; you may tell the compiler to use integer operations (see integer for a de- tailed explanation) from here to the end of the enclosing BLOCK. An inner BLOCK may countermand this by saying no integer; 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 "use integer", if you take the sqrt(2), you'll still get 1.4142135623731 or so. Used on numbers, the bitwise operators ("&" "|" "^" "~" "<<" ">>") always produce integral results. (But see also "Bitwise String Operators".) How- ever, "use integer" still has meaning for them. By default, their results are interpreted as unsigned integers, but if "use integer" is in effect, their results are interpreted as signed integers. For example, "~0" usu- ally evaluates to a large integral value. However, "use integer; ~0" is -1 on two's-complement machines. Floating-point Arithmetic While "use integer" provides integer-only arithmetic, there is no analogous mechanism to provide automatic rounding or truncation to a certain number of decimal places. For rounding to a certain number of digits, sprintf() or printf() is usually the easiest route. See perlfaq4. Floating-point numbers are only approximations to what a mathematician would call real numbers. There are infinitely more reals than floats, so some corners must be cut. For example: printf "%.20g\n", 123456789123456789; # produces 123456789123456784 Testing for exact floating-point equality or inequality is not a good idea. Here's a (relatively expensive) work-around to compare whether two float- ing-point numbers are equal to a particular number of decimal places. See Knuth, volume II, for a more robust treatment of this topic. sub fp_equal { my ($X, $Y, $POINTS) = @_; my ($tX, $tY); $tX = sprintf("%.${POINTS}g", $X); $tY = sprintf("%.${POINTS}g", $Y); return $tX eq $tY; } 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) defines mathematical functions that work on both the reals and the imaginary num- bers. "Math::Complex" is not as efficient as POSIX, but POSIX can't work with complex numbers. Rounding in financial applications can have serious implications, and the rounding method used should be specified precisely. In these cases, it probably pays not to trust whichever system rounding is being used by Perl, but to instead implement the rounding function you need yourself. Bigger Numbers The standard "Math::BigInt", "Math::BigRat", and "Math::BigFloat" modules, along with the "bignum", "bigint", and "bigrat" pragmas, provide vari- able-precision arithmetic and overloaded operators, although they're cur- rently pretty slow. At the cost of some space and considerable speed, they avoid the normal pitfalls associated with limited-precision representa- tions. use 5.010; use bigint; # easy interface to Math::BigInt $x = 123456789123456789; say $x * $x; +15241578780673678515622620750190521 Or with rationals: 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::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::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. C-style Logical Or This section has been superceded by "C-style Logical Or, Xor, and Defined Or". The heading is retained only to prevent breaking any pre-existing links to it from outside. C-style Logical Xor This section has been superceded by "C-style Logical Or, Xor, and Defined Or". The heading is retained only to prevent breaking any pre-existing links to it from outside. Logical Defined-Or This section has been superceded by "C-style Logical Or, Xor, and Defined Or". The heading is retained only to prevent breaking any pre-existing links to it from outside. Quote-Like Operators This section has been replaced by "Simpler Quote-Like Operators" Indented Here-docs This section has been merged into "Here-docs" APPENDIX List of Extra Paired Delimiters The complete list of accepted paired delimiters as of Unicode 16.0 is: ( ) U+0028, U+0029 LEFT/RIGHT PARENTHESIS < > U+003C, U+003E LESS-THAN/GREATER-THAN SIGN [ ] U+005B, U+005D LEFT/RIGHT SQUARE BRACKET { } U+007B, U+007D LEFT/RIGHT CURLY BRACKET A<< A>> U+00AB, U+00BB LEFT/RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK A>> A<< U+00BB, U+00AB RIGHT/LEFT-POINTING DOUBLE ANGLE QUOTATION MARK a1/4o a1/4>> U+0F3A, U+0F3B TIBETAN MARK GUG RTAGS GYON, TIBETAN MARK GUG RTAGS GYAS a1/41/4 a1/41/2 U+0F3C, U+0F3D TIBETAN MARK ANG KHANG GYON, TIBETAN MARK ANG KHANG GYAS a a U+169B, U+169C OGHAM FEATHER MARK, OGHAM REVERSED FEATHER MARK a a U+2018, U+2019 LEFT/RIGHT SINGLE QUOTATION MARK a a U+2019, U+2018 RIGHT/LEFT SINGLE QUOTATION MARK a a U+201C, U+201D LEFT/RIGHT DOUBLE QUOTATION MARK a a U+201D, U+201C RIGHT/LEFT DOUBLE QUOTATION MARK a<micro> a^2 U+2035, U+2032 REVERSED PRIME, PRIME a<paragraph> a^3 U+2036, U+2033 REVERSED DOUBLE PRIME, DOUBLE PRIME a. a' U+2037, U+2034 REVERSED TRIPLE PRIME, TRIPLE PRIME a^1 ao U+2039, U+203A SINGLE LEFT/RIGHT-POINTING ANGLE QUOTATION MARK ao a^1 U+203A, U+2039 SINGLE RIGHT/LEFT-POINTING ANGLE QUOTATION MARK a a U+2045, U+2046 LEFT/RIGHT SQUARE BRACKET WITH QUILL a a U+204D, U+204C BLACK RIGHT/LEFTWARDS BULLET a1/2 a3/4 U+207D, U+207E SUPERSCRIPT LEFT/RIGHT PARENTHESIS a a U+208D, U+208E SUBSCRIPT LEFT/RIGHT PARENTHESIS a a U+2192, U+2190 RIGHT/LEFTWARDS ARROW a a U+219B, U+219A RIGHT/LEFTWARDS ARROW WITH STROKE a a U+219D, U+219C RIGHT/LEFTWARDS WAVE ARROW a a U+21A0, U+219E RIGHT/LEFTWARDS TWO HEADED ARROW aL ac U+21A3, U+21A2 RIGHT/LEFTWARDS ARROW WITH TAIL a| ax U+21A6, U+21A4 RIGHT/LEFTWARDS ARROW FROM BAR aa a(C) U+21AA, U+21A9 RIGHT/LEFTWARDS ARROW WITH HOOK a~ a<< U+21AC, U+21AB RIGHT/LEFTWARDS ARROW WITH LOOP a+/- a<degree> U+21B1, U+21B0 UPWARDS ARROW WITH TIP RIGHT/LEFTWARDS a^3 a^2 U+21B3, U+21B2 DOWNWARDS ARROW WITH TIP RIGHT/LEFTWARDS a a1/4 U+21C0, U+21BC RIGHT/LEFTWARDS HARPOON WITH BARB UPWARDS a a1/2 U+21C1, U+21BD RIGHT/LEFTWARDS HARPOON WITH BARB DOWNWARDS a a U+21C9, U+21C7 RIGHT/LEFTWARDS PAIRED ARROWS a a U+21CF, U+21CD RIGHT/LEFTWARDS DOUBLE ARROW WITH STROKE a a U+21D2, U+21D0 RIGHT/LEFTWARDS DOUBLE ARROW a a U+21DB, U+21DA RIGHT/LEFTWARDS TRIPLE ARROW a a U+21DD, U+21DC RIGHT/LEFTWARDS SQUIGGLE ARROW ac a U+21E2, U+21E0 RIGHT/LEFTWARDS DASHED ARROW aY ax U+21E5, U+21E4 RIGHT/LEFTWARDS ARROW TO BAR a" a| U+21E8, U+21E6 RIGHT/LEFTWARDS WHITE ARROW a' a~<degree> U+21F4, U+2B30 RIGHT/LEFT ARROW WITH SMALL CIRCLE a<paragraph> a~+/- U+21F6, U+2B31 THREE RIGHT/LEFTWARDS ARROWS a, a. U+21F8, U+21F7 RIGHT/LEFTWARDS ARROW WITH VERTICAL STROKE a>> ao U+21FB, U+21FA RIGHT/LEFTWARDS ARROW WITH DOUBLE VERTICAL STROKE a3/4 a1/2 U+21FE, U+21FD RIGHT/LEFTWARDS OPEN-HEADED ARROW a a U+2208, U+220B ELEMENT OF, CONTAINS AS MEMBER a a U+2209, U+220C NOT AN ELEMENT OF, DOES NOT CONTAIN AS MEMBER a a U+220A, U+220D SMALL ELEMENT OF, SMALL CONTAINS AS MEMBER ax aY U+2264, U+2265 LESS-THAN/GREATER-THAN OR EQUAL TO a| a<section> U+2266, U+2267 LESS-THAN/GREATER-THAN OVER EQUAL TO a" a(C) U+2268, U+2269 LESS-THAN/GREATER-THAN BUT NOT EQUAL TO aa a<<_ U+226A, U+226B MUCH LESS-THAN/GREATER-THAN a(R) a U+226E, U+226F NOT LESS-THAN/GREATER-THAN a<degree> a+/- U+2270, U+2271 NEITHER LESS-THAN/GREATER-THAN NOR EQUAL TO a^2 a^3 U+2272, U+2273 LESS-THAN/GREATER-THAN OR EQUIVALENT TO a' a<micro> U+2274, U+2275 NEITHER LESS-THAN/GREATER-THAN NOR EQUIVALENT TO ao a>> U+227A, U+227B PRECEDES/SUCCEEDS a1/4 a1/2 U+227C, U+227D PRECEDES/SUCCEEDS OR EQUAL TO a3/4 a? U+227E, U+227F PRECEDES/SUCCEEDS OR EQUIVALENT TO a a U+2280, U+2281 DOES NOT PRECEDE/SUCCEED a a U+2282, U+2283 SUBSET/SUPERSET OF a a U+2284, U+2285 NOT A SUBSET/SUPERSET OF a a U+2286, U+2287 SUBSET/SUPERSET OF OR EQUAL TO a a U+2288, U+2289 NEITHER A SUBSET/SUPERSET OF NOR EQUAL TO a a U+228A, U+228B SUBSET/SUPERSET OF WITH NOT EQUAL TO aL ac U+22A3, U+22A2 LEFT/RIGHT TACK a| a<< U+22A6, U+2ADE ASSERTION, SHORT LEFT TACK a" a<<x U+22A8, U+2AE4 TRUE, VERTICAL BAR DOUBLE LEFT TURNSTILE a(C) a<<L U+22A9, U+2AE3 FORCES, DOUBLE VERTICAL BAR LEFT TURNSTILE a<degree> a+/- U+22B0, U+22B1 PRECEDES/SUCCEEDS UNDER RELATION a a U+22D0, U+22D1 DOUBLE SUBSET/SUPERSET a a U+22D6, U+22D7 LESS-THAN/GREATER-THAN WITH DOT a a U+22D8, U+22D9 VERY MUCH LESS-THAN/GREATER-THAN a a U+22DC, U+22DD EQUAL TO OR LESS-THAN/GREATER-THAN a a U+22DE, U+22DF EQUAL TO OR PRECEDES/SUCCEEDS a a! U+22E0, U+22E1 DOES NOT PRECEDE/SUCCEED OR EQUAL a| a<section> U+22E6, U+22E7 LESS-THAN/GREATER-THAN BUT NOT EQUIVALENT TO a" a(C) U+22E8, U+22E9 PRECEDES/SUCCEEDS BUT NOT EQUIVALENT TO a^2 ao U+22F2, U+22FA ELEMENT OF/CONTAINS WITH LONG HORIZONTAL STROKE a^3 a>> U+22F3, U+22FB ELEMENT OF/CONTAINS WITH VERTICAL BAR AT END OF HORIZONTAL STROKE a' a1/4 U+22F4, U+22FC SMALL ELEMENT OF/CONTAINS WITH VERTICAL BAR AT END OF HORIZONTAL STROKE a<paragraph> a1/2 U+22F6, U+22FD ELEMENT OF/CONTAINS WITH OVERBAR a. a3/4 U+22F7, U+22FE SMALL ELEMENT OF/CONTAINS WITH OVERBAR a a U+2308, U+2309 LEFT/RIGHT CEILING a a U+230A, U+230B LEFT/RIGHT FLOOR a| a<< U+2326, U+232B ERASE TO THE RIGHT/LEFT a(C) aa U+2329, U+232A LEFT/RIGHT-POINTING ANGLE BRACKET a a U+2348, U+2347 APL FUNCTIONAL SYMBOL QUAD RIGHT/LEFTWARDS ARROW a(C) aa U+23E9, U+23EA BLACK RIGHT/LEFT-POINTING DOUBLE TRIANGLE a a(R) U+23ED, U+23EE BLACK RIGHT/LEFT-POINTING DOUBLE TRIANGLE WITH VERTICAL BAR a a U+261B, U+261A BLACK RIGHT/LEFT POINTING INDEX a a U+261E, U+261C WHITE RIGHT/LEFT POINTING INDEX a a U+269E, U+269F THREE LINES CONVERGING RIGHT/LEFT a" a(C) U+2768, U+2769 MEDIUM LEFT/RIGHT PARENTHESIS ORNAMENT aa a<< U+276A, U+276B MEDIUM FLATTENED LEFT/RIGHT PARENTHESIS ORNAMENT a~ a U+276C, U+276D MEDIUM LEFT/RIGHT-POINTING ANGLE BRACKET _ ORNAMENT a(R) a U+276E, U+276F HEAVY LEFT/RIGHT-POINTING ANGLE QUOTATION MARK ORNAMENT a<degree> a+/- U+2770, U+2771 HEAVY LEFT/RIGHT-POINTING ANGLE BRACKET ORNAMENT a^2 a^3 U+2772, U+2773 LIGHT LEFT/RIGHT TORTOISE SHELL BRACKET ORNAMENT a' a<micro> U+2774, U+2775 MEDIUM LEFT/RIGHT CURLY BRACKET ORNAMENT a a U+27C3, U+27C4 OPEN SUBSET/SUPERSET a a U+27C5, U+27C6 LEFT/RIGHT S-SHAPED BAG DELIMITER a a U+27C8, U+27C9 REVERSE SOLIDUS PRECEDING SUBSET, SUPERSET PRECEDING SOLIDUS a a U+27DE, U+27DD LONG LEFT/RIGHT TACK a| a<section> U+27E6, U+27E7 MATHEMATICAL LEFT/RIGHT WHITE SQUARE BRACKET a" a(C) U+27E8, U+27E9 MATHEMATICAL LEFT/RIGHT ANGLE BRACKET aa a<< U+27EA, U+27EB MATHEMATICAL LEFT/RIGHT DOUBLE ANGLE BRACKET a~ a U+27EC, U+27ED MATHEMATICAL LEFT/RIGHT WHITE TORTOISE SHELL _ BRACKET a(R) a U+27EE, U+27EF MATHEMATICAL LEFT/RIGHT FLATTENED PARENTHESIS a' a~^2 U+27F4, U+2B32 RIGHT/LEFT ARROW WITH CIRCLED PLUS a<paragraph> a<micro> U+27F6, U+27F5 LONG RIGHT/LEFTWARDS ARROW a^1 a, U+27F9, U+27F8 LONG RIGHT/LEFTWARDS DOUBLE ARROW a1/4 a>> U+27FC, U+27FB LONG RIGHT/LEFTWARDS ARROW FROM BAR a3/4 a1/2 U+27FE, U+27FD LONG RIGHT/LEFTWARDS DOUBLE ARROW FROM BAR a? a~^3 U+27FF, U+2B33 LONG RIGHT/LEFTWARDS SQUIGGLE ARROW ax a~' U+2900, U+2B34 RIGHT/LEFTWARDS TWO-HEADED ARROW WITH VERTICAL STROKE ax a~<micro> U+2901, U+2B35 RIGHT/LEFTWARDS TWO-HEADED ARROW WITH DOUBLE VERTICAL STROKE ax ax U+2903, U+2902 RIGHT/LEFTWARDS DOUBLE ARROW WITH VERTICAL STROKE ax a~<paragraph> U+2905, U+2B36 RIGHT/LEFTWARDS TWO-HEADED ARROW FROM BAR ax ax U+2907, U+2906 RIGHT/LEFTWARDS DOUBLE ARROW FROM BAR ax ax U+290D, U+290C RIGHT/LEFTWARDS DOUBLE DASH ARROW ax ax U+290F, U+290E RIGHT/LEFTWARDS TRIPLE DASH ARROW ax a~. U+2910, U+2B37 RIGHT/LEFTWARDS TWO-HEADED TRIPLE DASH ARROW ax a~, U+2911, U+2B38 RIGHT/LEFTWARDS ARROW WITH DOTTED STEM ax a~^1 U+2914, U+2B39 RIGHT/LEFTWARDS ARROW WITH TAIL WITH VERTICAL STROKE ax a~o U+2915, U+2B3A RIGHT/LEFTWARDS ARROW WITH TAIL WITH DOUBLE VERTICAL STROKE ax a~>> U+2916, U+2B3B RIGHT/LEFTWARDS TWO-HEADED ARROW WITH TAIL ax a~1/4 U+2917, U+2B3C RIGHT/LEFTWARDS TWO-HEADED ARROW WITH TAIL WITH VERTICAL STROKE ax a~1/2 U+2918, U+2B3D RIGHT/LEFTWARDS TWO-HEADED ARROW WITH TAIL WITH DOUBLE VERTICAL STROKE ax ax U+291A, U+2919 RIGHT/LEFTWARDS ARROW-TAIL ax ax U+291C, U+291B RIGHT/LEFTWARDS DOUBLE ARROW-TAIL ax ax U+291E, U+291D RIGHT/LEFTWARDS ARROW TO BLACK DIAMOND ax ax U+2920, U+291F RIGHT/LEFTWARDS ARROW FROM BAR TO BLACK DIAMOND ax^3 a~? U+2933, U+2B3F WAVE ARROW POINTING DIRECTLY RIGHT/LEFT ax. ax<paragraph> U+2937, U+2936 ARROW POINTING DOWNWARDS THEN CURVING RIGHT/ LEFTWARDS aY aY U+2945, U+2946 RIGHT/LEFTWARDS ARROW WITH PLUS BELOW aY a~3/4 U+2947, U+2B3E RIGHT/LEFTWARDS ARROW THROUGH X aY aY U+2953, U+2952 RIGHT/LEFTWARDS HARPOON WITH BARB UP TO BAR aY aY U+2957, U+2956 RIGHT/LEFTWARDS HARPOON WITH BARB DOWN TO BAR aY aY U+295B, U+295A RIGHT/LEFTWARDS HARPOON WITH BARB UP FROM BAR aY aY U+295F, U+295E RIGHT/LEFTWARDS HARPOON WITH BARB DOWN FROM BAR aYx aYc U+2964, U+2962 RIGHT/LEFTWARDS HARPOON WITH BARB UP ABOVE RIGHT/LEFTWARDS HARPOON WITH BARB DOWN aY~ aYa U+296C, U+296A RIGHT/LEFTWARDS HARPOON WITH BARB UP ABOVE LONG DASH aY aY<< U+296D, U+296B RIGHT/LEFTWARDS HARPOON WITH BARB DOWN BELOW LONG DASH aY+/- a U+2971, U+2B40 EQUALS SIGN ABOVE RIGHT/LEFTWARDS ARROW aY^2 a U+2972, U+2B41 TILDE OPERATOR ABOVE RIGHTWARDS ARROW, REVERSE TILDE OPERATOR ABOVE LEFTWARDS ARROW aY' a U+2974, U+2B4B RIGHTWARDS ARROW ABOVE TILDE OPERATOR, LEFTWARDS ARROW ABOVE REVERSE TILDE OPERATOR aY<micro> a U+2975, U+2B42 RIGHTWARDS ARROW ABOVE ALMOST EQUAL TO, LEFTWARDS ARROW ABOVE REVERSE ALMOST EQUAL TO aY^1 aY>> U+2979, U+297B SUBSET/SUPERSET ABOVE RIGHT/LEFTWARDS ARROW a| a| U+2983, U+2984 LEFT/RIGHT WHITE CURLY BRACKET a| a| U+2985, U+2986 LEFT/RIGHT WHITE PARENTHESIS a| a| U+2987, U+2988 Z NOTATION LEFT/RIGHT IMAGE BRACKET a| a| U+2989, U+298A Z NOTATION LEFT/RIGHT BINDING BRACKET a| a| U+298B, U+298C LEFT/RIGHT SQUARE BRACKET WITH UNDERBAR a| a| U+298D, U+2990 LEFT/RIGHT SQUARE BRACKET WITH TICK IN TOP CORNER a| a| U+298F, U+298E LEFT/RIGHT SQUARE BRACKET WITH TICK IN BOTTOM CORNER a| a| U+2991, U+2992 LEFT/RIGHT ANGLE BRACKET WITH DOT a| a| U+2993, U+2994 LEFT/RIGHT ARC LESS-THAN/GREATER-THAN BRACKET a| a| U+2995, U+2996 DOUBLE LEFT/RIGHT ARC GREATER-THAN/LESS-THAN BRACKET a| a| U+2997, U+2998 LEFT/RIGHT BLACK TORTOISE SHELL BRACKET a|" a|(C) U+29A8, U+29A9 MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING UP AND RIGHT/LEFT a|a a|<< U+29AA, U+29AB MEASURED ANGLE WITH OPEN ARM ENDING IN ARROW POINTING DOWN AND RIGHT/LEFT a|^3 a|' U+29B3, U+29B4 EMPTY SET WITH RIGHT/LEFT ARROW ABOVE a<section> a<section> U+29C0, U+29C1 CIRCLED LESS-THAN/GREATER-THAN a<section> a<section> U+29D8, U+29D9 LEFT/RIGHT WIGGLY FENCE a<section> a<section> U+29DA, U+29DB LEFT/RIGHT DOUBLE WIGGLY FENCE a<section>1/4 a<section>1/2 U+29FC, U+29FD LEFT/RIGHT-POINTING CURVED ANGLE BRACKET a(C)^1 a(C)o U+2A79, U+2A7A LESS-THAN/GREATER-THAN WITH CIRCLE INSIDE a(C)>> a(C)1/4 U+2A7B, U+2A7C LESS-THAN/GREATER-THAN WITH QUESTION MARK ABOVE a(C)1/2 a(C)3/4 U+2A7D, U+2A7E LESS-THAN/GREATER-THAN OR SLANTED EQUAL TO a(C)? aa U+2A7F, U+2A80 LESS-THAN/GREATER-THAN OR SLANTED EQUAL TO WITH DOT INSIDE aa aa U+2A81, U+2A82 LESS-THAN/GREATER-THAN OR SLANTED EQUAL TO WITH DOT ABOVE aa aa U+2A83, U+2A84 LESS-THAN/GREATER-THAN OR SLANTED EQUAL TO WITH DOT ABOVE RIGHT/LEFT aa aa U+2A85, U+2A86 LESS-THAN/GREATER-THAN OR APPROXIMATE aa aa U+2A87, U+2A88 LESS-THAN/GREATER-THAN AND SINGLE-LINE NOT EQUAL TO aa aa U+2A89, U+2A8A LESS-THAN/GREATER-THAN AND NOT APPROXIMATE aa aa U+2A8D, U+2A8E LESS-THAN/GREATER-THAN ABOVE SIMILAR OR EQUAL aa aa U+2A95, U+2A96 SLANTED EQUAL TO OR LESS-THAN/GREATER-THAN aa aa U+2A97, U+2A98 SLANTED EQUAL TO OR LESS-THAN/GREATER-THAN WITH DOT INSIDE aa aa U+2A99, U+2A9A DOUBLE-LINE EQUAL TO OR LESS-THAN/GREATER-THAN aa aa U+2A9B, U+2A9C DOUBLE-LINE SLANTED EQUAL TO OR LESS-THAN/ GREATER-THAN aa aa U+2A9D, U+2A9E SIMILAR OR LESS-THAN/GREATER-THAN aa aa U+2A9F, U+2AA0 SIMILAR ABOVE LESS-THAN/GREATER-THAN ABOVE EQUALS SIGN aa! aac U+2AA1, U+2AA2 DOUBLE NESTED LESS-THAN/GREATER-THAN aa| aa<section> U+2AA6, U+2AA7 LESS-THAN/GREATER-THAN CLOSED BY CURVE aa" aa(C) U+2AA8, U+2AA9 LESS-THAN/GREATER-THAN CLOSED BY CURVE ABOVE SLANTED EQUAL aaa aa<< U+2AAA, U+2AAB SMALLER THAN/LARGER THAN aa_ aa U+2AAC, U+2AAD SMALLER THAN/LARGER THAN OR EQUAL TO aa aa<degree> U+2AAF, U+2AB0 PRECEDES/SUCCEEDS ABOVE SINGLE-LINE EQUALS SIGN aa+/- aa^2 U+2AB1, U+2AB2 PRECEDES/SUCCEEDS ABOVE SINGLE-LINE NOT EQUAL TO aa^3 aa' U+2AB3, U+2AB4 PRECEDES/SUCCEEDS ABOVE EQUALS SIGN aa<micro> aa<paragraph> U+2AB5, U+2AB6 PRECEDES/SUCCEEDS ABOVE NOT EQUAL TO aa. aa, U+2AB7, U+2AB8 PRECEDES/SUCCEEDS ABOVE ALMOST EQUAL TO aa^1 aao U+2AB9, U+2ABA PRECEDES/SUCCEEDS ABOVE NOT ALMOST EQUAL TO aa>> aa1/4 U+2ABB, U+2ABC DOUBLE PRECEDES/SUCCEEDS aa1/2 aa3/4 U+2ABD, U+2ABE SUBSET/SUPERSET WITH DOT aa? a<< U+2ABF, U+2AC0 SUBSET/SUPERSET WITH PLUS SIGN BELOW a<< a<< U+2AC1, U+2AC2 SUBSET/SUPERSET WITH MULTIPLICATION SIGN BELOW a<< a<< U+2AC3, U+2AC4 SUBSET/SUPERSET OF OR EQUAL TO WITH DOT ABOVE a<< a<< U+2AC5, U+2AC6 SUBSET/SUPERSET OF ABOVE EQUALS SIGN a<< a<< U+2AC7, U+2AC8 SUBSET/SUPERSET OF ABOVE TILDE OPERATOR a<< a<< U+2AC9, U+2ACA SUBSET/SUPERSET OF ABOVE ALMOST EQUAL TO a<< a<< U+2ACB, U+2ACC SUBSET/SUPERSET OF ABOVE NOT EQUAL TO a<< a<< U+2ACF, U+2AD0 CLOSED SUBSET/SUPERSET a<< a<< U+2AD1, U+2AD2 CLOSED SUBSET/SUPERSET OR EQUAL TO a<< a<< U+2AD5, U+2AD6 SUBSET/SUPERSET ABOVE SUBSET/SUPERSET a<<Y a<< U+2AE5, U+22AB DOUBLE VERTICAL BAR DOUBLE LEFT/RIGHT TURNSTILE a<<. a<<, U+2AF7, U+2AF8 TRIPLE NESTED LESS-THAN/GREATER-THAN a<<^1 a<<o U+2AF9, U+2AFA DOUBLE-LINE SLANTED LESS-THAN/GREATER-THAN OR EQUAL TO a a U+2B46, U+2B45 RIGHT/LEFTWARDS QUADRUPLE ARROW a a U+2B47, U+2B49 REVERSE TILDE OPERATOR ABOVE RIGHTWARDS ARROW, TILDE OPERATOR ABOVE LEFTWARDS ARROW a a U+2B48, U+2B4A RIGHTWARDS ARROW ABOVE REVERSE ALMOST EQUAL TO, LEFTWARDS ARROW ABOVE ALMOST EQUAL TO a aY^3 U+2B4C, U+2973 RIGHTWARDS ARROW ABOVE REVERSE TILDE OPERATOR, LEFTWARDS ARROW ABOVE TILDE OPERATOR ac a U+2B62, U+2B60 RIGHT/LEFTWARDS TRIANGLE-HEADED ARROW a~ aa U+2B6C, U+2B6A RIGHT/LEFTWARDS TRIANGLE-HEADED DASHED ARROW a^2 a<degree> U+2B72, U+2B70 RIGHT/LEFTWARDS TRIANGLE-HEADED ARROW TO BAR a1/4 ao U+2B7C, U+2B7A RIGHT/LEFTWARDS TRIANGLE-HEADED ARROW WITH DOUBLE VERTICAL STROKE a(R) a(R) U+2B86, U+2B84 RIGHT/LEFTWARDS TRIANGLE-HEADED PAIRED ARROWS a(R) a(R) U+2B8A, U+2B88 RIGHT/LEFTWARDS BLACK CIRCLED WHITE ARROW a(R) a~ U+2B95, U+2B05 RIGHT/LEFTWARDS BLACK ARROW a(R) a(R) U+2B9A, U+2B98 THREE-D TOP-LIGHTED RIGHT/LEFTWARDS EQUILATERAL ARROWHEAD a(R) a(R) U+2B9E, U+2B9C BLACK RIGHT/LEFTWARDS EQUILATERAL ARROWHEAD a(R)! a(R) U+2BA1, U+2BA0 DOWNWARDS TRIANGLE-HEADED ARROW WITH LONG TIP RIGHT/LEFTWARDS a(R)L a(R)c U+2BA3, U+2BA2 UPWARDS TRIANGLE-HEADED ARROW WITH LONG TIP RIGHT/LEFTWARDS a(R)(C) a(R)" U+2BA9, U+2BA8 BLACK CURVED DOWNWARDS AND RIGHT/LEFTWARDS ARROW a(R)<< a(R)a U+2BAB, U+2BAA BLACK CURVED UPWARDS AND RIGHT/LEFTWARDS ARROW a(R)+/- a(R)<degree> U+2BB1, U+2BB0 RIBBON ARROW DOWN RIGHT/LEFT a_R)^3 _(R)^2 U+2BB3, U+2BB2 RIBBON ARROW UP RIGHT/LEFT a (R) a ~ U+2BEE, U+2BEC RIGHT/LEFTWARDS TWO-HEADED ARROW WITH TRIANGLE ARROWHEADS a, a, U+2E02, U+2E03 LEFT/RIGHT SUBSTITUTION BRACKET a, a, U+2E03, U+2E02 RIGHT/LEFT SUBSTITUTION BRACKET a, a, U+2E04, U+2E05 LEFT/RIGHT DOTTED SUBSTITUTION BRACKET a, a, U+2E05, U+2E04 RIGHT/LEFT DOTTED SUBSTITUTION BRACKET a, a, U+2E09, U+2E0A LEFT/RIGHT TRANSPOSITION BRACKET a, a, U+2E0A, U+2E09 RIGHT/LEFT TRANSPOSITION BRACKET a, a, U+2E0C, U+2E0D LEFT/RIGHT RAISED OMISSION BRACKET a, a, U+2E0D, U+2E0C RIGHT/LEFT RAISED OMISSION BRACKET a, a, U+2E11, U+2E10 REVERSED FORKED PARAGRAPHOS, FORKED PARAGRAPHOS a, a, U+2E1C, U+2E1D LEFT/RIGHT LOW PARAPHRASE BRACKET a, a, U+2E1D, U+2E1C RIGHT/LEFT LOW PARAPHRASE BRACKET a, a,! U+2E20, U+2E21 LEFT/RIGHT VERTICAL BAR WITH QUILL a,! a, U+2E21, U+2E20 RIGHT/LEFT VERTICAL BAR WITH QUILL a,c a,L U+2E22, U+2E23 TOP LEFT/RIGHT HALF BRACKET a,x a,Y U+2E24, U+2E25 BOTTOM LEFT/RIGHT HALF BRACKET a,| a,<section> U+2E26, U+2E27 LEFT/RIGHT SIDEWAYS U BRACKET a," a,(C) U+2E28, U+2E29 LEFT/RIGHT DOUBLE PARENTHESIS a,<paragraph> a,. U+2E36, U+2E37 DAGGER WITH LEFT/RIGHT GUARD a^1 a U+2E42, U+201E DOUBLE LOW-REVERSED-9 QUOTATION MARK, DOUBLE LOW-9 QUOTATION MARK a^1 a^1 U+2E55, U+2E56 LEFT/RIGHT SQUARE BRACKET WITH STROKE a^1 a^1 U+2E57, U+2E58 LEFT/RIGHT SQUARE BRACKET WITH DOUBLE STROKE a^1 a^1 U+2E59, U+2E5A TOP HALF LEFT/RIGHT PARENTHESIS a^1 a^1 U+2E5B, U+2E5C BOTTOM HALF LEFT/RIGHT PARENTHESIS a a U+3008, U+3009 LEFT/RIGHT ANGLE BRACKET a a U+300A, U+300B LEFT/RIGHT DOUBLE ANGLE BRACKET a a U+300C, U+300D LEFT/RIGHT CORNER BRACKET a a U+300E, U+300F LEFT/RIGHT WHITE CORNER BRACKET a a U+3010, U+3011 LEFT/RIGHT BLACK LENTICULAR BRACKET a a U+3014, U+3015 LEFT/RIGHT TORTOISE SHELL BRACKET a a U+3016, U+3017 LEFT/RIGHT WHITE LENTICULAR BRACKET a a U+3018, U+3019 LEFT/RIGHT WHITE TORTOISE SHELL BRACKET a a U+301A, U+301B LEFT/RIGHT WHITE SQUARE BRACKET a a U+301D, U+301E REVERSED DOUBLE PRIME QUOTATION MARK, DOUBLE PRIME QUOTATION MARK e<section> e<section> U+A9C1, U+A9C2 JAVANESE LEFT/RIGHT RERENGGAN i'3/4 i'? U+FD3E, U+FD3F ORNATE LEFT/RIGHT PARENTHESIS i^1 i^1 U+FE59, U+FE5A SMALL LEFT/RIGHT PARENTHESIS i^1 i^1 U+FE5B, U+FE5C SMALL LEFT/RIGHT CURLY BRACKET i^1 i^1 U+FE5D, U+FE5E SMALL LEFT/RIGHT TORTOISE SHELL BRACKET i^1x i^1Y U+FE64, U+FE65 SMALL LESS-THAN/GREATER-THAN SIGN i1/4 i1/4 U+FF08, U+FF09 FULLWIDTH LEFT/RIGHT PARENTHESIS i1/4 i1/4 U+FF1C, U+FF1E FULLWIDTH LESS-THAN/GREATER-THAN SIGN i1/4>> i1/41/2 U+FF3B, U+FF3D FULLWIDTH LEFT/RIGHT SQUARE BRACKET i1/2 i1/2 U+FF5B, U+FF5D FULLWIDTH LEFT/RIGHT CURLY BRACKET i1/2 i1/2 U+FF5F, U+FF60 FULLWIDTH LEFT/RIGHT WHITE PARENTHESIS i1/2c i1/2L U+FF62, U+FF63 HALFWIDTH LEFT/RIGHT CORNER BRACKET i?<< i?(C) U+FFEB, U+FFE9 HALFWIDTH RIGHT/LEFTWARDS ARROW dh dh U+1D103, U+1D102 MUSICAL SYMBOL REVERSE FINAL BARLINE, MUSICAL SYMBOL FINAL BARLINE dh dh U+1D106, U+1D107 MUSICAL SYMBOL LEFT/RIGHT REPEAT SIGN dh dh U+1F449, U+1F448 WHITE RIGHT/LEFT POINTING BACKHAND INDEX dh dh" U+1F508, U+1F568 SPEAKER, RIGHT SPEAKER dh dh(C) U+1F509, U+1F569 SPEAKER WITH ONE SOUND WAVE, RIGHT SPEAKER WITH ONE SOUND WAVE dh dha U+1F50A, U+1F56A SPEAKER WITH THREE SOUND WAVES, RIGHT SPEAKER WITH THREE SOUND WAVES dh>> dh1/2 U+1F57B, U+1F57D LEFT/RIGHT HAND TELEPHONE RECEIVER dh dh U+1F599, U+1F598 SIDEWAYS WHITE RIGHT/LEFT POINTING INDEX dh dh U+1F59B, U+1F59A SIDEWAYS BLACK RIGHT/LEFT POINTING INDEX dh dh U+1F59D, U+1F59C BLACK RIGHT/LEFT POINTING BACKHAND INDEX dh| dh<section> U+1F5E6, U+1F5E7 THREE RAYS LEFT/RIGHT dh dh U+1F802, U+1F800 RIGHT/LEFTWARDS ARROW WITH SMALL TRIANGLE ARROWHEAD dh dh U+1F806, U+1F804 RIGHT/LEFTWARDS ARROW WITH MEDIUM TRIANGLE ARROWHEAD dh dh U+1F80A, U+1F808 RIGHT/LEFTWARDS ARROW WITH LARGE TRIANGLE ARROWHEAD dh dh U+1F812, U+1F810 RIGHT/LEFTWARDS ARROW WITH SMALL EQUILATERAL ARROWHEAD dh dh U+1F816, U+1F814 RIGHT/LEFTWARDS ARROW WITH EQUILATERAL ARROWHEAD dh dh U+1F81A, U+1F818 HEAVY RIGHT/LEFTWARDS ARROW WITH EQUILATERAL ARROWHEAD dh dh U+1F81E, U+1F81C HEAVY RIGHT/LEFTWARDS ARROW WITH LARGE EQUILATERAL ARROWHEAD dh c dh U+1F822, U+1F820 RIGHT/LEFTWARDS TRIANGLE-HEADED ARROW WITH NARROW SHAFT dh | dh x U+1F826, U+1F824 RIGHT/LEFTWARDS TRIANGLE-HEADED ARROW WITH MEDIUM SHAFT dh a dh " U+1F82A, U+1F828 RIGHT/LEFTWARDS TRIANGLE-HEADED ARROW WITH BOLD SHAFT dh (R) dh ~ U+1F82E, U+1F82C RIGHT/LEFTWARDS TRIANGLE-HEADED ARROW WITH HEAVY SHAFT dh ^2 dh <degree> U+1F832, U+1F830 RIGHT/LEFTWARDS TRIANGLE-HEADED ARROW WITH VERY HEAVY SHAFT dh <paragraph> dh ' U+1F836, U+1F834 RIGHT/LEFTWARDS FINGER-POST ARROW dh o dh , U+1F83A, U+1F838 RIGHT/LEFTWARDS SQUARED ARROW dh 3/4 dh 1/4 U+1F83E, U+1F83C RIGHT/LEFTWARDS COMPRESSED ARROW dh! dh! U+1F842, U+1F840 RIGHT/LEFTWARDS HEAVY COMPRESSED ARROW dh! dh! U+1F846, U+1F844 RIGHT/LEFTWARDS HEAVY ARROW dh! dh! U+1F852, U+1F850 RIGHT/LEFTWARDS SANS-SERIF ARROW dh!c dh! U+1F862, U+1F860 WIDE-HEADED RIGHT/LEFTWARDS LIGHT BARB ARROW dh!a dh!" U+1F86A, U+1F868 WIDE-HEADED RIGHT/LEFTWARDS BARB ARROW dh!^2 dh!<degree> U+1F872, U+1F870 WIDE-HEADED RIGHT/LEFTWARDS MEDIUM BARB ARROW dh!o dh!, U+1F87A, U+1F878 WIDE-HEADED RIGHT/LEFTWARDS HEAVY BARB ARROW dhc dhc U+1F882, U+1F880 WIDE-HEADED RIGHT/LEFTWARDS VERY HEAVY BARB ARROW dhc dhc U+1F892, U+1F890 RIGHT/LEFTWARDS TRIANGLE ARROWHEAD dhc dhc U+1F896, U+1F894 RIGHT/LEFTWARDS WHITE ARROW WITHIN TRIANGLE ARROWHEAD dhc dhc U+1F89A, U+1F898 RIGHT/LEFTWARDS ARROW WITH NOTCHED TAIL dhc! dhc U+1F8A1, U+1F8A0 RIGHTWARDS BOTTOM SHADED WHITE ARROW, LEFTWARDS BOTTOM-SHADED WHITE ARROW dhcL dhcc U+1F8A3, U+1F8A2 RIGHT/LEFTWARDS TOP SHADED WHITE ARROW dhcY dhc| U+1F8A5, U+1F8A6 RIGHT/LEFTWARDS RIGHT-SHADED WHITE ARROW dhc<section> dhcx U+1F8A7, U+1F8A4 RIGHT/LEFTWARDS LEFT-SHADED WHITE ARROW dhc(C) dhc" U+1F8A9, U+1F8A8 RIGHT/LEFTWARDS BACK-TILTED SHADOWED WHITE ARROW dhc<< dhca U+1F8AB, U+1F8AA RIGHT/LEFTWARDS FRONT-TILTED SHADOWED WHITE ARROW dhc<paragraph> dhc' U+1F8B6, U+1F8B4 NEGATIVE SQUARED RIGHT/LEFTWARDS ARROW perl v5.43.9 2026-03-18 PERLOP(1)
NAME | DESCRIPTION | APPENDIX
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