3 perlop - Perl operators and precedence
7 Perl operators have the following associativity and precedence,
8 listed from highest precedence to lowest. Operators borrowed from
9 C keep the same precedence relationship with each other, even where
10 C's precedence is slightly screwy. (This makes learning Perl easier
11 for C folks.) With very few exceptions, these all operate on scalar
12 values only, not array values.
14 left terms and list operators (leftward)
18 right ! ~ \ and unary + and -
23 nonassoc named unary operators
24 nonassoc < > <= >= lt gt le ge
25 nonassoc == != <=> eq ne cmp
34 nonassoc list operators (rightward)
39 In the following sections, these operators are covered in precedence order.
41 Many operators can be overloaded for objects. See L<overload>.
45 =head2 Terms and List Operators (Leftward)
47 A TERM has the highest precedence in Perl. They include variables,
48 quote and quote-like operators, any expression in parentheses,
49 and any function whose arguments are parenthesized. Actually, there
50 aren't really functions in this sense, just list operators and unary
51 operators behaving as functions because you put parentheses around
52 the arguments. These are all documented in L<perlfunc>.
54 If any list operator (print(), etc.) or any unary operator (chdir(), etc.)
55 is followed by a left parenthesis as the next token, the operator and
56 arguments within parentheses are taken to be of highest precedence,
57 just like a normal function call.
59 In the absence of parentheses, the precedence of list operators such as
60 C<print>, C<sort>, or C<chmod> is either very high or very low depending on
61 whether you are looking at the left side or the right side of the operator.
64 @ary = (1, 3, sort 4, 2);
65 print @ary; # prints 1324
67 the commas on the right of the sort are evaluated before the sort,
68 but the commas on the left are evaluated after. In other words,
69 list operators tend to gobble up all arguments that follow, and
70 then act like a simple TERM with regard to the preceding expression.
71 Be careful with parentheses:
73 # These evaluate exit before doing the print:
74 print($foo, exit); # Obviously not what you want.
75 print $foo, exit; # Nor is this.
77 # These do the print before evaluating exit:
78 (print $foo), exit; # This is what you want.
79 print($foo), exit; # Or this.
80 print ($foo), exit; # Or even this.
84 print ($foo & 255) + 1, "\n";
86 probably doesn't do what you expect at first glance. See
87 L<Named Unary Operators> for more discussion of this.
89 Also parsed as terms are the C<do {}> and C<eval {}> constructs, as
90 well as subroutine and method calls, and the anonymous
91 constructors C<[]> and C<{}>.
93 See also L<Quote and Quote-like Operators> toward the end of this section,
94 as well as L<"I/O Operators">.
96 =head2 The Arrow Operator
98 "C<< -> >>" is an infix dereference operator, just as it is in C
99 and C++. If the right side is either a C<[...]>, C<{...}>, or a
100 C<(...)> subscript, then the left side must be either a hard or
101 symbolic reference to an array, a hash, or a subroutine respectively.
102 (Or technically speaking, a location capable of holding a hard
103 reference, if it's an array or hash reference being used for
104 assignment.) See L<perlreftut> and L<perlref>.
106 Otherwise, the right side is a method name or a simple scalar
107 variable containing either the method name or a subroutine reference,
108 and the left side must be either an object (a blessed reference)
109 or a class name (that is, a package name). See L<perlobj>.
111 =head2 Auto-increment and Auto-decrement
113 "++" and "--" work as in C. That is, if placed before a variable, they
114 increment or decrement the variable before returning the value, and if
115 placed after, increment or decrement the variable after returning the value.
117 The auto-increment operator has a little extra builtin magic to it. If
118 you increment a variable that is numeric, or that has ever been used in
119 a numeric context, you get a normal increment. If, however, the
120 variable has been used in only string contexts since it was set, and
121 has a value that is not the empty string and matches the pattern
122 C</^[a-zA-Z]*[0-9]*\z/>, the increment is done as a string, preserving each
123 character within its range, with carry:
125 print ++($foo = '99'); # prints '100'
126 print ++($foo = 'a0'); # prints 'a1'
127 print ++($foo = 'Az'); # prints 'Ba'
128 print ++($foo = 'zz'); # prints 'aaa'
130 C<undef> is always treated as numeric, and in particular is changed
131 to C<0> before incrementing (so that a post-increment of an undef value
132 will return C<0> rather than C<undef>).
134 The auto-decrement operator is not magical.
136 =head2 Exponentiation
138 Binary "**" is the exponentiation operator. It binds even more
139 tightly than unary minus, so -2**4 is -(2**4), not (-2)**4. (This is
140 implemented using C's pow(3) function, which actually works on doubles
143 =head2 Symbolic Unary Operators
145 Unary "!" performs logical negation, i.e., "not". See also C<not> for a lower
146 precedence version of this.
148 Unary "-" performs arithmetic negation if the operand is numeric. If
149 the operand is an identifier, a string consisting of a minus sign
150 concatenated with the identifier is returned. Otherwise, if the string
151 starts with a plus or minus, a string starting with the opposite sign
152 is returned. One effect of these rules is that C<-bareword> is equivalent
155 Unary "~" performs bitwise negation, i.e., 1's complement. For
156 example, C<0666 & ~027> is 0640. (See also L<Integer Arithmetic> and
157 L<Bitwise String Operators>.) Note that the width of the result is
158 platform-dependent: ~0 is 32 bits wide on a 32-bit platform, but 64
159 bits wide on a 64-bit platform, so if you are expecting a certain bit
160 width, remember use the & operator to mask off the excess bits.
162 Unary "+" has no effect whatsoever, even on strings. It is useful
163 syntactically for separating a function name from a parenthesized expression
164 that would otherwise be interpreted as the complete list of function
165 arguments. (See examples above under L<Terms and List Operators (Leftward)>.)
167 Unary "\" creates a reference to whatever follows it. See L<perlreftut>
168 and L<perlref>. Do not confuse this behavior with the behavior of
169 backslash within a string, although both forms do convey the notion
170 of protecting the next thing from interpolation.
172 =head2 Binding Operators
174 Binary "=~" binds a scalar expression to a pattern match. Certain operations
175 search or modify the string $_ by default. This operator makes that kind
176 of operation work on some other string. The right argument is a search
177 pattern, substitution, or transliteration. The left argument is what is
178 supposed to be searched, substituted, or transliterated instead of the default
179 $_. When used in scalar context, the return value generally indicates the
180 success of the operation. Behavior in list context depends on the particular
181 operator. See L</"Regexp Quote-Like Operators"> for details.
183 If the right argument is an expression rather than a search pattern,
184 substitution, or transliteration, it is interpreted as a search pattern at run
187 Binary "!~" is just like "=~" except the return value is negated in
190 =head2 Multiplicative Operators
192 Binary "*" multiplies two numbers.
194 Binary "/" divides two numbers.
196 Binary "%" computes the modulus of two numbers. Given integer
197 operands C<$a> and C<$b>: If C<$b> is positive, then C<$a % $b> is
198 C<$a> minus the largest multiple of C<$b> that is not greater than
199 C<$a>. If C<$b> is negative, then C<$a % $b> is C<$a> minus the
200 smallest multiple of C<$b> that is not less than C<$a> (i.e. the
201 result will be less than or equal to zero).
202 Note that when C<use integer> is in scope, "%" gives you direct access
203 to the modulus operator as implemented by your C compiler. This
204 operator is not as well defined for negative operands, but it will
207 Binary "x" is the repetition operator. In scalar context or if the left
208 operand is not enclosed in parentheses, it returns a string consisting
209 of the left operand repeated the number of times specified by the right
210 operand. In list context, if the left operand is enclosed in
211 parentheses, it repeats the list.
213 print '-' x 80; # print row of dashes
215 print "\t" x ($tab/8), ' ' x ($tab%8); # tab over
217 @ones = (1) x 80; # a list of 80 1's
218 @ones = (5) x @ones; # set all elements to 5
221 =head2 Additive Operators
223 Binary "+" returns the sum of two numbers.
225 Binary "-" returns the difference of two numbers.
227 Binary "." concatenates two strings.
229 =head2 Shift Operators
231 Binary "<<" returns the value of its left argument shifted left by the
232 number of bits specified by the right argument. Arguments should be
233 integers. (See also L<Integer Arithmetic>.)
235 Binary ">>" returns the value of its left argument shifted right by
236 the number of bits specified by the right argument. Arguments should
237 be integers. (See also L<Integer Arithmetic>.)
239 Note that both "<<" and ">>" in Perl are implemented directly using
240 "<<" and ">>" in C. If C<use integer> (see L<Integer Arithmetic>) is
241 in force then signed C integers are used, else unsigned C integers are
242 used. Either way, the implementation isn't going to generate results
243 larger than the size of the integer type Perl was built with (32 bits
246 The result of overflowing the range of the integers is undefined
247 because it is undefined also in C. In other words, using 32-bit
248 integers, C<< 1 << 32 >> is undefined. Shifting by a negative number
249 of bits is also undefined.
251 =head2 Named Unary Operators
253 The various named unary operators are treated as functions with one
254 argument, with optional parentheses. These include the filetest
255 operators, like C<-f>, C<-M>, etc. See L<perlfunc>.
257 If any list operator (print(), etc.) or any unary operator (chdir(), etc.)
258 is followed by a left parenthesis as the next token, the operator and
259 arguments within parentheses are taken to be of highest precedence,
260 just like a normal function call. For example,
261 because named unary operators are higher precedence than ||:
263 chdir $foo || die; # (chdir $foo) || die
264 chdir($foo) || die; # (chdir $foo) || die
265 chdir ($foo) || die; # (chdir $foo) || die
266 chdir +($foo) || die; # (chdir $foo) || die
268 but, because * is higher precedence than named operators:
270 chdir $foo * 20; # chdir ($foo * 20)
271 chdir($foo) * 20; # (chdir $foo) * 20
272 chdir ($foo) * 20; # (chdir $foo) * 20
273 chdir +($foo) * 20; # chdir ($foo * 20)
275 rand 10 * 20; # rand (10 * 20)
276 rand(10) * 20; # (rand 10) * 20
277 rand (10) * 20; # (rand 10) * 20
278 rand +(10) * 20; # rand (10 * 20)
280 See also L<"Terms and List Operators (Leftward)">.
282 =head2 Relational Operators
284 Binary "<" returns true if the left argument is numerically less than
287 Binary ">" returns true if the left argument is numerically greater
288 than the right argument.
290 Binary "<=" returns true if the left argument is numerically less than
291 or equal to the right argument.
293 Binary ">=" returns true if the left argument is numerically greater
294 than or equal to the right argument.
296 Binary "lt" returns true if the left argument is stringwise less than
299 Binary "gt" returns true if the left argument is stringwise greater
300 than the right argument.
302 Binary "le" returns true if the left argument is stringwise less than
303 or equal to the right argument.
305 Binary "ge" returns true if the left argument is stringwise greater
306 than or equal to the right argument.
308 =head2 Equality Operators
310 Binary "==" returns true if the left argument is numerically equal to
313 Binary "!=" returns true if the left argument is numerically not equal
314 to the right argument.
316 Binary "<=>" returns -1, 0, or 1 depending on whether the left
317 argument is numerically less than, equal to, or greater than the right
318 argument. If your platform supports NaNs (not-a-numbers) as numeric
319 values, using them with "<=>" returns undef. NaN is not "<", "==", ">",
320 "<=" or ">=" anything (even NaN), so those 5 return false. NaN != NaN
321 returns true, as does NaN != anything else. If your platform doesn't
322 support NaNs then NaN is just a string with numeric value 0.
324 perl -le '$a = NaN; print "No NaN support here" if $a == $a'
325 perl -le '$a = NaN; print "NaN support here" if $a != $a'
327 Binary "eq" returns true if the left argument is stringwise equal to
330 Binary "ne" returns true if the left argument is stringwise not equal
331 to the right argument.
333 Binary "cmp" returns -1, 0, or 1 depending on whether the left
334 argument is stringwise less than, equal to, or greater than the right
337 "lt", "le", "ge", "gt" and "cmp" use the collation (sort) order specified
338 by the current locale if C<use locale> is in effect. See L<perllocale>.
342 Binary "&" returns its operands ANDed together bit by bit.
343 (See also L<Integer Arithmetic> and L<Bitwise String Operators>.)
345 Note that "&" has lower priority than relational operators, so for example
346 the brackets are essential in a test like
348 print "Even\n" if ($x & 1) == 0;
350 =head2 Bitwise Or and Exclusive Or
352 Binary "|" returns its operands ORed together bit by bit.
353 (See also L<Integer Arithmetic> and L<Bitwise String Operators>.)
355 Binary "^" returns its operands XORed together bit by bit.
356 (See also L<Integer Arithmetic> and L<Bitwise String Operators>.)
358 Note that "|" and "^" have lower priority than relational operators, so
359 for example the brackets are essential in a test like
361 print "false\n" if (8 | 2) != 10;
363 =head2 C-style Logical And
365 Binary "&&" performs a short-circuit logical AND operation. That is,
366 if the left operand is false, the right operand is not even evaluated.
367 Scalar or list context propagates down to the right operand if it
370 =head2 C-style Logical Or
372 Binary "||" performs a short-circuit logical OR operation. That is,
373 if the left operand is true, the right operand is not even evaluated.
374 Scalar or list context propagates down to the right operand if it
377 =head2 C-style Logical Defined-Or
379 Although it has no direct equivalent in C, Perl's C<//> operator is related
380 to its C-style or. In fact, it's exactly the same as C<||>, except that it
381 tests the left hand side's definedness instead of its truth. Thus, C<$a // $b>
382 is similar to C<defined($a) || $b> (except that it returns the value of C<$a>
383 rather than the value of C<defined($a)>) and is exactly equivalent to
384 C<defined($a) ? $a : $b>. This is very useful for providing default values
385 for variables. If you actually want to test if at least one of C<$a> and C<$b> is
386 defined, use C<defined($a // $b)>.
388 The C<||>, C<//> and C<&&> operators differ from C's in that, rather than returning
389 0 or 1, they return the last value evaluated. Thus, a reasonably portable
390 way to find out the home directory might be:
392 $home = $ENV{'HOME'} // $ENV{'LOGDIR'} //
393 (getpwuid($<))[7] // die "You're homeless!\n";
395 In particular, this means that you shouldn't use this
396 for selecting between two aggregates for assignment:
398 @a = @b || @c; # this is wrong
399 @a = scalar(@b) || @c; # really meant this
400 @a = @b ? @b : @c; # this works fine, though
402 As more readable alternatives to C<&&>, C<//> and C<||> when used for
403 control flow, Perl provides C<and>, C<err> and C<or> operators (see below).
404 The short-circuit behavior is identical. The precedence of "and", "err"
405 and "or" is much lower, however, so that you can safely use them after a
406 list operator without the need for parentheses:
408 unlink "alpha", "beta", "gamma"
409 or gripe(), next LINE;
411 With the C-style operators that would have been written like this:
413 unlink("alpha", "beta", "gamma")
414 || (gripe(), next LINE);
416 Using "or" for assignment is unlikely to do what you want; see below.
418 =head2 Range Operators
420 Binary ".." is the range operator, which is really two different
421 operators depending on the context. In list context, it returns an
422 list of values counting (up by ones) from the left value to the right
423 value. If the left value is greater than the right value then it
424 returns the empty array. The range operator is useful for writing
425 C<foreach (1..10)> loops and for doing slice operations on arrays. In
426 the current implementation, no temporary array is created when the
427 range operator is used as the expression in C<foreach> loops, but older
428 versions of Perl might burn a lot of memory when you write something
431 for (1 .. 1_000_000) {
435 The range operator also works on strings, using the magical auto-increment,
438 In scalar context, ".." returns a boolean value. The operator is
439 bistable, like a flip-flop, and emulates the line-range (comma) operator
440 of B<sed>, B<awk>, and various editors. Each ".." operator maintains its
441 own boolean state. It is false as long as its left operand is false.
442 Once the left operand is true, the range operator stays true until the
443 right operand is true, I<AFTER> which the range operator becomes false
444 again. It doesn't become false till the next time the range operator is
445 evaluated. It can test the right operand and become false on the same
446 evaluation it became true (as in B<awk>), but it still returns true once.
447 If you don't want it to test the right operand till the next
448 evaluation, as in B<sed>, just use three dots ("...") instead of
449 two. In all other regards, "..." behaves just like ".." does.
451 The right operand is not evaluated while the operator is in the
452 "false" state, and the left operand is not evaluated while the
453 operator is in the "true" state. The precedence is a little lower
454 than || and &&. The value returned is either the empty string for
455 false, or a sequence number (beginning with 1) for true. The
456 sequence number is reset for each range encountered. The final
457 sequence number in a range has the string "E0" appended to it, which
458 doesn't affect its numeric value, but gives you something to search
459 for if you want to exclude the endpoint. You can exclude the
460 beginning point by waiting for the sequence number to be greater
461 than 1. If either operand of scalar ".." is a constant expression,
462 that operand is implicitly compared to the C<$.> variable, the
463 current line number. Examples:
465 As a scalar operator:
467 if (101 .. 200) { print; } # print 2nd hundred lines
468 next line if (1 .. /^$/); # skip header lines
469 s/^/> / if (/^$/ .. eof()); # quote body
471 # parse mail messages
473 $in_header = 1 .. /^$/;
474 $in_body = /^$/ .. eof();
475 # do something based on those
477 close ARGV if eof; # reset $. each file
482 for (101 .. 200) { print; } # print $_ 100 times
483 @foo = @foo[0 .. $#foo]; # an expensive no-op
484 @foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items
486 The range operator (in list context) makes use of the magical
487 auto-increment algorithm if the operands are strings. You
490 @alphabet = ('A' .. 'Z');
492 to get all normal letters of the English alphabet, or
494 $hexdigit = (0 .. 9, 'a' .. 'f')[$num & 15];
496 to get a hexadecimal digit, or
498 @z2 = ('01' .. '31'); print $z2[$mday];
500 to get dates with leading zeros. If the final value specified is not
501 in the sequence that the magical increment would produce, the sequence
502 goes until the next value would be longer than the final value
505 =head2 Conditional Operator
507 Ternary "?:" is the conditional operator, just as in C. It works much
508 like an if-then-else. If the argument before the ? is true, the
509 argument before the : is returned, otherwise the argument after the :
510 is returned. For example:
512 printf "I have %d dog%s.\n", $n,
513 ($n == 1) ? '' : "s";
515 Scalar or list context propagates downward into the 2nd
516 or 3rd argument, whichever is selected.
518 $a = $ok ? $b : $c; # get a scalar
519 @a = $ok ? @b : @c; # get an array
520 $a = $ok ? @b : @c; # oops, that's just a count!
522 The operator may be assigned to if both the 2nd and 3rd arguments are
523 legal lvalues (meaning that you can assign to them):
525 ($a_or_b ? $a : $b) = $c;
527 Because this operator produces an assignable result, using assignments
528 without parentheses will get you in trouble. For example, this:
530 $a % 2 ? $a += 10 : $a += 2
534 (($a % 2) ? ($a += 10) : $a) += 2
538 ($a % 2) ? ($a += 10) : ($a += 2)
540 That should probably be written more simply as:
542 $a += ($a % 2) ? 10 : 2;
544 =head2 Assignment Operators
546 "=" is the ordinary assignment operator.
548 Assignment operators work as in C. That is,
556 although without duplicating any side effects that dereferencing the lvalue
557 might trigger, such as from tie(). Other assignment operators work similarly.
558 The following are recognized:
565 Although these are grouped by family, they all have the precedence
568 Unlike in C, the scalar assignment operator produces a valid lvalue.
569 Modifying an assignment is equivalent to doing the assignment and
570 then modifying the variable that was assigned to. This is useful
571 for modifying a copy of something, like this:
573 ($tmp = $global) =~ tr [A-Z] [a-z];
584 Similarly, a list assignment in list context produces the list of
585 lvalues assigned to, and a list assignment in scalar context returns
586 the number of elements produced by the expression on the right hand
587 side of the assignment.
589 =head2 Comma Operator
591 Binary "," is the comma operator. In scalar context it evaluates
592 its left argument, throws that value away, then evaluates its right
593 argument and returns that value. This is just like C's comma operator.
595 In list context, it's just the list argument separator, and inserts
596 both its arguments into the list.
598 The => digraph is mostly just a synonym for the comma operator. It's useful for
599 documenting arguments that come in pairs. As of release 5.001, it also forces
600 any word to the left of it to be interpreted as a string.
602 =head2 List Operators (Rightward)
604 On the right side of a list operator, it has very low precedence,
605 such that it controls all comma-separated expressions found there.
606 The only operators with lower precedence are the logical operators
607 "and", "or", and "not", which may be used to evaluate calls to list
608 operators without the need for extra parentheses:
610 open HANDLE, "filename"
611 or die "Can't open: $!\n";
613 See also discussion of list operators in L<Terms and List Operators (Leftward)>.
617 Unary "not" returns the logical negation of the expression to its right.
618 It's the equivalent of "!" except for the very low precedence.
622 Binary "and" returns the logical conjunction of the two surrounding
623 expressions. It's equivalent to && except for the very low
624 precedence. This means that it short-circuits: i.e., the right
625 expression is evaluated only if the left expression is true.
627 =head2 Logical or, Defined or, and Exclusive Or
629 Binary "or" returns the logical disjunction of the two surrounding
630 expressions. It's equivalent to || except for the very low precedence.
631 This makes it useful for control flow
633 print FH $data or die "Can't write to FH: $!";
635 This means that it short-circuits: i.e., the right expression is evaluated
636 only if the left expression is false. Due to its precedence, you should
637 probably avoid using this for assignment, only for control flow.
639 $a = $b or $c; # bug: this is wrong
640 ($a = $b) or $c; # really means this
641 $a = $b || $c; # better written this way
643 However, when it's a list-context assignment and you're trying to use
644 "||" for control flow, you probably need "or" so that the assignment
645 takes higher precedence.
647 @info = stat($file) || die; # oops, scalar sense of stat!
648 @info = stat($file) or die; # better, now @info gets its due
650 Then again, you could always use parentheses.
652 Binary "err" is equivalent to C<//>--it's just like binary "or", except it tests
653 its left argument's definedness instead of its truth. There are two ways to
654 remember "err": either because many functions return C<undef> on an B<err>or,
655 or as a sort of correction: C<$a=($b err 'default')>
657 Binary "xor" returns the exclusive-OR of the two surrounding expressions.
658 It cannot short circuit, of course.
660 =head2 C Operators Missing From Perl
662 Here is what C has that Perl doesn't:
668 Address-of operator. (But see the "\" operator for taking a reference.)
672 Dereference-address operator. (Perl's prefix dereferencing
673 operators are typed: $, @, %, and &.)
677 Type-casting operator.
681 =head2 Quote and Quote-like Operators
683 While we usually think of quotes as literal values, in Perl they
684 function as operators, providing various kinds of interpolating and
685 pattern matching capabilities. Perl provides customary quote characters
686 for these behaviors, but also provides a way for you to choose your
687 quote character for any of them. In the following table, a C<{}> represents
688 any pair of delimiters you choose.
690 Customary Generic Meaning Interpolates
695 // m{} Pattern match yes*
697 s{}{} Substitution yes*
698 tr{}{} Transliteration no (but see below)
701 * unless the delimiter is ''.
703 Non-bracketing delimiters use the same character fore and aft, but the four
704 sorts of brackets (round, angle, square, curly) will all nest, which means
713 Note, however, that this does not always work for quoting Perl code:
715 $s = q{ if($a eq "}") ... }; # WRONG
717 is a syntax error. The C<Text::Balanced> module (from CPAN, and
718 starting from Perl 5.8 part of the standard distribution) is able
721 There can be whitespace between the operator and the quoting
722 characters, except when C<#> is being used as the quoting character.
723 C<q#foo#> is parsed as the string C<foo>, while C<q #foo#> is the
724 operator C<q> followed by a comment. Its argument will be taken
725 from the next line. This allows you to write:
727 s {foo} # Replace foo
730 The following escape sequences are available in constructs that interpolate
731 and in transliterations.
738 \a alarm (bell) (BEL)
740 \033 octal char (ESC)
742 \x{263a} wide hex char (SMILEY)
743 \c[ control char (ESC)
744 \N{name} named Unicode character
746 The following escape sequences are available in constructs that interpolate
747 but not in transliterations.
749 \l lowercase next char
750 \u uppercase next char
753 \E end case modification
754 \Q quote non-word characters till \E
756 If C<use locale> is in effect, the case map used by C<\l>, C<\L>,
757 C<\u> and C<\U> is taken from the current locale. See L<perllocale>.
758 If Unicode (for example, C<\N{}> or wide hex characters of 0x100 or
759 beyond) is being used, the case map used by C<\l>, C<\L>, C<\u> and
760 C<\U> is as defined by Unicode. For documentation of C<\N{name}>,
763 All systems use the virtual C<"\n"> to represent a line terminator,
764 called a "newline". There is no such thing as an unvarying, physical
765 newline character. It is only an illusion that the operating system,
766 device drivers, C libraries, and Perl all conspire to preserve. Not all
767 systems read C<"\r"> as ASCII CR and C<"\n"> as ASCII LF. For example,
768 on a Mac, these are reversed, and on systems without line terminator,
769 printing C<"\n"> may emit no actual data. In general, use C<"\n"> when
770 you mean a "newline" for your system, but use the literal ASCII when you
771 need an exact character. For example, most networking protocols expect
772 and prefer a CR+LF (C<"\015\012"> or C<"\cM\cJ">) for line terminators,
773 and although they often accept just C<"\012">, they seldom tolerate just
774 C<"\015">. If you get in the habit of using C<"\n"> for networking,
775 you may be burned some day.
777 For constructs that do interpolate, variables beginning with "C<$>"
778 or "C<@>" are interpolated. Subscripted variables such as C<$a[3]> or
779 C<< $href->{key}[0] >> are also interpolated, as are array and hash slices.
780 But method calls such as C<< $obj->meth >> are not.
782 Interpolating an array or slice interpolates the elements in order,
783 separated by the value of C<$">, so is equivalent to interpolating
784 C<join $", @array>. "Punctuation" arrays such as C<@+> are only
785 interpolated if the name is enclosed in braces C<@{+}>.
787 You cannot include a literal C<$> or C<@> within a C<\Q> sequence.
788 An unescaped C<$> or C<@> interpolates the corresponding variable,
789 while escaping will cause the literal string C<\$> to be inserted.
790 You'll need to write something like C<m/\Quser\E\@\Qhost/>.
792 Patterns are subject to an additional level of interpretation as a
793 regular expression. This is done as a second pass, after variables are
794 interpolated, so that regular expressions may be incorporated into the
795 pattern from the variables. If this is not what you want, use C<\Q> to
796 interpolate a variable literally.
798 Apart from the behavior described above, Perl does not expand
799 multiple levels of interpolation. In particular, contrary to the
800 expectations of shell programmers, back-quotes do I<NOT> interpolate
801 within double quotes, nor do single quotes impede evaluation of
802 variables when used within double quotes.
804 =head2 Regexp Quote-Like Operators
806 Here are the quote-like operators that apply to pattern
807 matching and related activities.
813 This is just like the C</pattern/> search, except that it matches only
814 once between calls to the reset() operator. This is a useful
815 optimization when you want to see only the first occurrence of
816 something in each file of a set of files, for instance. Only C<??>
817 patterns local to the current package are reset.
821 # blank line between header and body
824 reset if eof; # clear ?? status for next file
827 This usage is vaguely deprecated, which means it just might possibly
828 be removed in some distant future version of Perl, perhaps somewhere
829 around the year 2168.
831 =item m/PATTERN/cgimosx
833 =item /PATTERN/cgimosx
835 Searches a string for a pattern match, and in scalar context returns
836 true if it succeeds, false if it fails. If no string is specified
837 via the C<=~> or C<!~> operator, the $_ string is searched. (The
838 string specified with C<=~> need not be an lvalue--it may be the
839 result of an expression evaluation, but remember the C<=~> binds
840 rather tightly.) See also L<perlre>. See L<perllocale> for
841 discussion of additional considerations that apply when C<use locale>
846 c Do not reset search position on a failed match when /g is in effect.
847 g Match globally, i.e., find all occurrences.
848 i Do case-insensitive pattern matching.
849 m Treat string as multiple lines.
850 o Compile pattern only once.
851 s Treat string as single line.
852 x Use extended regular expressions.
854 If "/" is the delimiter then the initial C<m> is optional. With the C<m>
855 you can use any pair of non-alphanumeric, non-whitespace characters
856 as delimiters. This is particularly useful for matching path names
857 that contain "/", to avoid LTS (leaning toothpick syndrome). If "?" is
858 the delimiter, then the match-only-once rule of C<?PATTERN?> applies.
859 If "'" is the delimiter, no interpolation is performed on the PATTERN.
861 PATTERN may contain variables, which will be interpolated (and the
862 pattern recompiled) every time the pattern search is evaluated, except
863 for when the delimiter is a single quote. (Note that C<$(>, C<$)>, and
864 C<$|> are not interpolated because they look like end-of-string tests.)
865 If you want such a pattern to be compiled only once, add a C</o> after
866 the trailing delimiter. This avoids expensive run-time recompilations,
867 and is useful when the value you are interpolating won't change over
868 the life of the script. However, mentioning C</o> constitutes a promise
869 that you won't change the variables in the pattern. If you change them,
870 Perl won't even notice. See also L<"qr/STRING/imosx">.
872 If the PATTERN evaluates to the empty string, the last
873 I<successfully> matched regular expression is used instead. In this
874 case, only the C<g> and C<c> flags on the empty pattern is honoured -
875 the other flags are taken from the original pattern. If no match has
876 previously succeeded, this will (silently) act instead as a genuine
877 empty pattern (which will always match).
879 Note that it's possible to confuse Perl into thinking C<//> (the empty
880 regex) is really C<//> (the defined-or operator). Perl is usually pretty
881 good about this, but some pathological cases might trigger this, such as
882 C<$a///> (is that C<($a) / (//)> or C<$a // />?) and C<print $fh //>
883 (C<print $fh(//> or C<print($fh //>?). In all of these examples, Perl
884 will assume you meant defined-or. If you meant the empty regex, just
885 use parentheses or spaces to disambiguate, or even prefix the empty
886 regex with an C<m> (so C<//> becomes C<m//>).
888 If the C</g> option is not used, C<m//> in list context returns a
889 list consisting of the subexpressions matched by the parentheses in the
890 pattern, i.e., (C<$1>, C<$2>, C<$3>...). (Note that here C<$1> etc. are
891 also set, and that this differs from Perl 4's behavior.) When there are
892 no parentheses in the pattern, the return value is the list C<(1)> for
893 success. With or without parentheses, an empty list is returned upon
898 open(TTY, '/dev/tty');
899 <TTY> =~ /^y/i && foo(); # do foo if desired
901 if (/Version: *([0-9.]*)/) { $version = $1; }
903 next if m#^/usr/spool/uucp#;
908 print if /$arg/o; # compile only once
911 if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))
913 This last example splits $foo into the first two words and the
914 remainder of the line, and assigns those three fields to $F1, $F2, and
915 $Etc. The conditional is true if any variables were assigned, i.e., if
918 The C</g> modifier specifies global pattern matching--that is,
919 matching as many times as possible within the string. How it behaves
920 depends on the context. In list context, it returns a list of the
921 substrings matched by any capturing parentheses in the regular
922 expression. If there are no parentheses, it returns a list of all
923 the matched strings, as if there were parentheses around the whole
926 In scalar context, each execution of C<m//g> finds the next match,
927 returning true if it matches, and false if there is no further match.
928 The position after the last match can be read or set using the pos()
929 function; see L<perlfunc/pos>. A failed match normally resets the
930 search position to the beginning of the string, but you can avoid that
931 by adding the C</c> modifier (e.g. C<m//gc>). Modifying the target
932 string also resets the search position.
934 You can intermix C<m//g> matches with C<m/\G.../g>, where C<\G> is a
935 zero-width assertion that matches the exact position where the previous
936 C<m//g>, if any, left off. Without the C</g> modifier, the C<\G> assertion
937 still anchors at pos(), but the match is of course only attempted once.
938 Using C<\G> without C</g> on a target string that has not previously had a
939 C</g> match applied to it is the same as using the C<\A> assertion to match
940 the beginning of the string. Note also that, currently, C<\G> is only
941 properly supported when anchored at the very beginning of the pattern.
946 ($one,$five,$fifteen) = (`uptime` =~ /(\d+\.\d+)/g);
950 while (defined($paragraph = <>)) {
951 while ($paragraph =~ /[a-z]['")]*[.!?]+['")]*\s/g) {
955 print "$sentences\n";
957 # using m//gc with \G
961 print $1 while /(o)/gc; print "', pos=", pos, "\n";
963 print $1 if /\G(q)/gc; print "', pos=", pos, "\n";
965 print $1 while /(p)/gc; print "', pos=", pos, "\n";
967 print "Final: '$1', pos=",pos,"\n" if /\G(.)/;
969 The last example should print:
979 Notice that the final match matched C<q> instead of C<p>, which a match
980 without the C<\G> anchor would have done. Also note that the final match
981 did not update C<pos> -- C<pos> is only updated on a C</g> match. If the
982 final match did indeed match C<p>, it's a good bet that you're running an
983 older (pre-5.6.0) Perl.
985 A useful idiom for C<lex>-like scanners is C</\G.../gc>. You can
986 combine several regexps like this to process a string part-by-part,
987 doing different actions depending on which regexp matched. Each
988 regexp tries to match where the previous one leaves off.
991 $url = new URI::URL "http://www/"; die if $url eq "xXx";
995 print(" digits"), redo LOOP if /\G\d+\b[,.;]?\s*/gc;
996 print(" lowercase"), redo LOOP if /\G[a-z]+\b[,.;]?\s*/gc;
997 print(" UPPERCASE"), redo LOOP if /\G[A-Z]+\b[,.;]?\s*/gc;
998 print(" Capitalized"), redo LOOP if /\G[A-Z][a-z]+\b[,.;]?\s*/gc;
999 print(" MiXeD"), redo LOOP if /\G[A-Za-z]+\b[,.;]?\s*/gc;
1000 print(" alphanumeric"), redo LOOP if /\G[A-Za-z0-9]+\b[,.;]?\s*/gc;
1001 print(" line-noise"), redo LOOP if /\G[^A-Za-z0-9]+/gc;
1002 print ". That's all!\n";
1005 Here is the output (split into several lines):
1007 line-noise lowercase line-noise lowercase UPPERCASE line-noise
1008 UPPERCASE line-noise lowercase line-noise lowercase line-noise
1009 lowercase lowercase line-noise lowercase lowercase line-noise
1010 MiXeD line-noise. That's all!
1016 A single-quoted, literal string. A backslash represents a backslash
1017 unless followed by the delimiter or another backslash, in which case
1018 the delimiter or backslash is interpolated.
1020 $foo = q!I said, "You said, 'She said it.'"!;
1021 $bar = q('This is it.');
1022 $baz = '\n'; # a two-character string
1028 A double-quoted, interpolated string.
1031 (*** The previous line contains the naughty word "$1".\n)
1032 if /\b(tcl|java|python)\b/i; # :-)
1033 $baz = "\n"; # a one-character string
1035 =item qr/STRING/imosx
1037 This operator quotes (and possibly compiles) its I<STRING> as a regular
1038 expression. I<STRING> is interpolated the same way as I<PATTERN>
1039 in C<m/PATTERN/>. If "'" is used as the delimiter, no interpolation
1040 is done. Returns a Perl value which may be used instead of the
1041 corresponding C</STRING/imosx> expression.
1045 $rex = qr/my.STRING/is;
1052 The result may be used as a subpattern in a match:
1055 $string =~ /foo${re}bar/; # can be interpolated in other patterns
1056 $string =~ $re; # or used standalone
1057 $string =~ /$re/; # or this way
1059 Since Perl may compile the pattern at the moment of execution of qr()
1060 operator, using qr() may have speed advantages in some situations,
1061 notably if the result of qr() is used standalone:
1064 my $patterns = shift;
1065 my @compiled = map qr/$_/i, @$patterns;
1068 foreach my $pat (@compiled) {
1069 $success = 1, last if /$pat/;
1075 Precompilation of the pattern into an internal representation at
1076 the moment of qr() avoids a need to recompile the pattern every
1077 time a match C</$pat/> is attempted. (Perl has many other internal
1078 optimizations, but none would be triggered in the above example if
1079 we did not use qr() operator.)
1083 i Do case-insensitive pattern matching.
1084 m Treat string as multiple lines.
1085 o Compile pattern only once.
1086 s Treat string as single line.
1087 x Use extended regular expressions.
1089 See L<perlre> for additional information on valid syntax for STRING, and
1090 for a detailed look at the semantics of regular expressions.
1096 A string which is (possibly) interpolated and then executed as a
1097 system command with C</bin/sh> or its equivalent. Shell wildcards,
1098 pipes, and redirections will be honored. The collected standard
1099 output of the command is returned; standard error is unaffected. In
1100 scalar context, it comes back as a single (potentially multi-line)
1101 string, or undef if the command failed. In list context, returns a
1102 list of lines (however you've defined lines with $/ or
1103 $INPUT_RECORD_SEPARATOR), or an empty list if the command failed.
1105 Because backticks do not affect standard error, use shell file descriptor
1106 syntax (assuming the shell supports this) if you care to address this.
1107 To capture a command's STDERR and STDOUT together:
1109 $output = `cmd 2>&1`;
1111 To capture a command's STDOUT but discard its STDERR:
1113 $output = `cmd 2>/dev/null`;
1115 To capture a command's STDERR but discard its STDOUT (ordering is
1118 $output = `cmd 2>&1 1>/dev/null`;
1120 To exchange a command's STDOUT and STDERR in order to capture the STDERR
1121 but leave its STDOUT to come out the old STDERR:
1123 $output = `cmd 3>&1 1>&2 2>&3 3>&-`;
1125 To read both a command's STDOUT and its STDERR separately, it's easiest
1126 and safest to redirect them separately to files, and then read from those
1127 files when the program is done:
1129 system("program args 1>/tmp/program.stdout 2>/tmp/program.stderr");
1131 Using single-quote as a delimiter protects the command from Perl's
1132 double-quote interpolation, passing it on to the shell instead:
1134 $perl_info = qx(ps $$); # that's Perl's $$
1135 $shell_info = qx'ps $$'; # that's the new shell's $$
1137 How that string gets evaluated is entirely subject to the command
1138 interpreter on your system. On most platforms, you will have to protect
1139 shell metacharacters if you want them treated literally. This is in
1140 practice difficult to do, as it's unclear how to escape which characters.
1141 See L<perlsec> for a clean and safe example of a manual fork() and exec()
1142 to emulate backticks safely.
1144 On some platforms (notably DOS-like ones), the shell may not be
1145 capable of dealing with multiline commands, so putting newlines in
1146 the string may not get you what you want. You may be able to evaluate
1147 multiple commands in a single line by separating them with the command
1148 separator character, if your shell supports that (e.g. C<;> on many Unix
1149 shells; C<&> on the Windows NT C<cmd> shell).
1151 Beginning with v5.6.0, Perl will attempt to flush all files opened for
1152 output before starting the child process, but this may not be supported
1153 on some platforms (see L<perlport>). To be safe, you may need to set
1154 C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method of
1155 C<IO::Handle> on any open handles.
1157 Beware that some command shells may place restrictions on the length
1158 of the command line. You must ensure your strings don't exceed this
1159 limit after any necessary interpolations. See the platform-specific
1160 release notes for more details about your particular environment.
1162 Using this operator can lead to programs that are difficult to port,
1163 because the shell commands called vary between systems, and may in
1164 fact not be present at all. As one example, the C<type> command under
1165 the POSIX shell is very different from the C<type> command under DOS.
1166 That doesn't mean you should go out of your way to avoid backticks
1167 when they're the right way to get something done. Perl was made to be
1168 a glue language, and one of the things it glues together is commands.
1169 Just understand what you're getting yourself into.
1171 See L<"I/O Operators"> for more discussion.
1175 Evaluates to a list of the words extracted out of STRING, using embedded
1176 whitespace as the word delimiters. It can be understood as being roughly
1179 split(' ', q/STRING/);
1181 the difference being that it generates a real list at compile time. So
1186 is semantically equivalent to the list:
1190 Some frequently seen examples:
1192 use POSIX qw( setlocale localeconv )
1193 @EXPORT = qw( foo bar baz );
1195 A common mistake is to try to separate the words with comma or to
1196 put comments into a multi-line C<qw>-string. For this reason, the
1197 C<use warnings> pragma and the B<-w> switch (that is, the C<$^W> variable)
1198 produces warnings if the STRING contains the "," or the "#" character.
1200 =item s/PATTERN/REPLACEMENT/egimosx
1202 Searches a string for a pattern, and if found, replaces that pattern
1203 with the replacement text and returns the number of substitutions
1204 made. Otherwise it returns false (specifically, the empty string).
1206 If no string is specified via the C<=~> or C<!~> operator, the C<$_>
1207 variable is searched and modified. (The string specified with C<=~> must
1208 be scalar variable, an array element, a hash element, or an assignment
1209 to one of those, i.e., an lvalue.)
1211 If the delimiter chosen is a single quote, no interpolation is
1212 done on either the PATTERN or the REPLACEMENT. Otherwise, if the
1213 PATTERN contains a $ that looks like a variable rather than an
1214 end-of-string test, the variable will be interpolated into the pattern
1215 at run-time. If you want the pattern compiled only once the first time
1216 the variable is interpolated, use the C</o> option. If the pattern
1217 evaluates to the empty string, the last successfully executed regular
1218 expression is used instead. See L<perlre> for further explanation on these.
1219 See L<perllocale> for discussion of additional considerations that apply
1220 when C<use locale> is in effect.
1224 e Evaluate the right side as an expression.
1225 g Replace globally, i.e., all occurrences.
1226 i Do case-insensitive pattern matching.
1227 m Treat string as multiple lines.
1228 o Compile pattern only once.
1229 s Treat string as single line.
1230 x Use extended regular expressions.
1232 Any non-alphanumeric, non-whitespace delimiter may replace the
1233 slashes. If single quotes are used, no interpretation is done on the
1234 replacement string (the C</e> modifier overrides this, however). Unlike
1235 Perl 4, Perl 5 treats backticks as normal delimiters; the replacement
1236 text is not evaluated as a command. If the
1237 PATTERN is delimited by bracketing quotes, the REPLACEMENT has its own
1238 pair of quotes, which may or may not be bracketing quotes, e.g.,
1239 C<s(foo)(bar)> or C<< s<foo>/bar/ >>. A C</e> will cause the
1240 replacement portion to be treated as a full-fledged Perl expression
1241 and evaluated right then and there. It is, however, syntax checked at
1242 compile-time. A second C<e> modifier will cause the replacement portion
1243 to be C<eval>ed before being run as a Perl expression.
1247 s/\bgreen\b/mauve/g; # don't change wintergreen
1249 $path =~ s|/usr/bin|/usr/local/bin|;
1251 s/Login: $foo/Login: $bar/; # run-time pattern
1253 ($foo = $bar) =~ s/this/that/; # copy first, then change
1255 $count = ($paragraph =~ s/Mister\b/Mr./g); # get change-count
1258 s/\d+/$&*2/e; # yields 'abc246xyz'
1259 s/\d+/sprintf("%5d",$&)/e; # yields 'abc 246xyz'
1260 s/\w/$& x 2/eg; # yields 'aabbcc 224466xxyyzz'
1262 s/%(.)/$percent{$1}/g; # change percent escapes; no /e
1263 s/%(.)/$percent{$1} || $&/ge; # expr now, so /e
1264 s/^=(\w+)/&pod($1)/ge; # use function call
1266 # expand variables in $_, but dynamics only, using
1267 # symbolic dereferencing
1270 # Add one to the value of any numbers in the string
1273 # This will expand any embedded scalar variable
1274 # (including lexicals) in $_ : First $1 is interpolated
1275 # to the variable name, and then evaluated
1278 # Delete (most) C comments.
1280 /\* # Match the opening delimiter.
1281 .*? # Match a minimal number of characters.
1282 \*/ # Match the closing delimiter.
1285 s/^\s*(.*?)\s*$/$1/; # trim white space in $_, expensively
1287 for ($variable) { # trim white space in $variable, cheap
1292 s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields
1294 Note the use of $ instead of \ in the last example. Unlike
1295 B<sed>, we use the \<I<digit>> form in only the left hand side.
1296 Anywhere else it's $<I<digit>>.
1298 Occasionally, you can't use just a C</g> to get all the changes
1299 to occur that you might want. Here are two common cases:
1301 # put commas in the right places in an integer
1302 1 while s/(\d)(\d\d\d)(?!\d)/$1,$2/g;
1304 # expand tabs to 8-column spacing
1305 1 while s/\t+/' ' x (length($&)*8 - length($`)%8)/e;
1307 =item tr/SEARCHLIST/REPLACEMENTLIST/cds
1309 =item y/SEARCHLIST/REPLACEMENTLIST/cds
1311 Transliterates all occurrences of the characters found in the search list
1312 with the corresponding character in the replacement list. It returns
1313 the number of characters replaced or deleted. If no string is
1314 specified via the =~ or !~ operator, the $_ string is transliterated. (The
1315 string specified with =~ must be a scalar variable, an array element, a
1316 hash element, or an assignment to one of those, i.e., an lvalue.)
1318 A character range may be specified with a hyphen, so C<tr/A-J/0-9/>
1319 does the same replacement as C<tr/ACEGIBDFHJ/0246813579/>.
1320 For B<sed> devotees, C<y> is provided as a synonym for C<tr>. If the
1321 SEARCHLIST is delimited by bracketing quotes, the REPLACEMENTLIST has
1322 its own pair of quotes, which may or may not be bracketing quotes,
1323 e.g., C<tr[A-Z][a-z]> or C<tr(+\-*/)/ABCD/>.
1325 Note that C<tr> does B<not> do regular expression character classes
1326 such as C<\d> or C<[:lower:]>. The <tr> operator is not equivalent to
1327 the tr(1) utility. If you want to map strings between lower/upper
1328 cases, see L<perlfunc/lc> and L<perlfunc/uc>, and in general consider
1329 using the C<s> operator if you need regular expressions.
1331 Note also that the whole range idea is rather unportable between
1332 character sets--and even within character sets they may cause results
1333 you probably didn't expect. A sound principle is to use only ranges
1334 that begin from and end at either alphabets of equal case (a-e, A-E),
1335 or digits (0-4). Anything else is unsafe. If in doubt, spell out the
1336 character sets in full.
1340 c Complement the SEARCHLIST.
1341 d Delete found but unreplaced characters.
1342 s Squash duplicate replaced characters.
1344 If the C</c> modifier is specified, the SEARCHLIST character set
1345 is complemented. If the C</d> modifier is specified, any characters
1346 specified by SEARCHLIST not found in REPLACEMENTLIST are deleted.
1347 (Note that this is slightly more flexible than the behavior of some
1348 B<tr> programs, which delete anything they find in the SEARCHLIST,
1349 period.) If the C</s> modifier is specified, sequences of characters
1350 that were transliterated to the same character are squashed down
1351 to a single instance of the character.
1353 If the C</d> modifier is used, the REPLACEMENTLIST is always interpreted
1354 exactly as specified. Otherwise, if the REPLACEMENTLIST is shorter
1355 than the SEARCHLIST, the final character is replicated till it is long
1356 enough. If the REPLACEMENTLIST is empty, the SEARCHLIST is replicated.
1357 This latter is useful for counting characters in a class or for
1358 squashing character sequences in a class.
1362 $ARGV[1] =~ tr/A-Z/a-z/; # canonicalize to lower case
1364 $cnt = tr/*/*/; # count the stars in $_
1366 $cnt = $sky =~ tr/*/*/; # count the stars in $sky
1368 $cnt = tr/0-9//; # count the digits in $_
1370 tr/a-zA-Z//s; # bookkeeper -> bokeper
1372 ($HOST = $host) =~ tr/a-z/A-Z/;
1374 tr/a-zA-Z/ /cs; # change non-alphas to single space
1377 [\000-\177]; # delete 8th bit
1379 If multiple transliterations are given for a character, only the
1384 will transliterate any A to X.
1386 Because the transliteration table is built at compile time, neither
1387 the SEARCHLIST nor the REPLACEMENTLIST are subjected to double quote
1388 interpolation. That means that if you want to use variables, you
1391 eval "tr/$oldlist/$newlist/";
1394 eval "tr/$oldlist/$newlist/, 1" or die $@;
1398 A line-oriented form of quoting is based on the shell "here-document"
1399 syntax. Following a C<< << >> you specify a string to terminate
1400 the quoted material, and all lines following the current line down to
1401 the terminating string are the value of the item. The terminating
1402 string may be either an identifier (a word), or some quoted text. If
1403 quoted, the type of quotes you use determines the treatment of the
1404 text, just as in regular quoting. An unquoted identifier works like
1405 double quotes. There must be no space between the C<< << >> and
1406 the identifier, unless the identifier is quoted. (If you put a space it
1407 will be treated as a null identifier, which is valid, and matches the first
1408 empty line.) The terminating string must appear by itself (unquoted and
1409 with no surrounding whitespace) on the terminating line.
1412 The price is $Price.
1415 print << "EOF"; # same as above
1416 The price is $Price.
1419 print << `EOC`; # execute commands
1424 print <<"foo", <<"bar"; # you can stack them
1430 myfunc(<< "THIS", 23, <<'THAT');
1437 Just don't forget that you have to put a semicolon on the end
1438 to finish the statement, as Perl doesn't know you're not going to
1446 If you want your here-docs to be indented with the
1447 rest of the code, you'll need to remove leading whitespace
1448 from each line manually:
1450 ($quote = <<'FINIS') =~ s/^\s+//gm;
1451 The Road goes ever on and on,
1452 down from the door where it began.
1455 If you use a here-doc within a delimited construct, such as in C<s///eg>,
1456 the quoted material must come on the lines following the final delimiter.
1471 If the terminating identifier is on the last line of the program, you
1472 must be sure there is a newline after it; otherwise, Perl will give the
1473 warning B<Can't find string terminator "END" anywhere before EOF...>.
1475 Additionally, the quoting rules for the identifier are not related to
1476 Perl's quoting rules -- C<q()>, C<qq()>, and the like are not supported
1477 in place of C<''> and C<"">, and the only interpolation is for backslashing
1478 the quoting character:
1480 print << "abc\"def";
1484 Finally, quoted strings cannot span multiple lines. The general rule is
1485 that the identifier must be a string literal. Stick with that, and you
1490 =head2 Gory details of parsing quoted constructs
1492 When presented with something that might have several different
1493 interpretations, Perl uses the B<DWIM> (that's "Do What I Mean")
1494 principle to pick the most probable interpretation. This strategy
1495 is so successful that Perl programmers often do not suspect the
1496 ambivalence of what they write. But from time to time, Perl's
1497 notions differ substantially from what the author honestly meant.
1499 This section hopes to clarify how Perl handles quoted constructs.
1500 Although the most common reason to learn this is to unravel labyrinthine
1501 regular expressions, because the initial steps of parsing are the
1502 same for all quoting operators, they are all discussed together.
1504 The most important Perl parsing rule is the first one discussed
1505 below: when processing a quoted construct, Perl first finds the end
1506 of that construct, then interprets its contents. If you understand
1507 this rule, you may skip the rest of this section on the first
1508 reading. The other rules are likely to contradict the user's
1509 expectations much less frequently than this first one.
1511 Some passes discussed below are performed concurrently, but because
1512 their results are the same, we consider them individually. For different
1513 quoting constructs, Perl performs different numbers of passes, from
1514 one to five, but these passes are always performed in the same order.
1518 =item Finding the end
1520 The first pass is finding the end of the quoted construct, whether
1521 it be a multicharacter delimiter C<"\nEOF\n"> in the C<<<EOF>
1522 construct, a C</> that terminates a C<qq//> construct, a C<]> which
1523 terminates C<qq[]> construct, or a C<< > >> which terminates a
1524 fileglob started with C<< < >>.
1526 When searching for single-character non-pairing delimiters, such
1527 as C</>, combinations of C<\\> and C<\/> are skipped. However,
1528 when searching for single-character pairing delimiter like C<[>,
1529 combinations of C<\\>, C<\]>, and C<\[> are all skipped, and nested
1530 C<[>, C<]> are skipped as well. When searching for multicharacter
1531 delimiters, nothing is skipped.
1533 For constructs with three-part delimiters (C<s///>, C<y///>, and
1534 C<tr///>), the search is repeated once more.
1536 During this search no attention is paid to the semantics of the construct.
1539 "$hash{"$foo/$bar"}"
1544 bar # NOT a comment, this slash / terminated m//!
1547 do not form legal quoted expressions. The quoted part ends on the
1548 first C<"> and C</>, and the rest happens to be a syntax error.
1549 Because the slash that terminated C<m//> was followed by a C<SPACE>,
1550 the example above is not C<m//x>, but rather C<m//> with no C</x>
1551 modifier. So the embedded C<#> is interpreted as a literal C<#>.
1553 =item Removal of backslashes before delimiters
1555 During the second pass, text between the starting and ending
1556 delimiters is copied to a safe location, and the C<\> is removed
1557 from combinations consisting of C<\> and delimiter--or delimiters,
1558 meaning both starting and ending delimiters will should these differ.
1559 This removal does not happen for multi-character delimiters.
1560 Note that the combination C<\\> is left intact, just as it was.
1562 Starting from this step no information about the delimiters is
1567 The next step is interpolation in the text obtained, which is now
1568 delimiter-independent. There are four different cases.
1572 =item C<<<'EOF'>, C<m''>, C<s'''>, C<tr///>, C<y///>
1574 No interpolation is performed.
1578 The only interpolation is removal of C<\> from pairs C<\\>.
1580 =item C<"">, C<``>, C<qq//>, C<qx//>, C<< <file*glob> >>
1582 C<\Q>, C<\U>, C<\u>, C<\L>, C<\l> (possibly paired with C<\E>) are
1583 converted to corresponding Perl constructs. Thus, C<"$foo\Qbaz$bar">
1584 is converted to C<$foo . (quotemeta("baz" . $bar))> internally.
1585 The other combinations are replaced with appropriate expansions.
1587 Let it be stressed that I<whatever falls between C<\Q> and C<\E>>
1588 is interpolated in the usual way. Something like C<"\Q\\E"> has
1589 no C<\E> inside. instead, it has C<\Q>, C<\\>, and C<E>, so the
1590 result is the same as for C<"\\\\E">. As a general rule, backslashes
1591 between C<\Q> and C<\E> may lead to counterintuitive results. So,
1592 C<"\Q\t\E"> is converted to C<quotemeta("\t")>, which is the same
1593 as C<"\\\t"> (since TAB is not alphanumeric). Note also that:
1598 may be closer to the conjectural I<intention> of the writer of C<"\Q\t\E">.
1600 Interpolated scalars and arrays are converted internally to the C<join> and
1601 C<.> catenation operations. Thus, C<"$foo XXX '@arr'"> becomes:
1603 $foo . " XXX '" . (join $", @arr) . "'";
1605 All operations above are performed simultaneously, left to right.
1607 Because the result of C<"\Q STRING \E"> has all metacharacters
1608 quoted, there is no way to insert a literal C<$> or C<@> inside a
1609 C<\Q\E> pair. If protected by C<\>, C<$> will be quoted to became
1610 C<"\\\$">; if not, it is interpreted as the start of an interpolated
1613 Note also that the interpolation code needs to make a decision on
1614 where the interpolated scalar ends. For instance, whether
1615 C<< "a $b -> {c}" >> really means:
1617 "a " . $b . " -> {c}";
1623 Most of the time, the longest possible text that does not include
1624 spaces between components and which contains matching braces or
1625 brackets. because the outcome may be determined by voting based
1626 on heuristic estimators, the result is not strictly predictable.
1627 Fortunately, it's usually correct for ambiguous cases.
1629 =item C<?RE?>, C</RE/>, C<m/RE/>, C<s/RE/foo/>,
1631 Processing of C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, and interpolation
1632 happens (almost) as with C<qq//> constructs, but the substitution
1633 of C<\> followed by RE-special chars (including C<\>) is not
1634 performed. Moreover, inside C<(?{BLOCK})>, C<(?# comment )>, and
1635 a C<#>-comment in a C<//x>-regular expression, no processing is
1636 performed whatsoever. This is the first step at which the presence
1637 of the C<//x> modifier is relevant.
1639 Interpolation has several quirks: C<$|>, C<$(>, and C<$)> are not
1640 interpolated, and constructs C<$var[SOMETHING]> are voted (by several
1641 different estimators) to be either an array element or C<$var>
1642 followed by an RE alternative. This is where the notation
1643 C<${arr[$bar]}> comes handy: C</${arr[0-9]}/> is interpreted as
1644 array element C<-9>, not as a regular expression from the variable
1645 C<$arr> followed by a digit, which would be the interpretation of
1646 C</$arr[0-9]/>. Since voting among different estimators may occur,
1647 the result is not predictable.
1649 It is at this step that C<\1> is begrudgingly converted to C<$1> in
1650 the replacement text of C<s///> to correct the incorrigible
1651 I<sed> hackers who haven't picked up the saner idiom yet. A warning
1652 is emitted if the C<use warnings> pragma or the B<-w> command-line flag
1653 (that is, the C<$^W> variable) was set.
1655 The lack of processing of C<\\> creates specific restrictions on
1656 the post-processed text. If the delimiter is C</>, one cannot get
1657 the combination C<\/> into the result of this step. C</> will
1658 finish the regular expression, C<\/> will be stripped to C</> on
1659 the previous step, and C<\\/> will be left as is. Because C</> is
1660 equivalent to C<\/> inside a regular expression, this does not
1661 matter unless the delimiter happens to be character special to the
1662 RE engine, such as in C<s*foo*bar*>, C<m[foo]>, or C<?foo?>; or an
1663 alphanumeric char, as in:
1667 In the RE above, which is intentionally obfuscated for illustration, the
1668 delimiter is C<m>, the modifier is C<mx>, and after backslash-removal the
1669 RE is the same as for C<m/ ^ a s* b /mx>). There's more than one
1670 reason you're encouraged to restrict your delimiters to non-alphanumeric,
1671 non-whitespace choices.
1675 This step is the last one for all constructs except regular expressions,
1676 which are processed further.
1678 =item Interpolation of regular expressions
1680 Previous steps were performed during the compilation of Perl code,
1681 but this one happens at run time--although it may be optimized to
1682 be calculated at compile time if appropriate. After preprocessing
1683 described above, and possibly after evaluation if catenation,
1684 joining, casing translation, or metaquoting are involved, the
1685 resulting I<string> is passed to the RE engine for compilation.
1687 Whatever happens in the RE engine might be better discussed in L<perlre>,
1688 but for the sake of continuity, we shall do so here.
1690 This is another step where the presence of the C<//x> modifier is
1691 relevant. The RE engine scans the string from left to right and
1692 converts it to a finite automaton.
1694 Backslashed characters are either replaced with corresponding
1695 literal strings (as with C<\{>), or else they generate special nodes
1696 in the finite automaton (as with C<\b>). Characters special to the
1697 RE engine (such as C<|>) generate corresponding nodes or groups of
1698 nodes. C<(?#...)> comments are ignored. All the rest is either
1699 converted to literal strings to match, or else is ignored (as is
1700 whitespace and C<#>-style comments if C<//x> is present).
1702 Parsing of the bracketed character class construct, C<[...]>, is
1703 rather different than the rule used for the rest of the pattern.
1704 The terminator of this construct is found using the same rules as
1705 for finding the terminator of a C<{}>-delimited construct, the only
1706 exception being that C<]> immediately following C<[> is treated as
1707 though preceded by a backslash. Similarly, the terminator of
1708 C<(?{...})> is found using the same rules as for finding the
1709 terminator of a C<{}>-delimited construct.
1711 It is possible to inspect both the string given to RE engine and the
1712 resulting finite automaton. See the arguments C<debug>/C<debugcolor>
1713 in the C<use L<re>> pragma, as well as Perl's B<-Dr> command-line
1714 switch documented in L<perlrun/"Command Switches">.
1716 =item Optimization of regular expressions
1718 This step is listed for completeness only. Since it does not change
1719 semantics, details of this step are not documented and are subject
1720 to change without notice. This step is performed over the finite
1721 automaton that was generated during the previous pass.
1723 It is at this stage that C<split()> silently optimizes C</^/> to
1728 =head2 I/O Operators
1730 There are several I/O operators you should know about.
1732 A string enclosed by backticks (grave accents) first undergoes
1733 double-quote interpolation. It is then interpreted as an external
1734 command, and the output of that command is the value of the
1735 backtick string, like in a shell. In scalar context, a single string
1736 consisting of all output is returned. In list context, a list of
1737 values is returned, one per line of output. (You can set C<$/> to use
1738 a different line terminator.) The command is executed each time the
1739 pseudo-literal is evaluated. The status value of the command is
1740 returned in C<$?> (see L<perlvar> for the interpretation of C<$?>).
1741 Unlike in B<csh>, no translation is done on the return data--newlines
1742 remain newlines. Unlike in any of the shells, single quotes do not
1743 hide variable names in the command from interpretation. To pass a
1744 literal dollar-sign through to the shell you need to hide it with a
1745 backslash. The generalized form of backticks is C<qx//>. (Because
1746 backticks always undergo shell expansion as well, see L<perlsec> for
1749 In scalar context, evaluating a filehandle in angle brackets yields
1750 the next line from that file (the newline, if any, included), or
1751 C<undef> at end-of-file or on error. When C<$/> is set to C<undef>
1752 (sometimes known as file-slurp mode) and the file is empty, it
1753 returns C<''> the first time, followed by C<undef> subsequently.
1755 Ordinarily you must assign the returned value to a variable, but
1756 there is one situation where an automatic assignment happens. If
1757 and only if the input symbol is the only thing inside the conditional
1758 of a C<while> statement (even if disguised as a C<for(;;)> loop),
1759 the value is automatically assigned to the global variable $_,
1760 destroying whatever was there previously. (This may seem like an
1761 odd thing to you, but you'll use the construct in almost every Perl
1762 script you write.) The $_ variable is not implicitly localized.
1763 You'll have to put a C<local $_;> before the loop if you want that
1766 The following lines are equivalent:
1768 while (defined($_ = <STDIN>)) { print; }
1769 while ($_ = <STDIN>) { print; }
1770 while (<STDIN>) { print; }
1771 for (;<STDIN>;) { print; }
1772 print while defined($_ = <STDIN>);
1773 print while ($_ = <STDIN>);
1774 print while <STDIN>;
1776 This also behaves similarly, but avoids $_ :
1778 while (my $line = <STDIN>) { print $line }
1780 In these loop constructs, the assigned value (whether assignment
1781 is automatic or explicit) is then tested to see whether it is
1782 defined. The defined test avoids problems where line has a string
1783 value that would be treated as false by Perl, for example a "" or
1784 a "0" with no trailing newline. If you really mean for such values
1785 to terminate the loop, they should be tested for explicitly:
1787 while (($_ = <STDIN>) ne '0') { ... }
1788 while (<STDIN>) { last unless $_; ... }
1790 In other boolean contexts, C<< <I<filehandle>> >> without an
1791 explicit C<defined> test or comparison elicit a warning if the
1792 C<use warnings> pragma or the B<-w>
1793 command-line switch (the C<$^W> variable) is in effect.
1795 The filehandles STDIN, STDOUT, and STDERR are predefined. (The
1796 filehandles C<stdin>, C<stdout>, and C<stderr> will also work except
1797 in packages, where they would be interpreted as local identifiers
1798 rather than global.) Additional filehandles may be created with
1799 the open() function, amongst others. See L<perlopentut> and
1800 L<perlfunc/open> for details on this.
1802 If a <FILEHANDLE> is used in a context that is looking for
1803 a list, a list comprising all input lines is returned, one line per
1804 list element. It's easy to grow to a rather large data space this
1805 way, so use with care.
1807 <FILEHANDLE> may also be spelled C<readline(*FILEHANDLE)>.
1808 See L<perlfunc/readline>.
1810 The null filehandle <> is special: it can be used to emulate the
1811 behavior of B<sed> and B<awk>. Input from <> comes either from
1812 standard input, or from each file listed on the command line. Here's
1813 how it works: the first time <> is evaluated, the @ARGV array is
1814 checked, and if it is empty, C<$ARGV[0]> is set to "-", which when opened
1815 gives you standard input. The @ARGV array is then processed as a list
1816 of filenames. The loop
1819 ... # code for each line
1822 is equivalent to the following Perl-like pseudo code:
1824 unshift(@ARGV, '-') unless @ARGV;
1825 while ($ARGV = shift) {
1828 ... # code for each line
1832 except that it isn't so cumbersome to say, and will actually work.
1833 It really does shift the @ARGV array and put the current filename
1834 into the $ARGV variable. It also uses filehandle I<ARGV>
1835 internally--<> is just a synonym for <ARGV>, which
1836 is magical. (The pseudo code above doesn't work because it treats
1837 <ARGV> as non-magical.)
1839 You can modify @ARGV before the first <> as long as the array ends up
1840 containing the list of filenames you really want. Line numbers (C<$.>)
1841 continue as though the input were one big happy file. See the example
1842 in L<perlfunc/eof> for how to reset line numbers on each file.
1844 If you want to set @ARGV to your own list of files, go right ahead.
1845 This sets @ARGV to all plain text files if no @ARGV was given:
1847 @ARGV = grep { -f && -T } glob('*') unless @ARGV;
1849 You can even set them to pipe commands. For example, this automatically
1850 filters compressed arguments through B<gzip>:
1852 @ARGV = map { /\.(gz|Z)$/ ? "gzip -dc < $_ |" : $_ } @ARGV;
1854 If you want to pass switches into your script, you can use one of the
1855 Getopts modules or put a loop on the front like this:
1857 while ($_ = $ARGV[0], /^-/) {
1860 if (/^-D(.*)/) { $debug = $1 }
1861 if (/^-v/) { $verbose++ }
1862 # ... # other switches
1866 # ... # code for each line
1869 The <> symbol will return C<undef> for end-of-file only once.
1870 If you call it again after this, it will assume you are processing another
1871 @ARGV list, and if you haven't set @ARGV, will read input from STDIN.
1873 If what the angle brackets contain is a simple scalar variable (e.g.,
1874 <$foo>), then that variable contains the name of the
1875 filehandle to input from, or its typeglob, or a reference to the
1881 If what's within the angle brackets is neither a filehandle nor a simple
1882 scalar variable containing a filehandle name, typeglob, or typeglob
1883 reference, it is interpreted as a filename pattern to be globbed, and
1884 either a list of filenames or the next filename in the list is returned,
1885 depending on context. This distinction is determined on syntactic
1886 grounds alone. That means C<< <$x> >> is always a readline() from
1887 an indirect handle, but C<< <$hash{key}> >> is always a glob().
1888 That's because $x is a simple scalar variable, but C<$hash{key}> is
1889 not--it's a hash element.
1891 One level of double-quote interpretation is done first, but you can't
1892 say C<< <$foo> >> because that's an indirect filehandle as explained
1893 in the previous paragraph. (In older versions of Perl, programmers
1894 would insert curly brackets to force interpretation as a filename glob:
1895 C<< <${foo}> >>. These days, it's considered cleaner to call the
1896 internal function directly as C<glob($foo)>, which is probably the right
1897 way to have done it in the first place.) For example:
1903 is roughly equivalent to:
1905 open(FOO, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|");
1911 except that the globbing is actually done internally using the standard
1912 C<File::Glob> extension. Of course, the shortest way to do the above is:
1916 A (file)glob evaluates its (embedded) argument only when it is
1917 starting a new list. All values must be read before it will start
1918 over. In list context, this isn't important because you automatically
1919 get them all anyway. However, in scalar context the operator returns
1920 the next value each time it's called, or C<undef> when the list has
1921 run out. As with filehandle reads, an automatic C<defined> is
1922 generated when the glob occurs in the test part of a C<while>,
1923 because legal glob returns (e.g. a file called F<0>) would otherwise
1924 terminate the loop. Again, C<undef> is returned only once. So if
1925 you're expecting a single value from a glob, it is much better to
1928 ($file) = <blurch*>;
1934 because the latter will alternate between returning a filename and
1937 If you're trying to do variable interpolation, it's definitely better
1938 to use the glob() function, because the older notation can cause people
1939 to become confused with the indirect filehandle notation.
1941 @files = glob("$dir/*.[ch]");
1942 @files = glob($files[$i]);
1944 =head2 Constant Folding
1946 Like C, Perl does a certain amount of expression evaluation at
1947 compile time whenever it determines that all arguments to an
1948 operator are static and have no side effects. In particular, string
1949 concatenation happens at compile time between literals that don't do
1950 variable substitution. Backslash interpolation also happens at
1951 compile time. You can say
1953 'Now is the time for all' . "\n" .
1954 'good men to come to.'
1956 and this all reduces to one string internally. Likewise, if
1959 foreach $file (@filenames) {
1960 if (-s $file > 5 + 100 * 2**16) { }
1963 the compiler will precompute the number which that expression
1964 represents so that the interpreter won't have to.
1966 =head2 Bitwise String Operators
1968 Bitstrings of any size may be manipulated by the bitwise operators
1971 If the operands to a binary bitwise op are strings of different
1972 sizes, B<|> and B<^> ops act as though the shorter operand had
1973 additional zero bits on the right, while the B<&> op acts as though
1974 the longer operand were truncated to the length of the shorter.
1975 The granularity for such extension or truncation is one or more
1978 # ASCII-based examples
1979 print "j p \n" ^ " a h"; # prints "JAPH\n"
1980 print "JA" | " ph\n"; # prints "japh\n"
1981 print "japh\nJunk" & '_____'; # prints "JAPH\n";
1982 print 'p N$' ^ " E<H\n"; # prints "Perl\n";
1984 If you are intending to manipulate bitstrings, be certain that
1985 you're supplying bitstrings: If an operand is a number, that will imply
1986 a B<numeric> bitwise operation. You may explicitly show which type of
1987 operation you intend by using C<""> or C<0+>, as in the examples below.
1989 $foo = 150 | 105 ; # yields 255 (0x96 | 0x69 is 0xFF)
1990 $foo = '150' | 105 ; # yields 255
1991 $foo = 150 | '105'; # yields 255
1992 $foo = '150' | '105'; # yields string '155' (under ASCII)
1994 $baz = 0+$foo & 0+$bar; # both ops explicitly numeric
1995 $biz = "$foo" ^ "$bar"; # both ops explicitly stringy
1997 See L<perlfunc/vec> for information on how to manipulate individual bits
2000 =head2 Integer Arithmetic
2002 By default, Perl assumes that it must do most of its arithmetic in
2003 floating point. But by saying
2007 you may tell the compiler that it's okay to use integer operations
2008 (if it feels like it) from here to the end of the enclosing BLOCK.
2009 An inner BLOCK may countermand this by saying
2013 which lasts until the end of that BLOCK. Note that this doesn't
2014 mean everything is only an integer, merely that Perl may use integer
2015 operations if it is so inclined. For example, even under C<use
2016 integer>, if you take the C<sqrt(2)>, you'll still get C<1.4142135623731>
2019 Used on numbers, the bitwise operators ("&", "|", "^", "~", "<<",
2020 and ">>") always produce integral results. (But see also
2021 L<Bitwise String Operators>.) However, C<use integer> still has meaning for
2022 them. By default, their results are interpreted as unsigned integers, but
2023 if C<use integer> is in effect, their results are interpreted
2024 as signed integers. For example, C<~0> usually evaluates to a large
2025 integral value. However, C<use integer; ~0> is C<-1> on twos-complement
2028 =head2 Floating-point Arithmetic
2030 While C<use integer> provides integer-only arithmetic, there is no
2031 analogous mechanism to provide automatic rounding or truncation to a
2032 certain number of decimal places. For rounding to a certain number
2033 of digits, sprintf() or printf() is usually the easiest route.
2036 Floating-point numbers are only approximations to what a mathematician
2037 would call real numbers. There are infinitely more reals than floats,
2038 so some corners must be cut. For example:
2040 printf "%.20g\n", 123456789123456789;
2041 # produces 123456789123456784
2043 Testing for exact equality of floating-point equality or inequality is
2044 not a good idea. Here's a (relatively expensive) work-around to compare
2045 whether two floating-point numbers are equal to a particular number of
2046 decimal places. See Knuth, volume II, for a more robust treatment of
2050 my ($X, $Y, $POINTS) = @_;
2052 $tX = sprintf("%.${POINTS}g", $X);
2053 $tY = sprintf("%.${POINTS}g", $Y);
2057 The POSIX module (part of the standard perl distribution) implements
2058 ceil(), floor(), and other mathematical and trigonometric functions.
2059 The Math::Complex module (part of the standard perl distribution)
2060 defines mathematical functions that work on both the reals and the
2061 imaginary numbers. Math::Complex not as efficient as POSIX, but
2062 POSIX can't work with complex numbers.
2064 Rounding in financial applications can have serious implications, and
2065 the rounding method used should be specified precisely. In these
2066 cases, it probably pays not to trust whichever system rounding is
2067 being used by Perl, but to instead implement the rounding function you
2070 =head2 Bigger Numbers
2072 The standard Math::BigInt and Math::BigFloat modules provide
2073 variable-precision arithmetic and overloaded operators, although
2074 they're currently pretty slow. At the cost of some space and
2075 considerable speed, they avoid the normal pitfalls associated with
2076 limited-precision representations.
2079 $x = Math::BigInt->new('123456789123456789');
2082 # prints +15241578780673678515622620750190521
2084 There are several modules that let you calculate with (bound only by
2085 memory and cpu-time) unlimited or fixed precision. There are also
2086 some non-standard modules that provide faster implementations via
2087 external C libraries.
2089 Here is a short, but incomplete summary:
2091 Math::Fraction big, unlimited fractions like 9973 / 12967
2092 Math::String treat string sequences like numbers
2093 Math::FixedPrecision calculate with a fixed precision
2094 Math::Currency for currency calculations
2095 Bit::Vector manipulate bit vectors fast (uses C)
2096 Math::BigIntFast Bit::Vector wrapper for big numbers
2097 Math::Pari provides access to the Pari C library
2098 Math::BigInteger uses an external C library
2099 Math::Cephes uses external Cephes C library (no big numbers)
2100 Math::Cephes::Fraction fractions via the Cephes library
2101 Math::GMP another one using an external C library