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 The auto-decrement operator is not magical.
132 =head2 Exponentiation
134 Binary "**" is the exponentiation operator. It binds even more
135 tightly than unary minus, so -2**4 is -(2**4), not (-2)**4. (This is
136 implemented using C's pow(3) function, which actually works on doubles
139 =head2 Symbolic Unary Operators
141 Unary "!" performs logical negation, i.e., "not". See also C<not> for a lower
142 precedence version of this.
144 Unary "-" performs arithmetic negation if the operand is numeric. If
145 the operand is an identifier, a string consisting of a minus sign
146 concatenated with the identifier is returned. Otherwise, if the string
147 starts with a plus or minus, a string starting with the opposite sign
148 is returned. One effect of these rules is that C<-bareword> is equivalent
151 Unary "~" performs bitwise negation, i.e., 1's complement. For
152 example, C<0666 & ~027> is 0640. (See also L<Integer Arithmetic> and
153 L<Bitwise String Operators>.) Note that the width of the result is
154 platform-dependent: ~0 is 32 bits wide on a 32-bit platform, but 64
155 bits wide on a 64-bit platform, so if you are expecting a certain bit
156 width, remember use the & operator to mask off the excess bits.
158 Unary "+" has no effect whatsoever, even on strings. It is useful
159 syntactically for separating a function name from a parenthesized expression
160 that would otherwise be interpreted as the complete list of function
161 arguments. (See examples above under L<Terms and List Operators (Leftward)>.)
163 Unary "\" creates a reference to whatever follows it. See L<perlreftut>
164 and L<perlref>. Do not confuse this behavior with the behavior of
165 backslash within a string, although both forms do convey the notion
166 of protecting the next thing from interpolation.
168 =head2 Binding Operators
170 Binary "=~" binds a scalar expression to a pattern match. Certain operations
171 search or modify the string $_ by default. This operator makes that kind
172 of operation work on some other string. The right argument is a search
173 pattern, substitution, or transliteration. The left argument is what is
174 supposed to be searched, substituted, or transliterated instead of the default
175 $_. When used in scalar context, the return value generally indicates the
176 success of the operation. Behavior in list context depends on the particular
177 operator. See L</"Regexp Quote-Like Operators"> for details.
179 If the right argument is an expression rather than a search pattern,
180 substitution, or transliteration, it is interpreted as a search pattern at run
181 time. This can be less efficient than an explicit search, because the
182 pattern must be compiled every time the expression is evaluated.
184 Binary "!~" is just like "=~" except the return value is negated in
187 =head2 Multiplicative Operators
189 Binary "*" multiplies two numbers.
191 Binary "/" divides two numbers.
193 Binary "%" computes the modulus of two numbers. Given integer
194 operands C<$a> and C<$b>: If C<$b> is positive, then C<$a % $b> is
195 C<$a> minus the largest multiple of C<$b> that is not greater than
196 C<$a>. If C<$b> is negative, then C<$a % $b> is C<$a> minus the
197 smallest multiple of C<$b> that is not less than C<$a> (i.e. the
198 result will be less than or equal to zero).
199 Note that when C<use integer> is in scope, "%" gives you direct access
200 to the modulus operator as implemented by your C compiler. This
201 operator is not as well defined for negative operands, but it will
204 Binary "x" is the repetition operator. In scalar context or if the left
205 operand is not enclosed in parentheses, it returns a string consisting
206 of the left operand repeated the number of times specified by the right
207 operand. In list context, if the left operand is enclosed in
208 parentheses, it repeats the list.
210 print '-' x 80; # print row of dashes
212 print "\t" x ($tab/8), ' ' x ($tab%8); # tab over
214 @ones = (1) x 80; # a list of 80 1's
215 @ones = (5) x @ones; # set all elements to 5
218 =head2 Additive Operators
220 Binary "+" returns the sum of two numbers.
222 Binary "-" returns the difference of two numbers.
224 Binary "." concatenates two strings.
226 =head2 Shift Operators
228 Binary "<<" returns the value of its left argument shifted left by the
229 number of bits specified by the right argument. Arguments should be
230 integers. (See also L<Integer Arithmetic>.)
232 Binary ">>" returns the value of its left argument shifted right by
233 the number of bits specified by the right argument. Arguments should
234 be integers. (See also L<Integer Arithmetic>.)
236 Note that both "<<" and ">>" in Perl are implemented directly using
237 "<<" and ">>" in C. If C<use integer> (see L<Integer Arithmetic>) is
238 in force then signed C integers are used, else unsigned C integers are
239 used. Either way, the implementation isn't going to generate results
240 larger than the size of the integer type Perl was built with (32 bits
243 The result of overflowing the range of the integers is undefined
244 because it is undefined also in C. In other words, using 32-bit
245 integers, C<< 1 << 32 >> is undefined. Shifting by a negative number
246 of bits is also undefined.
248 =head2 Named Unary Operators
250 The various named unary operators are treated as functions with one
251 argument, with optional parentheses. These include the filetest
252 operators, like C<-f>, C<-M>, etc. See L<perlfunc>.
254 If any list operator (print(), etc.) or any unary operator (chdir(), etc.)
255 is followed by a left parenthesis as the next token, the operator and
256 arguments within parentheses are taken to be of highest precedence,
257 just like a normal function call. For example,
258 because named unary operators are higher precedence than ||:
260 chdir $foo || die; # (chdir $foo) || die
261 chdir($foo) || die; # (chdir $foo) || die
262 chdir ($foo) || die; # (chdir $foo) || die
263 chdir +($foo) || die; # (chdir $foo) || die
265 but, because * is higher precedence than named operators:
267 chdir $foo * 20; # chdir ($foo * 20)
268 chdir($foo) * 20; # (chdir $foo) * 20
269 chdir ($foo) * 20; # (chdir $foo) * 20
270 chdir +($foo) * 20; # chdir ($foo * 20)
272 rand 10 * 20; # rand (10 * 20)
273 rand(10) * 20; # (rand 10) * 20
274 rand (10) * 20; # (rand 10) * 20
275 rand +(10) * 20; # rand (10 * 20)
277 See also L<"Terms and List Operators (Leftward)">.
279 =head2 Relational Operators
281 Binary "<" returns true if the left argument is numerically less than
284 Binary ">" returns true if the left argument is numerically greater
285 than the right argument.
287 Binary "<=" returns true if the left argument is numerically less than
288 or equal to the right argument.
290 Binary ">=" returns true if the left argument is numerically greater
291 than or equal to the right argument.
293 Binary "lt" returns true if the left argument is stringwise less than
296 Binary "gt" returns true if the left argument is stringwise greater
297 than the right argument.
299 Binary "le" returns true if the left argument is stringwise less than
300 or equal to the right argument.
302 Binary "ge" returns true if the left argument is stringwise greater
303 than or equal to the right argument.
305 =head2 Equality Operators
307 Binary "==" returns true if the left argument is numerically equal to
310 Binary "!=" returns true if the left argument is numerically not equal
311 to the right argument.
313 Binary "<=>" returns -1, 0, or 1 depending on whether the left
314 argument is numerically less than, equal to, or greater than the right
315 argument. If your platform supports NaNs (not-a-numbers) as numeric
316 values, using them with "<=>" returns undef. NaN is not "<", "==", ">",
317 "<=" or ">=" anything (even NaN), so those 5 return false. NaN != NaN
318 returns true, as does NaN != anything else. If your platform doesn't
319 support NaNs then NaN is just a string with numeric value 0.
321 perl -le '$a = NaN; print "No NaN support here" if $a == $a'
322 perl -le '$a = NaN; print "NaN support here" if $a != $a'
324 Binary "eq" returns true if the left argument is stringwise equal to
327 Binary "ne" returns true if the left argument is stringwise not equal
328 to the right argument.
330 Binary "cmp" returns -1, 0, or 1 depending on whether the left
331 argument is stringwise less than, equal to, or greater than the right
334 "lt", "le", "ge", "gt" and "cmp" use the collation (sort) order specified
335 by the current locale if C<use locale> is in effect. See L<perllocale>.
339 Binary "&" returns its operands ANDed together bit by bit.
340 (See also L<Integer Arithmetic> and L<Bitwise String Operators>.)
342 Note that "&" has lower priority than relational operators, so for example
343 the brackets are essential in a test like
345 print "Even\n" if ($x & 1) == 0;
347 =head2 Bitwise Or and Exclusive Or
349 Binary "|" returns its operands ORed together bit by bit.
350 (See also L<Integer Arithmetic> and L<Bitwise String Operators>.)
352 Binary "^" returns its operands XORed together bit by bit.
353 (See also L<Integer Arithmetic> and L<Bitwise String Operators>.)
355 Note that "|" and "^" have lower priority than relational operators, so
356 for example the brackets are essential in a test like
358 print "false\n" if (8 | 2) != 10;
360 =head2 C-style Logical And
362 Binary "&&" performs a short-circuit logical AND operation. That is,
363 if the left operand is false, the right operand is not even evaluated.
364 Scalar or list context propagates down to the right operand if it
367 =head2 C-style Logical Or
369 Binary "||" performs a short-circuit logical OR operation. That is,
370 if the left operand is true, the right operand is not even evaluated.
371 Scalar or list context propagates down to the right operand if it
374 =head2 C-style Logical Defined-Or
376 Although it has no direct equivalent in C, Perl's C<//> operator is related
377 to its C-style or. In fact, it's exactly the same as C<||>, except that it
378 tests the left hand side's definedness instead of its truth. Thus, C<$a // $b>
379 is similar to C<defined($a) || $b> (except that it returns the value of C<$a>
380 rather than the value of C<defined($a)>) and is exactly equivalent to
381 C<defined($a) ? $a : $b>. This is very useful for providing default values
382 for variables. If you actually want to test if at least one of C<$a> and C<$b> is
383 defined, use C<defined($a // $b)>.
385 The C<||>, C<//> and C<&&> operators differ from C's in that, rather than returning
386 0 or 1, they return the last value evaluated. Thus, a reasonably portable
387 way to find out the home directory might be:
389 $home = $ENV{'HOME'} // $ENV{'LOGDIR'} //
390 (getpwuid($<))[7] // die "You're homeless!\n";
392 In particular, this means that you shouldn't use this
393 for selecting between two aggregates for assignment:
395 @a = @b || @c; # this is wrong
396 @a = scalar(@b) || @c; # really meant this
397 @a = @b ? @b : @c; # this works fine, though
399 As more readable alternatives to C<&&>, C<//> and C<||> when used for
400 control flow, Perl provides C<and>, C<err> and C<or> operators (see below).
401 The short-circuit behavior is identical. The precedence of "and", "err"
402 and "or" is much lower, however, so that you can safely use them after a
403 list operator without the need for parentheses:
405 unlink "alpha", "beta", "gamma"
406 or gripe(), next LINE;
408 With the C-style operators that would have been written like this:
410 unlink("alpha", "beta", "gamma")
411 || (gripe(), next LINE);
413 Using "or" for assignment is unlikely to do what you want; see below.
415 =head2 Range Operators
417 Binary ".." is the range operator, which is really two different
418 operators depending on the context. In list context, it returns an
419 list of values counting (up by ones) from the left value to the right
420 value. If the left value is greater than the right value then it
421 returns the empty array. The range operator is useful for writing
422 C<foreach (1..10)> loops and for doing slice operations on arrays. In
423 the current implementation, no temporary array is created when the
424 range operator is used as the expression in C<foreach> loops, but older
425 versions of Perl might burn a lot of memory when you write something
428 for (1 .. 1_000_000) {
432 The range operator also works on strings, using the magical auto-increment,
435 In scalar context, ".." returns a boolean value. The operator is
436 bistable, like a flip-flop, and emulates the line-range (comma) operator
437 of B<sed>, B<awk>, and various editors. Each ".." operator maintains its
438 own boolean state. It is false as long as its left operand is false.
439 Once the left operand is true, the range operator stays true until the
440 right operand is true, I<AFTER> which the range operator becomes false
441 again. It doesn't become false till the next time the range operator is
442 evaluated. It can test the right operand and become false on the same
443 evaluation it became true (as in B<awk>), but it still returns true once.
444 If you don't want it to test the right operand till the next
445 evaluation, as in B<sed>, just use three dots ("...") instead of
446 two. In all other regards, "..." behaves just like ".." does.
448 The right operand is not evaluated while the operator is in the
449 "false" state, and the left operand is not evaluated while the
450 operator is in the "true" state. The precedence is a little lower
451 than || and &&. The value returned is either the empty string for
452 false, or a sequence number (beginning with 1) for true. The
453 sequence number is reset for each range encountered. The final
454 sequence number in a range has the string "E0" appended to it, which
455 doesn't affect its numeric value, but gives you something to search
456 for if you want to exclude the endpoint. You can exclude the
457 beginning point by waiting for the sequence number to be greater
458 than 1. If either operand of scalar ".." is a constant expression,
459 that operand is implicitly compared to the C<$.> variable, the
460 current line number. Examples:
462 As a scalar operator:
464 if (101 .. 200) { print; } # print 2nd hundred lines
465 next line if (1 .. /^$/); # skip header lines
466 s/^/> / if (/^$/ .. eof()); # quote body
468 # parse mail messages
470 $in_header = 1 .. /^$/;
471 $in_body = /^$/ .. eof();
472 # do something based on those
474 close ARGV if eof; # reset $. each file
479 for (101 .. 200) { print; } # print $_ 100 times
480 @foo = @foo[0 .. $#foo]; # an expensive no-op
481 @foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items
483 The range operator (in list context) makes use of the magical
484 auto-increment algorithm if the operands are strings. You
487 @alphabet = ('A' .. 'Z');
489 to get all normal letters of the English alphabet, or
491 $hexdigit = (0 .. 9, 'a' .. 'f')[$num & 15];
493 to get a hexadecimal digit, or
495 @z2 = ('01' .. '31'); print $z2[$mday];
497 to get dates with leading zeros. If the final value specified is not
498 in the sequence that the magical increment would produce, the sequence
499 goes until the next value would be longer than the final value
502 =head2 Conditional Operator
504 Ternary "?:" is the conditional operator, just as in C. It works much
505 like an if-then-else. If the argument before the ? is true, the
506 argument before the : is returned, otherwise the argument after the :
507 is returned. For example:
509 printf "I have %d dog%s.\n", $n,
510 ($n == 1) ? '' : "s";
512 Scalar or list context propagates downward into the 2nd
513 or 3rd argument, whichever is selected.
515 $a = $ok ? $b : $c; # get a scalar
516 @a = $ok ? @b : @c; # get an array
517 $a = $ok ? @b : @c; # oops, that's just a count!
519 The operator may be assigned to if both the 2nd and 3rd arguments are
520 legal lvalues (meaning that you can assign to them):
522 ($a_or_b ? $a : $b) = $c;
524 Because this operator produces an assignable result, using assignments
525 without parentheses will get you in trouble. For example, this:
527 $a % 2 ? $a += 10 : $a += 2
531 (($a % 2) ? ($a += 10) : $a) += 2
535 ($a % 2) ? ($a += 10) : ($a += 2)
537 That should probably be written more simply as:
539 $a += ($a % 2) ? 10 : 2;
541 =head2 Assignment Operators
543 "=" is the ordinary assignment operator.
545 Assignment operators work as in C. That is,
553 although without duplicating any side effects that dereferencing the lvalue
554 might trigger, such as from tie(). Other assignment operators work similarly.
555 The following are recognized:
562 Although these are grouped by family, they all have the precedence
565 Unlike in C, the scalar assignment operator produces a valid lvalue.
566 Modifying an assignment is equivalent to doing the assignment and
567 then modifying the variable that was assigned to. This is useful
568 for modifying a copy of something, like this:
570 ($tmp = $global) =~ tr [A-Z] [a-z];
581 Similarly, a list assignment in list context produces the list of
582 lvalues assigned to, and a list assignment in scalar context returns
583 the number of elements produced by the expression on the right hand
584 side of the assignment.
586 =head2 Comma Operator
588 Binary "," is the comma operator. In scalar context it evaluates
589 its left argument, throws that value away, then evaluates its right
590 argument and returns that value. This is just like C's comma operator.
592 In list context, it's just the list argument separator, and inserts
593 both its arguments into the list.
595 The => digraph is mostly just a synonym for the comma operator. It's useful for
596 documenting arguments that come in pairs. As of release 5.001, it also forces
597 any word to the left of it to be interpreted as a string.
599 =head2 List Operators (Rightward)
601 On the right side of a list operator, it has very low precedence,
602 such that it controls all comma-separated expressions found there.
603 The only operators with lower precedence are the logical operators
604 "and", "or", and "not", which may be used to evaluate calls to list
605 operators without the need for extra parentheses:
607 open HANDLE, "filename"
608 or die "Can't open: $!\n";
610 See also discussion of list operators in L<Terms and List Operators (Leftward)>.
614 Unary "not" returns the logical negation of the expression to its right.
615 It's the equivalent of "!" except for the very low precedence.
619 Binary "and" returns the logical conjunction of the two surrounding
620 expressions. It's equivalent to && except for the very low
621 precedence. This means that it short-circuits: i.e., the right
622 expression is evaluated only if the left expression is true.
624 =head2 Logical or, Defined or, and Exclusive Or
626 Binary "or" returns the logical disjunction of the two surrounding
627 expressions. It's equivalent to || except for the very low precedence.
628 This makes it useful for control flow
630 print FH $data or die "Can't write to FH: $!";
632 This means that it short-circuits: i.e., the right expression is evaluated
633 only if the left expression is false. Due to its precedence, you should
634 probably avoid using this for assignment, only for control flow.
636 $a = $b or $c; # bug: this is wrong
637 ($a = $b) or $c; # really means this
638 $a = $b || $c; # better written this way
640 However, when it's a list-context assignment and you're trying to use
641 "||" for control flow, you probably need "or" so that the assignment
642 takes higher precedence.
644 @info = stat($file) || die; # oops, scalar sense of stat!
645 @info = stat($file) or die; # better, now @info gets its due
647 Then again, you could always use parentheses.
649 Binary "err" is equivalent to C<//>--it's just like binary "or", except it tests
650 its left argument's definedness instead of its truth. There are two ways to
651 remember "err": either because many functions return C<undef> on an B<err>or,
652 or as a sort of correction: C<$a=($b err 'default')>
654 Binary "xor" returns the exclusive-OR of the two surrounding expressions.
655 It cannot short circuit, of course.
657 =head2 C Operators Missing From Perl
659 Here is what C has that Perl doesn't:
665 Address-of operator. (But see the "\" operator for taking a reference.)
669 Dereference-address operator. (Perl's prefix dereferencing
670 operators are typed: $, @, %, and &.)
674 Type-casting operator.
678 =head2 Quote and Quote-like Operators
680 While we usually think of quotes as literal values, in Perl they
681 function as operators, providing various kinds of interpolating and
682 pattern matching capabilities. Perl provides customary quote characters
683 for these behaviors, but also provides a way for you to choose your
684 quote character for any of them. In the following table, a C<{}> represents
685 any pair of delimiters you choose.
687 Customary Generic Meaning Interpolates
692 // m{} Pattern match yes*
694 s{}{} Substitution yes*
695 tr{}{} Transliteration no (but see below)
698 * unless the delimiter is ''.
700 Non-bracketing delimiters use the same character fore and aft, but the four
701 sorts of brackets (round, angle, square, curly) will all nest, which means
710 Note, however, that this does not always work for quoting Perl code:
712 $s = q{ if($a eq "}") ... }; # WRONG
714 is a syntax error. The C<Text::Balanced> module (from CPAN, and
715 starting from Perl 5.8 part of the standard distribution) is able
718 There can be whitespace between the operator and the quoting
719 characters, except when C<#> is being used as the quoting character.
720 C<q#foo#> is parsed as the string C<foo>, while C<q #foo#> is the
721 operator C<q> followed by a comment. Its argument will be taken
722 from the next line. This allows you to write:
724 s {foo} # Replace foo
727 The following escape sequences are available in constructs that interpolate
728 and in transliterations.
735 \a alarm (bell) (BEL)
737 \033 octal char (ESC)
739 \x{263a} wide hex char (SMILEY)
740 \c[ control char (ESC)
741 \N{name} named Unicode character
743 The following escape sequences are available in constructs that interpolate
744 but not in transliterations.
746 \l lowercase next char
747 \u uppercase next char
750 \E end case modification
751 \Q quote non-word characters till \E
753 If C<use locale> is in effect, the case map used by C<\l>, C<\L>,
754 C<\u> and C<\U> is taken from the current locale. See L<perllocale>.
755 If Unicode (for example, C<\N{}> or wide hex characters of 0x100 or
756 beyond) is being used, the case map used by C<\l>, C<\L>, C<\u> and
757 C<\U> is as defined by Unicode. For documentation of C<\N{name}>,
760 All systems use the virtual C<"\n"> to represent a line terminator,
761 called a "newline". There is no such thing as an unvarying, physical
762 newline character. It is only an illusion that the operating system,
763 device drivers, C libraries, and Perl all conspire to preserve. Not all
764 systems read C<"\r"> as ASCII CR and C<"\n"> as ASCII LF. For example,
765 on a Mac, these are reversed, and on systems without line terminator,
766 printing C<"\n"> may emit no actual data. In general, use C<"\n"> when
767 you mean a "newline" for your system, but use the literal ASCII when you
768 need an exact character. For example, most networking protocols expect
769 and prefer a CR+LF (C<"\015\012"> or C<"\cM\cJ">) for line terminators,
770 and although they often accept just C<"\012">, they seldom tolerate just
771 C<"\015">. If you get in the habit of using C<"\n"> for networking,
772 you may be burned some day.
774 For constructs that do interpolate, variables beginning with "C<$>"
775 or "C<@>" are interpolated. Subscripted variables such as C<$a[3]> or
776 C<< $href->{key}[0] >> are also interpolated, as are array and hash slices.
777 But method calls such as C<< $obj->meth >> are not.
779 Interpolating an array or slice interpolates the elements in order,
780 separated by the value of C<$">, so is equivalent to interpolating
781 C<join $", @array>. "Punctuation" arrays such as C<@+> are only
782 interpolated if the name is enclosed in braces C<@{+}>.
784 You cannot include a literal C<$> or C<@> within a C<\Q> sequence.
785 An unescaped C<$> or C<@> interpolates the corresponding variable,
786 while escaping will cause the literal string C<\$> to be inserted.
787 You'll need to write something like C<m/\Quser\E\@\Qhost/>.
789 Patterns are subject to an additional level of interpretation as a
790 regular expression. This is done as a second pass, after variables are
791 interpolated, so that regular expressions may be incorporated into the
792 pattern from the variables. If this is not what you want, use C<\Q> to
793 interpolate a variable literally.
795 Apart from the behavior described above, Perl does not expand
796 multiple levels of interpolation. In particular, contrary to the
797 expectations of shell programmers, back-quotes do I<NOT> interpolate
798 within double quotes, nor do single quotes impede evaluation of
799 variables when used within double quotes.
801 =head2 Regexp Quote-Like Operators
803 Here are the quote-like operators that apply to pattern
804 matching and related activities.
810 This is just like the C</pattern/> search, except that it matches only
811 once between calls to the reset() operator. This is a useful
812 optimization when you want to see only the first occurrence of
813 something in each file of a set of files, for instance. Only C<??>
814 patterns local to the current package are reset.
818 # blank line between header and body
821 reset if eof; # clear ?? status for next file
824 This usage is vaguely deprecated, which means it just might possibly
825 be removed in some distant future version of Perl, perhaps somewhere
826 around the year 2168.
828 =item m/PATTERN/cgimosx
830 =item /PATTERN/cgimosx
832 Searches a string for a pattern match, and in scalar context returns
833 true if it succeeds, false if it fails. If no string is specified
834 via the C<=~> or C<!~> operator, the $_ string is searched. (The
835 string specified with C<=~> need not be an lvalue--it may be the
836 result of an expression evaluation, but remember the C<=~> binds
837 rather tightly.) See also L<perlre>. See L<perllocale> for
838 discussion of additional considerations that apply when C<use locale>
843 c Do not reset search position on a failed match when /g is in effect.
844 g Match globally, i.e., find all occurrences.
845 i Do case-insensitive pattern matching.
846 m Treat string as multiple lines.
847 o Compile pattern only once.
848 s Treat string as single line.
849 x Use extended regular expressions.
851 If "/" is the delimiter then the initial C<m> is optional. With the C<m>
852 you can use any pair of non-alphanumeric, non-whitespace characters
853 as delimiters. This is particularly useful for matching path names
854 that contain "/", to avoid LTS (leaning toothpick syndrome). If "?" is
855 the delimiter, then the match-only-once rule of C<?PATTERN?> applies.
856 If "'" is the delimiter, no interpolation is performed on the PATTERN.
858 PATTERN may contain variables, which will be interpolated (and the
859 pattern recompiled) every time the pattern search is evaluated, except
860 for when the delimiter is a single quote. (Note that C<$(>, C<$)>, and
861 C<$|> are not interpolated because they look like end-of-string tests.)
862 If you want such a pattern to be compiled only once, add a C</o> after
863 the trailing delimiter. This avoids expensive run-time recompilations,
864 and is useful when the value you are interpolating won't change over
865 the life of the script. However, mentioning C</o> constitutes a promise
866 that you won't change the variables in the pattern. If you change them,
867 Perl won't even notice. See also L<"qr/STRING/imosx">.
869 If the PATTERN evaluates to the empty string, the last
870 I<successfully> matched regular expression is used instead. In this
871 case, only the C<g> and C<c> flags on the empty pattern is honoured -
872 the other flags are taken from the original pattern. If no match has
873 previously succeeded, this will (silently) act instead as a genuine
874 empty pattern (which will always match).
876 Note that it's possible to confuse Perl into thinking C<//> (the empty
877 regex) is really C<//> (the defined-or operator). Perl is usually pretty
878 good about this, but some pathological cases might trigger this, such as
879 C<$a///> (is that C<($a) / (//)> or C<$a // />?) and C<print $fh //>
880 (C<print $fh(//> or C<print($fh //>?). In all of these examples, Perl
881 will assume you meant defined-or. If you meant the empty regex, just
882 use parentheses or spaces to disambiguate, or even prefix the empty
883 regex with an C<m> (so C<//> becomes C<m//>).
885 If the C</g> option is not used, C<m//> in list context returns a
886 list consisting of the subexpressions matched by the parentheses in the
887 pattern, i.e., (C<$1>, C<$2>, C<$3>...). (Note that here C<$1> etc. are
888 also set, and that this differs from Perl 4's behavior.) When there are
889 no parentheses in the pattern, the return value is the list C<(1)> for
890 success. With or without parentheses, an empty list is returned upon
895 open(TTY, '/dev/tty');
896 <TTY> =~ /^y/i && foo(); # do foo if desired
898 if (/Version: *([0-9.]*)/) { $version = $1; }
900 next if m#^/usr/spool/uucp#;
905 print if /$arg/o; # compile only once
908 if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))
910 This last example splits $foo into the first two words and the
911 remainder of the line, and assigns those three fields to $F1, $F2, and
912 $Etc. The conditional is true if any variables were assigned, i.e., if
915 The C</g> modifier specifies global pattern matching--that is,
916 matching as many times as possible within the string. How it behaves
917 depends on the context. In list context, it returns a list of the
918 substrings matched by any capturing parentheses in the regular
919 expression. If there are no parentheses, it returns a list of all
920 the matched strings, as if there were parentheses around the whole
923 In scalar context, each execution of C<m//g> finds the next match,
924 returning true if it matches, and false if there is no further match.
925 The position after the last match can be read or set using the pos()
926 function; see L<perlfunc/pos>. A failed match normally resets the
927 search position to the beginning of the string, but you can avoid that
928 by adding the C</c> modifier (e.g. C<m//gc>). Modifying the target
929 string also resets the search position.
931 You can intermix C<m//g> matches with C<m/\G.../g>, where C<\G> is a
932 zero-width assertion that matches the exact position where the previous
933 C<m//g>, if any, left off. Without the C</g> modifier, the C<\G> assertion
934 still anchors at pos(), but the match is of course only attempted once.
935 Using C<\G> without C</g> on a target string that has not previously had a
936 C</g> match applied to it is the same as using the C<\A> assertion to match
937 the beginning of the string. Note also that, currently, C<\G> is only
938 properly supported when anchored at the very beginning of the pattern.
943 ($one,$five,$fifteen) = (`uptime` =~ /(\d+\.\d+)/g);
947 while (defined($paragraph = <>)) {
948 while ($paragraph =~ /[a-z]['")]*[.!?]+['")]*\s/g) {
952 print "$sentences\n";
954 # using m//gc with \G
958 print $1 while /(o)/gc; print "', pos=", pos, "\n";
960 print $1 if /\G(q)/gc; print "', pos=", pos, "\n";
962 print $1 while /(p)/gc; print "', pos=", pos, "\n";
964 print "Final: '$1', pos=",pos,"\n" if /\G(.)/;
966 The last example should print:
976 Notice that the final match matched C<q> instead of C<p>, which a match
977 without the C<\G> anchor would have done. Also note that the final match
978 did not update C<pos> -- C<pos> is only updated on a C</g> match. If the
979 final match did indeed match C<p>, it's a good bet that you're running an
980 older (pre-5.6.0) Perl.
982 A useful idiom for C<lex>-like scanners is C</\G.../gc>. You can
983 combine several regexps like this to process a string part-by-part,
984 doing different actions depending on which regexp matched. Each
985 regexp tries to match where the previous one leaves off.
988 $url = new URI::URL "http://www/"; die if $url eq "xXx";
992 print(" digits"), redo LOOP if /\G\d+\b[,.;]?\s*/gc;
993 print(" lowercase"), redo LOOP if /\G[a-z]+\b[,.;]?\s*/gc;
994 print(" UPPERCASE"), redo LOOP if /\G[A-Z]+\b[,.;]?\s*/gc;
995 print(" Capitalized"), redo LOOP if /\G[A-Z][a-z]+\b[,.;]?\s*/gc;
996 print(" MiXeD"), redo LOOP if /\G[A-Za-z]+\b[,.;]?\s*/gc;
997 print(" alphanumeric"), redo LOOP if /\G[A-Za-z0-9]+\b[,.;]?\s*/gc;
998 print(" line-noise"), redo LOOP if /\G[^A-Za-z0-9]+/gc;
999 print ". That's all!\n";
1002 Here is the output (split into several lines):
1004 line-noise lowercase line-noise lowercase UPPERCASE line-noise
1005 UPPERCASE line-noise lowercase line-noise lowercase line-noise
1006 lowercase lowercase line-noise lowercase lowercase line-noise
1007 MiXeD line-noise. That's all!
1013 A single-quoted, literal string. A backslash represents a backslash
1014 unless followed by the delimiter or another backslash, in which case
1015 the delimiter or backslash is interpolated.
1017 $foo = q!I said, "You said, 'She said it.'"!;
1018 $bar = q('This is it.');
1019 $baz = '\n'; # a two-character string
1025 A double-quoted, interpolated string.
1028 (*** The previous line contains the naughty word "$1".\n)
1029 if /\b(tcl|java|python)\b/i; # :-)
1030 $baz = "\n"; # a one-character string
1032 =item qr/STRING/imosx
1034 This operator quotes (and possibly compiles) its I<STRING> as a regular
1035 expression. I<STRING> is interpolated the same way as I<PATTERN>
1036 in C<m/PATTERN/>. If "'" is used as the delimiter, no interpolation
1037 is done. Returns a Perl value which may be used instead of the
1038 corresponding C</STRING/imosx> expression.
1042 $rex = qr/my.STRING/is;
1049 The result may be used as a subpattern in a match:
1052 $string =~ /foo${re}bar/; # can be interpolated in other patterns
1053 $string =~ $re; # or used standalone
1054 $string =~ /$re/; # or this way
1056 Since Perl may compile the pattern at the moment of execution of qr()
1057 operator, using qr() may have speed advantages in some situations,
1058 notably if the result of qr() is used standalone:
1061 my $patterns = shift;
1062 my @compiled = map qr/$_/i, @$patterns;
1065 foreach my $pat (@compiled) {
1066 $success = 1, last if /$pat/;
1072 Precompilation of the pattern into an internal representation at
1073 the moment of qr() avoids a need to recompile the pattern every
1074 time a match C</$pat/> is attempted. (Perl has many other internal
1075 optimizations, but none would be triggered in the above example if
1076 we did not use qr() operator.)
1080 i Do case-insensitive pattern matching.
1081 m Treat string as multiple lines.
1082 o Compile pattern only once.
1083 s Treat string as single line.
1084 x Use extended regular expressions.
1086 See L<perlre> for additional information on valid syntax for STRING, and
1087 for a detailed look at the semantics of regular expressions.
1093 A string which is (possibly) interpolated and then executed as a
1094 system command with C</bin/sh> or its equivalent. Shell wildcards,
1095 pipes, and redirections will be honored. The collected standard
1096 output of the command is returned; standard error is unaffected. In
1097 scalar context, it comes back as a single (potentially multi-line)
1098 string, or undef if the command failed. In list context, returns a
1099 list of lines (however you've defined lines with $/ or
1100 $INPUT_RECORD_SEPARATOR), or an empty list if the command failed.
1102 Because backticks do not affect standard error, use shell file descriptor
1103 syntax (assuming the shell supports this) if you care to address this.
1104 To capture a command's STDERR and STDOUT together:
1106 $output = `cmd 2>&1`;
1108 To capture a command's STDOUT but discard its STDERR:
1110 $output = `cmd 2>/dev/null`;
1112 To capture a command's STDERR but discard its STDOUT (ordering is
1115 $output = `cmd 2>&1 1>/dev/null`;
1117 To exchange a command's STDOUT and STDERR in order to capture the STDERR
1118 but leave its STDOUT to come out the old STDERR:
1120 $output = `cmd 3>&1 1>&2 2>&3 3>&-`;
1122 To read both a command's STDOUT and its STDERR separately, it's easiest
1123 and safest to redirect them separately to files, and then read from those
1124 files when the program is done:
1126 system("program args 1>/tmp/program.stdout 2>/tmp/program.stderr");
1128 Using single-quote as a delimiter protects the command from Perl's
1129 double-quote interpolation, passing it on to the shell instead:
1131 $perl_info = qx(ps $$); # that's Perl's $$
1132 $shell_info = qx'ps $$'; # that's the new shell's $$
1134 How that string gets evaluated is entirely subject to the command
1135 interpreter on your system. On most platforms, you will have to protect
1136 shell metacharacters if you want them treated literally. This is in
1137 practice difficult to do, as it's unclear how to escape which characters.
1138 See L<perlsec> for a clean and safe example of a manual fork() and exec()
1139 to emulate backticks safely.
1141 On some platforms (notably DOS-like ones), the shell may not be
1142 capable of dealing with multiline commands, so putting newlines in
1143 the string may not get you what you want. You may be able to evaluate
1144 multiple commands in a single line by separating them with the command
1145 separator character, if your shell supports that (e.g. C<;> on many Unix
1146 shells; C<&> on the Windows NT C<cmd> shell).
1148 Beginning with v5.6.0, Perl will attempt to flush all files opened for
1149 output before starting the child process, but this may not be supported
1150 on some platforms (see L<perlport>). To be safe, you may need to set
1151 C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method of
1152 C<IO::Handle> on any open handles.
1154 Beware that some command shells may place restrictions on the length
1155 of the command line. You must ensure your strings don't exceed this
1156 limit after any necessary interpolations. See the platform-specific
1157 release notes for more details about your particular environment.
1159 Using this operator can lead to programs that are difficult to port,
1160 because the shell commands called vary between systems, and may in
1161 fact not be present at all. As one example, the C<type> command under
1162 the POSIX shell is very different from the C<type> command under DOS.
1163 That doesn't mean you should go out of your way to avoid backticks
1164 when they're the right way to get something done. Perl was made to be
1165 a glue language, and one of the things it glues together is commands.
1166 Just understand what you're getting yourself into.
1168 See L<"I/O Operators"> for more discussion.
1172 Evaluates to a list of the words extracted out of STRING, using embedded
1173 whitespace as the word delimiters. It can be understood as being roughly
1176 split(' ', q/STRING/);
1178 the difference being that it generates a real list at compile time. So
1183 is semantically equivalent to the list:
1187 Some frequently seen examples:
1189 use POSIX qw( setlocale localeconv )
1190 @EXPORT = qw( foo bar baz );
1192 A common mistake is to try to separate the words with comma or to
1193 put comments into a multi-line C<qw>-string. For this reason, the
1194 C<use warnings> pragma and the B<-w> switch (that is, the C<$^W> variable)
1195 produces warnings if the STRING contains the "," or the "#" character.
1197 =item s/PATTERN/REPLACEMENT/egimosx
1199 Searches a string for a pattern, and if found, replaces that pattern
1200 with the replacement text and returns the number of substitutions
1201 made. Otherwise it returns false (specifically, the empty string).
1203 If no string is specified via the C<=~> or C<!~> operator, the C<$_>
1204 variable is searched and modified. (The string specified with C<=~> must
1205 be scalar variable, an array element, a hash element, or an assignment
1206 to one of those, i.e., an lvalue.)
1208 If the delimiter chosen is a single quote, no interpolation is
1209 done on either the PATTERN or the REPLACEMENT. Otherwise, if the
1210 PATTERN contains a $ that looks like a variable rather than an
1211 end-of-string test, the variable will be interpolated into the pattern
1212 at run-time. If you want the pattern compiled only once the first time
1213 the variable is interpolated, use the C</o> option. If the pattern
1214 evaluates to the empty string, the last successfully executed regular
1215 expression is used instead. See L<perlre> for further explanation on these.
1216 See L<perllocale> for discussion of additional considerations that apply
1217 when C<use locale> is in effect.
1221 e Evaluate the right side as an expression.
1222 g Replace globally, i.e., all occurrences.
1223 i Do case-insensitive pattern matching.
1224 m Treat string as multiple lines.
1225 o Compile pattern only once.
1226 s Treat string as single line.
1227 x Use extended regular expressions.
1229 Any non-alphanumeric, non-whitespace delimiter may replace the
1230 slashes. If single quotes are used, no interpretation is done on the
1231 replacement string (the C</e> modifier overrides this, however). Unlike
1232 Perl 4, Perl 5 treats backticks as normal delimiters; the replacement
1233 text is not evaluated as a command. If the
1234 PATTERN is delimited by bracketing quotes, the REPLACEMENT has its own
1235 pair of quotes, which may or may not be bracketing quotes, e.g.,
1236 C<s(foo)(bar)> or C<< s<foo>/bar/ >>. A C</e> will cause the
1237 replacement portion to be treated as a full-fledged Perl expression
1238 and evaluated right then and there. It is, however, syntax checked at
1239 compile-time. A second C<e> modifier will cause the replacement portion
1240 to be C<eval>ed before being run as a Perl expression.
1244 s/\bgreen\b/mauve/g; # don't change wintergreen
1246 $path =~ s|/usr/bin|/usr/local/bin|;
1248 s/Login: $foo/Login: $bar/; # run-time pattern
1250 ($foo = $bar) =~ s/this/that/; # copy first, then change
1252 $count = ($paragraph =~ s/Mister\b/Mr./g); # get change-count
1255 s/\d+/$&*2/e; # yields 'abc246xyz'
1256 s/\d+/sprintf("%5d",$&)/e; # yields 'abc 246xyz'
1257 s/\w/$& x 2/eg; # yields 'aabbcc 224466xxyyzz'
1259 s/%(.)/$percent{$1}/g; # change percent escapes; no /e
1260 s/%(.)/$percent{$1} || $&/ge; # expr now, so /e
1261 s/^=(\w+)/&pod($1)/ge; # use function call
1263 # expand variables in $_, but dynamics only, using
1264 # symbolic dereferencing
1267 # Add one to the value of any numbers in the string
1270 # This will expand any embedded scalar variable
1271 # (including lexicals) in $_ : First $1 is interpolated
1272 # to the variable name, and then evaluated
1275 # Delete (most) C comments.
1277 /\* # Match the opening delimiter.
1278 .*? # Match a minimal number of characters.
1279 \*/ # Match the closing delimiter.
1282 s/^\s*(.*?)\s*$/$1/; # trim white space in $_, expensively
1284 for ($variable) { # trim white space in $variable, cheap
1289 s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields
1291 Note the use of $ instead of \ in the last example. Unlike
1292 B<sed>, we use the \<I<digit>> form in only the left hand side.
1293 Anywhere else it's $<I<digit>>.
1295 Occasionally, you can't use just a C</g> to get all the changes
1296 to occur that you might want. Here are two common cases:
1298 # put commas in the right places in an integer
1299 1 while s/(\d)(\d\d\d)(?!\d)/$1,$2/g;
1301 # expand tabs to 8-column spacing
1302 1 while s/\t+/' ' x (length($&)*8 - length($`)%8)/e;
1304 =item tr/SEARCHLIST/REPLACEMENTLIST/cds
1306 =item y/SEARCHLIST/REPLACEMENTLIST/cds
1308 Transliterates all occurrences of the characters found in the search list
1309 with the corresponding character in the replacement list. It returns
1310 the number of characters replaced or deleted. If no string is
1311 specified via the =~ or !~ operator, the $_ string is transliterated. (The
1312 string specified with =~ must be a scalar variable, an array element, a
1313 hash element, or an assignment to one of those, i.e., an lvalue.)
1315 A character range may be specified with a hyphen, so C<tr/A-J/0-9/>
1316 does the same replacement as C<tr/ACEGIBDFHJ/0246813579/>.
1317 For B<sed> devotees, C<y> is provided as a synonym for C<tr>. If the
1318 SEARCHLIST is delimited by bracketing quotes, the REPLACEMENTLIST has
1319 its own pair of quotes, which may or may not be bracketing quotes,
1320 e.g., C<tr[A-Z][a-z]> or C<tr(+\-*/)/ABCD/>.
1322 Note that C<tr> does B<not> do regular expression character classes
1323 such as C<\d> or C<[:lower:]>. The <tr> operator is not equivalent to
1324 the tr(1) utility. If you want to map strings between lower/upper
1325 cases, see L<perlfunc/lc> and L<perlfunc/uc>, and in general consider
1326 using the C<s> operator if you need regular expressions.
1328 Note also that the whole range idea is rather unportable between
1329 character sets--and even within character sets they may cause results
1330 you probably didn't expect. A sound principle is to use only ranges
1331 that begin from and end at either alphabets of equal case (a-e, A-E),
1332 or digits (0-4). Anything else is unsafe. If in doubt, spell out the
1333 character sets in full.
1337 c Complement the SEARCHLIST.
1338 d Delete found but unreplaced characters.
1339 s Squash duplicate replaced characters.
1341 If the C</c> modifier is specified, the SEARCHLIST character set
1342 is complemented. If the C</d> modifier is specified, any characters
1343 specified by SEARCHLIST not found in REPLACEMENTLIST are deleted.
1344 (Note that this is slightly more flexible than the behavior of some
1345 B<tr> programs, which delete anything they find in the SEARCHLIST,
1346 period.) If the C</s> modifier is specified, sequences of characters
1347 that were transliterated to the same character are squashed down
1348 to a single instance of the character.
1350 If the C</d> modifier is used, the REPLACEMENTLIST is always interpreted
1351 exactly as specified. Otherwise, if the REPLACEMENTLIST is shorter
1352 than the SEARCHLIST, the final character is replicated till it is long
1353 enough. If the REPLACEMENTLIST is empty, the SEARCHLIST is replicated.
1354 This latter is useful for counting characters in a class or for
1355 squashing character sequences in a class.
1359 $ARGV[1] =~ tr/A-Z/a-z/; # canonicalize to lower case
1361 $cnt = tr/*/*/; # count the stars in $_
1363 $cnt = $sky =~ tr/*/*/; # count the stars in $sky
1365 $cnt = tr/0-9//; # count the digits in $_
1367 tr/a-zA-Z//s; # bookkeeper -> bokeper
1369 ($HOST = $host) =~ tr/a-z/A-Z/;
1371 tr/a-zA-Z/ /cs; # change non-alphas to single space
1374 [\000-\177]; # delete 8th bit
1376 If multiple transliterations are given for a character, only the
1381 will transliterate any A to X.
1383 Because the transliteration table is built at compile time, neither
1384 the SEARCHLIST nor the REPLACEMENTLIST are subjected to double quote
1385 interpolation. That means that if you want to use variables, you
1388 eval "tr/$oldlist/$newlist/";
1391 eval "tr/$oldlist/$newlist/, 1" or die $@;
1395 A line-oriented form of quoting is based on the shell "here-document"
1396 syntax. Following a C<< << >> you specify a string to terminate
1397 the quoted material, and all lines following the current line down to
1398 the terminating string are the value of the item. The terminating
1399 string may be either an identifier (a word), or some quoted text. If
1400 quoted, the type of quotes you use determines the treatment of the
1401 text, just as in regular quoting. An unquoted identifier works like
1402 double quotes. There must be no space between the C<< << >> and
1403 the identifier, unless the identifier is quoted. (If you put a space it
1404 will be treated as a null identifier, which is valid, and matches the first
1405 empty line.) The terminating string must appear by itself (unquoted and
1406 with no surrounding whitespace) on the terminating line.
1409 The price is $Price.
1412 print << "EOF"; # same as above
1413 The price is $Price.
1416 print << `EOC`; # execute commands
1421 print <<"foo", <<"bar"; # you can stack them
1427 myfunc(<< "THIS", 23, <<'THAT');
1434 Just don't forget that you have to put a semicolon on the end
1435 to finish the statement, as Perl doesn't know you're not going to
1443 If you want your here-docs to be indented with the
1444 rest of the code, you'll need to remove leading whitespace
1445 from each line manually:
1447 ($quote = <<'FINIS') =~ s/^\s+//gm;
1448 The Road goes ever on and on,
1449 down from the door where it began.
1452 If you use a here-doc within a delimited construct, such as in C<s///eg>,
1453 the quoted material must come on the lines following the final delimiter.
1468 If the terminating identifier is on the last line of the program, you
1469 must be sure there is a newline after it; otherwise, Perl will give the
1470 warning B<Can't find string terminator "END" anywhere before EOF...>.
1472 Additionally, the quoting rules for the identifier are not related to
1473 Perl's quoting rules -- C<q()>, C<qq()>, and the like are not supported
1474 in place of C<''> and C<"">, and the only interpolation is for backslashing
1475 the quoting character:
1477 print << "abc\"def";
1481 Finally, quoted strings cannot span multiple lines. The general rule is
1482 that the identifier must be a string literal. Stick with that, and you
1487 =head2 Gory details of parsing quoted constructs
1489 When presented with something that might have several different
1490 interpretations, Perl uses the B<DWIM> (that's "Do What I Mean")
1491 principle to pick the most probable interpretation. This strategy
1492 is so successful that Perl programmers often do not suspect the
1493 ambivalence of what they write. But from time to time, Perl's
1494 notions differ substantially from what the author honestly meant.
1496 This section hopes to clarify how Perl handles quoted constructs.
1497 Although the most common reason to learn this is to unravel labyrinthine
1498 regular expressions, because the initial steps of parsing are the
1499 same for all quoting operators, they are all discussed together.
1501 The most important Perl parsing rule is the first one discussed
1502 below: when processing a quoted construct, Perl first finds the end
1503 of that construct, then interprets its contents. If you understand
1504 this rule, you may skip the rest of this section on the first
1505 reading. The other rules are likely to contradict the user's
1506 expectations much less frequently than this first one.
1508 Some passes discussed below are performed concurrently, but because
1509 their results are the same, we consider them individually. For different
1510 quoting constructs, Perl performs different numbers of passes, from
1511 one to five, but these passes are always performed in the same order.
1515 =item Finding the end
1517 The first pass is finding the end of the quoted construct, whether
1518 it be a multicharacter delimiter C<"\nEOF\n"> in the C<<<EOF>
1519 construct, a C</> that terminates a C<qq//> construct, a C<]> which
1520 terminates C<qq[]> construct, or a C<< > >> which terminates a
1521 fileglob started with C<< < >>.
1523 When searching for single-character non-pairing delimiters, such
1524 as C</>, combinations of C<\\> and C<\/> are skipped. However,
1525 when searching for single-character pairing delimiter like C<[>,
1526 combinations of C<\\>, C<\]>, and C<\[> are all skipped, and nested
1527 C<[>, C<]> are skipped as well. When searching for multicharacter
1528 delimiters, nothing is skipped.
1530 For constructs with three-part delimiters (C<s///>, C<y///>, and
1531 C<tr///>), the search is repeated once more.
1533 During this search no attention is paid to the semantics of the construct.
1536 "$hash{"$foo/$bar"}"
1541 bar # NOT a comment, this slash / terminated m//!
1544 do not form legal quoted expressions. The quoted part ends on the
1545 first C<"> and C</>, and the rest happens to be a syntax error.
1546 Because the slash that terminated C<m//> was followed by a C<SPACE>,
1547 the example above is not C<m//x>, but rather C<m//> with no C</x>
1548 modifier. So the embedded C<#> is interpreted as a literal C<#>.
1550 =item Removal of backslashes before delimiters
1552 During the second pass, text between the starting and ending
1553 delimiters is copied to a safe location, and the C<\> is removed
1554 from combinations consisting of C<\> and delimiter--or delimiters,
1555 meaning both starting and ending delimiters will should these differ.
1556 This removal does not happen for multi-character delimiters.
1557 Note that the combination C<\\> is left intact, just as it was.
1559 Starting from this step no information about the delimiters is
1564 The next step is interpolation in the text obtained, which is now
1565 delimiter-independent. There are four different cases.
1569 =item C<<<'EOF'>, C<m''>, C<s'''>, C<tr///>, C<y///>
1571 No interpolation is performed.
1575 The only interpolation is removal of C<\> from pairs C<\\>.
1577 =item C<"">, C<``>, C<qq//>, C<qx//>, C<< <file*glob> >>
1579 C<\Q>, C<\U>, C<\u>, C<\L>, C<\l> (possibly paired with C<\E>) are
1580 converted to corresponding Perl constructs. Thus, C<"$foo\Qbaz$bar">
1581 is converted to C<$foo . (quotemeta("baz" . $bar))> internally.
1582 The other combinations are replaced with appropriate expansions.
1584 Let it be stressed that I<whatever falls between C<\Q> and C<\E>>
1585 is interpolated in the usual way. Something like C<"\Q\\E"> has
1586 no C<\E> inside. instead, it has C<\Q>, C<\\>, and C<E>, so the
1587 result is the same as for C<"\\\\E">. As a general rule, backslashes
1588 between C<\Q> and C<\E> may lead to counterintuitive results. So,
1589 C<"\Q\t\E"> is converted to C<quotemeta("\t")>, which is the same
1590 as C<"\\\t"> (since TAB is not alphanumeric). Note also that:
1595 may be closer to the conjectural I<intention> of the writer of C<"\Q\t\E">.
1597 Interpolated scalars and arrays are converted internally to the C<join> and
1598 C<.> catenation operations. Thus, C<"$foo XXX '@arr'"> becomes:
1600 $foo . " XXX '" . (join $", @arr) . "'";
1602 All operations above are performed simultaneously, left to right.
1604 Because the result of C<"\Q STRING \E"> has all metacharacters
1605 quoted, there is no way to insert a literal C<$> or C<@> inside a
1606 C<\Q\E> pair. If protected by C<\>, C<$> will be quoted to became
1607 C<"\\\$">; if not, it is interpreted as the start of an interpolated
1610 Note also that the interpolation code needs to make a decision on
1611 where the interpolated scalar ends. For instance, whether
1612 C<< "a $b -> {c}" >> really means:
1614 "a " . $b . " -> {c}";
1620 Most of the time, the longest possible text that does not include
1621 spaces between components and which contains matching braces or
1622 brackets. because the outcome may be determined by voting based
1623 on heuristic estimators, the result is not strictly predictable.
1624 Fortunately, it's usually correct for ambiguous cases.
1626 =item C<?RE?>, C</RE/>, C<m/RE/>, C<s/RE/foo/>,
1628 Processing of C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, and interpolation
1629 happens (almost) as with C<qq//> constructs, but the substitution
1630 of C<\> followed by RE-special chars (including C<\>) is not
1631 performed. Moreover, inside C<(?{BLOCK})>, C<(?# comment )>, and
1632 a C<#>-comment in a C<//x>-regular expression, no processing is
1633 performed whatsoever. This is the first step at which the presence
1634 of the C<//x> modifier is relevant.
1636 Interpolation has several quirks: C<$|>, C<$(>, and C<$)> are not
1637 interpolated, and constructs C<$var[SOMETHING]> are voted (by several
1638 different estimators) to be either an array element or C<$var>
1639 followed by an RE alternative. This is where the notation
1640 C<${arr[$bar]}> comes handy: C</${arr[0-9]}/> is interpreted as
1641 array element C<-9>, not as a regular expression from the variable
1642 C<$arr> followed by a digit, which would be the interpretation of
1643 C</$arr[0-9]/>. Since voting among different estimators may occur,
1644 the result is not predictable.
1646 It is at this step that C<\1> is begrudgingly converted to C<$1> in
1647 the replacement text of C<s///> to correct the incorrigible
1648 I<sed> hackers who haven't picked up the saner idiom yet. A warning
1649 is emitted if the C<use warnings> pragma or the B<-w> command-line flag
1650 (that is, the C<$^W> variable) was set.
1652 The lack of processing of C<\\> creates specific restrictions on
1653 the post-processed text. If the delimiter is C</>, one cannot get
1654 the combination C<\/> into the result of this step. C</> will
1655 finish the regular expression, C<\/> will be stripped to C</> on
1656 the previous step, and C<\\/> will be left as is. Because C</> is
1657 equivalent to C<\/> inside a regular expression, this does not
1658 matter unless the delimiter happens to be character special to the
1659 RE engine, such as in C<s*foo*bar*>, C<m[foo]>, or C<?foo?>; or an
1660 alphanumeric char, as in:
1664 In the RE above, which is intentionally obfuscated for illustration, the
1665 delimiter is C<m>, the modifier is C<mx>, and after backslash-removal the
1666 RE is the same as for C<m/ ^ a s* b /mx>). There's more than one
1667 reason you're encouraged to restrict your delimiters to non-alphanumeric,
1668 non-whitespace choices.
1672 This step is the last one for all constructs except regular expressions,
1673 which are processed further.
1675 =item Interpolation of regular expressions
1677 Previous steps were performed during the compilation of Perl code,
1678 but this one happens at run time--although it may be optimized to
1679 be calculated at compile time if appropriate. After preprocessing
1680 described above, and possibly after evaluation if catenation,
1681 joining, casing translation, or metaquoting are involved, the
1682 resulting I<string> is passed to the RE engine for compilation.
1684 Whatever happens in the RE engine might be better discussed in L<perlre>,
1685 but for the sake of continuity, we shall do so here.
1687 This is another step where the presence of the C<//x> modifier is
1688 relevant. The RE engine scans the string from left to right and
1689 converts it to a finite automaton.
1691 Backslashed characters are either replaced with corresponding
1692 literal strings (as with C<\{>), or else they generate special nodes
1693 in the finite automaton (as with C<\b>). Characters special to the
1694 RE engine (such as C<|>) generate corresponding nodes or groups of
1695 nodes. C<(?#...)> comments are ignored. All the rest is either
1696 converted to literal strings to match, or else is ignored (as is
1697 whitespace and C<#>-style comments if C<//x> is present).
1699 Parsing of the bracketed character class construct, C<[...]>, is
1700 rather different than the rule used for the rest of the pattern.
1701 The terminator of this construct is found using the same rules as
1702 for finding the terminator of a C<{}>-delimited construct, the only
1703 exception being that C<]> immediately following C<[> is treated as
1704 though preceded by a backslash. Similarly, the terminator of
1705 C<(?{...})> is found using the same rules as for finding the
1706 terminator of a C<{}>-delimited construct.
1708 It is possible to inspect both the string given to RE engine and the
1709 resulting finite automaton. See the arguments C<debug>/C<debugcolor>
1710 in the C<use L<re>> pragma, as well as Perl's B<-Dr> command-line
1711 switch documented in L<perlrun/"Command Switches">.
1713 =item Optimization of regular expressions
1715 This step is listed for completeness only. Since it does not change
1716 semantics, details of this step are not documented and are subject
1717 to change without notice. This step is performed over the finite
1718 automaton that was generated during the previous pass.
1720 It is at this stage that C<split()> silently optimizes C</^/> to
1725 =head2 I/O Operators
1727 There are several I/O operators you should know about.
1729 A string enclosed by backticks (grave accents) first undergoes
1730 double-quote interpolation. It is then interpreted as an external
1731 command, and the output of that command is the value of the
1732 backtick string, like in a shell. In scalar context, a single string
1733 consisting of all output is returned. In list context, a list of
1734 values is returned, one per line of output. (You can set C<$/> to use
1735 a different line terminator.) The command is executed each time the
1736 pseudo-literal is evaluated. The status value of the command is
1737 returned in C<$?> (see L<perlvar> for the interpretation of C<$?>).
1738 Unlike in B<csh>, no translation is done on the return data--newlines
1739 remain newlines. Unlike in any of the shells, single quotes do not
1740 hide variable names in the command from interpretation. To pass a
1741 literal dollar-sign through to the shell you need to hide it with a
1742 backslash. The generalized form of backticks is C<qx//>. (Because
1743 backticks always undergo shell expansion as well, see L<perlsec> for
1746 In scalar context, evaluating a filehandle in angle brackets yields
1747 the next line from that file (the newline, if any, included), or
1748 C<undef> at end-of-file or on error. When C<$/> is set to C<undef>
1749 (sometimes known as file-slurp mode) and the file is empty, it
1750 returns C<''> the first time, followed by C<undef> subsequently.
1752 Ordinarily you must assign the returned value to a variable, but
1753 there is one situation where an automatic assignment happens. If
1754 and only if the input symbol is the only thing inside the conditional
1755 of a C<while> statement (even if disguised as a C<for(;;)> loop),
1756 the value is automatically assigned to the global variable $_,
1757 destroying whatever was there previously. (This may seem like an
1758 odd thing to you, but you'll use the construct in almost every Perl
1759 script you write.) The $_ variable is not implicitly localized.
1760 You'll have to put a C<local $_;> before the loop if you want that
1763 The following lines are equivalent:
1765 while (defined($_ = <STDIN>)) { print; }
1766 while ($_ = <STDIN>) { print; }
1767 while (<STDIN>) { print; }
1768 for (;<STDIN>;) { print; }
1769 print while defined($_ = <STDIN>);
1770 print while ($_ = <STDIN>);
1771 print while <STDIN>;
1773 This also behaves similarly, but avoids $_ :
1775 while (my $line = <STDIN>) { print $line }
1777 In these loop constructs, the assigned value (whether assignment
1778 is automatic or explicit) is then tested to see whether it is
1779 defined. The defined test avoids problems where line has a string
1780 value that would be treated as false by Perl, for example a "" or
1781 a "0" with no trailing newline. If you really mean for such values
1782 to terminate the loop, they should be tested for explicitly:
1784 while (($_ = <STDIN>) ne '0') { ... }
1785 while (<STDIN>) { last unless $_; ... }
1787 In other boolean contexts, C<< <I<filehandle>> >> without an
1788 explicit C<defined> test or comparison elicit a warning if the
1789 C<use warnings> pragma or the B<-w>
1790 command-line switch (the C<$^W> variable) is in effect.
1792 The filehandles STDIN, STDOUT, and STDERR are predefined. (The
1793 filehandles C<stdin>, C<stdout>, and C<stderr> will also work except
1794 in packages, where they would be interpreted as local identifiers
1795 rather than global.) Additional filehandles may be created with
1796 the open() function, amongst others. See L<perlopentut> and
1797 L<perlfunc/open> for details on this.
1799 If a <FILEHANDLE> is used in a context that is looking for
1800 a list, a list comprising all input lines is returned, one line per
1801 list element. It's easy to grow to a rather large data space this
1802 way, so use with care.
1804 <FILEHANDLE> may also be spelled C<readline(*FILEHANDLE)>.
1805 See L<perlfunc/readline>.
1807 The null filehandle <> is special: it can be used to emulate the
1808 behavior of B<sed> and B<awk>. Input from <> comes either from
1809 standard input, or from each file listed on the command line. Here's
1810 how it works: the first time <> is evaluated, the @ARGV array is
1811 checked, and if it is empty, C<$ARGV[0]> is set to "-", which when opened
1812 gives you standard input. The @ARGV array is then processed as a list
1813 of filenames. The loop
1816 ... # code for each line
1819 is equivalent to the following Perl-like pseudo code:
1821 unshift(@ARGV, '-') unless @ARGV;
1822 while ($ARGV = shift) {
1825 ... # code for each line
1829 except that it isn't so cumbersome to say, and will actually work.
1830 It really does shift the @ARGV array and put the current filename
1831 into the $ARGV variable. It also uses filehandle I<ARGV>
1832 internally--<> is just a synonym for <ARGV>, which
1833 is magical. (The pseudo code above doesn't work because it treats
1834 <ARGV> as non-magical.)
1836 You can modify @ARGV before the first <> as long as the array ends up
1837 containing the list of filenames you really want. Line numbers (C<$.>)
1838 continue as though the input were one big happy file. See the example
1839 in L<perlfunc/eof> for how to reset line numbers on each file.
1841 If you want to set @ARGV to your own list of files, go right ahead.
1842 This sets @ARGV to all plain text files if no @ARGV was given:
1844 @ARGV = grep { -f && -T } glob('*') unless @ARGV;
1846 You can even set them to pipe commands. For example, this automatically
1847 filters compressed arguments through B<gzip>:
1849 @ARGV = map { /\.(gz|Z)$/ ? "gzip -dc < $_ |" : $_ } @ARGV;
1851 If you want to pass switches into your script, you can use one of the
1852 Getopts modules or put a loop on the front like this:
1854 while ($_ = $ARGV[0], /^-/) {
1857 if (/^-D(.*)/) { $debug = $1 }
1858 if (/^-v/) { $verbose++ }
1859 # ... # other switches
1863 # ... # code for each line
1866 The <> symbol will return C<undef> for end-of-file only once.
1867 If you call it again after this, it will assume you are processing another
1868 @ARGV list, and if you haven't set @ARGV, will read input from STDIN.
1870 If what the angle brackets contain is a simple scalar variable (e.g.,
1871 <$foo>), then that variable contains the name of the
1872 filehandle to input from, or its typeglob, or a reference to the
1878 If what's within the angle brackets is neither a filehandle nor a simple
1879 scalar variable containing a filehandle name, typeglob, or typeglob
1880 reference, it is interpreted as a filename pattern to be globbed, and
1881 either a list of filenames or the next filename in the list is returned,
1882 depending on context. This distinction is determined on syntactic
1883 grounds alone. That means C<< <$x> >> is always a readline() from
1884 an indirect handle, but C<< <$hash{key}> >> is always a glob().
1885 That's because $x is a simple scalar variable, but C<$hash{key}> is
1886 not--it's a hash element.
1888 One level of double-quote interpretation is done first, but you can't
1889 say C<< <$foo> >> because that's an indirect filehandle as explained
1890 in the previous paragraph. (In older versions of Perl, programmers
1891 would insert curly brackets to force interpretation as a filename glob:
1892 C<< <${foo}> >>. These days, it's considered cleaner to call the
1893 internal function directly as C<glob($foo)>, which is probably the right
1894 way to have done it in the first place.) For example:
1900 is roughly equivalent to:
1902 open(FOO, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|");
1908 except that the globbing is actually done internally using the standard
1909 C<File::Glob> extension. Of course, the shortest way to do the above is:
1913 A (file)glob evaluates its (embedded) argument only when it is
1914 starting a new list. All values must be read before it will start
1915 over. In list context, this isn't important because you automatically
1916 get them all anyway. However, in scalar context the operator returns
1917 the next value each time it's called, or C<undef> when the list has
1918 run out. As with filehandle reads, an automatic C<defined> is
1919 generated when the glob occurs in the test part of a C<while>,
1920 because legal glob returns (e.g. a file called F<0>) would otherwise
1921 terminate the loop. Again, C<undef> is returned only once. So if
1922 you're expecting a single value from a glob, it is much better to
1925 ($file) = <blurch*>;
1931 because the latter will alternate between returning a filename and
1934 If you're trying to do variable interpolation, it's definitely better
1935 to use the glob() function, because the older notation can cause people
1936 to become confused with the indirect filehandle notation.
1938 @files = glob("$dir/*.[ch]");
1939 @files = glob($files[$i]);
1941 =head2 Constant Folding
1943 Like C, Perl does a certain amount of expression evaluation at
1944 compile time whenever it determines that all arguments to an
1945 operator are static and have no side effects. In particular, string
1946 concatenation happens at compile time between literals that don't do
1947 variable substitution. Backslash interpolation also happens at
1948 compile time. You can say
1950 'Now is the time for all' . "\n" .
1951 'good men to come to.'
1953 and this all reduces to one string internally. Likewise, if
1956 foreach $file (@filenames) {
1957 if (-s $file > 5 + 100 * 2**16) { }
1960 the compiler will precompute the number which that expression
1961 represents so that the interpreter won't have to.
1963 =head2 Bitwise String Operators
1965 Bitstrings of any size may be manipulated by the bitwise operators
1968 If the operands to a binary bitwise op are strings of different
1969 sizes, B<|> and B<^> ops act as though the shorter operand had
1970 additional zero bits on the right, while the B<&> op acts as though
1971 the longer operand were truncated to the length of the shorter.
1972 The granularity for such extension or truncation is one or more
1975 # ASCII-based examples
1976 print "j p \n" ^ " a h"; # prints "JAPH\n"
1977 print "JA" | " ph\n"; # prints "japh\n"
1978 print "japh\nJunk" & '_____'; # prints "JAPH\n";
1979 print 'p N$' ^ " E<H\n"; # prints "Perl\n";
1981 If you are intending to manipulate bitstrings, be certain that
1982 you're supplying bitstrings: If an operand is a number, that will imply
1983 a B<numeric> bitwise operation. You may explicitly show which type of
1984 operation you intend by using C<""> or C<0+>, as in the examples below.
1986 $foo = 150 | 105 ; # yields 255 (0x96 | 0x69 is 0xFF)
1987 $foo = '150' | 105 ; # yields 255
1988 $foo = 150 | '105'; # yields 255
1989 $foo = '150' | '105'; # yields string '155' (under ASCII)
1991 $baz = 0+$foo & 0+$bar; # both ops explicitly numeric
1992 $biz = "$foo" ^ "$bar"; # both ops explicitly stringy
1994 See L<perlfunc/vec> for information on how to manipulate individual bits
1997 =head2 Integer Arithmetic
1999 By default, Perl assumes that it must do most of its arithmetic in
2000 floating point. But by saying
2004 you may tell the compiler that it's okay to use integer operations
2005 (if it feels like it) from here to the end of the enclosing BLOCK.
2006 An inner BLOCK may countermand this by saying
2010 which lasts until the end of that BLOCK. Note that this doesn't
2011 mean everything is only an integer, merely that Perl may use integer
2012 operations if it is so inclined. For example, even under C<use
2013 integer>, if you take the C<sqrt(2)>, you'll still get C<1.4142135623731>
2016 Used on numbers, the bitwise operators ("&", "|", "^", "~", "<<",
2017 and ">>") always produce integral results. (But see also
2018 L<Bitwise String Operators>.) However, C<use integer> still has meaning for
2019 them. By default, their results are interpreted as unsigned integers, but
2020 if C<use integer> is in effect, their results are interpreted
2021 as signed integers. For example, C<~0> usually evaluates to a large
2022 integral value. However, C<use integer; ~0> is C<-1> on twos-complement
2025 =head2 Floating-point Arithmetic
2027 While C<use integer> provides integer-only arithmetic, there is no
2028 analogous mechanism to provide automatic rounding or truncation to a
2029 certain number of decimal places. For rounding to a certain number
2030 of digits, sprintf() or printf() is usually the easiest route.
2033 Floating-point numbers are only approximations to what a mathematician
2034 would call real numbers. There are infinitely more reals than floats,
2035 so some corners must be cut. For example:
2037 printf "%.20g\n", 123456789123456789;
2038 # produces 123456789123456784
2040 Testing for exact equality of floating-point equality or inequality is
2041 not a good idea. Here's a (relatively expensive) work-around to compare
2042 whether two floating-point numbers are equal to a particular number of
2043 decimal places. See Knuth, volume II, for a more robust treatment of
2047 my ($X, $Y, $POINTS) = @_;
2049 $tX = sprintf("%.${POINTS}g", $X);
2050 $tY = sprintf("%.${POINTS}g", $Y);
2054 The POSIX module (part of the standard perl distribution) implements
2055 ceil(), floor(), and other mathematical and trigonometric functions.
2056 The Math::Complex module (part of the standard perl distribution)
2057 defines mathematical functions that work on both the reals and the
2058 imaginary numbers. Math::Complex not as efficient as POSIX, but
2059 POSIX can't work with complex numbers.
2061 Rounding in financial applications can have serious implications, and
2062 the rounding method used should be specified precisely. In these
2063 cases, it probably pays not to trust whichever system rounding is
2064 being used by Perl, but to instead implement the rounding function you
2067 =head2 Bigger Numbers
2069 The standard Math::BigInt and Math::BigFloat modules provide
2070 variable-precision arithmetic and overloaded operators, although
2071 they're currently pretty slow. At the cost of some space and
2072 considerable speed, they avoid the normal pitfalls associated with
2073 limited-precision representations.
2076 $x = Math::BigInt->new('123456789123456789');
2079 # prints +15241578780673678515622620750190521
2081 There are several modules that let you calculate with (bound only by
2082 memory and cpu-time) unlimited or fixed precision. There are also
2083 some non-standard modules that provide faster implementations via
2084 external C libraries.
2086 Here is a short, but incomplete summary:
2088 Math::Fraction big, unlimited fractions like 9973 / 12967
2089 Math::String treat string sequences like numbers
2090 Math::FixedPrecision calculate with a fixed precision
2091 Math::Currency for currency calculations
2092 Bit::Vector manipulate bit vectors fast (uses C)
2093 Math::BigIntFast Bit::Vector wrapper for big numbers
2094 Math::Pari provides access to the Pari C library
2095 Math::BigInteger uses an external C library
2096 Math::Cephes uses external Cephes C library (no big numbers)
2097 Math::Cephes::Fraction fractions via the Cephes library
2098 Math::GMP another one using an external C library