left || //
nonassoc .. ...
right ?:
- right = += -= *= etc.
+ right = += -= *= etc. goto last next redo dump
left , =>
nonassoc list operators (rightward)
right not
=head2 Symbolic Unary Operators
X<unary operator> X<operator, unary>
-Unary "!" performs logical negation, i.e., "not". See also C<not> for a lower
+Unary "!" performs logical negation, that is, "not". See also C<not> for a lower
precedence version of this.
X<!>
B<Argument "the string" isn't numeric in negation (-) at ...>.
X<-> X<negation, arithmetic>
-Unary "~" performs bitwise negation, i.e., 1's complement. For
+Unary "~" performs bitwise negation, that is, 1's complement. For
example, C<0666 & ~027> is 0640. (See also L<Integer Arithmetic> and
L<Bitwise String Operators>.) Note that the width of the result is
platform-dependent: ~0 is 32 bits wide on a 32-bit platform, but 64
substitution, or transliteration, it is interpreted as a search pattern at run
time. Note that this means that its contents will be interpolated twice, so
- '\\' =~ q'\\';
+ '\\' =~ q'\\';
is not ok, as the regex engine will end up trying to compile the
pattern C<\>, which it will consider a syntax error.
operands C<$a> and C<$b>: If C<$b> is positive, then C<$a % $b> is
C<$a> minus the largest multiple of C<$b> less than or equal to
C<$a>. If C<$b> is negative, then C<$a % $b> is C<$a> minus the
-smallest multiple of C<$b> that is not less than C<$a> (i.e. the
+smallest multiple of C<$b> that is not less than C<$a> (that is, the
result will be less than or equal to zero). If the operands
C<$a> and C<$b> are floating point values and the absolute value of
C<$b> (that is C<abs($b)>) is less than C<(UV_MAX + 1)>, only
=head2 Additive Operators
X<operator, additive>
-Binary "+" returns the sum of two numbers.
+Binary C<+> returns the sum of two numbers.
X<+>
-Binary "-" returns the difference of two numbers.
+Binary C<-> returns the difference of two numbers.
X<->
-Binary "." concatenates two strings.
+Binary C<.> concatenates two strings.
X<string, concatenation> X<concatenation>
X<cat> X<concat> X<concatenate> X<.>
X<<< >> >>> X<right shift> X<left shift> X<bitwise shift>
X<shl> X<shr> X<shift, right> X<shift, left>
-Binary "<<" returns the value of its left argument shifted left by the
+Binary C<<< << >>> returns the value of its left argument shifted left by the
number of bits specified by the right argument. Arguments should be
integers. (See also L<Integer Arithmetic>.)
-Binary ">>" returns the value of its left argument shifted right by
+Binary C<<< >> >>> returns the value of its left argument shifted right by
the number of bits specified by the right argument. Arguments should
be integers. (See also L<Integer Arithmetic>.)
-Note that both "<<" and ">>" in Perl are implemented directly using
-"<<" and ">>" in C. If C<use integer> (see L<Integer Arithmetic>) is
+Note that both C<<< << >>> and C<<< >> >>> in Perl are implemented directly using
+C<<< << >>> and C<<< >> >>> in C. If C<use integer> (see L<Integer Arithmetic>) is
in force then signed C integers are used, else unsigned C integers are
used. Either way, the implementation isn't going to generate results
larger than the size of the integer type Perl was built with (32 bits
integers, C<< 1 << 32 >> is undefined. Shifting by a negative number
of bits is also undefined.
+If you get tired of being subject to your platform's native integers,
+the C<use bigint> pragma neatly sidesteps the issue altogether:
+
+ print 20 << 20; # 20971520
+ print 20 << 40; # 5120 on 32-bit machines,
+ # 21990232555520 on 64-bit machines
+ use bigint;
+ print 20 << 100; # 25353012004564588029934064107520
+
=head2 Named Unary Operators
X<operator, named unary>
is followed by a left parenthesis as the next token, the operator and
arguments within parentheses are taken to be of highest precedence,
just like a normal function call. For example,
-because named unary operators are higher precedence than ||:
+because named unary operators are higher precedence than C<||>:
chdir $foo || die; # (chdir $foo) || die
chdir($foo) || die; # (chdir $foo) || die
=head2 Relational Operators
X<relational operator> X<operator, relational>
+Perl operators that return true or false generally return values
+that can be safely used as numbers. For example, the relational
+operators in this section and the equality operators in the next
+one return C<1> for true and a special version of the defined empty
+string, C<"">, which counts as a zero but is exempt from warnings
+about improper numeric conversions, just as C<"0 but true"> is.
+
Binary "<" returns true if the left argument is numerically less than
the right argument.
X<< < >>
support NaNs then NaN is just a string with numeric value 0.
X<< <=> >> X<spaceship>
- perl -le '$a = "NaN"; print "No NaN support here" if $a == $a'
- perl -le '$a = "NaN"; print "NaN support here" if $a != $a'
+ $ perl -le '$a = "NaN"; print "No NaN support here" if $a == $a'
+ $ perl -le '$a = "NaN"; print "NaN support here" if $a != $a'
+
+(Note that the L<bigint>, L<bigrat>, and L<bignum> pragmas all
+support "NaN".)
Binary "eq" returns true if the left argument is stringwise equal to
the right argument.
argument.
X<cmp>
-Binary "~~" does a smart match between its arguments. Smart matching
-is described in L<perlsyn/"Smart matching in detail">.
+Binary "~~" does a smartmatch between its arguments. Smart matching
+is described in the next section.
X<~~>
"lt", "le", "ge", "gt" and "cmp" use the collation (sort) order specified
-by the current locale if C<use locale> is in effect. See L<perllocale>.
+by the current locale if a legacy C<use locale> (but not
+C<use locale ':not_characters'>) is in effect. See
+L<perllocale>. Do not mix these with Unicode, only with legacy binary
+encodings. The standard L<Unicode::Collate> and
+L<Unicode::Collate::Locale> modules offer much more powerful solutions to
+collation issues.
+
+=head2 Smartmatch Operator
+
+First available in Perl 5.10.1 (the 5.10.0 version behaved differently),
+binary C<~~> does a "smartmatch" between its arguments. This is mostly
+used implicitly in the C<when> construct described in L<perlsyn>, although
+not all C<when> clauses call the smartmatch operator. Unique among all of
+Perl's operators, the smartmatch operator can recurse.
+
+It is also unique in that all other Perl operators impose a context
+(usually string or numeric context) on their operands, autoconverting
+those operands to those imposed contexts. In contrast, smartmatch
+I<infers> contexts from the actual types of its operands and uses that
+type information to select a suitable comparison mechanism.
+
+The C<~~> operator compares its operands "polymorphically", determining how
+to compare them according to their actual types (numeric, string, array,
+hash, etc.) Like the equality operators with which it shares the same
+precedence, C<~~> returns 1 for true and C<""> for false. It is often best
+read aloud as "in", "inside of", or "is contained in", because the left
+operand is often looked for I<inside> the right operand. That makes the
+order of the operands to the smartmatch operand often opposite that of
+the regular match operator. In other words, the "smaller" thing is usually
+placed in the left operand and the larger one in the right.
+
+The behavior of a smartmatch depends on what type of things its arguments
+are, as determined by the following table. The first row of the table
+whose types apply determines the smartmatch behavior. Because what
+actually happens is mostly determined by the type of the second operand,
+the table is sorted on the right operand instead of on the left.
+
+ Left Right Description and pseudocode
+ ===============================================================
+ Any undef check whether Any is undefined
+ like: !defined Any
+
+ Any Object invoke ~~ overloading on Object, or die
+
+ Right operand is an ARRAY:
+
+ Left Right Description and pseudocode
+ ===============================================================
+ ARRAY1 ARRAY2 recurse on paired elements of ARRAY1 and ARRAY2[2]
+ like: (ARRAY1[0] ~~ ARRAY2[0])
+ && (ARRAY1[1] ~~ ARRAY2[1]) && ...
+ HASH ARRAY any ARRAY elements exist as HASH keys
+ like: grep { exists HASH->{$_} } ARRAY
+ Regexp ARRAY any ARRAY elements pattern match Regexp
+ like: grep { /Regexp/ } ARRAY
+ undef ARRAY undef in ARRAY
+ like: grep { !defined } ARRAY
+ Any ARRAY smartmatch each ARRAY element[3]
+ like: grep { Any ~~ $_ } ARRAY
+
+ Right operand is a HASH:
+
+ Left Right Description and pseudocode
+ ===============================================================
+ HASH1 HASH2 all same keys in both HASHes
+ like: keys HASH1 ==
+ grep { exists HASH2->{$_} } keys HASH1
+ ARRAY HASH any ARRAY elements exist as HASH keys
+ like: grep { exists HASH->{$_} } ARRAY
+ Regexp HASH any HASH keys pattern match Regexp
+ like: grep { /Regexp/ } keys HASH
+ undef HASH always false (undef can't be a key)
+ like: 0 == 1
+ Any HASH HASH key existence
+ like: exists HASH->{Any}
+
+ Right operand is CODE:
+
+ Left Right Description and pseudocode
+ ===============================================================
+ ARRAY CODE sub returns true on all ARRAY elements[1]
+ like: !grep { !CODE->($_) } ARRAY
+ HASH CODE sub returns true on all HASH keys[1]
+ like: !grep { !CODE->($_) } keys HASH
+ Any CODE sub passed Any returns true
+ like: CODE->(Any)
+
+Right operand is a Regexp:
+
+ Left Right Description and pseudocode
+ ===============================================================
+ ARRAY Regexp any ARRAY elements match Regexp
+ like: grep { /Regexp/ } ARRAY
+ HASH Regexp any HASH keys match Regexp
+ like: grep { /Regexp/ } keys HASH
+ Any Regexp pattern match
+ like: Any =~ /Regexp/
+
+ Other:
+
+ Left Right Description and pseudocode
+ ===============================================================
+ Object Any invoke ~~ overloading on Object,
+ or fall back to...
+
+ Any Num numeric equality
+ like: Any == Num
+ Num nummy[4] numeric equality
+ like: Num == nummy
+ undef Any check whether undefined
+ like: !defined(Any)
+ Any Any string equality
+ like: Any eq Any
+
+
+Notes:
+
+=over
+
+=item 1.
+Empty hashes or arrays match.
+
+=item 2.
+That is, each element smartmatches the element of the same index in the other array.[3]
+
+=item 3.
+If a circular reference is found, fall back to referential equality.
+
+=item 4.
+Either an actual number, or a string that looks like one.
+
+=back
+
+The smartmatch implicitly dereferences any non-blessed hash or array
+reference, so the C<I<HASH>> and C<I<ARRAY>> entries apply in those cases.
+For blessed references, the C<I<Object>> entries apply. Smartmatches
+involving hashes only consider hash keys, never hash values.
+
+The "like" code entry is not always an exact rendition. For example, the
+smartmatch operator short-circuits whenever possible, but C<grep> does
+not. Also, C<grep> in scalar context returns the number of matches, but
+C<~~> returns only true or false.
+
+Unlike most operators, the smartmatch operator knows to treat C<undef>
+specially:
+
+ use v5.10.1;
+ @array = (1, 2, 3, undef, 4, 5);
+ say "some elements undefined" if undef ~~ @array;
+
+Each operand is considered in a modified scalar context, the modification
+being that array and hash variables are passed by reference to the
+operator, which implicitly dereferences them. Both elements
+of each pair are the same:
+
+ use v5.10.1;
+
+ my %hash = (red => 1, blue => 2, green => 3,
+ orange => 4, yellow => 5, purple => 6,
+ black => 7, grey => 8, white => 9);
+
+ my @array = qw(red blue green);
+
+ say "some array elements in hash keys" if @array ~~ %hash;
+ say "some array elements in hash keys" if \@array ~~ \%hash;
+
+ say "red in array" if "red" ~~ @array;
+ say "red in array" if "red" ~~ \@array;
+
+ say "some keys end in e" if /e$/ ~~ %hash;
+ say "some keys end in e" if /e$/ ~~ \%hash;
+
+Two arrays smartmatch if each element in the first array smartmatches
+(that is, is "in") the corresponding element in the second array,
+recursively.
+
+ use v5.10.1;
+ my @little = qw(red blue green);
+ my @bigger = ("red", "blue", [ "orange", "green" ] );
+ if (@little ~~ @bigger) { # true!
+ say "little is contained in bigger";
+ }
+
+Because the smartmatch operator recurses on nested arrays, this
+will still report that "red" is in the array.
+
+ use v5.10.1;
+ my @array = qw(red blue green);
+ my $nested_array = [[[[[[[ @array ]]]]]]];
+ say "red in array" if "red" ~~ $nested_array;
+
+If two arrays smartmatch each other, then they are deep
+copies of each others' values, as this example reports:
+
+ use v5.12.0;
+ my @a = (0, 1, 2, [3, [4, 5], 6], 7);
+ my @b = (0, 1, 2, [3, [4, 5], 6], 7);
+
+ if (@a ~~ @b && @b ~~ @a) {
+ say "a and b are deep copies of each other";
+ }
+ elsif (@a ~~ @b) {
+ say "a smartmatches in b";
+ }
+ elsif (@b ~~ @a) {
+ say "b smartmatches in a";
+ }
+ else {
+ say "a and b don't smartmatch each other at all";
+ }
+
+
+If you were to set C<$b[3] = 4>, then instead of reporting that "a and b
+are deep copies of each other", it now reports that "b smartmatches in a".
+That because the corresponding position in C<@a> contains an array that
+(eventually) has a 4 in it.
+
+Smartmatching one hash against another reports whether both contain the
+same keys, no more and no less. This could be used to see whether two
+records have the same field names, without caring what values those fields
+might have. For example:
+
+ use v5.10.1;
+ sub make_dogtag {
+ state $REQUIRED_FIELDS = { name=>1, rank=>1, serial_num=>1 };
+
+ my ($class, $init_fields) = @_;
+
+ die "Must supply (only) name, rank, and serial number"
+ unless $init_fields ~~ $REQUIRED_FIELDS;
+
+ ...
+ }
+
+or, if other non-required fields are allowed, use ARRAY ~~ HASH:
+
+ use v5.10.1;
+ sub make_dogtag {
+ state $REQUIRED_FIELDS = { name=>1, rank=>1, serial_num=>1 };
+
+ my ($class, $init_fields) = @_;
+
+ die "Must supply (at least) name, rank, and serial number"
+ unless [keys %{$init_fields}] ~~ $REQUIRED_FIELDS;
+
+ ...
+ }
+
+The smartmatch operator is most often used as the implicit operator of a
+C<when> clause. See the section on "Switch Statements" in L<perlsyn>.
+
+=head3 Smartmatching of Objects
+
+To avoid relying on an object's underlying representation, if the
+smartmatch's right operand is an object that doesn't overload C<~~>,
+it raises the exception "C<Smartmatching a non-overloaded object
+breaks encapsulation>". That's because one has no business digging
+around to see whether something is "in" an object. These are all
+illegal on objects without a C<~~> overload:
+
+ %hash ~~ $object
+ 42 ~~ $object
+ "fred" ~~ $object
+
+However, you can change the way an object is smartmatched by overloading
+the C<~~> operator. This is allowed to extend the usual smartmatch semantics.
+For objects that do have an C<~~> overload, see L<overload>.
+
+Using an object as the left operand is allowed, although not very useful.
+Smartmatching rules take precedence over overloading, so even if the
+object in the left operand has smartmatch overloading, this will be
+ignored. A left operand that is a non-overloaded object falls back on a
+string or numeric comparison of whatever the C<ref> operator returns. That
+means that
+
+ $object ~~ X
+
+does I<not> invoke the overload method with C<I<X>> as an argument.
+Instead the above table is consulted as normal, and based on the type of
+C<I<X>>, overloading may or may not be invoked. For simple strings or
+numbers, in becomes equivalent to this:
+
+ $object ~~ $number ref($object) == $number
+ $object ~~ $string ref($object) eq $string
+
+For example, this reports that the handle smells IOish
+(but please don't really do this!):
+
+ use IO::Handle;
+ my $fh = IO::Handle->new();
+ if ($fh ~~ /\bIO\b/) {
+ say "handle smells IOish";
+ }
+
+That's because it treats C<$fh> as a string like
+C<"IO::Handle=GLOB(0x8039e0)">, then pattern matches against that.
=head2 Bitwise And
X<operator, bitwise, and> X<bitwise and> X<&>
(See also L<Integer Arithmetic> and L<Bitwise String Operators>.)
Note that "&" has lower priority than relational operators, so for example
-the brackets are essential in a test like
+the parentheses are essential in a test like
- print "Even\n" if ($x & 1) == 0;
+ print "Even\n" if ($x & 1) == 0;
=head2 Bitwise Or and Exclusive Or
X<operator, bitwise, or> X<bitwise or> X<|> X<operator, bitwise, xor>
Note that "|" and "^" have lower priority than relational operators, so
for example the brackets are essential in a test like
- print "false\n" if (8 | 2) != 10;
+ print "false\n" if (8 | 2) != 10;
=head2 C-style Logical And
X<&&> X<logical and> X<operator, logical, and>
Scalar or list context propagates down to the right operand if it
is evaluated.
-=head2 C-style Logical Defined-Or
+=head2 Logical Defined-Or
X<//> X<operator, logical, defined-or>
Although it has no direct equivalent in C, Perl's C<//> operator is related
to its C-style or. In fact, it's exactly the same as C<||>, except that it
-tests the left hand side's definedness instead of its truth. Thus, C<$a // $b>
-is similar to C<defined($a) || $b> (except that it returns the value of C<$a>
-rather than the value of C<defined($a)>) and yields the same result as
-C<defined($a) ? $a : $b> (except that the ternary-operator form can be
-used as a lvalue, while C<$a // $b> cannot). This is very useful for
+tests the left hand side's definedness instead of its truth. Thus,
+C<< EXPR1 // EXPR2 >> returns the value of C<< EXPR1 >> if it's defined,
+otherwise, the value of C<< EXPR2 >> is returned. (C<< EXPR1 >> is evaluated
+in scalar context, C<< EXPR2 >> in the context of C<< // >> itself). Usually,
+this is the same result as C<< defined(EXPR1) ? EXPR1 : EXPR2 >> (except that
+the ternary-operator form can be used as a lvalue, while C<< EXPR1 // EXPR2 >>
+cannot). This is very useful for
providing default values for variables. If you actually want to test if
at least one of C<$a> and C<$b> is defined, use C<defined($a // $b)>.
@a = scalar(@b) || @c; # really meant this
@a = @b ? @b : @c; # this works fine, though
-As more readable alternatives to C<&&> and C<||> when used for
+As alternatives to C<&&> and C<||> when used for
control flow, Perl provides the C<and> and C<or> operators (see below).
The short-circuit behavior is identical. The precedence of "and"
and "or" is much lower, however, so that you can safely use them after a
unlink("alpha", "beta", "gamma")
|| (gripe(), next LINE);
+It would be even more readable to write that this way:
+
+ unless(unlink("alpha", "beta", "gamma")) {
+ gripe();
+ next LINE;
+ }
+
Using "or" for assignment is unlikely to do what you want; see below.
=head2 Range Operators
And now some examples as a list operator:
- for (101 .. 200) { print; } # print $_ 100 times
- @foo = @foo[0 .. $#foo]; # an expensive no-op
- @foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items
+ for (101 .. 200) { print } # print $_ 100 times
+ @foo = @foo[0 .. $#foo]; # an expensive no-op
+ @foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items
The range operator (in list context) makes use of the magical
auto-increment algorithm if the operands are strings. You
to get a hexadecimal digit, or
- @z2 = ("01" .. "31"); print $z2[$mday];
+ @z2 = ("01" .. "31");
+ print $z2[$mday];
to get dates with leading zeros.
you could use this instead:
use charnames "greek";
- my @greek_small = map { chr }
- ord "\N{alpha}" .. ord "\N{omega}";
+ my @greek_small = map { chr } ( ord("\N{alpha}")
+ ..
+ ord("\N{omega}")
+ );
However, because there are I<many> other lowercase Greek characters than
just those, to match lowercase Greek characters in a regular expression,
then modifying the variable that was assigned to. This is useful
for modifying a copy of something, like this:
- ($tmp = $global) =~ tr [0-9] [a-j];
+ ($tmp = $global) =~ tr/13579/24680/;
+
+Although as of 5.14, that can be also be accomplished this way:
+
+ use v5.14;
+ $tmp = ($global =~ tr/13579/24680/r);
Likewise,
the number of elements produced by the expression on the right hand
side of the assignment.
-=head2 The Triple-Dot Operator
-X<...> X<... operator> X<yada-yada operator> X<whatever operator>
-X<triple-dot operator>
-
-The triple-dot operator, C<...>, sometimes called the "whatever operator", the
-"yada-yada operator", or the "I<et cetera>" operator, is a placeholder for
-code. Perl parses it without error, but when you try to execute a whatever,
-it throws an exception with the text C<Unimplemented>:
-
- sub unimplemented { ... }
-
- eval { unimplemented() };
- if ($@ eq "Unimplemented" ) {
- say "Oh look, an exception--whatever.";
- }
-
-You can only use the triple-dot operator to stand in for a complete statement.
-These examples of the triple-dot work:
-
- { ... }
-
- sub foo { ... }
-
- ...;
-
- eval { ... };
-
- sub foo {
- my ($self) = shift;
- ...;
- }
-
- do {
- my $variable;
- ...;
- say "Hurrah!";
- } while $cheering;
-
-The yada-yada--or whatever--cannot stand in for an expression that is
-part of a larger statement since the C<...> is also the three-dot version
-of the binary range operator (see L<Range Operators>). These examples of
-the whatever operator are still syntax errors:
-
- print ...;
-
- open(PASSWD, ">", "/dev/passwd") or ...;
-
- if ($condition && ...) { say "Hello" }
-
-There are some cases where Perl can't immediately tell the difference
-between an expression and a statement. For instance, the syntax for a
-block and an anonymous hash reference constructor look the same unless
-there's something in the braces that give Perl a hint. The whatever
-is a syntax error if Perl doesn't guess that the C<{ ... }> is a
-block. In that case, it doesn't think the C<...> is the whatever
-because it's expecting an expression instead of a statement:
-
- my @transformed = map { ... } @input; # syntax error
-
-You can use a C<;> inside your block to denote that the C<{ ... }> is
-a block and not a hash reference constructor. Now the whatever works:
-
- my @transformed = map {; ... } @input; # ; disambiguates
-
- my @transformed = map { ...; } @input; # ; disambiguates
-
=head2 Comma Operator
X<comma> X<operator, comma> X<,>
both its arguments into the list. These arguments are also evaluated
from left to right.
-The C<< => >> operator is a synonym for the comma except that it causes
-its left operand to be interpreted as a string if it begins with a letter
+The C<< => >> operator is a synonym for the comma except that it causes a
+word on its left to be interpreted as a string if it begins with a letter
or underscore and is composed only of letters, digits and underscores.
This includes operands that might otherwise be interpreted as operators,
constants, single number v-strings or function calls. If in doubt about
The C<< => >> operator is helpful in documenting the correspondence
between keys and values in hashes, and other paired elements in lists.
- %hash = ( $key => $value );
- login( $username => $password );
+ %hash = ( $key => $value );
+ login( $username => $password );
+
+The special quoting behavior ignores precedence, and hence may apply to
+I<part> of the left operand:
+
+ print time.shift => "bbb";
+
+That example prints something like "1314363215shiftbbb", because the
+C<< => >> implicitly quotes the C<shift> immediately on its left, ignoring
+the fact that C<time.shift> is the entire left operand.
=head2 List Operators (Rightward)
X<operator, list, rightward> X<list operator>
such that it controls all comma-separated expressions found there.
The only operators with lower precedence are the logical operators
"and", "or", and "not", which may be used to evaluate calls to list
-operators without the need for extra parentheses:
+operators without the need for parentheses:
+
+ open HANDLE, "< :utf8", "filename" or die "Can't open: $!\n";
+
+However, some people find that code harder to read than writing
+it with parentheses:
- open HANDLE, "< $file"
- or die "Can't open $file: $!\n";
+ open(HANDLE, "< :utf8", "filename") or die "Can't open: $!\n";
+
+in which case you might as well just use the more customary "||" operator:
+
+ open(HANDLE, "< :utf8", "filename") || die "Can't open: $!\n";
See also discussion of list operators in L<Terms and List Operators (Leftward)>.
precedence. This means that it short-circuits: the right
expression is evaluated only if the left expression is true.
-=head2 Logical or, Defined or, and Exclusive Or
+=head2 Logical or and Exclusive Or
X<operator, logical, or> X<operator, logical, xor>
-X<operator, logical, defined or> X<operator, logical, exclusive or>
+X<operator, logical, exclusive or>
X<or> X<xor>
Binary "or" returns the logical disjunction of the two surrounding
Then again, you could always use parentheses.
-Binary "xor" returns the exclusive-OR of the two surrounding expressions.
+Binary C<xor> returns the exclusive-OR of the two surrounding expressions.
It cannot short-circuit (of course).
+There is no low precedence operator for defined-OR.
+
=head2 C Operators Missing From Perl
X<operator, missing from perl> X<&> X<*>
X<typecasting> X<(TYPE)>
Use of any other character following the "c" besides those listed above is
discouraged, and some are deprecated with the intention of removing
-those in Perl 5.16. What happens for any of these
+those in a later Perl version. What happens for any of these
other characters currently though, is that the value is derived by xor'ing
with the seventh bit, which is 64.
Some contexts allow 2 or even 1 digit, but any usage without exactly
three digits, the first being a zero, may give unintended results. (For
-example, see L<perlrebackslash/Octal escapes>.) Starting in Perl 5.14, you may
+example, in a regular expression it may be confused with a backreference;
+see L<perlrebackslash/Octal escapes>.) Starting in Perl 5.14, you may
use C<\o{}> instead, which avoids all these problems. Otherwise, it is best to
use this construct only for ordinals C<\077> and below, remembering to pad to
the left with zeros to make three digits. For larger ordinals, either use
-C<\o{}> , or convert to something else, such as to hex and use C<\x{}>
+C<\o{}>, or convert to something else, such as to hex and use C<\x{}>
instead.
Having fewer than 3 digits may lead to a misleading warning message that says
that what follows is ignored. For example, C<"\128"> in the ASCII character set
is equivalent to the two characters C<"\n8">, but the warning C<Illegal octal
-digit '8' ignored> will be thrown. To avoid this warning, make sure to pad
-your octal number with C<0>'s: C<"\0128">.
+digit '8' ignored> will be thrown. If C<"\n8"> is what you want, you can
+avoid this warning by padding your octal number with C<0>'s: C<"\0128">.
=item [8]
from 0) is the letter "P", and in EBCDIC it is the ampersand symbol "&".
C<\x{100}> and C<\o{400}> are both 256 in decimal, so the number is interpreted
as a Unicode code point no matter what the native encoding is. The name of the
-character in the 100th position (indexed by 0) in Unicode is
+character in the 256th position (indexed by 0) in Unicode is
C<LATIN CAPITAL LETTER A WITH MACRON>.
-There are a couple of exceptions to the above rule. C<\N{U+I<hex number>}> is
+There are a couple of exceptions to the above rule. S<C<\N{U+I<hex number>}>> is
always interpreted as a Unicode code point, so that C<\N{U+0050}> is "P" even
on EBCDIC platforms. And if L<C<S<use encoding>>|encoding> is in effect, the
number is considered to be in that encoding, and is translated from that into
=back
B<NOTE>: Unlike C and other languages, Perl has no C<\v> escape sequence for
-the vertical tab (VT - ASCII 11), but you may use C<\ck> or C<\x0b>. (C<\v>
+the vertical tab (VT, which is 11 in both ASCII and EBCDIC), but you may
+use C<\ck> or
+C<\x0b>. (C<\v>
does have meaning in regular expression patterns in Perl, see L<perlre>.)
The following escape sequences are available in constructs that interpolate,
but not in transliterations.
-X<\l> X<\u> X<\L> X<\U> X<\E> X<\Q>
+X<\l> X<\u> X<\L> X<\U> X<\E> X<\Q> X<\F>
\l lowercase next character only
\u titlecase (not uppercase!) next character only
- \L lowercase all characters till \E seen
- \U uppercase all characters till \E seen
- \Q quote non-word characters till \E
+ \L lowercase all characters till \E or end of string
+ \U uppercase all characters till \E or end of string
+ \F foldcase all characters till \E or end of string
+ \Q quote (disable) pattern metacharacters till \E or
+ end of string
\E end either case modification or quoted section
(whichever was last seen)
-C<\L>, C<\U>, and C<\Q> can stack, in which case you need one
+See L<perlfunc/quotemeta> for the exact definition of characters that
+are quoted by C<\Q>.
+
+C<\L>, C<\U>, C<\F>, and C<\Q> can stack, in which case you need one
C<\E> for each. For example:
- say "This \Qquoting \ubusiness \Uhere isn't quite\E done yet,\E is it?";
- This quoting\ Business\ HERE\ ISN\'T\ QUITE\ done\ yet\, is it?
+ say"This \Qquoting \ubusiness \Uhere isn't quite\E done yet,\E is it?";
+ This quoting\ Business\ HERE\ ISN\'T\ QUITE\ done\ yet\, is it?
-If C<use locale> is in effect, the case map used by C<\l>, C<\L>,
+If C<use locale> is in effect (but not C<use locale ':not_characters'>),
+the case map used by C<\l>, C<\L>,
C<\u>, and C<\U> is taken from the current locale. See L<perllocale>.
If Unicode (for example, C<\N{}> or code points of 0x100 or
beyond) is being used, the case map used by C<\l>, C<\L>, C<\u>, and
C<\U> is as defined by Unicode. That means that case-mapping
a single character can sometimes produce several characters.
+Under C<use locale>, C<\F> produces the same results as C<\L>.
All systems use the virtual C<"\n"> to represent a line terminator,
called a "newline". There is no such thing as an unvarying, physical
is done. Returns a Perl value which may be used instead of the
corresponding C</STRING/msixpodual> expression. The returned value is a
normalized version of the original pattern. It magically differs from
-a string containing the same characters: C<ref(qr/x/)> returns "Regexp",
-even though dereferencing the result returns undef.
+a string containing the same characters: C<ref(qr/x/)> returns "Regexp";
+however, dereferencing it is not well defined (you currently get the
+normalized version of the original pattern, but this may change).
+
For example,
The result may be used as a subpattern in a match:
$re = qr/$pattern/;
- $string =~ /foo${re}bar/; # can be interpolated in other patterns
+ $string =~ /foo${re}bar/; # can be interpolated in other
+ # patterns
$string =~ $re; # or used standalone
$string =~ /$re/; # or this way
i Do case-insensitive pattern matching.
x Use extended regular expressions.
p When matching preserve a copy of the matched string so
- that ${^PREMATCH}, ${^MATCH}, ${^POSTMATCH} will be defined.
+ that ${^PREMATCH}, ${^MATCH}, ${^POSTMATCH} will be
+ defined.
o Compile pattern only once.
- a ASCII-restrict: Use ASCII for \d, \s, \w; specifying two a's
- further restricts /i matching so that no ASCII character will
- match a non-ASCII one
+ a ASCII-restrict: Use ASCII for \d, \s, \w; specifying two
+ a's further restricts /i matching so that no ASCII
+ character will match a non-ASCII one
l Use the locale
u Use Unicode rules
d Use Unicode or native charset, as in 5.12 and earlier
See L<perlre> for additional information on valid syntax for STRING, and
for a detailed look at the semantics of regular expressions. In
-particular, all the modifiers execpt C</o> are further explained in
-L<perlre/Modifiers>. C</o> is described in the next section.
+particular, all modifiers except the largely obsolete C</o> are further
+
explained in L<perlre/Modifiers>. C</o> is described in the next section.
=item m/PATTERN/msixpodualgc
X<m> X<operator, match>
process modifiers are available:
g Match globally, i.e., find all occurrences.
- c Do not reset search position on a failed match when /g is in effect.
+ c Do not reset search position on a failed match when /g is
+ in effect.
If "/" is the delimiter then the initial C<m> is optional. With the C<m>
you can use any pair of non-whitespace (ASCII) characters
regardless of whether they change or not. (But there are saner ways
of accomplishing this than using C</o>.)
+=item 3
+
+If the pattern contains embedded code, such as
+
+ use re 'eval';
+ $code = 'foo(?{ $x })';
+ /$code/
+
+then perl will recompile each time, even though the pattern string hasn't
+changed, to ensure that the current value of C<$x> is seen each time.
+Use C</o> if you want to avoid this.
+
=back
The bottom line is that using C</o> is almost never a good idea.
If the C</g> option is not used, C<m//> in list context returns a
list consisting of the subexpressions matched by the parentheses in the
-pattern, i.e., (C<$1>, C<$2>, C<$3>...). (Note that here C<$1> etc. are
-also set, and that this differs from Perl 4's behavior.) When there are
-no parentheses in the pattern, the return value is the list C<(1)> for
-success. With or without parentheses, an empty list is returned upon
-failure.
+pattern, that is, (C<$1>, C<$2>, C<$3>...) (Note that here C<$1> etc. are
+also set). When there are no parentheses in the pattern, the return
+value is the list C<(1)> for success.
+With or without parentheses, an empty list is returned upon failure.
Examples:
- open(TTY, "+>/dev/tty")
- || die "can't access /dev/tty: $!";
+ open(TTY, "+</dev/tty")
+ || die "can't access /dev/tty: $!";
- <TTY> =~ /^y/i && foo(); # do foo if desired
+ <TTY> =~ /^y/i && foo(); # do foo if desired
- if (/Version: *([0-9.]*)/) { $version = $1; }
+ if (/Version: *([0-9.]*)/) { $version = $1; }
- next if m#^/usr/spool/uucp#;
+ next if m#^/usr/spool/uucp#;
- # poor man's grep
- $arg = shift;
- while (<>) {
- print if /$arg/o; # compile only once (no longer needed!)
- }
+ # poor man's grep
+ $arg = shift;
+ while (<>) {
+ print if /$arg/o; # compile only once (no longer needed!)
+ }
- if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))
+ if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))
This last example splits $foo into the first two words and the
remainder of the line, and assigns those three fields to $F1, $F2, and
The position after the last match can be read or set using the C<pos()>
function; see L<perlfunc/pos>. A failed match normally resets the
search position to the beginning of the string, but you can avoid that
-by adding the C</c> modifier (e.g. C<m//gc>). Modifying the target
+by adding the C</c> modifier (for example, C<m//gc>). Modifying the target
string also resets the search position.
=item \G assertion
Here's another way to check for sentences in a paragraph:
- my $sentence_rx = qr{
- (?: (?<= ^ ) | (?<= \s ) ) # after start-of-string or whitespace
- \p{Lu} # capital letter
- .*? # a bunch of anything
- (?<= \S ) # that ends in non-whitespace
- (?<! \b [DMS]r ) # but isn't a common abbreviation
- (?<! \b Mrs )
- (?<! \b Sra )
- (?<! \b St )
- [.?!] # followed by a sentence ender
- (?= $ | \s ) # in front of end-of-string or whitespace
- }sx;
- local $/ = "";
- while (my $paragraph = <>) {
- say "NEW PARAGRAPH";
- my $count = 0;
- while ($paragraph =~ /($sentence_rx)/g) {
- printf "\tgot sentence %d: <%s>\n", ++$count, $1;
- }
+ my $sentence_rx = qr{
+ (?: (?<= ^ ) | (?<= \s ) ) # after start-of-string or
+ # whitespace
+ \p{Lu} # capital letter
+ .*? # a bunch of anything
+ (?<= \S ) # that ends in non-
+ # whitespace
+ (?<! \b [DMS]r ) # but isn't a common abbr.
+ (?<! \b Mrs )
+ (?<! \b Sra )
+ (?<! \b St )
+ [.?!] # followed by a sentence
+ # ender
+ (?= $ | \s ) # in front of end-of-string
+ # or whitespace
+ }sx;
+ local $/ = "";
+ while (my $paragraph = <>) {
+ say "NEW PARAGRAPH";
+ my $count = 0;
+ while ($paragraph =~ /($sentence_rx)/g) {
+ printf "\tgot sentence %d: <%s>\n", ++$count, $1;
}
+ }
Here's how to use C<m//gc> with C<\G>:
regexp tries to match where the previous one leaves off.
$_ = <<'EOL';
- $url = URI::URL->new( "http://example.com/" ); die if $url eq "xXx";
+ $url = URI::URL->new( "http://example.com/" );
+ die if $url eq "xXx";
EOL
LOOP: {
print(" digits"), redo LOOP if /\G\d+\b[,.;]?\s*/gc;
- print(" lowercase"), redo LOOP if /\G\p{Ll}+\b[,.;]?\s*/gc;
- print(" UPPERCASE"), redo LOOP if /\G\p{Lu}+\b[,.;]?\s*/gc;
- print(" Capitalized"), redo LOOP if /\G\p{Lu}\p{Ll}+\b[,.;]?\s*/gc;
+ print(" lowercase"), redo LOOP
+ if /\G\p{Ll}+\b[,.;]?\s*/gc;
+ print(" UPPERCASE"), redo LOOP
+ if /\G\p{Lu}+\b[,.;]?\s*/gc;
+ print(" Capitalized"), redo LOOP
+ if /\G\p{Lu}\p{Ll}+\b[,.;]?\s*/gc;
print(" MiXeD"), redo LOOP if /\G\pL+\b[,.;]?\s*/gc;
- print(" alphanumeric"), redo LOOP if /\G[\p{Alpha}\pN]+\b[,.;]?\s*/gc;
+ print(" alphanumeric"), redo LOOP
+ if /\G[\p{Alpha}\pN]+\b[,.;]?\s*/gc;
print(" line-noise"), redo LOOP if /\G\W+/gc;
print ". That's all!\n";
}
Here is the output (split into several lines):
- line-noise lowercase line-noise UPPERCASE line-noise UPPERCASE
- line-noise lowercase line-noise lowercase line-noise lowercase
- lowercase line-noise lowercase lowercase line-noise lowercase
- lowercase line-noise MiXeD line-noise. That's all!
+ line-noise lowercase line-noise UPPERCASE line-noise UPPERCASE
+ line-noise lowercase line-noise lowercase line-noise lowercase
+ lowercase line-noise lowercase lowercase line-noise lowercase
+ lowercase line-noise MiXeD line-noise. That's all!
=item m?PATTERN?msixpodualgc
X<?> X<operator, match-once>
specific options:
e Evaluate the right side as an expression.
- ee Evaluate the right side as a string then eval the result.
- r Return substitution and leave the original string untouched.
+ ee Evaluate the right side as a string then eval the
+ result.
+ r Return substitution and leave the original string
+ untouched.
Any non-whitespace delimiter may replace the slashes. Add space after
the C<s> when using a character allowed in identifiers. If single quotes
are used, no interpretation is done on the replacement string (the C</e>
-modifier overrides this, however). Unlike Perl 4, Perl 5 treats backticks
+modifier overrides this, however). Note that Perl treats backticks
as normal delimiters; the replacement text is not evaluated as a command.
If the PATTERN is delimited by bracketing quotes, the REPLACEMENT has
-its own pair of quotes, which may or may not be bracketing quotes, e.g.,
+its own pair of quotes, which may or may not be bracketing quotes, for example,
C<s(foo)(bar)> or C<< s<foo>/bar/ >>. A C</e> will cause the
replacement portion to be treated as a full-fledged Perl expression
and evaluated right then and there. It is, however, syntax checked at
Examples:
- s/\bgreen\b/mauve/g; # don't change wintergreen
+ s/\bgreen\b/mauve/g; # don't change wintergreen
$path =~ s|/usr/bin|/usr/local/bin|;
s/Login: $foo/Login: $bar/; # run-time pattern
- ($foo = $bar) =~ s/this/that/; # copy first, then change
- ($foo = "$bar") =~ s/this/that/; # convert to string, copy, then change
+ ($foo = $bar) =~ s/this/that/; # copy first, then
+ # change
+ ($foo = "$bar") =~ s/this/that/; # convert to string,
+ # copy, then change
$foo = $bar =~ s/this/that/r; # Same as above using /r
$foo = $bar =~ s/this/that/r
- =~ s/that/the other/r; # Chained substitutes using /r
- @foo = map { s/this/that/r } @bar # /r is very useful in maps
+ =~ s/that/the other/r; # Chained substitutes
+ # using /r
+ @foo = map { s/this/that/r } @bar # /r is very useful in
+ # maps
- $count = ($paragraph =~ s/Mister\b/Mr./g); # get change-count
+ $count = ($paragraph =~ s/Mister\b/Mr./g); # get change-cnt
$_ = 'abc123xyz';
s/\d+/$&*2/e; # yields 'abc246xyz'
\*/ # Match the closing delimiter.
} []gsx;
- s/^\s*(.*?)\s*$/$1/; # trim whitespace in $_, expensively
+ s/^\s*(.*?)\s*$/$1/; # trim whitespace in $_,
+ # expensively
- for ($variable) { # trim whitespace in $variable, cheap
+ for ($variable) { # trim whitespace in $variable,
+ # cheap
s/^\s+//;
s/\s+$//;
}
# expand tabs to 8-column spacing
1 while s/\t+/' ' x (length($&)*8 - length($`)%8)/e;
-C<s///le> is treated as a substitution followed by the C<le> operator, not
-the C</le> flags. This may change in a future version of Perl. It
-produces a warning if warnings are enabled. To disambiguate, use a space
-or change the order of the flags:
-
- s/foo/bar/ le 5; # "le" infix operator
- s/foo/bar/el; # "e" and "l" flags
-
=back
=head2 Quote-Like Operators
capable of dealing with multiline commands, so putting newlines in
the string may not get you what you want. You may be able to evaluate
multiple commands in a single line by separating them with the command
-separator character, if your shell supports that (e.g. C<;> on many Unix
-shells; C<&> on the Windows NT C<cmd> shell).
+separator character, if your shell supports that (for example, C<;> on
+many Unix shells and C<&> on the Windows NT C<cmd> shell).
-Beginning with v5.6.0, Perl will attempt to flush all files opened for
+Perl will attempt to flush all files opened for
output before starting the child process, but this may not be supported
on some platforms (see L<perlport>). To be safe, you may need to set
C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method of
FINIS
If you use a here-doc within a delimited construct, such as in C<s///eg>,
-the quoted material must come on the lines following the final delimiter.
-So instead of
+the quoted material must still come on the line following the
+C<<< <<FOO >>> marker, which means it may be inside the delimited
+construct:
s/this/<<E . 'that'
the other
E
. 'more '/eg;
-you have to write
+It works this way as of Perl 5.18. Historically, it was inconsistent, and
+you would have to write
s/this/<<E . 'that'
. 'more '/eg;
the other
E
-If the terminating identifier is on the last line of the program, you
-must be sure there is a newline after it; otherwise, Perl will give the
-warning B<Can't find string terminator "END" anywhere before EOF...>.
+outside of string evals.
Additionally, quoting rules for the end-of-string identifier are
unrelated to Perl's quoting rules. C<q()>, C<qq()>, and the like are not
C<qq[]> and C<qq]]> constructs.
When searching for single-character delimiters, escaped delimiters
-and C<\\> are skipped. For example, while searching for terminating C</>,
+and C<\\> are skipped. For example, while searching for terminating C</>,
combinations of C<\\> and C<\/> are skipped. If the delimiters are
bracketing, nested pairs are also skipped. For example, while searching
for closing C<]> paired with the opening C<[>, combinations of C<\\>, C<\]>,
and C<\[> are all skipped, and nested C<[> and C<]> are skipped as well.
However, when backslashes are used as the delimiters (like C<qq\\> and
C<tr\\\>), nothing is skipped.
-During the search for the end, backslashes that escape delimiters
-are removed (exactly speaking, they are not copied to the safe location).
+During the search for the end, backslashes that escape delimiters or
+other backslashes are removed (exactly speaking, they are not copied to the
+safe location).
For constructs with three-part delimiters (C<s///>, C<y///>, and
C<tr///>), the search is repeated once more.
=item C<"">, C<``>, C<qq//>, C<qx//>, C<< <file*glob> >>, C<<<"EOF">
-C<\Q>, C<\U>, C<\u>, C<\L>, C<\l> (possibly paired with C<\E>) are
+C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, C<\F> (possibly paired with C<\E>) are
converted to corresponding Perl constructs. Thus, C<"$foo\Qbaz$bar">
is converted to C<$foo . (quotemeta("baz" . $bar))> internally.
The other escape sequences such as C<\200> and C<\t> and backslashed
=item the replacement of C<s///>
-Processing of C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, and interpolation
+Processing of C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, C<\F> and interpolation
happens as with C<qq//> constructs.
It is at this step that C<\1> is begrudgingly converted to C<$1> in
=item C<RE> in C<?RE?>, C</RE/>, C<m/RE/>, C<s/RE/foo/>,
-Processing of C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, C<\E>,
+Processing of C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, C<\F>, C<\E>,
and interpolation happens (almost) as with C<qq//> constructs.
Processing of C<\N{...}> is also done here, and compiled into an intermediate
treated as an array symbol (for example C<@foo>),
even though the same text in C<qq//> gives interpolation of C<\c@>.
+Code blocks such as C<(?{BLOCK})> are handled by temporarily passing control
+back to the perl parser, in a similar way that an interpolated array
+subscript expression such as C<"foo$array[1+f("[xyz")]bar"> would be.
+
Moreover, inside C<(?{BLOCK})>, C<(?# comment )>, and
a C<#>-comment in a C<//x>-regular expression, no processing is
performed whatsoever. This is the first step at which the presence
The terminator of this construct is found using the same rules as
for finding the terminator of a C<{}>-delimited construct, the only
exception being that C<]> immediately following C<[> is treated as
-though preceded by a backslash. Similarly, the terminator of
-C<(?{...})> is found using the same rules as for finding the
-terminator of a C<{}>-delimited construct.
+though preceded by a backslash.
+
+The terminator of runtime C<(?{...})> is found by temporarily switching
+control to the perl parser, which should stop at the point where the
+logically balancing terminating C<}> is found.
It is possible to inspect both the string given to RE engine and the
resulting finite automaton. See the arguments C<debug>/C<debugcolor>
print while ($_ = <STDIN>);
print while <STDIN>;
-This also behaves similarly, but avoids $_ :
+This also behaves similarly, but assigns to a lexical variable
+instead of to C<$_>:
while (my $line = <STDIN>) { print $line }
In these loop constructs, the assigned value (whether assignment
is automatic or explicit) is then tested to see whether it is
-defined. The defined test avoids problems where line has a string
-value that would be treated as false by Perl, for example a "" or
+defined. The defined test avoids problems where the line has a string
+value that would be treated as false by Perl; for example a "" or
a "0" with no trailing newline. If you really mean for such values
to terminate the loop, they should be tested for explicitly:
while (($_ = <STDIN>) ne '0') { ... }
while (<STDIN>) { last unless $_; ... }
-In other boolean contexts, C<< <filehandle> >> without an
+In other boolean contexts, C<< <FILEHANDLE> >> without an
explicit C<defined> test or comparison elicits a warning if the
C<use warnings> pragma or the B<-w>
command-line switch (the C<$^W> variable) is in effect.
See L<perlfunc/readline>.
The null filehandle <> is special: it can be used to emulate the
-behavior of B<sed> and B<awk>. Input from <> comes either from
+behavior of B<sed> and B<awk>, and any other Unix filter program
+that takes a list of filenames, doing the same to each line
+of input from all of them. Input from <> comes either from
standard input, or from each file listed on the command line. Here's
how it works: the first time <> is evaluated, the @ARGV array is
checked, and if it is empty, C<$ARGV[0]> is set to "-", which when opened
If you call it again after this, it will assume you are processing another
@ARGV list, and if you haven't set @ARGV, will read input from STDIN.
-If what the angle brackets contain is a simple scalar variable (e.g.,
+If what the angle brackets contain is a simple scalar variable (for example,
<$foo>), then that variable contains the name of the
filehandle to input from, or its typeglob, or a reference to the
same. For example:
the next value each time it's called, or C<undef> when the list has
run out. As with filehandle reads, an automatic C<defined> is
generated when the glob occurs in the test part of a C<while>,
-because legal glob returns (e.g. a file called F<0>) would otherwise
+because legal glob returns (for example,
+a file called F<0>) would otherwise
terminate the loop. Again, C<undef> is returned only once. So if
you're expecting a single value from a glob, it is much better to
say
variable substitution. Backslash interpolation also happens at
compile time. You can say
- 'Now is the time for all' . "\n" .
- 'good men to come to.'
+ 'Now is the time for all'
+ . "\n"
+ . 'good men to come to.'
and this all reduces to one string internally. Likewise, if
you say
if (-s $file > 5 + 100 * 2**16) { }
}
-the compiler will precompute the number which that expression
+the compiler precomputes the number which that expression
represents so that the interpreter won't have to.
=head2 No-ops
X<no-op> X<nop>
Perl doesn't officially have a no-op operator, but the bare constants
-C<0> and C<1> are special-cased to not produce a warning in a void
+C<0> and C<1> are special-cased not to produce a warning in void
context, so you can for example safely do
1 while foo();
X<number, arbitrary precision>
The standard C<Math::BigInt>, C<Math::BigRat>, and C<Math::BigFloat> modules,
-along with the C<bigint>, C<bigrat>, and C<bitfloat> pragmas, provide
+along with the C<bignum>, C<bigint>, and C<bigrat> pragmas, provide
variable-precision arithmetic and overloaded operators, although
they're currently pretty slow. At the cost of some space and
considerable speed, they avoid the normal pitfalls associated with
Here is a short, but incomplete summary:
- Math::Fraction big, unlimited fractions like 9973 / 12967
Math::String treat string sequences like numbers
Math::FixedPrecision calculate with a fixed precision
Math::Currency for currency calculations
Bit::Vector manipulate bit vectors fast (uses C)
Math::BigIntFast Bit::Vector wrapper for big numbers
Math::Pari provides access to the Pari C library
- Math::BigInteger uses an external C library
- Math::Cephes uses external Cephes C library (no big numbers)
+ Math::Cephes uses the external Cephes C library (no
+ big numbers)
Math::Cephes::Fraction fractions via the Cephes library
Math::GMP another one using an external C library
+ Math::GMPz an alternative interface to libgmp's big ints
+ Math::GMPq an interface to libgmp's fraction numbers
+ Math::GMPf an interface to libgmp's floating point numbers
Choose wisely.
https://perl5.git.perl.org / perl5.git / blobdiff