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
+in force then signed C integers are used, else unsigned C integers are
+used. Either way, the implementation isn't going to generate results
+larger than the size of the integer type Perl was built with (32 bits
+or 64 bits).
+
+The result of overflowing the range of the integers is undefined
+because it is undefined also in C. In other words, using 32-bit
+integers, C<< 1 << 32 >> is undefined. Shifting by a negative number
+of bits is also undefined.
+
=head2 Named Unary Operators
The various named unary operators are treated as functions with one
If any list operator (print(), etc.) or any unary operator (chdir(), etc.)
is followed by a left parenthesis as the next token, the operator and
arguments within parentheses are taken to be of highest precedence,
-just like a normal function call. Examples:
+just like a normal function call. For example,
+because named unary operators are higher precedence than ||:
chdir $foo || die; # (chdir $foo) || die
chdir($foo) || die; # (chdir $foo) || die
chdir ($foo) || die; # (chdir $foo) || die
chdir +($foo) || die; # (chdir $foo) || die
-but, because * is higher precedence than ||:
+but, because * is higher precedence than named operators:
chdir $foo * 20; # chdir ($foo * 20)
chdir($foo) * 20; # (chdir $foo) * 20
Customary Generic Meaning Interpolates
'' q{} Literal no
"" qq{} Literal yes
- qu{} Literal yes (UTF-8, see below)
- `` qx{} Command yes (unless '' is delimiter)
+ `` qx{} Command yes*
qw{} Word list no
- // m{} Pattern match yes (unless '' is delimiter)
- qr{} Pattern yes (unless '' is delimiter)
- s{}{} Substitution yes (unless '' is delimiter)
+ // m{} Pattern match yes*
+ qr{} Pattern yes*
+ s{}{} Substitution yes*
tr{}{} Transliteration no (but see below)
+ * unless the delimiter is ''.
+
Non-bracketing delimiters use the same character fore and aft, but the four
sorts of brackets (round, angle, square, curly) will all nest, which means
that
$s = q{ if($a eq "}") ... }; # WRONG
-is a syntax error. The C<Text::Balanced> module on CPAN is able to do this
-properly.
+is a syntax error. The C<Text::Balanced> module (from CPAN, and
+starting from Perl 5.8 part of the standard distribution) is able
+to do this properly.
There can be whitespace between the operator and the quoting
characters, except when C<#> is being used as the quoting character.
s {foo} # Replace foo
{bar} # with bar.
-For constructs that do interpolate, variables beginning with "C<$>"
-or "C<@>" are interpolated, as are the following escape sequences. Within
-a transliteration, the first eleven of these sequences may be used.
+The following escape sequences are available in constructs that interpolate
+and in transliterations.
\t tab (HT, TAB)
\n newline (NL)
\c[ control char (ESC)
\N{name} named char
+The following escape sequences are available in constructs that interpolate
+but not in transliterations.
+
\l lowercase next char
\u uppercase next char
\L lowercase till \E
C<"\015">. If you get in the habit of using C<"\n"> for networking,
you may be burned some day.
+For constructs that do interpolate, variables beginning with "C<$>"
+or "C<@>" are interpolated. Subscripted variables such as C<$a[3]> or
+C<$href->{key}[0]> are also interpolated, as are array and hash slices.
+But method calls such as C<$obj->meth> are not.
+
+Interpolating an array or slice interpolates the elements in order,
+separated by the value of C<$">, so is equivalent to interpolating
+C<join $", @array>. "Punctuation" arrays such as C<@+> are only
+interpolated if the name is enclosed in braces C<@{+}>.
+
You cannot include a literal C<$> or C<@> within a C<\Q> sequence.
An unescaped C<$> or C<@> interpolates the corresponding variable,
while escaping will cause the literal string C<\$> to be inserted.
reset if eof; # clear ?? status for next file
}
-This usage is vaguely depreciated, which means it just might possibly
+This usage is vaguely deprecated, which means it just might possibly
be removed in some distant future version of Perl, perhaps somewhere
around the year 2168.
See L<perlre> for additional information on valid syntax for STRING, and
for a detailed look at the semantics of regular expressions.
-=item qw/STRING/
-
-Evaluates to a list of the words extracted out of STRING, using embedded
-whitespace as the word delimiters. It can be understood as being roughly
-equivalent to:
-
- split(' ', q/STRING/);
-
-the difference being that it generates a real list at compile time. So
-this expression:
-
- qw(foo bar baz)
-
-is semantically equivalent to the list:
-
- 'foo', 'bar', 'baz'
-
-Some frequently seen examples:
-
- use POSIX qw( setlocale localeconv )
- @EXPORT = qw( foo bar baz );
-
-A common mistake is to try to separate the words with comma or to
-put comments into a multi-line C<qw>-string. For this reason, the
-C<use warnings> pragma and the B<-w> switch (that is, the C<$^W> variable)
-produces warnings if the STRING contains the "," or the "#" character.
-
-=item qu/STRING/
-
-Like L<qq> but explicitly generates UTF-8 from the \0ooo, \xHH, and
-\x{HH} constructs if the code point is in the 0x80..0xff range (and
-of course for the 0x100.. range).
-
-Normally you do not need to use this because whether characters are
-internally encoded in UTF-8 should be transparent, and you can just
-just use qq, also known as "".
-
-(In qq/STRING/ the \0ooo, \xHH, and the \x{HHH...} constructs
-generate bytes for the 0x80..0xff range. For the whole 0x00..0xff
-range the generated bytes are host-dependent: in ISO 8859-1 they will
-be ISO 8859-1, in EBCDIC they will EBCDIC, and so on.)
-
=item qx/STRING/
=item `STRING`
See L<"I/O Operators"> for more discussion.
+=item qw/STRING/
+
+Evaluates to a list of the words extracted out of STRING, using embedded
+whitespace as the word delimiters. It can be understood as being roughly
+equivalent to:
+
+ split(' ', q/STRING/);
+
+the difference being that it generates a real list at compile time. So
+this expression:
+
+ qw(foo bar baz)
+
+is semantically equivalent to the list:
+
+ 'foo', 'bar', 'baz'
+
+Some frequently seen examples:
+
+ use POSIX qw( setlocale localeconv )
+ @EXPORT = qw( foo bar baz );
+
+A common mistake is to try to separate the words with comma or to
+put comments into a multi-line C<qw>-string. For this reason, the
+C<use warnings> pragma and the B<-w> switch (that is, the C<$^W> variable)
+produces warnings if the STRING contains the "," or the "#" character.
+
=item s/PATTERN/REPLACEMENT/egimosx
Searches a string for a pattern, and if found, replaces that pattern
A string enclosed by backticks (grave accents) first undergoes
double-quote interpolation. It is then interpreted as an external
command, and the output of that command is the value of the
-pseudo-literal, j
-string consisting of all output is returned. In list context, a
-list of values is returned, one per line of output. (You can set
-C<$/> to use a different line terminator.) The command is executed
-each time the pseudo-literal is evaluated. The status value of the
-command is returned in C<$?> (see L<perlvar> for the interpretation
-of C<$?>). Unlike in B<csh>, no translation is done on the return
-data--newlines remain newlines. Unlike in any of the shells, single
-quotes do not hide variable names in the command from interpretation.
-To pass a literal dollar-sign through to the shell you need to hide
-it with a backslash. The generalized form of backticks is C<qx//>.
-(Because backticks always undergo shell expansion as well, see
-L<perlsec> for security concerns.)
+backtick string, like in a shell. In scalar context, a single string
+consisting of all output is returned. In list context, a list of
+values is returned, one per line of output. (You can set C<$/> to use
+a different line terminator.) The command is executed each time the
+pseudo-literal is evaluated. The status value of the command is
+returned in C<$?> (see L<perlvar> for the interpretation of C<$?>).
+Unlike in B<csh>, no translation is done on the return data--newlines
+remain newlines. Unlike in any of the shells, single quotes do not
+hide variable names in the command from interpretation. To pass a
+literal dollar-sign through to the shell you need to hide it with a
+backslash. The generalized form of backticks is C<qx//>. (Because
+backticks always undergo shell expansion as well, see L<perlsec> for
+security concerns.)
In scalar context, evaluating a filehandle in angle brackets yields
the next line from that file (the newline, if any, included), or
the value is automatically assigned to the global variable $_,
destroying whatever was there previously. (This may seem like an
odd thing to you, but you'll use the construct in almost every Perl
-script you write.) The $_ variables is not implicitly localized.
+script you write.) The $_ variable is not implicitly localized.
You'll have to put a C<local $_;> before the loop if you want that
to happen.
If you call it again after this, it will assume you are processing another
@ARGV list, and if you haven't set @ARGV, will read input from STDIN.
-If angle brackets contain is a simple scalar variable (e.g.,
+If what the angle brackets contain is a simple scalar variable (e.g.,
<$foo>), then that variable contains the name of the
filehandle to input from, or its typeglob, or a reference to the
same. For example:
because the latter will alternate between returning a filename and
returning false.
-It you're trying to do variable interpolation, it's definitely better
+If you're trying to do variable interpolation, it's definitely better
to use the glob() function, because the older notation can cause people
to become confused with the indirect filehandle notation.
The standard Math::BigInt and Math::BigFloat modules provide
variable-precision arithmetic and overloaded operators, although
-they're currently pretty slow. At the cost of some space and
+they're currently pretty slow. At the cost of some space and
considerable speed, they avoid the normal pitfalls associated with
limited-precision representations.
# prints +15241578780673678515622620750190521
-The non-standard modules SSLeay::BN and Math::Pari provide
-equivalent functionality (and much more) with a substantial
-performance savings.
+There are several modules that let you calculate with (bound only by
+memory and cpu-time) unlimited or fixed precision. There are also
+some non-standard modules that provide faster implementations via
+external C libraries.
+
+Here is a short, but incomplete summary:
+
+ Math::Fraction big, unlimited fractions like 9973 / 12967
+ Math::String treat string sequences like numbers
+ Math::FixedPrecision calculate with a fixed precision
+ Math::Currency for currency calculations
+ Bit::Vector manipulate bit vectors fast (uses C)
+ Math::BigIntFast Bit::Vector wrapper for big numbers
+ Math::Pari provides access to the Pari C library
+ Math::BigInteger uses an external C library
+ Math::Cephes uses external Cephes C library (no big numbers)
+ Math::Cephes::Fraction fractions via the Cephes library
+ Math::GMP another one using an external C library
+
+Choose wisely.
=cut
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