X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlop.pod;h=9ae391821a97f31934ee69e63cda0ce7b19eb329;hb=5269aecde866056a77e32c937c7c3182bb599487;hp=0bb506ddc708ada8a8988131bf1243676f097a0d;hpb=360eb788a3c30916019278c140e3ebfb207f591f;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlop.pod b/pod/perlop.pod index 0bb506d..9ae3918 100644 --- a/pod/perlop.pod +++ b/pod/perlop.pod @@ -233,6 +233,18 @@ Binary ">>" 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.) +Note that both "<<" and ">>" in Perl are implemented directly using +"<<" and ">>" in C. If C (see L) 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 @@ -242,14 +254,15 @@ operators, like C<-f>, C<-M>, etc. See L. 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 @@ -645,13 +658,15 @@ any pair of delimiters you choose. Customary Generic Meaning Interpolates '' q{} Literal no "" qq{} Literal yes - `` 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 @@ -666,8 +681,9 @@ Note, however, that this does not always work for quoting Perl code: $s = q{ if($a eq "}") ... }; # WRONG -is a syntax error. The C module on CPAN is able to do this -properly. +is a syntax error. The C 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. @@ -678,9 +694,8 @@ from the next line. This allows you to write: s {foo} # Replace foo {bar} # with bar. -For constructs that do interpolate, variables beginning with "C<$>" -or "C<@>" are interpolated, as are the following escape sequences. Within -a transliteration, the first eleven of these sequences may be used. +The following escape sequences are available in constructs that interpolate +and in transliterations. \t tab (HT, TAB) \n newline (NL) @@ -695,6 +710,9 @@ a transliteration, the first eleven of these sequences may be used. \c[ control char (ESC) \N{name} named char +The following escape sequences are available in constructs that interpolate +but not in transliterations. + \l lowercase next char \u uppercase next char \L lowercase till \E @@ -720,6 +738,16 @@ and although they often accept just C<"\012">, they seldom tolerate just C<"\015">. If you get in the habit of using C<"\n"> for networking, you may be burned some day. +For constructs that do interpolate, variables beginning with "C<$>" +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. "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. @@ -760,7 +788,7 @@ patterns local to the current package are reset. 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. @@ -1562,19 +1590,19 @@ There are several I/O operators you should know about. A string enclosed by backticks (grave accents) first undergoes double-quote interpolation. It is then interpreted as an external command, and the 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 for the interpretation -of C<$?>). Unlike in B, no translation is done on the return -data--newlines remain newlines. Unlike in any of the shells, single -quotes do not hide variable names in the command from interpretation. -To pass a literal dollar-sign through to the shell you need to hide -it with a backslash. The generalized form of backticks is C. -(Because backticks always undergo shell expansion as well, see -L for security concerns.) +backtick string, like in a shell. In scalar context, a single string +consisting of all output is returned. In list context, a list of +values is returned, one per line of output. (You can set C<$/> 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<$?> (see L for the interpretation of C<$?>). +Unlike in B, 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. (Because +backticks always undergo shell expansion as well, see L 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 @@ -1589,7 +1617,7 @@ of a C statement (even if disguised as a C loop), 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 $_ variable is not implicitly localized. You'll have to put a C before the loop if you want that to happen. @@ -1700,7 +1728,7 @@ The <> symbol will return C for end-of-file only once. If you call it again after this, it will assume you are processing another @ARGV list, and if you haven't set @ARGV, will read input from STDIN. -If angle brackets contain is a simple scalar variable (e.g., +If what the angle brackets contain is a simple scalar variable (e.g., <$foo>), then that variable contains the name of the filehandle to input from, or its typeglob, or a reference to the same. For example: @@ -1734,7 +1762,7 @@ is roughly equivalent to: open(FOO, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|"); while () { - chop; + chomp; chmod 0644, $_; } @@ -1764,7 +1792,7 @@ than 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. @@ -1901,7 +1929,7 @@ need yourself. 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. @@ -1911,8 +1939,25 @@ 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