X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlop.pod;h=9ae391821a97f31934ee69e63cda0ce7b19eb329;hb=5269aecde866056a77e32c937c7c3182bb599487;hp=b4caed9155cef2ba0a43fedfa685ffde0aa94f3b;hpb=1f24770523b86085797280e0a7daee28bb477133;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlop.pod b/pod/perlop.pod index b4caed9..9ae3918 100644 --- a/pod/perlop.pod +++ b/pod/perlop.pod @@ -119,7 +119,7 @@ you increment a variable that is numeric, or that has ever been used in a numeric context, you get a normal increment. If, however, the variable has been used in only string contexts since it was set, and has a value that is not the empty string and matches the pattern -C, the increment is done as a string, preserving each +C, the increment is done as a string, preserving each character within its range, with carry: print ++($foo = '99'); # prints '100' @@ -196,7 +196,7 @@ C<$a> minus the largest multiple of C<$b> that is not greater than C<$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 result will be less than or equal to zero). -Note than when C is in scope, "%" give you direct access +Note than when C is in scope, "%" gives you direct access to the modulus operator as implemented by your C compiler. This operator is not as well defined for negative operands, but it will execute faster. @@ -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 $foo) * 20 @@ -299,7 +312,14 @@ to the right argument. Binary "<=>" returns -1, 0, or 1 depending on whether the left argument is numerically less than, equal to, or greater than the right -argument. +argument. If your platform supports NaNs (not-a-numbers) as numeric +values, using them with "<=>" returns undef. NaN is not "<", "==", ">", +"<=" or ">=" anything (even NaN), so those 5 return false. NaN != NaN +returns true, as does NaN != anything else. If your platform doesn't +support NaNs then NaN is just a string with numeric value 0. + + perl -le '$a = NaN; print "No NaN support here" if $a == $a' + perl -le '$a = NaN; print "NaN support here" if $a != $a' Binary "eq" returns true if the left argument is stringwise equal to the right argument. @@ -307,8 +327,9 @@ the right argument. Binary "ne" returns true if the left argument is stringwise not equal to the right argument. -Binary "cmp" returns -1, 0, or 1 depending on whether the left argument is stringwise -less than, equal to, or greater than the right argument. +Binary "cmp" returns -1, 0, or 1 depending on whether the left +argument is stringwise less than, equal to, or greater than the right +argument. "lt", "le", "ge", "gt" and "cmp" use the collation (sort) order specified by the current locale if C is in effect. See L. @@ -637,13 +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 @@ -658,8 +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. @@ -670,9 +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<$>" -or "C<@>" are interpolated, as are the following escape sequences. Within -a transliteration, the first eleven of these sequences may be used. +The following escape sequences are available in constructs that interpolate +and in transliterations. \t tab (HT, TAB) \n newline (NL) @@ -687,6 +710,9 @@ a transliteration, the first eleven of these sequences may be used. \c[ control char (ESC) \N{name} named char +The following escape sequences are available in constructs that interpolate +but not in transliterations. + \l lowercase next char \u uppercase next char \L lowercase till \E @@ -707,11 +733,21 @@ on a Mac, these are reversed, and on systems without line terminator, printing C<"\n"> may emit no actual data. In general, use C<"\n"> when you mean a "newline" for your system, but use the literal ASCII when you need an exact character. For example, most networking protocols expect -and prefer a CR+LF (C<"\012\015"> or C<"\cJ\cM">) for line terminators, +and prefer a CR+LF (C<"\015\012"> or C<"\cM\cJ">) for line terminators, and although they often accept just C<"\012">, they seldom tolerate just C<"\015">. If you get in the habit of using C<"\n"> for networking, you may be burned some day. +For constructs that do interpolate, variables beginning with "C<$>" +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. @@ -752,7 +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. @@ -795,7 +831,7 @@ the trailing delimiter. This avoids expensive run-time recompilations, and is useful when the value you are interpolating won't change over the life of the script. However, mentioning C constitutes a promise that you won't change the variables in the pattern. If you change them, -Perl won't even notice. See also L<"qr//">. +Perl won't even notice. See also L<"qr/STRING/imosx">. If the PATTERN evaluates to the empty string, the last I matched regular expression is used instead. @@ -848,9 +884,11 @@ string also resets the search position. You can intermix C matches with C, where C<\G> is a zero-width assertion that matches the exact position where the previous -C, if any, left off. The C<\G> assertion is not supported without -the C modifier. (Currently, without C, C<\G> behaves just like -C<\A>, but that's accidental and may change in the future.) +C, if any, left off. Without the C modifier, the C<\G> assertion +still anchors at pos(), but the match is of course only attempted once. +Using C<\G> without C on a target string that has not previously had a +C match applied to it is the same as using the C<\A> assertion to match +the beginning of the string. Examples: @@ -858,7 +896,7 @@ Examples: ($one,$five,$fifteen) = (`uptime` =~ /(\d+\.\d+)/g); # scalar context - $/ = ""; $* = 1; # $* deprecated in modern perls + $/ = ""; while (defined($paragraph = <>)) { while ($paragraph =~ /[a-z]['")]*[.!?]+['")]*\s/g) { $sentences++; @@ -876,6 +914,7 @@ Examples: print "3: '"; print $1 while /(p)/gc; print "', pos=", pos, "\n"; } + print "Final: '$1', pos=",pos,"\n" if /\G(.)/; The last example should print: @@ -885,6 +924,13 @@ The last example should print: 1: '', pos=7 2: 'q', pos=8 3: '', pos=8 + Final: 'q', pos=8 + +Notice that the final match matched C instead of C

, which a match +without the C<\G> anchor would have done. Also note that the final match +did not update C -- C is only updated on a C match. If the +final match did indeed match C

, it's a good bet that you're running an +older (pre-5.6.0) Perl. A useful idiom for C-like scanners is C. You can combine several regexps like this to process a string part-by-part, @@ -938,7 +984,7 @@ A double-quoted, interpolated string. =item qr/STRING/imosx -This operators quotes--and compiles--its I as a regular +This operator quotes (and possibly compiles) its I as a regular expression. I is interpolated the same way as I in C. If "'" is used as the delimiter, no interpolation is done. Returns a Perl value which may be used instead of the @@ -997,13 +1043,14 @@ for a detailed look at the semantics of regular expressions. =item `STRING` -A string which is (possibly) interpolated and then executed as a system -command with C or its equivalent. Shell wildcards, pipes, -and redirections will be honored. The collected standard output of the -command is returned; standard error is unaffected. In scalar context, -it comes back as a single (potentially multi-line) string. In list -context, returns a list of lines (however you've defined lines with $/ -or $INPUT_RECORD_SEPARATOR). +A string which is (possibly) interpolated and then executed as a +system command with C or its equivalent. Shell wildcards, +pipes, and redirections will be honored. The collected standard +output of the command is returned; standard error is unaffected. In +scalar context, it comes back as a single (potentially multi-line) +string, or undef if the command failed. In list context, returns a +list of lines (however you've defined lines with $/ or +$INPUT_RECORD_SEPARATOR), or an empty list if the command failed. Because backticks do not affect standard error, use shell file descriptor syntax (assuming the shell supports this) if you care to address this. @@ -1207,9 +1254,9 @@ to occur that you might want. Here are two common cases: # expand tabs to 8-column spacing 1 while s/\t+/' ' x (length($&)*8 - length($`)%8)/e; -=item tr/SEARCHLIST/REPLACEMENTLIST/cdsUC +=item tr/SEARCHLIST/REPLACEMENTLIST/cds -=item y/SEARCHLIST/REPLACEMENTLIST/cdsUC +=item y/SEARCHLIST/REPLACEMENTLIST/cds Transliterates all occurrences of the characters found in the search list with the corresponding character in the replacement list. It returns @@ -1243,8 +1290,6 @@ Options: c Complement the SEARCHLIST. d Delete found but unreplaced characters. s Squash duplicate replaced characters. - U Translate to/from UTF-8. - C Translate to/from 8-bit char (octet). If the C modifier is specified, the SEARCHLIST character set is complemented. If the C modifier is specified, any characters @@ -1262,10 +1307,6 @@ enough. If the REPLACEMENTLIST is empty, the SEARCHLIST is replicated. This latter is useful for counting characters in a class or for squashing character sequences in a class. -The first C or C modifier applies to the left side of the translation. -The second one applies to the right side. If present, these modifiers override -the current utf8 state. - Examples: $ARGV[1] =~ tr/A-Z/a-z/; # canonicalize to lower case @@ -1285,9 +1326,6 @@ Examples: tr [\200-\377] [\000-\177]; # delete 8th bit - tr/\0-\xFF//CU; # change Latin-1 to Unicode - tr/\0-\x{FF}//UC; # change Unicode to Latin-1 - If multiple transliterations are given for a character, only the first one is used: @@ -1333,7 +1371,7 @@ their results are the same, we consider them individually. For different quoting constructs, Perl performs different numbers of passes, from one to five, but these passes are always performed in the same order. -=over +=over 4 =item Finding the end @@ -1387,7 +1425,7 @@ used in parsing. The next step is interpolation in the text obtained, which is now delimiter-independent. There are four different cases. -=over +=over 4 =item C<<<'EOF'>, C, C, C, C @@ -1552,19 +1590,19 @@ There are several I/O operators you should know about. A string enclosed by backticks (grave accents) first undergoes double-quote interpolation. It is then interpreted as an external command, and the output of that command is the value of the -pseudo-literal, j -string consisting of all output is returned. In list context, a -list of values is returned, one per line of output. (You can set -C<$/> 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 @@ -1579,7 +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 $_ variable is not implicitly localized. You'll have to put a C before the loop if you want that to happen. @@ -1690,7 +1728,7 @@ The <> symbol will return C for end-of-file only once. If you call it again after this, it will assume you are processing another @ARGV list, and if you haven't set @ARGV, will read input from STDIN. -If angle brackets contain is a simple scalar variable (e.g., +If what the angle brackets contain is a simple scalar variable (e.g., <$foo>), then that variable contains the name of the filehandle to input from, or its typeglob, or a reference to the same. For example: @@ -1724,7 +1762,7 @@ is roughly equivalent to: open(FOO, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|"); while () { - chop; + chomp; chmod 0644, $_; } @@ -1754,7 +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. @@ -1837,8 +1875,8 @@ integer>, if you take the C, you'll still get C<1.4142135623731> or so. Used on numbers, the bitwise operators ("&", "|", "^", "~", "<<", -and ">>") always produce integral results. (But see also L.) However, C still has meaning for +and ">>") always produce integral results. (But see also +L.) However, C still has meaning for them. By default, their results are interpreted as unsigned integers, but if C is in effect, their results are interpreted as signed integers. For example, C<~0> usually evaluates to a large @@ -1891,7 +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. @@ -1901,8 +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