X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlfunc.pod;h=86a09ba8dc45ab9b52c3f2160307d6cad2824aa9;hb=f1c09d8aea4b00e7799b7273c877df50e0fd657a;hp=d54275443b3c9a920e8fcbb83122b37bf4031854;hpb=66670188cea1de9e5a28e46eaf556eccea649d2c;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod index d542754..86a09ba 100644 --- a/pod/perlfunc.pod +++ b/pod/perlfunc.pod @@ -450,13 +450,12 @@ on systems where the run-time libraries distinguish between binary and text files. If FILEHANDLE is an expression, the value is taken as the name of the filehandle. DISCIPLINE can be either of C<":raw"> for binary mode or C<":crlf"> for "text" mode. If the DISCIPLINE is -omitted, it defaults to C<":raw">. +omitted, it defaults to C<":raw">. Returns true on success, C on +failure. binmode() should be called after open() but before any I/O is done on the filehandle. -On many systems binmode() currently has no effect, but in future, it -will be extended to support user-defined input and output disciplines. On some systems binmode() is necessary when you're not working with a text file. For the sake of portability it is a good idea to always use it when appropriate, and to never use it when it isn't appropriate. @@ -475,15 +474,15 @@ representation matches the internal representation, but on some platforms the external representation of C<\n> is made up of more than one character. -Mac OS, all variants of Unix, and Stream_LF files on VMS use a single -character to end each line in the external representation of text (even +Mac OS, all variants of Unix, and Stream_LF files on VMS use a single +character to end each line in the external representation of text (even though that single character is CARRIAGE RETURN on Mac OS and LINE FEED -on Unix and most VMS files). Consequently binmode() has no effect on -these operating systems. In other systems like OS/2, DOS and the various -flavors of MS-Windows your program sees a C<\n> as a simple C<\cJ>, but -what's stored in text files are the two characters C<\cM\cJ>. That means -that, if you don't use binmode() on these systems, C<\cM\cJ> sequences on -disk will be converted to C<\n> on input, and any C<\n> in your program +on Unix and most VMS files). Consequently binmode() has no effect on +these operating systems. In other systems like OS/2, DOS and the various +flavors of MS-Windows your program sees a C<\n> as a simple C<\cJ>, but +what's stored in text files are the two characters C<\cM\cJ>. That means +that, if you don't use binmode() on these systems, C<\cM\cJ> sequences on +disk will be converted to C<\n> on input, and any C<\n> in your program will be converted back to C<\cM\cJ> on output. This is what you want for text files, but it can be disastrous for binary files. @@ -561,11 +560,12 @@ previous time C was called. =item chdir EXPR -Changes the working directory to EXPR, if possible. If EXPR is omitted, +Changes the working directory to EXPR, if possible. If EXPR is omitted, changes to the directory specified by C<$ENV{HOME}>, if set; if not, -changes to the directory specified by C<$ENV{LOGDIR}>. If neither is -set, C does nothing. It returns true upon success, false -otherwise. See the example under C. +changes to the directory specified by C<$ENV{LOGDIR}>. (Under VMS, the +variable C<$ENV{SYS$LOGIN}> is also checked, and used if it is set.) If +neither is set, C does nothing. It returns true upon success, +false otherwise. See the example under C. =item chmod LIST @@ -682,9 +682,9 @@ On POSIX systems, you can detect this condition this way: Returns the character represented by that NUMBER in the character set. For example, C is C<"A"> in either ASCII or Unicode, and -chr(0x263a) is a Unicode smiley face. Within the scope of C, -characters higher than 127 are encoded in Unicode; if you don't want -this, temporarily C or use C +chr(0x263a) is a Unicode smiley face. Note that characters from +127 to 255 (inclusive) are not encoded in Unicode for backward +compatibility reasons. For the reverse, use L. See L for more about Unicode. @@ -807,17 +807,29 @@ extirpated as a potential munition). This can prove useful for checking the password file for lousy passwords, amongst other things. Only the guys wearing white hats should do this. -Note that C is intended to be a one-way function, much like breaking -eggs to make an omelette. There is no (known) corresponding decrypt -function. As a result, this function isn't all that useful for +Note that C is intended to be a one-way function, much like +breaking eggs to make an omelette. There is no (known) corresponding +decrypt function (in other words, the crypt() is a one-way hash +function). As a result, this function isn't all that useful for cryptography. (For that, see your nearby CPAN mirror.) -When verifying an existing encrypted string you should use the encrypted -text as the salt (like C). This -allows your code to work with the standard C and with more -exotic implementations. When choosing a new salt create a random two -character string whose characters come from the set C<[./0-9A-Za-z]> -(like C). +When verifying an existing encrypted string you should use the +encrypted text as the salt (like C). This allows your code to work with the standard C +and with more exotic implementations. In other words, do not assume +anything about the returned string itself, or how many bytes in +the encrypted string matter. + +Traditionally the result is a string of 13 bytes: two first bytes of +the salt, followed by 11 bytes from the set C<[./0-9A-Za-z]>, and only +the first eight bytes of the encrypted string mattered, but +alternative hashing schemes (like MD5), higher level security schemes +(like C2), and implementations on non-UNIX platforms may produce +different strings. + +When choosing a new salt create a random two character string whose +characters come from the set C<[./0-9A-Za-z]> (like C). Here's an example that makes sure that whoever runs this program knows their own password: @@ -845,6 +857,11 @@ back. Look at the F and F directories on your favorite CPAN mirror for a slew of potentially useful modules. +If using crypt() on an Unicode string (which potentially has +characters with codepoints above 255), Perl tries to make sense of +the situation by using only the low eight bits of the characters when +calling crypt(). + =item dbmclose HASH [This function has been largely superseded by the C function.] @@ -2117,7 +2134,8 @@ L.) If EXPR is omitted, uses C<$_>. print hex 'aF'; # same Hex strings may only represent integers. Strings that would cause -integer overflow trigger a warning. +integer overflow trigger a warning. Leading whitespace is not stripped, +unlike oct(). =item import @@ -2310,9 +2328,9 @@ C work. =item lc Returns an lowercased version of EXPR. This is the internal function -implementing the C<\L> escape in double-quoted strings. -Respects current LC_CTYPE locale if C in force. See L -and L. +implementing the C<\L> escape in double-quoted strings. Respects +current LC_CTYPE locale if C in force. See L +and L. If EXPR is omitted, uses C<$_>. @@ -2320,9 +2338,10 @@ If EXPR is omitted, uses C<$_>. =item lcfirst -Returns the value of EXPR with the first character lowercased. This is -the internal function implementing the C<\l> escape in double-quoted strings. -Respects current LC_CTYPE locale if C in force. See L. +Returns the value of EXPR with the first character lowercased. This +is the internal function implementing the C<\l> escape in +double-quoted strings. Respects current LC_CTYPE locale if C in force. See L and L. If EXPR is omitted, uses C<$_>. @@ -2613,8 +2632,9 @@ See the L function, which C is the opposite of. Interprets EXPR as an octal string and returns the corresponding value. (If EXPR happens to start off with C<0x>, interprets it as a hex string. If EXPR starts off with C<0b>, it is interpreted as a -binary string.) The following will handle decimal, binary, octal, and -hex in the standard Perl or C notation: +binary string. Leading whitespace is ignored in all three cases.) +The following will handle decimal, binary, octal, and hex in the standard +Perl or C notation: $val = oct($val) if $val =~ /^0/; @@ -2629,15 +2649,18 @@ to be converted into a file mode, for example. (Although perl will automatically convert strings into numbers as needed, this automatic conversion assumes base 10.) -=item open FILEHANDLE,MODE,LIST - =item open FILEHANDLE,EXPR +=item open FILEHANDLE,MODE,EXPR + +=item open FILEHANDLE,MODE,EXPR,LIST + =item open FILEHANDLE Opens the file whose filename is given by EXPR, and associates it with -FILEHANDLE. If FILEHANDLE is an expression, its value is used as the -name of the real filehandle wanted. (This is considered a symbolic +FILEHANDLE. If FILEHANDLE is an undefined lexical (C) variable the variable is +assigned a reference to a new anonymous filehandle, otherwise if FILEHANDLE is an expression, +its value is used as the name of the real filehandle wanted. (This is considered a symbolic reference, so C should I be in effect.) If EXPR is omitted, the scalar @@ -2647,7 +2670,8 @@ for this purpose; so if you're using C, specify EXPR in your call to open.) See L for a kinder, gentler explanation of opening files. -If MODE is C<< '<' >> or nothing, the file is opened for input. +If three or more arguments are specified then the mode of opening and the file name +are separate. If MODE is C<< '<' >> or nothing, the file is opened for input. If MODE is C<< '>' >>, the file is truncated and opened for output, being created if necessary. If MODE is C<<< '>>' >>>, the file is opened for appending, again being created if necessary. @@ -2664,7 +2688,8 @@ C<'w'>, C<'w+'>, C<'a'>, and C<'a+'>. In the 2-arguments (and 1-argument) form of the call the mode and filename should be concatenated (in this order), possibly separated by -spaces. It is possible to omit the mode if the mode is C<< '<' >>. +spaces. It is possible to omit the mode in these forms if the mode is +C<< '<' >>. If the filename begins with C<'|'>, the filename is interpreted as a command to which output is to be piped, and if the filename ends with a @@ -2675,14 +2700,18 @@ that pipes both in I out, but see L, L, and L for alternatives.) -If MODE is C<'|-'>, the filename is interpreted as a +For three or more arguments if MODE is C<'|-'>, the filename is interpreted as a command to which output is to be piped, and if MODE is C<'-|'>, the filename is interpreted as a command which pipes output to us. In the 2-arguments (and 1-argument) form one should replace dash (C<'-'>) with the command. See L for more examples of this. (You are not allowed to C to a command that pipes both in I out, but see L, L, -and L for alternatives.) +and L for alternatives.) In 3+ arg form of +pipe opens then if LIST is specified (extra arguments after the command name) then +LIST becomes arguments to the command invoked if the platform supports it. +The meaning of C with more than three arguments for non-pipe modes +is not yet specified. Experimental "layers" may give extra LIST arguments meaning. In the 2-arguments (and 1-argument) form opening C<'-'> opens STDIN and opening C<< '>-' >> opens STDOUT. @@ -2700,6 +2729,10 @@ and those that don't is their text file formats. Systems like Unix, MacOS, and Plan9, which delimit lines with a single character, and which encode that character in C as C<"\n">, do not need C. The rest need it. +In the three argument form MODE may also contain a list of IO "layers" (see L and +L for more details) to be applied to the handle. This can be used to achieve the +effect of C as well as more complex behaviours. + When opening a file, it's usually a bad idea to continue normal execution if the request failed, so C is frequently used in connection with C. Even if C won't do what you want (say, in a CGI script, @@ -2715,6 +2748,7 @@ being C: opens a filehandle to an anonymous temporary file. + Examples: $ARTICLE = 100; @@ -2798,19 +2832,25 @@ STDERR: print STDOUT "stdout 2\n"; print STDERR "stderr 2\n"; -If you specify C<< '<&=N' >>, where C is a number, then Perl will do an -equivalent of C's C of that file descriptor; this is more -parsimonious of file descriptors. For example: +If you specify C<< '<&=N' >>, where C is a number, then Perl will +do an equivalent of C's C of that file descriptor; this is +more parsimonious of file descriptors. For example: open(FILEHANDLE, "<&=$fd") + or + open(FILEHANDLE, "<&=", $fd) -Note that if perl is using the standard C libaries fdopen() then on many UNIX systems, -fdopen() is known to fail when file descriptors +Note that if Perl is using the standard C libraries' fdopen() then on +many UNIX systems, fdopen() is known to fail when file descriptors exceed a certain value, typically 255. If you need more file descriptors than that, consider rebuilding Perl to use the C. +You can see whether Perl has been compiled with PerlIO or not by +running C and looking for C line. If C +is C, you have PerlIO, otherwise you don't. + If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'> with 2-arguments (or 1-argument) form of open(), then there is an implicit fork done, and the return value of open is the pid @@ -2980,7 +3020,7 @@ with it. B: This is an experimental feature that may be changed or removed in future releases of Perl. It should not be relied upon. -The only currently recognized attribute is C which indicates +The only currently recognized attribute is C which indicates that a single copy of the global is to be used by all interpreters should the program happen to be running in a multi-interpreter environment. (The default behaviour would be for each interpreter to @@ -2988,13 +3028,13 @@ have its own copy of the global.) In such an environment, this attribute also has the effect of making the global readonly. Examples: - our @EXPORT : shared = qw(foo); - our %EXPORT_TAGS : shared = (bar => [qw(aa bb cc)]); - our $VERSION : shared = "1.00"; + our @EXPORT : unique = qw(foo); + our %EXPORT_TAGS : unique = (bar => [qw(aa bb cc)]); + our $VERSION : unique = "1.00"; Multi-interpreter environments can come to being either through the fork() emulation on Windows platforms, or by embedding perl in a -multi-threaded application. The C attribute does nothing in +multi-threaded application. The C attribute does nothing in all other environments. =item pack TEMPLATE,LIST @@ -3060,8 +3100,8 @@ follows: P A pointer to a structure (fixed-length string). u A uuencoded string. - U A Unicode character number. Encodes to UTF-8 internally. - Works even if C is not in effect. + U A Unicode character number. Encodes to UTF-8 internally + (or UTF-EBCDIC in EBCDIC platforms). w A BER compressed integer. Its bytes represent an unsigned integer in base 128, most significant digit first, with as @@ -3384,8 +3424,10 @@ C<$::sail> is equivalent to C<$main::sail> (as well as to C<$main'sail>, still seen in older code). If NAMESPACE is omitted, then there is no current package, and all -identifiers must be fully qualified or lexicals. This is stricter -than C, since it also extends to function names. +identifiers must be fully qualified or lexicals. However, you are +strongly advised not to make use of this feature. Its use can cause +unexpected behaviour, even crashing some versions of Perl. It is +deprecated, and will be removed from a future release. See L for more information about packages, modules, and classes. See L for other scoping issues. @@ -3468,9 +3510,10 @@ you will have to use a block returning its value instead: Equivalent to C, except that C<$\> (the output record separator) is not appended. The first argument -of the list will be interpreted as the C format. If C is -in effect, the character used for the decimal point in formatted real numbers -is affected by the LC_NUMERIC locale. See L. +of the list will be interpreted as the C format. See C +for an explanation of the format argument. If C is in effect, +the character used for the decimal point in formatted real numbers is +affected by the LC_NUMERIC locale. See L. Don't fall into the trap of using a C when a simple C would do. The C is more efficient and less @@ -3532,8 +3575,8 @@ If EXPR is omitted, uses C<$_>. Returns a random fractional number greater than or equal to C<0> and less than the value of EXPR. (EXPR should be positive.) If EXPR is -omitted, the value C<1> is used. Automatically calls C unless -C has already been called. See also C. +omitted, or a C<0>, the value C<1> is used. Automatically calls C +unless C has already been called. See also C. Apply C to the value returned by C if you want random integers instead of random fractional numbers. For example, @@ -3713,19 +3756,23 @@ rename(2) manpage or equivalent system documentation for details. =item require -Demands some semantics specified by EXPR, or by C<$_> if EXPR is not -supplied. +Demands a version of Perl specified by VERSION, or demands some semantics +specified by EXPR or by C<$_> if EXPR is not supplied. + +VERSION may be either a numeric argument such as 5.006, which will be +compared to C<$]>, or a literal of the form v5.6.1, which will be compared +to C<$^V> (aka $PERL_VERSION). A fatal error is produced at run time if +VERSION is greater than the version of the current Perl interpreter. +Compare with L, which can do a similar check at compile time. -If a VERSION is specified as a literal of the form v5.6.1, -demands that the current version of Perl (C<$^V> or $PERL_VERSION) be -at least as recent as that version, at run time. (For compatibility -with older versions of Perl, a numeric argument will also be interpreted -as VERSION.) Compare with L, which can do a similar check at -compile time. +Specifying VERSION as a literal of the form v5.6.1 should generally be +avoided, because it leads to misleading error messages under earlier +versions of Perl which do not support this syntax. The equivalent numeric +version should be used instead. require v5.6.1; # run time version check require 5.6.1; # ditto - require 5.005_03; # float version allowed for compatibility + require 5.006_001; # ditto; preferred for backwards compatibility Otherwise, demands that a library file be included if it hasn't already been included. The file is included via the do-FILE mechanism, which is @@ -3784,6 +3831,60 @@ will complain about not finding "F" there. In this case you can do: eval "require $class"; +You can also insert hooks into the import facility, by putting directly +Perl code into the @INC array. There are three forms of hooks: subroutine +references, array references and blessed objects. + +Subroutine references are the simplest case. When the inclusion system +walks through @INC and encounters a subroutine, this subroutine gets +called with two parameters, the first being a reference to itself, and the +second the name of the file to be included (e.g. "F"). The +subroutine should return C or a filehandle, from which the file to +include will be read. If C is returned, C will look at +the remaining elements of @INC. + +If the hook is an array reference, its first element must be a subroutine +reference. This subroutine is called as above, but the first parameter is +the array reference. This enables to pass indirectly some arguments to +the subroutine. + +In other words, you can write: + + push @INC, \&my_sub; + sub my_sub { + my ($coderef, $filename) = @_; # $coderef is \&my_sub + ... + } + +or: + + push @INC, [ \&my_sub, $x, $y, ... ]; + sub my_sub { + my ($arrayref, $filename) = @_; + # Retrieve $x, $y, ... + my @parameters = @$arrayref[1..$#$arrayref]; + ... + } + +If the hook is an object, it must provide an INC method, that will be +called as above, the first parameter being the object itself. (Note that +you must fully qualify the sub's name, as it is always forced into package +C
.) Here is a typical code layout: + + # In Foo.pm + package Foo; + sub new { ... } + sub Foo::INC { + my ($self, $filename) = @_; + ... + } + + # In the main program + push @INC, new Foo(...); + +Note that these hooks are also permitted to set the %INC entry +corresponding to the files they have loaded. See L. + For a yet-more-powerful import facility, see L and L. =item reset EXPR @@ -4046,14 +4147,14 @@ documentation. =item semop KEY,OPSTRING Calls the System V IPC function semop to perform semaphore operations -such as signaling and waiting. OPSTRING must be a packed array of +such as signalling and waiting. OPSTRING must be a packed array of semop structures. Each semop structure can be generated with -C. The number of semaphore +C. The number of semaphore operations is implied by the length of OPSTRING. Returns true if successful, or false if there is an error. As an example, the following code waits on semaphore $semnum of semaphore id $semid: - $semop = pack("sss", $semnum, -1, 0); + $semop = pack("s!3", $semnum, -1, 0); die "Semaphore trouble: $!\n" unless semop($semid, $semop); To signal the semaphore, replace C<-1> with C<1>. See also @@ -4277,6 +4378,12 @@ loop control operators described in L or with C. When C is in effect, C sorts LIST according to the current collation locale. See L. +Perl does B guarantee that sort is stable. (A I sort +preserves the input order of elements that compare equal.) 5.7 and +5.8 happen to use a stable mergesort, but 5.6 and earlier used quicksort, +which is not stable. Do not assume that future perls will continue to +use a stable sort. + Examples: # sort lexically @@ -4433,11 +4540,15 @@ splits on whitespace (after skipping any leading whitespace). Anything matching PATTERN is taken to be a delimiter separating the fields. (Note that the delimiter may be longer than one character.) -If LIMIT is specified and positive, splits into no more than that -many fields (though it may split into fewer). If LIMIT is unspecified -or zero, trailing null fields are stripped (which potential users -of C would do well to remember). If LIMIT is negative, it is -treated as if an arbitrarily large LIMIT had been specified. +If LIMIT is specified and positive, it represents the maximum number +of fields the EXPR will be split into, though the actual number of +fields returned depends on the number of times PATTERN matches within +EXPR. If LIMIT is unspecified or zero, trailing null fields are +stripped (which potential users of C would do well to remember). +If LIMIT is negative, it is treated as if an arbitrarily large LIMIT +had been specified. Note that splitting an EXPR that evaluates to the +empty string always returns the empty list, regardless of the LIMIT +specified. A pattern matching the null string (not to be confused with a null pattern C, which is just one member of the set of patterns @@ -4448,6 +4559,10 @@ characters at each point it matches that way. For example: produces the output 'h:i:t:h:e:r:e'. +Using the empty pattern C specifically matches the null string, and is +not be confused with the use of C to mean "the last successful pattern +match". + Empty leading (or trailing) fields are produced when there positive width matches at the beginning (or end) of the string; a zero-width match at the beginning (or end) of the string does not produce an empty field. For @@ -4507,6 +4622,11 @@ Example: #... } +As with regular pattern matching, any capturing parentheses that are not +matched in a C will be set to C when returned: + + @fields = split /(A)|B/, "1A2B3"; + # @fields is (1, 'A', 2, undef, 3) =item sprintf FORMAT, LIST @@ -4685,19 +4805,42 @@ loaded the standard Math::Complex module. =item srand -Sets the random number seed for the C operator. If EXPR is -omitted, uses a semi-random value supplied by the kernel (if it supports -the F device) or based on the current time and process -ID, among other things. In versions of Perl prior to 5.004 the default -seed was just the current C