perlnews - what's new for perl5.004
This document describes differences between the 5.003 release (as documented in Programming Perl, second edition--the Camel Book) and this one.
Perl5.004 builds out of the box on Unix, Plan9, LynxOS, VMS, OS/2, QNX, and AmigaOS.
Most importantly, many bugs were fixed. See the Changes file in the distribution for details.
There is a new Configure question that asks if you want to maintain binary compatibility with Perl 5.003. If you choose binary compatibility, you do not have to recompile your extensions, but you might have symbol conflicts if you embed Perl in another application.
Filehandles are now stored internally as type IO::Handle. Although use FileHandle and *STDOUT{FILEHANDLE} are still supported for backwards compatibility use IO::Handle (or IO::Seekable or IO::File) and *STDOUT{IO} are the way of the future.
use FileHandle
*STDOUT{FILEHANDLE}
use IO::Handle
IO::Seekable
IO::File
*STDOUT{IO}
A new Opcode module subsumes 5.003's Safe module. The Safe interface is still available, so existing scripts should still work, but users are encouraged to read the new Opcode documentation.
It is now possible to build Perl with AT&T's sfio IO package instead of stdio. See perlapio for more details, and the INSTALL file for how to use it.
Extended error message under some platforms ($EXTENDED_OS_ERROR if you use English).
use English
The current set of syntax checks enabled by use strict. See the documentation of strict for more details. Not actually new, but newly documented. Because it is intended for internal use by Perl core components, there is no use English long name for this variable.
use strict
strict
By default, running out of memory it is not trappable. However, if compiled for this, Perl may use the contents of $^M as an emergency pool after die()ing with this message. Suppose that your Perl were compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
$^M
$^M = 'a' x (1<<16);
would allocate 64K buffer for use when in emergency. See the INSTALL file for information on how to enable this option. As a disincentive to casual use of this advanced feature, there is no use English long name for this variable.
This now works. (e.g. delete @ENV{'PATH', 'MANPATH'})
delete @ENV{'PATH', 'MANPATH'}
is now supported on more platforms, and prefers fcntl to lockf when emulating.
As an lvalue, keys allows you to increase the number of hash buckets allocated for the given associative array. This can gain you a measure of efficiency if you know the hash is going to get big. (This is similar to pre-extending an array by assigning a larger number to $#array.) If you say
keys
keys %hash = 200;
then %hash will have at least 200 buckets allocated for it. These buckets will be retained even if you do %hash = (); use undef %hash if you want to free the storage while %hash is still in scope. You can't shrink the number of buckets allocated for the hash using keys in this way (but you needn't worry about doing this by accident, as trying has no effect).
%hash
%hash = ()
undef %hash
You can now use my() (with or without the parentheses) in the control expressions of control structures such as:
while (my $line = <>) { $line = lc $line; } continue { print $line; } if ((my $answer = <STDIN>) =~ /^yes$/i) { user_agrees(); } elsif ($answer =~ /^no$/i) { user_disagrees(); } else { chomp $answer; die "'$answer' is neither 'yes' nor 'no'"; }
Also, you can declare a foreach loop control variable as lexical by preceding it with the word "my". For example, in:
foreach my $i (1, 2, 3) { some_function(); }
$i is a lexical variable, and the scope of $i extends to the end of the loop, but not beyond it.
Note that you still cannot use my() on global punctuation variables such as $_ and the like.
A new format 'w' represents a BER compressed integer (as defined in ASN.1). Its format is a sequence of one or more bytes, each of which provides seven bits of the total value, with the most significant first. Bit eight of each byte is set, except for the last byte, in which bit eight is clear.
If the first argument to use is a number, it is treated as a version number instead of a module name. If the version of the Perl interpreter is less than VERSION, then an error message is printed and Perl exits immediately. This is often useful if you need to check the current Perl version before useing library modules which have changed in incompatible ways from older versions of Perl. (We try not to do this more than we have to.)
use
If the VERSION argument is present between Module and LIST, then the use will fail if the $VERSION variable in package Module is less than VERSION.
Note that there is not a comma after the version!
Returns the prototype of a function as a string (or undef if the function has no prototype). FUNCTION is a reference to or the name of the function whose prototype you want to retrieve. (Not actually new; just never documented before.)
undef
Functions documented in the Camel to default to $_ now in fact do, and all those that do are so documented in perlfunc.
The UNIVERSAL package automatically contains the following methods that are inherited by all other classes:
UNIVERSAL
isa returns true if its object is blessed into a sub-class of CLASS
isa
CLASS
isa is also exportable and can be called as a sub with two arguments. This allows the ability to check what a reference points to. Example:
use UNIVERSAL qw(isa); if(isa($ref, 'ARRAY')) { ... }
can checks to see if its object has a method called METHOD, if it does then a reference to the sub is returned; if it does not then undef is returned.
can
METHOD
VERSION returns the version number of the class (package). If the NEED argument is given then it will check that the current version is not less than NEED and die if this is not the case. This method is normally called as a class method. This method is also called when the VERSION form of use is used.
VERSION
use A 1.2 qw(some imported subs); A->VERSION( 1.2 ); $ref->is_instance(); # True
class returns the class name of its object.
class
is_instance returns true if its object is an instance of some class, false if its object is the class (package) itself. Example
is_instance
A->is_instance(); # False $var = 'A'; $var->is_instance(); # False $ref = bless [], 'A'; $ref->is_instance(); # True
NOTE: can directly uses Perl's internal code for method lookup, and isa uses a very similar method and cache-ing strategy. This may cause strange effects if the Perl code dynamically changes @ISA in any package.
You may add other methods to the UNIVERSAL class via Perl or XS code. You do not need to use UNIVERSAL in order to make these methods available to your program. This is necessary only if you wish to have isa available as a plain subroutine in the current package.
use UNIVERSAL
This is the constructor for the class. That means it is expected to return an object of some sort. The reference can be used to hold some internal information.
sub TIEHANDLE { print "<shout>\n"; my $i; bless \$i, shift }
This method will be triggered every time the tied handle is printed to. Beyond its self reference it also expects the list that was passed to the print function.
sub PRINT { $r = shift; $$r++; print join($,,map(uc($_),@_)),$\ }
This method will be called when the handle is read from. The method should return undef when there is no more data.
sub READLINE { $r = shift; "PRINT called $$r times\n"; }
As with the other types of ties, this method will be called when the tied handle is about to be destroyed. This is useful for debugging and possibly for cleaning up.
sub DESTROY { print "</shout>\n" }
Three new pragmatic modules exist:
Looks for MakeMaker-like 'blib' directory structure starting in dir (or current directory) and working back up to five levels of parent directories.
Intended for use on command line with -M option as a way of testing arbitrary scripts against an uninstalled version of a package.
Tells the compiler to enable (or disable) the use of POSIX locales for built-in operations.
When use locale is in effect, the current LC_CTYPE locale is used for regular expressions and case mapping; LC_COLLATE for string ordering; and LC_NUMERIC for numeric formating in printf and sprintf (but not in print). LC_NUMERIC is always used in write, since lexical scoping of formats is problematic at best.
use locale
Each use locale or no locale affects statements to the end of the enclosing BLOCK or, if not inside a BLOCK, to the end of the current file. Locales can be switched and queried with POSIX::setlocale().
no locale
See perllocale for more information.
Restricts unsafe operations when compiling.
Brand new modules:
IO.pm Top-level interface to IO::* classes IO/File.pm IO::File extension Perl module IO/Handle.pm IO::Handle extension Perl module IO/Pipe.pm IO::Pipe extension Perl module IO/Seekable.pm IO::Seekable extension Perl module IO/Select.pm IO::Select extension Perl module IO/Socket.pm IO::Socket extension Perl module Opcode.pm Disable named opcodes when compiling Perl code ExtUtils/Embed.pm Utilities for embedding Perl in C programs ExtUtils/testlib.pm Fixes up @INC to use just-built extension Fatal.pm Make do-or-die equivalents of functions FindBin.pm Find path of currently executing program Class/Template.pm Structure/member template builder File/stat.pm Object-oriented wrapper around CORE::stat Net/hostent.pm Object-oriented wrapper around CORE::gethost* Net/netent.pm Object-oriented wrapper around CORE::getnet* Net/protoent.pm Object-oriented wrapper around CORE::getproto* Net/servent.pm Object-oriented wrapper around CORE::getserv* Time/gmtime.pm Object-oriented wrapper around CORE::gmtime Time/localtime.pm Object-oriented wrapper around CORE::localtime Time/tm.pm Perl implementation of "struct tm" for {gm,local}time User/grent.pm Object-oriented wrapper around CORE::getgr* User/pwent.pm Object-oriented wrapper around CORE::getpw* UNIVERSAL.pm Base class for *ALL* classes
The IO module provides a simple mechanism to load all of the IO modules at one go. Currently this includes:
IO::Handle IO::Seekable IO::File IO::Pipe IO::Socket
For more information on any of these modules, please see its respective documentation.
The Math::Complex module has been totally rewritten, and now supports more operations. These are overloaded:
+ - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
And these functions are now exported:
pi i Re Im arg log10 logn cbrt root tan cotan asin acos atan acotan sinh cosh tanh cotanh asinh acosh atanh acotanh cplx cplxe
Many of the Perl built-ins returning lists now have object-oriented overrides. These are:
File::stat Net::hostent Net::netent Net::protoent Net::servent Time::gmtime Time::localtime User::grent User::pwent
For example, you can now say
use File::stat; use User::pwent; $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
All hash keys with the same string are only allocated once, so even if you have 100 copies of the same hash, the immutable keys never have to be re-allocated.
Functions that do nothing but return a fixed value are now inlined.
Many of the base and library pods were updated. These new pods are included in section 1:
Internationalization.
Perl internal IO abstraction interface.
Tutorial on Perl OO programming.
Although not new, this has been massively updated.
Several new conditions will trigger warnings that were silent before. Some only affect certain platforms. The following new warnings and errors outline these:
(S) A lexical variable has been redeclared in the same scope, effectively eliminating all access to the previous instance. This is almost always a typographical error. Note that the earlier variable will still exist until the end of the scope or until all closure referents to it are destroyed.
(X) You can't allocate more than 64K on an MSDOS machine.
(F) You can't allocate more than 2^31+"small amount" bytes.
(P) Perl maintains a reference counted internal table of strings to optimize the storage and access of hash keys and other strings. This indicates someone tried to decrement the reference count of a string that can no longer be found in the table.
(W) You supplied a reference as the first argument to substr() used as an lvalue, which is pretty strange. Perhaps you forgot to dereference it first. See "substr" in perlfunc.
(F) Your version of executable does not support forking.
Note that under some systems, like OS/2, there may be different flavors of Perl executables, some of which may support fork, some not. Try changing the name you call Perl by to perl_, perl__, and so on.
perl_
perl__
(W) A warning peculiar to VMS. A logical name was encountered when preparing to iterate over %ENV which violates the syntactic rules governing logical names. Since it cannot be translated normally, it is skipped, and will not appear in %ENV. This may be a benign occurrence, as some software packages might directly modify logical name tables and introduce non-standard names, or it may indicate that a logical name table has been corrupted.
(S) The literal hex number you have specified is too big for your architecture. On a 32-bit architecture the largest hex literal is 0xFFFFFFFF.
(S) The literal octal number you have specified is too big for your architecture. On a 32-bit architecture the largest octal literal is 037777777777.
(F) The first argument to formline must be a valid format picture specification. It was found to be empty, which probably means you supplied it an uninitialized value. See perlform.
(F) You tried to do a read/write/send/recv operation with an offset pointing outside the buffer. This is difficult to imagine. The sole exception to this is that sysread()ing past the buffer will extend the buffer and zero pad the new area.
sysread()
(X|F) The malloc() function returned 0, indicating there was insufficient remaining memory (or virtual memory) to satisfy the request.
The request was judged to be small, so the possibility to trap it depends on the way Perl was compiled. By default it is not trappable. However, if compiled for this, Perl may use the contents of $^M as an emergency pool after die()ing with this message. In this case the error is trappable once.
(F) The malloc() function returned 0, indicating there was insufficient remaining memory (or virtual memory) to satisfy the request. However, the request was judged large enough (compile-time default is 64K), so a possibility to shut down by trapping this error is granted.
(W) You probably wrote something like this:
qw( a # a comment b # another comment ) ;
when you should have written this:
qw( a b ) ;
qw( a, b, c );
qw( a b c );
(W) A copy of the object returned from tie (or tied) was still valid when untie was called.
tie
tied
untie
(P) An error peculiar to OS/2. Most probably you use an obsolete version of Perl, and should not happen anyway.
(F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
prefix1;prefix2
or
prefix1 prefix2
with non-empty prefix1 and prefix2. If prefix1 is indeed a prefix of a builtin library search path, prefix2 is substituted. The error may appear if components are not found, or are too long. See "PERLLIB_PREFIX" in perlos2.
prefix1
(F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the sh-shell in. See "PERL_SH_DIR" in perlos2.
sh
(W) This is a standard message issued by OS/2 applications, while *nix applications die in silence. It is considered a feature of the OS/2 port. One can easily disable this by appropriate sighandlers, see "Signals" in perlipc. See "Process terminated by SIGTERM/SIGINT" in perlos2.
If you find what you think is a bug, you might check the headers of recently posted articles in the comp.lang.perl.misc newsgroup. There may also be information at http://www.perl.com/perl/, the Perl Home Page.
If you believe you have an unreported bug, please run the perlbug program included with your release. Make sure you trim your bug down to a tiny but sufficient test case. Your bug report, along with the output of perl -V, will be sent off to perlbug@perl.com to be analysed by the Perl porting team.
perl -V
The Changes file for exhaustive details on what changed.
The INSTALL file for how to build Perl. This file has been significantly updated for 5.004, so even veteran users should look through it.
The README file for general stuff.
The Copying file for copyright information.
Constructed by Tom Christiansen, grabbing material with permission from innumerable contributors, with kibitzing by more than a few Perl porters.
Last update: Wed Dec 18 16:18:27 EST 1996
To install lib, copy and paste the appropriate command in to your terminal.
cpanm
cpanm lib
CPAN shell
perl -MCPAN -e shell install lib
For more information on module installation, please visit the detailed CPAN module installation guide.