perldelta updates.

[p5sagit/p5-mst-13.2.git] / pod / perldelta.pod

=head1 NAME

perldelta - what is new for perl v5.8.0

=head1 DESCRIPTION

This document describes differences between the 5.6.0 release
and the 5.8.0 release.

Many of the bug fixes in 5.8.0 were already seen in the 5.6.1
maintenance release since the two releases were kept closely
coordinated.

If you are upgrading from Perl 5.005_03, you might also want
to read L<perl56delta>.

=head1 Highlights In 5.8.0

=over 4

=item *

Better Unicode support

=item *

New Thread Implementation

=item *

Many New Modules

=item *

Better Numeric Accuracy

=item *

Safe Signals

=item *

More Extensive Regression Testing

=back

=head1 Incompatible Changes

=head2 64-bit platforms and malloc

If your pointers are 64 bits wide, the Perl malloc is no longer being
used because it does not work well with 8-byte pointers.  Also,
usually the system mallocs on such platforms are much better optimized
for such large memory models than the Perl malloc.  Some memory-hungry
Perl applications like the PDL don't work well with Perl's malloc.
Finally, other applications than Perl (like modperl) tend to prefer
the system malloc.  Such platforms include Alpha and 64-bit HPPA,
MIPS, PPC, and Sparc.

=head2 AIX Dynaloading

The AIX dynaloading now uses in AIX releases 4.3 and newer the native
dlopen interface of AIX instead of the old emulated interface.  This
change will probably break backward compatibility with compiled
modules.  The change was made to make Perl more compliant with other
applications like modperl which are using the AIX native interface.

=head2 Attributes for C<my> variables now handled at run-time.

The C<my EXPR : ATTRS> syntax now applies variable attributes at
run-time.  (Subroutine and C<our> variables still get attributes applied
at compile-time.)  See L<attributes> for additional details.  In particular,
however, this allows variable attributes to be useful for C<tie> interfaces,
which was a deficiency of earlier releases.  Note that the new semantics
doesn't work with the Attribute::Handlers module (as of version 0.76).

=head2 Socket Extension Dynamic in VMS

The Socket extension is now dynamically loaded instead of being
statically built in.  This may or may not be a problem with ancient
TCP/IP stacks of VMS: we do not know since we weren't able to test
Perl in such configurations.

=head2 IEEE-format Floating Point Default on OpenVMS Alpha

Perl now uses IEEE format (T_FLOAT) as the default internal floating
point format on OpenVMS Alpha, potentially breaking binary compatibility
with external libraries or existing data.  G_FLOAT is still available as
a configuration option.  The default on VAX (D_FLOAT) has not changed.

=head2 New Unicode Properties

Unicode I<scripts> are now supported. Scripts are similar to (and superior
to) Unicode I<blocks>. The difference between scripts and blocks is that
scripts are the glyphs used by a language or a group of languages, while
the blocks are more artificial groupings of (mostly) 256 characters based
on the Unicode numbering.

In general, scripts are more inclusive, but not universally so. For
example, while the script C<Latin> includes all the Latin characters and
their various diacritic-adorned versions, it does not include the various
punctuation or digits (since they are not solely C<Latin>).

A number of other properties are now supported, including C<\p{L&}>,
C<\p{Any}> C<\p{Assigned}>, C<\p{Unassigned}>, C<\p{Blank}> and
C<\p{SpacePerl}> (along with their C<\P{...}> versions, of course).
See L<perlunicode> for details, and more additions.

The C<In> or C<Is> prefix to names used with the C<\p{...}> and C<\P{...}>
are now almost always optional. The only exception is that a C<In> prefix
is required to signify a Unicode block when a block name conflicts with a
script name. For example, C<\p{Tibetan}> refers to the script, while
C<\p{InTibetan}> refers to the block. When there is no name conflict, you
can omit the C<In> from the block name (e.g. C<\p{BraillePatterns}>), but
to be safe, it's probably best to always use the C<In>).

=head2 Perl Parser Stress Tested

The Perl parser has been stress tested using both random input and
Markov chain input and the few found crashes and lockups have been
fixed.

=head2 REF(...) Instead Of SCALAR(...)

A reference to a reference now stringifies as "REF(0x81485ec)" instead
of "SCALAR(0x81485ec)" in order to be more consistent with the return
value of ref().

=head2 pack/unpack D/F recycled

The undocumented pack/unpack template letters D/F have been recyled
for better use: now they stand for long double (if supported by the
platform) and NV (Perl internal floating point type).  (They used
to be aliases for f/d, but you never knew that.)

=head2 Deprecations

=over 4

=item *

The semantics of bless(REF, REF) were unclear and until someone proves
it to make some sense, it is forbidden.

=item *

The obsolete chat2 library that should never have been allowed
to escape the laboratory has been decommissioned.

=item *

The builtin dump() function has probably outlived most of its
usefulness.  The core-dumping functionality will remain in future
available as an explicit call to C<CORE::dump()>, but in future
releases the behaviour of an unqualified C<dump()> call may change.

=item *

The very dusty examples in the eg/ directory have been removed.
Suggestions for new shiny examples welcome but the main issue is that
the examples need to be documented, tested and (most importantly)
maintained.

=item *

The (bogus) escape sequences \8 and \9 now give an optional warning
("Unrecognized escape passed through").  There is no need to \-escape
any C<\w> character.

=item *

The list of filenames from glob() (or <...>) is now by default sorted
alphabetically to be csh-compliant (which is what happened before
in most UNIX platforms).  (bsd_glob() does still sort platform
natively, ASCII or EBCDIC, unless GLOB_ALPHASORT is specified.)

=item *

Spurious syntax errors generated in certain situations, when glob()
caused File::Glob to be loaded for the first time, have been fixed.

=item *

Although "you shouldn't do that", it was possible to write code that
depends on Perl's hashed key order (Data::Dumper does this).  The new
algorithm "One-at-a-Time" produces a different hashed key order.
More details are in L</"Performance Enhancements">.

=item *

lstat(FILEHANDLE) now gives a warning because the operation makes no sense.
In future releases this may become a fatal error.

=item *

The C<package;> syntax (C<package> without an argument) has been
deprecated.  Its semantics were never that clear and its
implementation even less so.  If you have used that feature to
disallow all but fully qualified variables, C<use strict;> instead.

=item *

The unimplemented POSIX regex features [[.cc.]] and [[=c=]] are still
recognised but now cause fatal errors.  The previous behaviour of
ignoring them by default and warning if requested was unacceptable
since it, in a way, falsely promised that the features could be used.

=item *

The current user-visible implementation of pseudo-hashes (the weird
use of the first array element) is deprecated starting from Perl 5.8.0
and will be removed in Perl 5.10.0, and the feature will be
implemented differently.  Not only is the current interface rather
ugly, but the current implementation slows down normal array and hash
use quite noticeably. The C<fields> pragma interface will remain
available.

=item *

The syntaxes C<< @a->[...] >> and  C<< %h->{...} >> have now been deprecated.

=item *

After years of trying the suidperl is considered to be too complex to
ever be considered truly secure.  The suidperl functionality is likely
to be removed in a future release.

=item *

The long deprecated uppercase aliases for the string comparison
operators (EQ, NE, LT, LE, GE, GT) have now been removed.

=item *

The tr///C and tr///U features have been removed and will not return;
the interface was a mistake.  Sorry about that.  For similar
functionality, see pack('U0', ...) and pack('C0', ...).

=item *

Earlier Perls treated "sub foo (@bar)" as equivalent to "sub foo (@)".
The prototypes are now checked at compile-time for invalid characters.
An optional warning is generated ("Illegal character in prototype...")
but this may be upgraded to a fatal error in a future release.

=back

=head1 Core Enhancements

=head2 PerlIO is Now The Default

=over 4

=item *

IO is now by default done via PerlIO rather than system's "stdio".
PerlIO allows "layers" to be "pushed" onto a file handle to alter the
handle's behaviour.  Layers can be specified at open time via 3-arg
form of open:

   open($fh,'>:crlf :utf8', $path) || ...

or on already opened handles via extended C<binmode>:

   binmode($fh,':encoding(iso-8859-7)');

The built-in layers are: unix (low level read/write), stdio (as in
previous Perls), perlio (re-implementation of stdio buffering in a
portable manner), crlf (does CRLF <=> "\n" translation as on Win32,
but available on any platform).  A mmap layer may be available if
platform supports it (mostly UNIXes).

Layers to be applied by default may be specified via the 'open' pragma.

See L</"Installation and Configuration Improvements"> for the effects
of PerlIO on your architecture name.

=item *

File handles can be marked as accepting Perl's internal encoding of Unicode
(UTF-8 or UTF-EBCDIC depending on platform) by a pseudo layer ":utf8" :

   open($fh,">:utf8","Uni.txt");

Note for EBCDIC users: the pseudo layer ":utf8" is erroneously named
for you since it's not UTF-8 what you will be getting but instead
UTF-EBCDIC.  See L<perlunicode>, L<utf8>, and
http://www.unicode.org/unicode/reports/tr16/ for more information.
In future releases this naming may change.

=item *

File handles can translate character encodings from/to Perl's internal
Unicode form on read/write via the ":encoding()" layer.

=item *

File handles can be opened to "in memory" files held in Perl scalars via:

   open($fh,'>', \$variable) || ...

=item *

Anonymous temporary files are available without need to
'use FileHandle' or other module via

   open($fh,"+>", undef) || ...

That is a literal undef, not an undefined value.

=item *

The list form of C<open> is now implemented for pipes (at least on UNIX):

   open($fh,"-|", 'cat', '/etc/motd')

creates a pipe, and runs the equivalent of exec('cat', '/etc/motd') in
the child process.

=back

=head2 Safe Signals

Perl used to be fragile in that signals arriving at inopportune moments
could corrupt Perl's internal state.  Now Perl postpones handling of
signals until it's safe (between opcodes).

This change may have surprising side effects because signals no longer
interrupt Perl instantly.  Perl will now first finish whatever it was
doing, like finishing an internal operation (like sort()) or an
external operation (like an I/O operation), and only then look at any
arrived signals (and before starting the next operation).  No more corrupt
internal state since the current operation is always finished first,
but the signal may take more time to get heard.

=head2 Unicode Overhaul

Unicode in general should be now much more usable than in Perl 5.6.0
(or even in 5.6.1).  Unicode can be used in hash keys, Unicode in
regular expressions should work now, Unicode in tr/// should work now,
Unicode in I/O should work now.

=over 4

=item *

The Unicode Character Database coming with Perl has been upgraded
to Unicode 3.1.1.  For more information, see http://www.unicode.org/.

=item *

For developers interested in enhancing Perl's Unicode capabilities:
almost all the UCD files are included with the Perl distribution in
the F<lib/unicore subdirectory>.  The most notable omission, for space
considerations, is the Unihan database.

=item *

The properties \p{Blank} and \p{SpacePerl} have been added. "Blank" is like
C isblank(), that is, it contains only "horizontal whitespace" (the space
character is, the newline isn't), and the "SpacePerl" is the Unicode
equivalent of C<\s> (\p{Space} isn't, since that includes the vertical
tabulator character, whereas C<\s> doesn't.)

See "New Unicode Properties" earlier in this document for additional
information on changes with Unicode properties.

=back

=head2 Understanding of Numbers

In general a lot of fixing has happened in the area of Perl's
understanding of numbers, both integer and floating point.  Since in
many systems the standard number parsing functions like C<strtoul()>
and C<atof()> seem to have bugs, Perl tries to work around their
deficiencies.  This results hopefully in more accurate numbers.

Perl now tries internally to use integer values in numeric conversions
and basic arithmetics (+ - * /) if the arguments are integers, and
tries also to keep the results stored internally as integers.
This change leads to often slightly faster and always less lossy
arithmetics. (Previously Perl always preferred floating point numbers
in its math.)

=head2 Miscellaneous Changes

=over 4

=item *

AUTOLOAD is now lvaluable, meaning that you can add the :lvalue attribute
to AUTOLOAD subroutines and you can assign to the AUTOLOAD return value.

=item *

C<perl -d:Module=arg,arg,arg> now works (previously one couldn't pass
in multiple arguments.)

=item *

The builtin dump() now gives an optional warning
C<Ambiguous call resolved as CORE::dump(), qualify as such or use &>
meaning that by default C<dump(...)> is resolved as the builtin 
dump() which dumps core and aborts, not as (possibly) user-defined
C<sub dump>.  To call the latter, qualify the call as C<&dump(...)>.
(The whole dump() feature is to considered deprecated, and possibly
removed/changed in future releases.)

=item *

chomp() and chop() have been demoted back to I<not> being overrideable
because they cannot really be overridden-- the problem is that their
prototype cannot be expressed and therefore one really cannot write
replacements to override these builtins.

=item *

END blocks are now run even if you exit/die in a BEGIN block.
Internally, the execution of END blocks is now controlled by 
PL_exit_flags & PERL_EXIT_DESTRUCT_END. This enables the new
behaviour for Perl embedders. This will default in 5.10. See
L<perlembed>.

=item *

Formats now support zero-padded decimal fields.

=item *

Lvalue subroutines can now return C<undef> in list context.
However, the lvalue subroutine feature still remains experimental.

=item *

A lost warning "Can't declare ... dereference in my" has been
restored (Perl had it earlier but it became lost in later releases.)

=item *

A new special regular expression variable has been introduced:
C<$^N>, which contains the most-recently closed group (submatch).

=item *

C<no Module;> now works even if there is no "sub unimport" in the Module.

=item *

The numerical comparison operators return C<undef> if either operand
is a NaN.  Previously the behaviour was unspecified.

=item *

The following builtin functions are now overridable: each(), keys(),
pop(), push(), shift(), splice(), unshift().

=item *

C<pack() / unpack()> now can group template letters with C<()> and then
apply repetition/count modifiers on the groups.

=item *

C<pack() / unpack()> can now process the Perl internal numeric types:
IVs, UVs, NVs-- and also long doubles, if supported by the platform.
The template letters are C<j>, C<J>, C<F>, and C<D>.

=item *

C<pack('U0a*', ...)> can now be used to force a string to UTF8.

=item *

my __PACKAGE__ $obj now works.

=item *

The printf() and sprintf() now support parameter reordering using the
C<%\d+\$> and C<*\d+\$> syntaxes.  For example

    print "%2\$s %1\$s\n", "foo", "bar";

will print "bar foo\n".  This feature helps in writing
internationalised software, and in general when the order
of the parameters can vary.

=item *

prototype(\&) is now available.

=item *

prototype(\[$@%&]) is now available to implicitly create references
(useful for example if you want to emulate the tie() interface).

=item *

A new command-line option, C<-t> is available.  It is the
little brother of C<-T>: instead of dieing on taint violations,
lexical warnings are given.  B<This is only meant as a temporary
debugging aid while securing the code of old legacy applications.
This is not a substitute for -T.>

=item *

In other taint news, the C<exec LIST> and C<system LIST> have now been
considered too risky (think C<exec @ARGV>: it can start any program
with any arguments), and now the said forms cause a warning.
You should carefully launder the arguments to guarantee their
validity.  In future releases of Perl the forms will become fatal
errors so consider starting laundering now.

=item *

If tr/// is just counting characters, it doesn't attempt to
modify its target.

=item *

untie() will now call an UNTIE() hook if it exists.  See L<perltie>
for details.

=item *

L<utime> now supports C<utime undef, undef, @files> to change the
file timestamps to the current time.

=item *

The rules for allowing underscores (underbars) in numeric constants
have been relaxed and simplified: now you can have an underscore
simply B<between digits>.

=back

=head1 Modules and Pragmata

=head2 New Modules and Pragmata

=over 4

=item *

C<Attribute::Handlers> allows a class to define attribute handlers.

    package MyPack;
    use Attribute::Handlers;
    sub Wolf :ATTR(SCALAR) { print "howl!\n" }

    # later, in some package using or inheriting from MyPack...

    my MyPack $Fluffy : Wolf; # the attribute handler Wolf will be called

Both variables and routines can have attribute handlers.  Handlers can
be specific to type (SCALAR, ARRAY, HASH, or CODE), or specific to the
exact compilation phase (BEGIN, CHECK, INIT, or END).

=item *

B<B::Concise> is a new compiler backend for walking the Perl syntax
tree, printing concise info about ops, from Stephen McCamant.  The
output is highly customisable.  See L<B::Concise>.

=item *

C<Class::ISA> for reporting the search path for a class's ISA tree,
by Sean Burke, has been added.  See L<Class::ISA>.

=item *

C<Cwd> has now a split personality: if possible, an XS extension is
used, (this will hopefully be faster, more secure, and more robust)
but if not possible, the familiar Perl implementation is used.

=item *

C<Devel::PPPort>, originally from Kenneth Albanowski and now
maintained by Paul Marquess, has been added.  It is primarily used
by C<h2xs> to enhance portability of of XS modules between different
versions of Perl.

=item *

C<Digest>, frontend module for calculating digests (checksums), from
Gisle Aas, has been added.  See L<Digest>.

=item *

C<Digest::MD5> for calculating MD5 digests (checksums) as defined in
RFC 1321, from Gisle Aas, has been added.  See L<Digest::MD5>.

    use Digest::MD5 'md5_hex';

    $digest = md5_hex("Thirsty Camel");

    print $digest, "\n"; # 01d19d9d2045e005c3f1b80e8b164de1

NOTE: the C<MD5> backward compatibility module is deliberately not
included since its further use is discouraged.

=item *

C<Encode>, by Nick Ing-Simmons, provides a mechanism to translate
between different character encodings.  Support for Unicode,
ISO-8859-*, ASCII, CP*, KOI8-R, and three variants of EBCDIC are
compiled in to the module.  Several other encodings (like Japanese,
Chinese, and MacIntosh encodings) are included and will be loaded at
runtime.  See L<Encode>.

Any encoding supported by Encode module is also available to the
":encoding()" layer if PerlIO is used.

=item *

C<I18N::Langinfo> can be use to query locale information.
See L<I18N::Langinfo>.

=item *

C<I18N::LangTags> has functions for dealing with RFC3066-style
language tags, by Sean Burke.  See L<I18N::LangTags>.

=item *

C<ExtUtils::Constant> is a new tool for extension writers for
generating XS code to import C header constants, by Nicholas Clark.
See L<ExtUtils::Constant>.

=item *

C<Filter::Simple> is an easy-to-use frontend to Filter::Util::Call,
from Damian Conway.  See L<Filter::Simple>.

    # in MyFilter.pm:

    package MyFilter;

    use Filter::Simple sub {
        while (my ($from, $to) = splice @_, 0, 2) {
                s/$from/$to/g;
        }
    };

    1;

    # in user's code:

    use MyFilter qr/red/ => 'green';

    print "red\n";   # this code is filtered, will print "green\n"
    print "bored\n"; # this code is filtered, will print "bogreen\n"

    no MyFilter;

    print "red\n";   # this code is not filtered, will print "red\n"

=item *

C<File::Temp> allows one to create temporary files and directories in
an easy, portable, and secure way, by Tim Jenness.  See L<File::Temp>.

=item *

C<Filter::Util::Call> provides you with the framework to write
I<Source Filters> in Perl, from Paul Marquess.  For most uses the
frontend Filter::Simple is to be preferred.  See L<Filter::Util::Call>.

=item *

C<if> is a new pragma for conditional inclusion of modules, from
Ilya Zakharevich.

=item *

L<libnet> is a collection of perl5 modules related to network
programming, from Graham Barr.  See L<Net::FTP>, L<Net::NNTP>,
L<Net::Ping>, L<Net::POP3>, L<Net::SMTP>, and L<Net::Time>.

Perl installation leaves libnet unconfigured, use F<libnetcfg> to configure.

=item *

C<List::Util> is a selection of general-utility list subroutines, like
sum(), min(), first(), and shuffle(), by Graham Barr.  See L<List::Util>.

=item *

C<Locale::Constants>, C<Locale::Country>, C<Locale::Currency>, and
C<Locale::Language>, from Neil Bowers, have been added.  They provide the
codes for various locale standards, such as "fr" for France, "usd" for
US Dollar, and "jp" for Japanese.

    use Locale::Country;

    $country = code2country('jp');               # $country gets 'Japan'
    $code    = country2code('Norway');           # $code gets 'no'

See L<Locale::Constants>, L<Locale::Country>, L<Locale::Currency>,
and L<Locale::Language>.

=item *

C<Locale::Maketext> is localization framework from Sean Burke.  See
L<Locale::Maketext>, and L<Locale::Maketext::TPJ13>.  The latter is an
article about software localization, originally published in The Perl
Journal #13, republished here with kind permission.

=item *

C<Memoize> can make your functions faster by trading space for time,
from Mark-Jason Dominus.  See L<Memoize>.

=item *

C<MIME::Base64> allows you to encode data in base64, from Gisle Aas,
as defined in RFC 2045 - I<MIME (Multipurpose Internet Mail
Extensions)>.

    use MIME::Base64;

    $encoded = encode_base64('Aladdin:open sesame');
    $decoded = decode_base64($encoded);

    print $encoded, "\n"; # "QWxhZGRpbjpvcGVuIHNlc2FtZQ=="

See L<MIME::Base64>.

=item *

C<MIME::QuotedPrint> allows you to encode data in quoted-printable
encoding, as defined in RFC 2045 - I<MIME (Multipurpose Internet Mail
Extensions)>, from Gisle Aas.

    use MIME::QuotedPrint;

    $encoded = encode_qp("Smiley in Unicode: \x{263a}");
    $decoded = decode_qp($encoded);

    print $encoded, "\n"; # "Smiley in Unicode: =263A"

MIME::QuotedPrint has been enhanced to provide the basic methods
necessary to use it with PerlIO::Via as in :

    use MIME::QuotedPrint;
    open($fh,">Via(MIME::QuotedPrint)",$path);

See L<MIME::QuotedPrint>.

=item *

C<NEXT> is pseudo-class for method redispatch, from Damian Conway.
See L<NEXT>.

=item *

C<open> is a new pragma for setting the default I/O disciplines
for open().

=item *

C<PerlIO::Scalar> provides the implementation of IO to "in memory"
Perl scalars as discussed above, from Nick Ing-Simmons.  It also
serves as an example of a loadable PerlIO layer.  Other future
possibilities include PerlIO::Array and PerlIO::Code.
See L<PerlIO::Scalar>.

=item *

C<PerlIO::Via> acts as a PerlIO layer and wraps PerlIO layer
functionality provided by a class (typically implemented in perl
code), from Nick Ing-Simmons.

    use MIME::QuotedPrint;
    open($fh,">Via(MIME::QuotedPrint)",$path);

This will automatically convert everything output to C<$fh>
to Quoted-Printable.  See L<PerlIO::Via>.

=item *

C<Pod::ParseLink>, by Russ Allbery, has been added,
to parse LZ<><> links in pods as described in the new
perlpodspec.

=item *

C<Pod::Text::Overstrike>, by Joe Smith, has been added.
It converts POD data to formatted overstrike text.
See L<Pod::Text::Overstrike>.

=item *

C<Scalar::Util> is a selection of general-utility scalar subroutines,
like blessed(), reftype(), and tainted().  See L<Scalar::Util>.

=item *

C<sort> is a new pragma for controlling the behaviour of sort().

=item *

C<Storable> gives persistence to Perl data structures by allowing the
storage and retrieval of Perl data to and from files in a fast and
compact binary format, from Raphael Manfredi.  See L<Storable>.

=item *

C<Switch>, from Damian Conway, has been added.  Just by saying

    use Switch;

you have C<switch> and C<case> available in Perl.

    use Switch;

    switch ($val) {

                case 1          { print "number 1" }
                case "a"        { print "string a" }
                case [1..10,42] { print "number in list" }
                case (@array)   { print "number in list" }
                case /\w+/      { print "pattern" }
                case qr/\w+/    { print "pattern" }
                case (%hash)    { print "entry in hash" }
                case (\%hash)   { print "entry in hash" }
                case (\&sub)    { print "arg to subroutine" }
                else            { print "previous case not true" }
    }

See L<Switch>.

=item *

C<Test::More> is yet another framework for writing test scripts,
more extensive than Test::Simple, by Michael Schwern.  See L<Test::More>.

=item *

C<Test::Simple> has basic utilities for writing tests, by Michael
Schwern.   See L<Test::Simple>.

=item *

C<Text::Balanced> has been added, for extracting delimited text
sequences from strings, from Damian Conway.

    use Text::Balanced 'extract_delimited';

    ($a, $b) = extract_delimited("'never say never', he never said", "'", '');

$a will be "'never say never'", $b will be ', he never said'.

In addition to extract_delimited() there are also extract_bracketed(),
extract_quotelike(), extract_codeblock(), extract_variable(),
extract_tagged(), extract_multiple(), gen_delimited_pat(), and
gen_extract_tagged().  With these you can implement rather advanced
parsing algorithms.  See L<Text::Balanced>.

=item *

C<threads> is an interface to interpreter threads, by Arthur Bergman.
Interpreter threads (ithreads) is the new thread model introduced in
Perl 5.6 but only available as an internal interface for extension
writers (and for Win32 Perl for C<fork()> emulation).  See L<threads>.

=item *

C<threads::shared> allows data sharing for interpreter threads, from
Arthur Bergman.  In the ithreads model any data sharing between
threads must be explicit, as opposed to the old 5.005 thread model
where data sharing was implicit.  See L<threads::shared>.

=item *

C<Tie::Memoize>, by Ilya Zakharevich, provides on-demand loaded hashes.

=item *

C<Tie::RefHash::Nestable>, by Edward Avis, allows storing hash
references (unlike the standard Tie::RefHash)  The module is contained
within Tie::RefHash, see L<Tie::RefHash>.

=item *

C<Time::HiRes> provides high resolution timing (ualarm, usleep,
and gettimeofday), from Douglas E. Wegscheid.  See L<Time::HiRes>.

=item *

C<Unicode::UCD> offers a querying interface to the Unicode Character
Database.  See L<Unicode::UCD>.

=item *

C<Unicode::Collate> implements the UCA (Unicode Collation Algorithm)
for sorting Unicode strings, by SADAHIRO Tomoyuki.  See L<Unicode::Collate>.

=item *

C<Unicode::Normalize> implements the various Unicode normalization
forms, by SADAHIRO Tomoyuki.  See L<Unicode::Normalize>.

=item *

C<XS::Typemap>, by Tim Jenness, is a test extension that exercises XS
typemaps.  Nothing gets installed but for extension writers the code
is worth studying.

=back

=head2 Updated And Improved Modules and Pragmata

=over 4

=item *

The following independently supported modules have been updated to the
newest versions from CPAN: CGI, CPAN, DB_File, File::Spec, File::Temp,
Getopt::Long, Math::BigFloat, Math::BigInt, the podlators bundle
(Pod::Man, Pod::Text), Pod::LaTeX, Pod::Parser, Storable,
Term::ANSIColor, Test, Text-Tabs+Wrap.

=item *

The attributes::reftype() now works on tied arguments.

=item *

AutoLoader can now be disabled with C<no AutoLoader;>.

=item *

B::Deparse has been significantly enhanced.  It now can deparse almost
all of the standard test suite (so that the tests still succeed).
There is a make target "test.deparse" for trying this out.

=item *

Class::Struct can now define the classes in compile time.

=item *

Class::Struct now assigns the array/hash element if the accessor
is called with an array/hash element as the B<sole> argument.

=item *

Data::Dumper has now an option to sort hashes.

=item *

Data::Dumper has now an option to dump code references
using B::Deparse.

=item *

DB_File now supports newer Berkeley DB versions, among
other improvements.

=item *

The English module can now be used without the infamous performance
hit by saying

        use English '-no_performance_hit';

(Assuming, of course, that one doesn't need the troublesome variables
C<$`>, C<$&>, or C<$'>.)  Also, introduced C<@LAST_MATCH_START> and
C<@LAST_MATCH_END> English aliases for C<@-> and C<@+>.

=item *

Fcntl, Socket, and Sys::Syslog have been rewritten to use the
new-style constant dispatch section (see L<ExtUtils::Constant>).
This means that they will be more robust and hopefully faster.

=item *

File::Find now chdir()s correctly when chasing symbolic links.

=item *

File::Find now has pre- and post-processing callbacks.  It also
correctly changes directories when chasing symbolic links.  Callbacks
(naughtily) exiting with "next;" instead of "return;" now work.

=item *

File::Find is now (again) reentrant.  It also has been made
more portable.

=item *

File::Glob::glob() renamed to File::Glob::bsd_glob() to avoid
prototype mismatch with CORE::glob().

=item *

File::Glob now supports C<GLOB_LIMIT> constant to limit the size of
the returned list of filenames.

=item *

Devel::Peek now has an interface for the Perl memory statistics
(this works only if you are using perl's malloc, and if you have
compiled with debugging).

=item *

IPC::Open3 now allows the use of numeric file descriptors.

=item *

IO::Socket has now atmark() method, which returns true if the socket
is positioned at the out-of-band mark.  The method is also exportable
as a sockatmark() function.

=item *

IO::Socket::INET has support for ReusePort option (if your platform
supports it).  The Reuse option now has an alias, ReuseAddr.  For clarity
you may want to prefer ReuseAddr.

=item *

IO::Socket::INET now supports C<LocalPort> of zero (usually meaning
that the operating system will make one up.)

=item *

use lib now works identically to @INC.  Removing directories
with 'no lib' now works.

=item *

ExtUtils::MakeMaker now uses File::Spec internally, which hopefully
leads into better portability.

=item *

Math::BigFloat and Math::BigInt have undergone a full rewrite.
They are now magnitudes faster, and they support various
bignum libraries such as GMP and PARI as their backends.

=item *

Math::Complex handles inf, NaN etc., better.

=item *

Net::Ping has been muchly enhanced.  Multihoming is now supported.
There is now "external" protocol which uses Net::Ping::External module
which runs external ping(1) and parses the output.  A version of
Net::Ping::External is available in CPAN.

=item *

POSIX::sigaction() is now much more flexible and robust.
You can now install coderef handlers, 'DEFAULT', and 'IGNORE'
handlers, installing new handlers was not atomic.

=item *

In Safe the C<%INC> now localised in a Safe compartment so that
use/require work.

=item *

In SDBM_File on dosish platforms, some keys went missing because of
lack of support for files with "holes".  A workaround for the problem
has been added.

=item *

In Search::Dict one can now have a pre-processing hook for the
lines being searched.

=item *

The Shell module now has an OO interface.

=item *

The Test module has been significantly enhanced.

=item *

The vars pragma now supports declaring fully qualified variables.
(Something that C<our()> does not and will not support.)

=item *

The C<utf8::> name space (as in the pragma) provides various
Perl-callable functions to provide low level access to Perl's
internal Unicode representation.  At the moment only length()
has been implemented.

=back

=head1 Utility Changes

=over 4

=item *

Emacs perl mode (emacs/cperl-mode.el) has been updated to version
4.31.

=item *

F<emacs/e2ctags.pl> is now much faster.

=item *

C<h2ph> now supports C trigraphs.

=item *

C<h2xs> now produces a template README.

=item *

C<h2xs> now uses C<Devel::PPort> for better portability between
different versions of Perl.

=item *

C<h2xs> uses the new L<ExtUtils::Constant> module which will affect
newly created extensions that define constants.  Since the new code is
more correct (if you have two constants where the first one is a
prefix of the second one, the first constant B<never> gets defined),
less lossy (it uses integers for integer constant, as opposed to the
old code that used floating point numbers even for integer constants),
and slightly faster, you might want to consider regenerating your
extension code (the new scheme makes regenerating easy).
L<h2xs> now also supports C trigraphs.

=item *

C<libnetcfg> has been added to configure the libnet.

=item *

C<perlbug> is now much more robust.  It also sends the bug report to
perl.org, not perl.com.

=item *

C<perlcc> has been rewritten and its user interface (that is,
command line) is much more like that of the UNIX C compiler, cc.
(The perlbc tools has been removed.  Use C<perlcc -B> instead.)

=item *

C<perlivp> is a new Installation Verification Procedure utility
for running any time after installing Perl.

=item *

C<pod2html> now allows specifying a cache directory.

=item *

C<s2p> has been completely rewritten in Perl.  (It is in fact a full
implementation of sed in Perl: you can use the sed functionality by
using the C<psed> utility.)

=item *

C<xsubpp> now understands POD documentation embedded in the *.xs files.

=item *

C<xsubpp> now supports OUT keyword.

=back

=head1 New Documentation

=over 4

=item *

perl56delta details the changes between the 5.005 release and the
5.6.0 release.

=item *

perlclib documents the internal replacements for standard C library
functions.  (Interesting only for extension writers and Perl core
hackers.)

=item *

perldebtut is a Perl debugging tutorial.

=item *

perlebcdic contains considerations for running Perl on EBCDIC platforms.

=item *

perlintro is a gentle introduction to Perl.

=item *

perliol documents the internals of PerlIO with layers.

=item *

perlmodstyle is a style guide for writing modules.

=item *

perlnewmod tells about writing and submitting a new module.

=item *

perlpacktut is a pack() tutorial.

=item *

perlpod has been rewritten to be clearer and to record the best
practices gathered over the years.

=item *

perlpodspec is a more formal specification of the pod format,
mainly of interest for writers of pod applications, not to
people writing in pod.

=item *

perlretut is a regular expression tutorial.

=item *

perlrequick is a regular expressions quick-start guide.
Yes, much quicker than perlretut.

=item *

perltodo has been updated.

=item *

perltootc has been renamed as perltooc (to not to conflict
with perltoot in filesystems restricted to "8.3" names)

=item *

perluniintro is an introduction to using Unicode in Perl.
(perlunicode is more of a detailed reference and background
information)

=item *

perlutil explains the command line utilities packaged with the Perl
distribution.

=back

The following platform-specific documents are available before
the installation as README.I<platform>, and after the installation
as perlI<platform>:

    perlaix perlamiga perlapollo perlbeos perlbs2000
    perlce perlcygwin perldgux perldos perlepoc perlhpux
    perlhurd perlmachten perlmacos perlmint perlmpeix
    perlnetware perlos2 perlos390 perlplan9 perlqnx perlsolaris
    perltru64 perluts perlvmesa perlvms perlvos perlwin32

=over 4

=item *

The documentation for the POSIX-BC platform is called "BS2000", to avoid
confusion with the Perl POSIX module.

=item *

The documentation for the WinCE platform is called "CE", to avoid
confusion with the perlwin32 documentation on 8.3-restricted filesystems.

=back

=head1 Performance Enhancements

=over 4

=item *

map() could get pathologically slow when the result list it generates
is larger than the source list.  The performance has been improved for
common scenarios.

=item *

sort() has been changed to use primarily mergesort internally as
opposed to the earlier quicksort.  For very small lists this may
result in slightly slower sorting times, but in general the speedup
should be at least 20%.  Additional bonuses are that the worst case
behaviour of sort() is now better (in computer science terms it now
runs in time O(N log N), as opposed to quicksort's Theta(N**2)
worst-case run time behaviour), and that sort() is now stable
(meaning that elements with identical keys will stay ordered as they
were before the sort).  See the C<sort> pragma for information.

The story in more detail: suppose you want to serve yourself a little
slice of Pi.

    @digits = ( 3,1,4,1,5,9 );

A numerical sort of the digits will yield (1,1,3,4,5,9), as expected.
Which C<1> comes first is hard to know, since one C<1> looks pretty
much like any other.  You can regard this as totally trivial,
or somewhat profound.  However, if you just want to sort the even
digits ahead of the odd ones, then what will

    sort { ($a % 2) <=> ($b % 2) } @digits;

yield?  The only even digit, C<4>, will come first.  But how about
the odd numbers, which all compare equal?  With the quicksort algorithm
used to implement Perl 5.6 and earlier, the order of ties is left up
to the sort.  So, as you add more and more digits of Pi, the order
in which the sorted even and odd digits appear will change.
and, for sufficiently large slices of Pi, the quicksort algorithm
in Perl 5.8 won't return the same results even if reinvoked with the
same input.  The justification for this rests with quicksort's
worst case behavior.  If you run

   sort { $a <=> $b } ( 1 .. $N , 1 .. $N );

(something you might approximate if you wanted to merge two sorted
arrays using sort), doubling $N doesn't just double the quicksort time,
it I<quadruples> it.  Quicksort has a worst case run time that can
grow like N**2, so-called I<quadratic> behaviour, and it can happen
on patterns that may well arise in normal use.  You won't notice this
for small arrays, but you I<will> notice it with larger arrays,
and you may not live long enough for the sort to complete on arrays
of a million elements.  So the 5.8 quicksort scrambles large arrays
before sorting them, as a statistical defence against quadratic behaviour.
But that means if you sort the same large array twice, ties may be
broken in different ways.

Because of the unpredictability of tie-breaking order, and the quadratic
worst-case behaviour, quicksort was I<almost> replaced completely with
a stable mergesort.  I<Stable> means that ties are broken to preserve
the original order of appearance in the input array.  So

    sort { ($a % 2) <=> ($b % 2) } (3,1,4,1,5,9);

will yield (4,3,1,1,5,9), guaranteed.  The even and odd numbers
appear in the output in the same order they appeared in the input.
Mergesort has worst case O(NlogN) behaviour, the best value
attainable.  And, ironically, this mergesort does particularly
well where quicksort goes quadratic:  mergesort sorts (1..$N, 1..$N)
in O(N) time.  But quicksort was rescued at the last moment because
it is faster than mergesort on certain inputs and platforms.
For example, if you really I<don't> care about the order of even
and odd digits, quicksort will run in O(N) time; it's very good
at sorting many repetitions of a small number of distinct elements.
The quicksort divide and conquer strategy works well on platforms
with relatively small, very fast, caches.  Eventually, the problem gets
whittled down to one that fits in the cache, from which point it
benefits from the increased memory speed.

Quicksort was rescued by implementing a sort pragma to control aspects
of the sort.  The B<stable> subpragma forces stable behaviour,
regardless of algorithm.  The B<_quicksort> and B<_mergesort>
subpragmas are heavy-handed ways to select the underlying implementation.
The leading C<_> is a reminder that these subpragmas may not survive
beyond 5.8.  More appropriate mechanisms for selecting the implementation
exist, but they wouldn't have arrived in time to save quicksort.

=item *

Hashes now use Bob Jenkins "One-at-a-Time" hashing key algorithm
(http://burtleburtle.net/bob/hash/doobs.html).  This algorithm is
reasonably fast while producing a much better spread of values than
the old hashing algorithm (originally by Chris Torek, later tweaked by
Ilya Zakharevich).  Hash values output from the algorithm on a hash of
all 3-char printable ASCII keys comes much closer to passing the
DIEHARD random number generation tests.  According to perlbench, this
change has not affected the overall speed of Perl.

=item *

unshift() should now be noticeably faster.

=back

=head1 Installation and Configuration Improvements

=head2 Generic Improvements

=over 4

=item *

INSTALL now explains how you can configure Perl to use 64-bit
integers even on non-64-bit platforms.

=item *

Policy.sh policy change: if you are reusing a Policy.sh file
(see INSTALL) and you use Configure -Dprefix=/foo/bar and in the old
Policy $prefix eq $siteprefix and $prefix eq $vendorprefix, all of
them will now be changed to the new prefix, /foo/bar.  (Previously
only $prefix changed.)  If you do not like this new behaviour,
specify prefix, siteprefix, and vendorprefix explicitly.

=item *

A new optional location for Perl libraries, otherlibdirs, is available.
It can be used for example for vendor add-ons without disturbing Perl's
own library directories.

=item *

In many platforms the vendor-supplied 'cc' is too stripped-down to
build Perl (basically, 'cc' doesn't do ANSI C).  If this seems
to be the case and 'cc' does not seem to be the GNU C compiler
'gcc', an automatic attempt is made to find and use 'gcc' instead.

=item *

gcc needs to closely track the operating system release to avoid
build problems. If Configure finds that gcc was built for a different
operating system release than is running, it now gives a clearly visible
warning that there may be trouble ahead.

=item *

If binary compatibility with the 5.005 release is not wanted, Configure
no longer suggests including the 5.005 modules in @INC.

=item *

Configure C<-S> can now run non-interactively.

=item *

Configure support for pdp11-style memory models has been removed due
to obsolescence.

=item *

configure.gnu now works with options with whitespace in them.

=item *

installperl now outputs everything to STDERR.

=item *

$Config{byteorder} is now computed dynamically (this is more robust
with "fat binaries" where an executable image contains binaries for
more than one binary platform.)

=item *

Because PerlIO is now the default on most platforms, "-perlio" doesn't
get appended to the $Config{archname} (also known as $^O) anymore.
Instead, if you explicitly choose not to use perlio (Configure command
line option -Uuseperlio), you will get "-stdio" appended.

=item *

Another change related to the architecture name is that "-64all"
(-Duse64bitall, or "maximally 64-bit") is appended only if your
pointers are 64 bits wide.  (To be exact, the use64bitall is ignored.)

=item *

In AFS installations one can configure the root of the AFS to be
somewhere else than the default F</afs> by using the Configure
parameter C<-Dafsroot=/some/where/else>.

=item *

APPLLIB_EXP, a less-know configuration-time definition, has been
documented.  It can be used to prepend site-specific directories
to Perl's default search path (@INC), see INSTALL for information.

=item *

The version of Berkeley DB used when the Perl (and, presumably, the
DB_File extension) was built is now available as
C<@Config{qw(db_version_major db_version_minor db_version_patch)}>
from Perl and as C<DB_VERSION_MAJOR_CFG DB_VERSION_MINOR_CFG
DB_VERSION_PATCH_CFG> from C.

=item *

Building Berkeley DB3 for compatibility modes for DB, NDBM, and ODBM
has been documented in INSTALL.

=item *

If you have CPAN access (either network or a local copy such as a
CD-ROM) you can during specify extra modules to Configure to build and
install with Perl using the -Dextras=...  option.  See INSTALL for
more details.

=item *

In addition to config.over a new override file, config.arch, is
available.  That is supposed to be used by hints file writers for
architecture-wide changes (as opposed to config.over which is for
site-wide changes).

=item *

If your file system supports symbolic links you can build Perl outside
of the source directory by

        mkdir /tmp/perl/build/directory
        cd /tmp/perl/build/directory
        sh /path/to/perl/source/Configure -Dmksymlinks ...

This will create in /tmp/perl/build/directory a tree of symbolic links
pointing to files in /path/to/perl/source.  The original files are left
unaffected.  After Configure has finished you can just say

        make all test

and Perl will be built and tested, all in /tmp/perl/build/directory.

=item *

For Perl developers several new make targets for profiling
and debugging have been added, see L<perlhack>.

=over 8

=item *

Use of the F<gprof> tool to profile Perl has been documented in
L<perlhack>.  There is a make target called "perl.gprof" for
generating a gprofiled Perl executable.

=item *

If you have GCC 3, there is a make target called "perl.gcov" for
creating a gcoved Perl executable for coverage analysis.  See
L<perlhack>.

=item *

If you are on IRIX or Tru64 platforms, new profiling/debugging options
have been added, see L<perlhack> for more information about pixie and
Third Degree.

=back

=item *

Guidelines of how to construct minimal Perl installations have
been added to INSTALL.

=item *

The Thread extension is now not built at all under ithreads
(C<Configure -Duseithreads>) because it wouldn't work anyway (the
Thread extension requires being Configured with C<-Duse5005threads>).

But note that the Thread.pm interface is now shared by both
thread models.

=back

=head2 New Or Improved Platforms

For the list of platforms known to support Perl,
see L<perlport/"Supported Platforms">.

=over 4

=item *

AIX dynamic loading should be now better supported.

=item *

AIX should now work better with gcc, threads, and 64-bitness.  Also the
long doubles support in AIX should be better now.  See L<perlaix>.

=item *

After a long pause, AmigaOS has been verified to be happy with Perl.

=item *

AtheOS (http://www.atheos.cx/) is a new platform.

=item *

BeOS has been reclaimed.

=item *

DG/UX platform now supports the 5.005-style threads.  See L<perldgux>.

=item *

DYNIX/ptx platform (a.k.a. dynixptx) is supported at or near osvers 4.5.2.

=item *

EBCDIC platforms (z/OS, also known as OS/390, POSIX-BC, and VM/ESA)
have been regained.  Many test suite tests still fail and the
co-existence of Unicode and EBCDIC isn't quite settled, but the
situation is much better than with Perl 5.6.  See L<perlos390>,
L<perlbs2000> (for POSIX-BC), and L<perlvmesa> for more information.

=item *

Building perl with -Duseithreads or -Duse5005threads now works under
HP-UX 10.20 (previously it only worked under 10.30 or later). You will
need a thread library package installed. See README.hpux.

=item *

MacOS Classic (MacPerl has of course been available since
perl 5.004 but now the source code bases of standard Perl
and MacPerl have been synchronised)

=item *

MacOS X (or Darwin) should now be able to build Perl even on HFS+
filesystems.  (The case-insensitivity confused the Perl build process.)

=item *

NCR MP-RAS is now supported.

=item *

All the NetBSD specific patches (except for the installation
specific ones) have been merged back to the main distribution.

=item *

NetWare from Novell is now supported.  See L<perlnetware>.

=item *

NonStop-UX is now supported.

=item *

NEC SUPER-UX is now supported.

=item *

All the OpenBSD specific patches (except for the installation
specific ones) have been merged back to the main distribution.

=item *

Perl has been tested with the GNU pth userlevel thread package
( http://www.gnu.org/software/pth/pth.html ) . All but one thread
test worked, and that one failure was because of test results arriving
in unexpected order.

=item *

Amdahl UTS UNIX mainframe platform is now supported.

=item *

WinCE is now supported.  See L<perlce>.

=item *

z/OS (formerly known as OS/390, formerly known as MVS OE) has now
support for dynamic loading.  This is not selected by default,
however, you must specify -Dusedl in the arguments of Configure.

=back

=head1 Selected Bug Fixes

Numerous memory leaks and uninitialized memory accesses have been
hunted down.  Most importantly anonymous subs used to leak quite
a bit.

=over 4

=item *

The autouse pragma didn't work for Multi::Part::Function::Names.

=item *

caller() could cause core dumps in certain situations.  Carp was sometimes
affected by this problem.

=item *

chop(@list) in list context returned the characters chopped in
reverse order.  This has been reversed to be in the right order.

=item *

Configure no longer includes the DBM libraries (dbm, gdbm, db, ndbm)
when building the Perl binary.  The only exception to this is SunOS 4.x,
which needs them.

=item *

The behaviour of non-decimal but numeric string constants such as
"0x23" was platform-dependent: in some platforms that was seen as 35,
in some as 0, in some as a floating point number (don't ask).  This
was caused by Perl using the operating system libraries in a situation
where the result of the string to number conversion is undefined: now
Perl consistently handles such strings as zero in numeric contexts.

=item *

The order of DESTROYs has been made more predictable.

=item *

Several debugger fixes: exit code now reflects the script exit code,
condition C<"0"> now treated correctly, the C<d> command now checks
line number, the C<$.> no longer gets corrupted, all debugger output
now goes correctly to the socket if RemotePort is set.

=item *

Perl 5.6.0 could emit spurious warnings about redefinition of dl_error()
when statically building extensions into perl.  This has been corrected.

=item *

L<dprofpp> -R didn't work.

=item *

C<*foo{FORMAT}> now works.
=item *

Infinity is now recognized as a number.

=item *

UNIVERSAL::isa no longer caches methods incorrectly.  (This broke
the Tk extension with 5.6.0.)

=item *

Lexicals I: lexicals outside an eval "" weren't resolved
correctly inside a subroutine definition inside the eval "" if they
were not already referenced in the top level of the eval""ed code.

=item *

Lexicals II: lexicals leaked at file scope into subroutines that
were declared before the lexicals.

=item *

Lexical warnings now propagating correctly between scopes
and into C<eval "...">.

=item *

C<use warnings qw(FATAL all)> did not work as intended.  This has been
corrected.

=item *

warnings::enabled() now reports the state of $^W correctly if the caller
isn't using lexical warnings.

=item *

Line renumbering with eval and C<#line> now works.

=item *

Fixed numerous memory leaks, especially in eval "".

=item *

mkdir() now ignores trailing slashes in the directory name,
as mandated by POSIX.

=item *

Some versions of glibc have a broken modfl().  This affects builds
with C<-Duselongdouble>.  This version of Perl detects this brokenness
and has a workaround for it.  The glibc release 2.2.2 is known to have
fixed the modfl() bug.

=item *

Modulus of unsigned numbers now works (4063328477 % 65535 used to
return 27406, instead of 27047).

=item *

Some "not a number" warnings introduced in 5.6.0 eliminated to be
more compatible with 5.005.  Infinity is now recognised as a number.

=item *

Numeric conversions did not recognize changes in the string value
properly in certain circumstances.

=item *

Attributes (like :shared) didn't work with our().

=item *

our() variables will not cause "will not stay shared" warnings.

=item *

"our" variables of the same name declared in two sibling blocks
resulted in bogus warnings about "redeclaration" of the variables.
The problem has been corrected.

=item *

pack "Z" now correctly terminates the string with "\0".

=item *

Fix password routines which in some shadow password platforms
(e.g. HP-UX) caused getpwent() to return every other entry.

=item *

The PERL5OPT environment variable (for passing command line arguments
to Perl) didn't work for more than a single group of options.

=item *

PERL5OPT with embedded spaces didn't work.

=item *

printf() no longer resets the numeric locale to "C".

=item *

C<qw(a\\b)> now parses correctly as C<'a\\b'>.

=item *

pos() did not return the correct value within s///ge in earlier
versions.  This is now handled correctly.

=item *

Printing quads (64-bit integers) with printf/sprintf now works
without the q L ll prefixes (assuming you are on a quad-capable platform).

=item *

Regular expressions on references and overloaded scalars now work.

=item *

Right-hand side magic (GMAGIC) could in many cases such as string
concatenation be invoked too many times.

=item *

scalar() now forces scalar context even when used in void context.

=item *

SOCKS support is now much more robust.

=item *

sort() arguments are now compiled in the right wantarray context
(they were accidentally using the context of the sort() itself).
The comparison block is now run in scalar context, and the arguments
to be sorted are always provided list context.

=item *

Changed the POSIX character class C<[[:space:]]> to include the (very
rarely used) vertical tab character.  Added a new POSIX-ish character
class C<[[:blank:]]> which stands for horizontal whitespace
(currently, the space and the tab).

=item *

The tainting behaviour of sprintf() has been rationalized.  It does
not taint the result of floating point formats anymore, making the
behaviour consistent with that of string interpolation.

=item *

Some cases of inconsistent taint propagation (such as within hash
values) have been fixed.

=item *

The RE engine found in Perl 5.6.0 accidentally pessimised certain kinds
of simple pattern matches.  These are now handled better.

=item *

Regular expression debug output (whether through C<use re 'debug'>
or via C<-Dr>) now looks better.

=item *

Multi-line matches like C<"a\nxb\n" =~ /(?!\A)x/m> were flawed.  The
bug has been fixed.

=item *

Use of $& could trigger a core dump under some situations.  This
is now avoided.

=item *

The regular expression captured submatches ($1, $2, ...) are now
more consistently unset if the match fails, instead of leaving false
data lying around in them.

=item *

readline() on files opened in "slurp" mode could return an extra "" at
the end in certain situations.  This has been corrected.

=item *

Autovivification of symbolic references of special variables described
in L<perlvar> (as in C<${$num}>) was accidentally disabled.  This works
again now.

=item *

Sys::Syslog ignored the C<LOG_AUTH> constant.

=item *

All but the first argument of the IO syswrite() method are now optional.

=item *

$AUTOLOAD, sort(), lock(), and spawning subprocesses
in multiple threads simultaneously are now thread-safe.

=item *

Tie::ARRAY SPLICE method was broken.

=item *

Allow read-only string on left hand side of non-modifying tr///.

=item *

Several Unicode fixes.

=over 8

=item *

BOMs (byte order marks) in the beginning of Perl files
(scripts, modules) should now be transparently skipped.
UTF-16 (UCS-2) encoded Perl files should now be read correctly.

=item *

The character tables have been updated to Unicode 3.1.1.

=item *

Comparing with utf8 data does not magically upgrade non-utf8 data
into utf8.  (This was a problem for example if you were mixing data
from I/O and Unicode data: your output might have got magically encoded
as UTF-8.)

=item *

Generating illegal Unicode code points like U+FFFE, or the UTF-16
surrogates, now also generates an optional warning.

=item *

C<IsAlnum>, C<IsAlpha>, and C<IsWord> now match titlecase.

=item *

Concatenation with the C<.> operator or via variable interpolation,
C<eq>, C<substr>, C<reverse>, C<quotemeta>, the C<x> operator,
substitution with C<s///>, single-quoted UTF8, should now work.

=item *

The C<tr///> operator now works.  Note that the C<tr///CU>
functionality has been removed (but see pack('U0', ...)).

=item *

C<eval "v200"> now works.

=item *

Perl 5.6.0 parsed m/\x{ab}/ incorrectly, leading to spurious warnings.
This has been corrected.

=item *

Zero entries were missing from the Unicode classes like C<IsDigit>.

=back

=item *

Large unsigned numbers (those above 2**31) could sometimes lose their
unsignedness, causing bogus results in arithmetic operations.

=back

=head2 Platform Specific Changes and Fixes

=over 4

=item *

BSDI 4.*

Perl now works on post-4.0 BSD/OSes.

=item *

All BSDs

Setting C<$0> now works (as much as possible; see L<perlvar> for details).

=item *

Cygwin

Numerous updates; currently synchronised with Cygwin 1.1.4.

=item *

Previously DYNIX/ptx had problems in its Configure probe for non-blocking I/O.

=item *

EPOC

EPOC update after Perl 5.6.0.  See README.epoc.

=item *

FreeBSD 3.*

Perl now works on post-3.0 FreeBSDs.

=item *

HP-UX

README.hpux updated; C<Configure -Duse64bitall> now almost works.

=item *

IRIX

Numerous compilation flag and hint enhancements; accidental mixing
of 32-bit and 64-bit libraries (a doomed attempt) made much harder.

=item *

Linux

=over 8

=item *

Long doubles should now work (see INSTALL).

=item *

Linux previously had problems related to sockaddrlen when using
accept(), revcfrom() (in Perl: recv()), getpeername(), and getsockname().

=back

=item *

MacOS Classic

Compilation of the standard Perl distribution in MacOS Classic should
now work if you have the Metrowerks development environment and
the missing Mac-specific toolkit bits.  Contact the macperl mailing
list for details.

=item *

MPE/iX

MPE/iX update after Perl 5.6.0.  See README.mpeix.

=item *

NetBSD/sparc

Perl now works on NetBSD/sparc.

=item *

OS/2

Now works with usethreads (see INSTALL).

=item *

Solaris

64-bitness using the Sun Workshop compiler now works.

=item *

Tru64 (aka Digital UNIX, aka DEC OSF/1)

The operating system version letter now recorded in $Config{osvers}.
Allow compiling with gcc (previously explicitly forbidden).  Compiling
with gcc still not recommended because buggy code results, even with
gcc 2.95.2.

=item *

Unicos

Fixed various alignment problems that lead into core dumps either
during build or later; no longer dies on math errors at runtime;
now using full quad integers (64 bits), previously was using 
only 46 bit integers for speed.

=item *

VMS

chdir() now works better despite a CRT bug; now works with MULTIPLICITY
(see INSTALL); now works with Perl's malloc.

The tainting of C<%ENV> elements via C<keys> or C<values> was previously
unimplemented.  It now works as documented.

The C<waitpid> emulation has been improved.  The worst bug (now fixed)
was that a pid of -1 would cause a wildcard search of all processes on
the system.  The most significant enhancement is that we can now
usually get the completion status of a terminated process.

POSIX-style signals are now emulated much better on VMS versions prior
to 7.0.

The C<system> function and backticks operator have improved
functionality and better error handling.

=item *

Windows

=over 8

=item *

accept() no longer leaks memory.

=item *

Borland C++ v5.5 is now a supported compiler that can build Perl.
However, the generated binaries continue to be incompatible with those
generated by the other supported compilers (GCC and Visual C++).

=item *

Better chdir() return value for a non-existent directory.

=item *

Duping socket handles with open(F, ">&MYSOCK") now works under Windows 9x.

=item *

New %ENV entries now propagate to subprocesses.

=item *

Current directory entries in %ENV are now correctly propagated to child
processes.

=item *

$ENV{LIB} now used to search for libs under Visual C.

=item *

fork() emulation has been improved in various ways, but still continues
to be experimental.  See L<perlfork> for known bugs and caveats.

=item *

A failed (pseudo)fork now returns undef and sets errno to EAGAIN.

=item *

Win32::GetCwd() correctly returns C:\ instead of C: when at the drive root.
Other bugs in chdir() and Cwd::cwd() have also been fixed.

=item *

HTML files will be installed in c:\perl\html instead of c:\perl\lib\pod\html

=item *

The makefiles now provide a single switch to bulk-enable all the features
enabled in ActiveState ActivePerl (a popular Win32 binary distribution).

=item *

Allow REG_EXPAND_SZ keys in the registry.

=item *

Can now send() from all threads, not just the first one.

=item *

Fake signal handling reenabled, bugs and all.

=item *

%SIG has been enabled under USE_ITHREADS, but its use is completely
unsupported under all configurations.

=item *

Less stack reserved per thread so that more threads can run
concurrently. (Still 16M per thread.)

=item *

C<File::Spec-&gt;tmpdir()> now prefers C:/temp over /tmp
(works better when perl is running as service).

=item *

Better UNC path handling under ithreads.

=item *

wait(), waitpid() and backticks now return the correct exit status under
Windows 9x.

=item *

winsock handle leak fixed.

=back

=back

=head1 New or Changed Diagnostics

=over 4

=item *

All regular expression compilation error messages are now hopefully
easier to understand both because the error message now comes before
the failed regex and because the point of failure is now clearly
marked by a C<E<lt>-- HERE> marker.

=item *

The various "opened only for", "on closed", "never opened" warnings
drop the C<main::> prefix for filehandles in the C<main> package,
for example C<STDIN> instead of C<main::STDIN>. 

=item *

The "Unrecognized escape" warning has been extended to include C<\8>,
C<\9>, and C<\_>.  There is no need to escape any of the C<\w> characters.

=item *

Two new debugging options have been added: if you have compiled your
Perl with debugging, you can use the -DT and -DR options to trace
tokenising and to add reference counts to displaying variables,
respectively.

=item *

perl5db.pl has been modified to present a more consistent commands
interface, via (CommandSet=580).  perl5db.t was also added to test the
changes, and as a placeholder for further tests.

See L<perldebug>

=item *

If an attempt to use a (non-blessed) reference as an array index
is made, a warning is given.

=item *

C<push @a;> and C<unshift @a;> (with no values to push or unshift)
now give a warning.  This may be a problem for generated and evaled
code.

=item *

If you try to L<perlfunc/pack> a number less than 0 or larger than 255
using the C<"C"> format you will get an optional warning.  Similarly
for the C<"c"> format and a number less than -128 or more than 127.

=item *

Certain regex modifiers such as C<(?o)> make sense only if applied to
the entire regex.  You will an optional warning if you try to do otherwise.

=item *

Using arrays or hashes as references (e.g. C<< %foo-&gt;{bar} >>
has been deprecated for a while.  Now you will get an optional warning.

=back

=head1 Changed Internals

=over 4

=item *

perlapi.pod (a companion to perlguts) now attempts to document the
internal API.

=item *

You can now build a really minimal perl called microperl.
Building microperl does not require even running Configure;
C<make -f Makefile.micro> should be enough.  Beware: microperl makes
many assumptions, some of which may be too bold; the resulting
executable may crash or otherwise misbehave in wondrous ways.
For careful hackers only.

=item *

Added rsignal(), whichsig(), do_join(), op_clear, op_null,
ptr_table_clear(), ptr_table_free(), sv_setref_uv(), and several UTF-8
interfaces to the publicised API.  For the full list of the available
APIs see L<perlapi>.

=item *

Made possible to propagate customised exceptions via croak()ing.

=item *

Now xsubs can have attributes just like subs.  (Well, at least the
built-in attributes.)

=item *

dTHR and djSP have been obsoleted; the former removed (because it's
a no-op) and the latter replaced with dSP.

=item *

PERL_OBJECT has been completely removed.

=item *

The MAGIC constants (e.g. C<'P'>) have been macrofied
(e.g. C<PERL_MAGIC_TIED>) for better source code readability
and maintainability.

=item *

The regex compiler now maintains a structure that identifies nodes in
the compiled bytecode with the corresponding syntactic features of the
original regex expression.  The information is attached to the new
C<offsets> member of the C<struct regexp>. See L<perldebguts> for more
complete information.

=item *

The C code has been made much more C<gcc -Wall> clean.  Some warning
messages still remain in some platforms, so if you are compiling with
gcc you may see some warnings about dubious practices.  The warnings
are being worked on.

=item *

F<perly.c>, F<sv.c>, and F<sv.h> have now been extensively commented.

=item *

Documentation on how to use the Perl source repository has been added
to F<Porting/repository.pod>.

=item *

There are now several profiling make targets.

=back

=head1 Security Vulnerability Closed

(This change was already made in 5.7.0 but bears repeating here.)

A potential security vulnerability in the optional suidperl component
of Perl was identified in August 2000.  suidperl is neither built nor
installed by default.  As of November 2001 the only known vulnerable
platform is Linux, most likely all Linux distributions.  CERT and
various vendors and distributors have been alerted about the vulnerability.
See http://www.cpan.org/src/5.0/sperl-2000-08-05/sperl-2000-08-05.txt
for more information.

The problem was caused by Perl trying to report a suspected security
exploit attempt using an external program, /bin/mail.  On Linux
platforms the /bin/mail program had an undocumented feature which
when combined with suidperl gave access to a root shell, resulting in
a serious compromise instead of reporting the exploit attempt.  If you
don't have /bin/mail, or if you have 'safe setuid scripts', or if
suidperl is not installed, you are safe.

The exploit attempt reporting feature has been completely removed from
Perl 5.8.0 (and the maintenance release 5.6.1, and it was removed also
from all the Perl 5.7 releases), so that particular vulnerability
isn't there anymore.  However, further security vulnerabilities are,
unfortunately, always possible.  The suidperl functionality is most
probably going to be removed in Perl 5.10.  In any case, suidperl
should only be used by security experts who know exactly what they are
doing and why they are using suidperl instead of some other solution
such as sudo (see http://www.courtesan.com/sudo/).

=head1 New Tests

Several new tests have been added, especially for the F<lib>
subsection.  There are now about 34 000 individual tests (spread over
about 530 test scripts), in the regression suite (5.6.1 has about
11700 tests, in 258 test scripts) Many of the new tests are introduced
by the new modules, but still in general Perl is now more thoroughly
tested.

Because of the large number of tests, running the regression suite
will take considerably longer time than it used to: expect the suite
to take up to 4-5 times longer to run than in perl 5.6.  In a really
fast machine you can hope to finish the suite in about 5 minutes
(wallclock time).

The tests are now reported in a different order than in earlier Perls.
(This happens because the test scripts from under t/lib have been moved
to be closer to the library/extension they are testing.)

=head1 Known Problems

=head2 AIX

=over 4

=item *

In AIX 4.2 Perl extensions that use C++ functions that use statics
may have problems in that the statics are not getting initialized.
In newer AIX releases this has been solved by linking Perl with
the libC_r library, but unfortunately in AIX 4.2 the said library
has an obscure bug where the various functions related to time
(such as time() and gettimeofday()) return broken values, and
therefore in AIX 4.2 Perl is not linked against the libC_r.

=item *

vac 5.0.0.0 May Produce Buggy Code For Perl

The AIX C compiler vac version 5.0.0.0 may produce buggy code,
resulting in few random tests failing, but when the failing tests
are run by hand, they succeed.  We suggest upgrading to at least
vac version 5.0.1.0, that has been known to compile Perl correctly.
"lslpp -L|grep vac.C" will tell you the vac version.

=back

=head2 Amiga Perl Invoking Mystery

One cannot call Perl using the C<volume:> syntax, that is, C<perl -v>
works, but for example C<bin:perl -v> doesn't.  The exact reason isn't
known but the current suspect is the F<ixemul> library.

=head2 lib/ftmp-security tests warn 'system possibly insecure'

Don't panic.  Read INSTALL 'make test' section instead.

=head2 Cygwin intermittent failures of lib/Memoize/t/expire_file 11 and 12

The subtests 11 and 12 sometimes fail and sometimes work.

=head2 HP-UX lib/io_multihomed Fails When LP64-Configured

The lib/io_multihomed test may hang in HP-UX if Perl has been
configured to be 64-bit. Because other 64-bit platforms do not hang in
this test, HP-UX is suspect. All other tests pass in 64-bit HP-UX. The
test attempts to create and connect to "multihomed" sockets (sockets
which have multiple IP addresses).

=head2  HP-UX lib/posix Subtest 9 Fails When LP64-Configured

If perl is configured with -Duse64bitall, the successful result of the
subtest 10 of lib/posix may arrive before the successful result of the
subtest 9, which confuses the test harness so much that it thinks the
subtest 9 failed.

=head2 Linux With Sfio Fails op/misc Test 48

No known fix.

=head2 Mac OS X

The following tests are known to fail:

 Failed Test                 Stat Wstat Total Fail  Failed  List of Failed
 -------------------------------------------------------------------------
 ../ext/DB_File/t/db-btree.t    0    11    ??   ??       %  ??
 ../ext/DB_File/t/db-recno.t              149    3   2.01%  61 63 65
 ../ext/POSIX/t/posix.t                    31    1   3.23%  10
 ../lib/warnings.t                        450    1   0.22%  316

=head2 OS/390

OS/390 has rather many test failures but the situation is actually
better than it was in 5.6.0, it's just that so many new modules and
tests have been added.

 Failed Test                     Stat Wstat Total Fail  Failed  List of Failed
 -----------------------------------------------------------------------------
 ../ext/B/Deparse.t                            14    1   7.14%  14
 ../ext/B/Showlex.t                             1    1 100.00%  1
 ../ext/Encode/Encode/Tcl.t                   610   13   2.13%  592 594 596 598
                                                                600 602 604-610
 ../ext/IO/lib/IO/t/io_unix.t     113 28928     5    3  60.00%  3-5
 ../ext/POSIX/POSIX.t                          29    1   3.45%  14
 ../ext/Storable/t/lock.t         255 65280     5    3  60.00%  3-5
 ../lib/locale.t                  129 33024   117   19  16.24%  99-117
 ../lib/warnings.t                            434    1   0.23%  75
 ../lib/ExtUtils.t                             27    1   3.70%  25
 ../lib/Math/BigInt/t/bigintpm.t             1190    1   0.08%  1145
 ../lib/Unicode/UCD.t                          81   48  59.26%  1-16 49-64 66-81
 ../lib/User/pwent.t                            9    1  11.11%  4
 op/pat.t                                     660    6   0.91%  242-243 424-425
                                                                626-627
 op/split.t                         0     9    ??   ??       %  ??
 op/taint.t                                   174    3   1.72%  156 162 168
 op/tr.t                                       70    3   4.29%  50 58-59
 Failed 16/422 test scripts, 96.21% okay. 105/23251 subtests failed, 99.55% okay.

=head2 op/sprintf tests 129 and 130

The op/sprintf tests 129 and 130 are known to fail on some platforms.
Examples include any platform using sfio, and Compaq/Tandem's NonStop-UX.
The failing platforms do not comply with the ANSI C Standard, line
19ff on page 134 of ANSI X3.159 1989 to be exact.  (They produce
something other than "1" and "-1" when formatting 0.6 and -0.6 using
the printf format "%.0f", most often they produce "0" and "-0".)

=head2  Failure of Thread tests

B<Note that support for 5.005-style threading remains experimental
and practically unsupported.>

The following tests are known to fail due to fundamental problems in
the 5.005 threading implementation. These are not new failures--Perl
5.005_0x has the same bugs, but didn't have these tests.

  ext/List/Util/t/first         2
  lib/autouse                   4
  ext/Thread/thr5005            19-20

These failures are unlikely to get fixed.

=head2 UNICOS

=over 4

=item *

ext/POSIX/sigaction subtests 6 and 13 may fail.

=item *

lib/ExtUtils may spuriously claim that subtest 28 failed,
which is interesting since the test only has 27 tests.

=item *

Numerous numerical test failures

  op/numconvert                 209,210,217,218
  op/override                   7
  ext/Time/HiRes/HiRes          9
  lib/Math/BigInt/t/bigintpm    1145
  lib/Math/Trig                 25

These tests fail because of yet unresolved floating point inaccuracies.

=back

=head2 UNICOS and UNICOS/mk

The io/fs test #31 is failing because in UNICOS and UNICOS/mk
truncate() cannot be used to grow the size of filehandles, only
to reduce the size.  The workaround is to truncate files instead
of filehandles.

=head2 UTS

There are a few known test failures, see L<perluts>.

=head2 VMS

There is one known test failure with a default configuration:

  [.run]switches..........................FAILED on test 1

=head2 Win32

In multi-CPU boxes there are some problems with the I/O buffering:
some output may appear twice.

=head2 Localising a Tied Variable Leaks Memory

    use Tie::Hash;
    tie my %tie_hash => 'Tie::StdHash';

    ...

    local($tie_hash{Foo}) = 1; # leaks

Code like the above is known to leak memory every time the local()
is executed.

=head2 Localising Tied Arrays and Hashes Is Broken

    local %tied_array;

doesn't work as one would expect: the old value is restored
incorrectly.

=head2 Self-tying of Arrays and Hashes Is Forbidden

Self-tying of arrays and hashes is broken in rather deep and
hard-to-fix ways.  As a stop-gap measure to avoid people from getting
frustrated at the mysterious results (core dumps, most often) it is
for now forbidden (you will get a fatal error even from an attempt).

=head2 Building Extensions Can Fail Because Of Largefiles

Some extensions like mod_perl are known to have issues with
`largefiles', a change brought by Perl 5.6.0 in which file offsets
default to 64 bits wide, where supported.  Modules may fail to compile
at all or compile and work incorrectly.  Currently there is no good
solution for the problem, but Configure now provides appropriate
non-largefile ccflags, ldflags, libswanted, and libs in the %Config
hash (e.g., $Config{ccflags_nolargefiles}) so the extensions that are
having problems can try configuring themselves without the
largefileness.  This is admittedly not a clean solution, and the
solution may not even work at all.  One potential failure is whether
one can (or, if one can, whether it's a good idea) link together at
all binaries with different ideas about file offsets, all this is
platform-dependent.

=head2 Unicode Support on EBCDIC Still Spotty

Though mostly working, Unicode support still has problem spots on
EBCDIC platforms.  One such known spot are the C<\p{}> and C<\P{}>
regular expression constructs for code points less than 256: the
pP are testing for Unicode code points, not knowing about EBCDIC.

=head2 The Compiler Suite Is Still Experimental

The compiler suite is slowly getting better but it continues to be
highly experimental.  Use in production environments is discouraged.

=head2 The Long Double Support Is Still Experimental

The ability to configure Perl's numbers to use "long doubles",
floating point numbers of hopefully better accuracy, is still
experimental.  The implementations of long doubles are not yet
widespread and the existing implementations are not quite mature
or standardised, therefore trying to support them is a rare
and moving target.  The gain of more precision may also be offset
by slowdown in computations (more bits to move around, and the
operations are more likely to be executed by less optimised
libraries).

=head2 Seen In Perl 5.7 But Gone Now

C<Time::Piece> (previously known as C<Time::Object>) was removed
because it was felt that it didn't have enough value in it to be a
core module.  It is still a useful module, though, and is available
from the CPAN.

=head1 Reporting Bugs

If you find what you think is a bug, you might check the articles
recently posted to the comp.lang.perl.misc newsgroup and the perl
bug database at http://bugs.perl.org.  There may also be
information at http://www.perl.com/, the Perl Home Page.

If you believe you have an unreported bug, please run the B<perlbug>
program included with your release.  Be sure to trim your bug down
to a tiny but sufficient test case.  Your bug report, along with the
output of C<perl -V>, will be sent off to perlbug@perl.org to be
analysed by the Perl porting team.

=head1 SEE ALSO

The F<Changes> file for exhaustive details on what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=head1 HISTORY

Written by Jarkko Hietaniemi <F<jhi@iki.fi>>.

=cut