perl5100delta.pod

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system() operator. See L<perlrun> for details. (Contributed by Gisle Aas.)

=item C<${^RE_TRIE_MAXBUF}>

See L</"Trie optimisation of literal string alternations">.

=item C<${^WIN32_SLOPPY_STAT}>

See L</"Sloppy stat on Windows">.

=back

=head2 Miscellaneous

C<unpack()> now defaults to unpacking the C<$_> variable.

C<mkdir()> without arguments now defaults to C<$_>.

The internal dump output has been improved, so that non-printable characters
such as newline and backspace are output in C<\x> notation, rather than
octal.

The B<-C> option can no longer be used on the C<#!> line. It wasn't
working there anyway, since the standard streams are already set up
at this point in the execution of the perl interpreter. You can use
binmode() instead to get the desired behaviour.

=head2 UCD 5.0.0

The copy of the Unicode Character Database included in Perl 5 has
been updated to version 5.0.0.

=head2 MAD

MAD, which stands for I<Miscellaneous Attribute Decoration>, is a
still-in-development work leading to a Perl 5 to Perl 6 converter. To
enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
obtained perl isn't binary compatible with a regular perl 5.10, and has
space and speed penalties; moreover not all regression tests still pass
with it. (Larry Wall, Nicholas Clark)

=head2 kill() on Windows

On Windows platforms, C<kill(-9, $pid)> now kills a process tree.
(On UNIX, this delivers the signal to all processes in the same process
group.)

=head1 Incompatible Changes

=head2 Packing and UTF-8 strings

The semantics of pack() and unpack() regarding UTF-8-encoded data has been
changed. Processing is now by default character per character instead of
byte per byte on the underlying encoding. Notably, code that used things
like C<pack("a*", $string)> to see through the encoding of string will now
simply get back the original $string. Packed strings can also get upgraded
during processing when you store upgraded characters. You can get the old
behaviour by using C<use bytes>.

To be consistent with pack(), the C<C0> in unpack() templates indicates
that the data is to be processed in character mode, i.e. character by
character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
the packed string is processed in its UTF-8-encoded Unicode form on a byte
by byte basis. This is reversed with regard to perl 5.8.X, but now consistent
between pack() and unpack().

Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
respectively character and byte modes.

C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
specified encoding mode, honoring parens grouping. Previously, parens were
ignored.

Also, there is a new pack() character format, C<W>, which is intended to
replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
the strings internal representation. C<W> represents unsigned (logical)
character values, which can be greater than 255. It is therefore more
robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
values outside the range 0..255, and not respect the string encoding).

In practice, that means that pack formats are now encoding-neutral, except
C<C>.

For consistency, C<A> in unpack() format now trims all Unicode whitespace
from the end of the string. Before perl 5.9.2, it used to strip only the
classical ASCII space characters.

=head2 Byte/character count feature in unpack()

A new unpack() template character, C<".">, returns the number of bytes or
characters (depending on the selected encoding mode, see above) read so far.

=head2 The C<$*> and C<$#> variables have been removed

C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
modifiers, has been removed.

The deprecated C<$#> variable (output format for numbers) has been
removed.

Two new severe warnings, C<$#/$* is no longer supported>, have been added.

=head2 substr() lvalues are no longer fixed-length

The lvalues returned by the three argument form of substr() used to be a
"fixed length window" on the original string. In some cases this could
cause surprising action at distance or other undefined behaviour. Now the
length of the window adjusts itself to the length of the string assigned to
it.

=head2 Parsing of C<-f _>

The identifier C<_> is now forced to be a bareword after a filetest
operator. This solves a number of misparsing issues when a global C<_>
subroutine is defined.

=head2 C<:unique>

The C<:unique> attribute has been made a no-op, since its current
implementation was fundamentally flawed and not threadsafe.

=head2 Effect of pragmas in eval

The compile-time value of the C<%^H> hint variable can now propagate into
eval("")uated code. This makes it more useful to implement lexical
pragmas.

As a side-effect of this, the overloaded-ness of constants now propagates
into eval("").

=head2 chdir FOO

A bareword argument to chdir() is now recognized as a file handle.
Earlier releases interpreted the bareword as a directory name.
(Gisle Aas)

=head2 Handling of .pmc files

An old feature of perl was that before C<require> or C<use> look for a
file with a F<.pm> extension, they will first look for a similar filename
with a F<.pmc> extension. If this file is found, it will be loaded in
place of any potentially existing file ending in a F<.pm> extension.

Previously, F<.pmc> files were loaded only if more recent than the
matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
they exist.

=head2 $^V is now a C<version> object instead of a v-string

$^V can still be used with the C<%vd> format in printf, but any
character-level operations will now access the string representation
of the C<version> object and not the ordinals of a v-string.
Expressions like C<< substr($^V, 0, 2) >> or C<< split //, $^V >>
no longer work and must be rewritten.

=head2 @- and @+ in patterns

The special arrays C<@-> and C<@+> are no longer interpolated in regular
expressions. (Sadahiro Tomoyuki)

=head2 $AUTOLOAD can now be tainted

If you call a subroutine by a tainted name, and if it defers to an
AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
(Rick Delaney)

=head2 Tainting and printf

When perl is run under taint mode, C<printf()> and C<sprintf()> will now
reject any tainted format argument. (Rafael Garcia-Suarez)

=head2 undef and signal handlers

Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)

=head2 strictures and dereferencing in defined()

C<use strict 'refs'> was ignoring taking a hard reference in an argument
to defined(), as in :

    use strict 'refs';
    my $x = 'foo';
    if (defined $$x) {...}

This now correctly produces the run-time error C<Can't use string as a
SCALAR ref while "strict refs" in use>.

C<defined @$foo> and C<defined %$bar> are now also subject to C<strict
'refs'> (that is, C<$foo> and C<$bar> shall be proper references there.)
(C<defined(@foo)> and C<defined(%bar)> are discouraged constructs anyway.)
(Nicholas Clark)

=head2 C<(?p{})> has been removed

The regular expression construct C<(?p{})>, which was deprecated in perl
5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)

=head2 Pseudo-hashes have been removed

Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
pragma remains here, but uses an alternate implementation.)

=head2 Removal of the bytecode compiler and of perlcc

C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
B::Bytecode, etc.) are no longer distributed with the perl sources. Those
experimental tools have never worked reliably, and, due to the lack of
volunteers to keep them in line with the perl interpreter developments, it
was decided to remove them instead of shipping a broken version of those.
The last version of those modules can be found with perl 5.9.4.

However the B compiler framework stays supported in the perl core, as with
the more useful modules it has permitted (among others, B::Deparse and
B::Concise).

=head2 Removal of the JPL

The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.

=head2 Recursive inheritance detected earlier

Perl will now immediately throw an exception if you modify any package's
C<@ISA> in such a way that it would cause recursive inheritance.

Previously, the exception would not occur until Perl attempted to make
use of the recursive inheritance while resolving a method or doing a
C<$foo-E<gt>isa($bar)> lookup.

=head1 Modules and Pragmata

=head2 Upgrading individual core modules

Even more core modules are now also available separately through the
CPAN.  If you wish to update one of these modules, you don't need to
wait for a new perl release.  From within the cpan shell, running the
'r' command will report on modules with upgrades available.  See
C<perldoc CPAN> for more information.

=head2 Pragmata Changes

=over 4

=item C<feature>

The new pragma C<feature> is used to enable new features that might break
old code. See L</"The C<feature> pragma"> above.

=item C<mro>

This new pragma enables to change the algorithm used to resolve inherited
methods. See L</"New Pragma, C<mro>"> above.

=item Scoping of the C<sort> pragma

The C<sort> pragma is now lexically scoped. Its effect used to be global.

=item Scoping of C<bignum>, C<bigint>, C<bigrat>

The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
lexically scoped. (Tels)

=item C<base>

The C<base> pragma now warns if a class tries to inherit from itself.
(Curtis "Ovid" Poe)

=item C<strict> and C<warnings>

C<strict> and C<warnings> will now complain loudly if they are loaded via
incorrect casing (as in C<use Strict;>). (Johan Vromans)

=item C<version>

The C<version> module provides support for version objects.

=item C<warnings>

The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
that used C<Carp> routines without having loaded it at compile time might
need to be adjusted; typically, the following (faulty) code won't work
anymore, and will require parentheses to be added after the function name:

    use warnings;
    require Carp;
    Carp::confess 'argh';

=item C<less>

C<less> now does something useful (or at least it tries to). In fact, it
has been turned into a lexical pragma. So, in your modules, you can now
test whether your users have requested to use less CPU, or less memory,
less magic, or maybe even less fat. See L<less> for more. (Joshua ben
Jore)

=back

=head2 New modules

=over 4

=item *

C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
whenever an ASCII character string containing high-bit bytes is implicitly
converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
perls, its effect is global.

=item *

C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
you what versions of core modules ship with any versions of Perl 5. It
comes with a command-line frontend, C<corelist>.

=item *

C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
C<Math::BigInt::Calc>.

=item *

C<Compress::Zlib> is an interface to the zlib compression library. It
comes with a bundled version of zlib, so having a working zlib is not a
prerequisite to install it. It's used by C<Archive::Tar> (see below).

=item *

C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.

=item *

C<Archive::Tar> is a module to manipulate C<tar> archives.

=item *

C<Digest::SHA> is a module used to calculate many types of SHA digests,
has been included for SHA support in the CPAN module.

=item *

C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.

=item *

C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
provides support for I<field hashes>: hashes that maintain an association
of a reference with a value, in a thread-safe garbage-collected way.
Such hashes are useful to implement inside-out objects.

=item *

C<Module::Build>, by Ken Williams, has been added. It's an alternative to
C<ExtUtils::MakeMaker> to build and install perl modules.

=item *

C<Module::Load>, by Jos Boumans, has been added. It provides a single
interface to load Perl modules and F<.pl> files.

=item *

C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
modules as loaded or unloaded.

=item *

C<Package::Constants>, by Jos Boumans, has been added. It's a simple
helper to list all constants declared in a given package.

=item *

C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
This module provides low-level access to Win32 system API calls for
files/dirs.

=item *

C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
included in the perl core; the behaviour of C<Locale::Maketext::Simple>
gracefully degrades when the later isn't present.

=item *

C<Params::Check> implements a generic input parsing/checking mechanism. It
is used by CPANPLUS.

=item *

C<Term::UI> simplifies the task to ask questions at a terminal prompt.

=item *

C<Object::Accessor> provides an interface to create per-object accessors.

=item *

C<Module::Pluggable> is a simple framework to create modules that accept