perldelta.pod

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=head1 NAME

perldelta - what's new for perl v5.6.x

=head1 DESCRIPTION

This document describes differences between the 5.005 release and the 5.6.1
release.

=head1 Summary of changes between 5.6.0 and 5.6.1

This section contains a summary of the changes between the 5.6.0 release
and the 5.6.1 release.  More details about the changes mentioned here
may be found in the F<Changes> files that accompany the Perl source
distribution.  See L<perlhack> for pointers to online resources where you
can inspect the individual patches described by these changes.

=head2 Security Issues

suidperl will not run /bin/mail anymore, because some platforms have
a /bin/mail that is vulnerable to buffer overflow attacks.

Note that suidperl is neither built nor installed by default in
any recent version of perl.  Use of suidperl is highly discouraged.
If you think you need it, try alternatives such as sudo first.
See http://www.courtesan.com/sudo/.

=head2 Core bug fixes

This is not an exhaustive list.  It is intended to cover only the
significant user-visible changes.

=over

=item C<UNIVERSAL::isa()>

A bug in the caching mechanism used by C<UNIVERSAL::isa()> that affected
base.pm has been fixed.  The bug has existed since the 5.005 releases,
but wasn't tickled by base.pm in those releases.

=item Memory leaks

Various cases of memory leaks and attempts to access uninitialized memory
have been cured.  See L</"Known Problems"> below for further issues.

=item Numeric conversions

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

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

Integer modulus on large unsigned integers sometimes returned
incorrect values.

Perl 5.6.0 generated "not a number" warnings on certain conversions where
previous versions didn't.

These problems have all been rectified.

Infinity is now recognized as a number.

=item qw(a\\b)

In Perl 5.6.0, qw(a\\b) produced a string with two backslashes instead
of one, in a departure from the behavior in previous versions.  The
older behavior has been reinstated.  

=item caller()

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

=item Bugs in regular expressions

Pattern matches on overloaded values are now handled correctly.

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

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

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

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

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

Match variables $1 et al., weren't being unset when a pattern match
was backtracking, and the anomaly showed up inside C</...(?{ ... }).../>
etc.  These variables are now tracked correctly.

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

=item "slurp" mode

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 to special variables

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

=item Lexical warnings 

Lexical warnings now propagate correctly into C<eval "...">.

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

Lexical warnings could leak into other scopes in some situations.
This is now fixed.

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

=item Spurious warnings and errors

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

"our" variables could result in bogus "Variable will not stay shared"
warnings.  This is now fixed.

"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 glob()

Compatibility of the builtin glob() with old csh-based glob has been
improved with the addition of GLOB_ALPHASORT option.  See C<File::Glob>.

File::Glob::glob() has been renamed to File::Glob::bsd_glob()
because the name clashes with the builtin glob().  The older
name is still available for compatibility, but is deprecated.

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

=item Tainting

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

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

=item sort()

Arguments to sort() weren't being provided the right wantarray() context.
The comparison block is now run in scalar context, and the arguments to
be sorted are always provided list context.

sort() is also fully reentrant, in the sense that the sort function
can itself call sort().  This did not work reliably in previous releases.

=item #line directives

#line directives now work correctly when they appear at the very
beginning of C<eval "...">.

=item Subroutine prototypes

The (\&) prototype now works properly.

=item map()

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 Debugger

Debugger exit code now reflects the script exit code.

Condition C<"0"> in breakpoints is now treated correctly.

The C<d> command now checks the line number.

C<$.> is no longer corrupted by the debugger.

All debugger output now correctly goes to the socket if RemotePort
is set.

=item PERL5OPT

PERL5OPT can be set to more than one switch group.  Previously,
it used to be limited to one group of options only.

=item chop()

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

=item Unicode support

Unicode support has seen a large number of incremental improvements,
but continues to be highly experimental.  It is not expected to be
fully supported in the 5.6.x maintenance releases.

substr(), join(), repeat(), reverse(), quotemeta() and string
concatenation were all handling Unicode strings incorrectly in
Perl 5.6.0.  This has been corrected.

Support for C<tr///CU> and C<tr///UC> etc., have been removed since
we realized the interface is broken.  For similar functionality,
see L<perlfunc/pack>.

The Unicode Character Database has been updated to version 3.0.1
with additions made available to the public as of August 30, 2000.

The Unicode character classes \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.)

If you are experimenting with Unicode support in perl, the development
versions of Perl may have more to offer.  In particular, I/O layers
are now available in the development track, but not in the maintenance
track, primarily to do backward compatibility issues.  Unicode support
is also evolving rapidly on a daily basis in the development track--the
maintenance track only reflects the most conservative of these changes.

=item 64-bit support

Support for 64-bit platforms has been improved, but continues to be
experimental.  The level of support varies greatly among platforms.

=item Compiler

The B Compiler and its various backends have had many incremental
improvements, but they continue to remain highly experimental.  Use in
production environments is discouraged.

The perlcc tool has been rewritten so that the user interface is much
more like that of a C compiler.

The perlbc tools has been removed.  Use C<perlcc -B> instead.

=item Lvalue subroutines

There have been various bugfixes to support lvalue subroutines better.
However, the feature still remains experimental.

=item IO::Socket

IO::Socket::INET failed to open the specified port if the service
name was not known.  It now correctly uses the supplied port number
as is.

=item File::Find

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

=item xsubpp

xsubpp now tolerates embedded POD sections.

=item C<no Module;>

C<no Module;> does not produce an error even if Module does not have an
unimport() method.  This parallels the behavior of C<use> vis-a-vis
C<import>.

=item Tests

A large number of tests have been added.

=back

=head2 Core features

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

The C<-DT> command line switch outputs copious tokenizing information.
See L<perlrun>.

Arrays are now always interpolated in double-quotish strings.  Previously,
C<"[e-mail]"> used to be a fatal error at compile time, if an array
C<@bar> was not used or declared.  This transitional behavior was
intended to help migrate perl4 code, and is deemed to be no longer useful.
See L</"Arrays now always interpolate into double-quoted strings">.

keys(), each(), pop(), push(), shift(), splice() and unshift()
can all be overridden now.

C<my __PACKAGE__ $obj> now does the expected thing.

=head2 Configuration issues

On some systems (IRIX and Solaris among them) the system malloc is demonstrably
better.  While the defaults haven't been changed in order to retain binary
compatibility with earlier releases, you may be better off building perl
with C<Configure -Uusemymalloc ...> as discussed in the F<INSTALL> file.

C<Configure> has been enhanced in various ways:

=over

=item *

Minimizes use of temporary files.

=item *

By default, does not link perl with libraries not used by it, such as
the various dbm libraries.  SunOS 4.x hints preserve behavior on that
platform.

=item *

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

=item *

Building outside the source tree is supported on systems that have
symbolic links. This is done by running

    sh /path/to/source/Configure -Dmksymlinks ...
    make all test install

in a directory other than the perl source directory.  See F<INSTALL>.

=item *

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

=back

=head2 Documentation

README.aix, README.solaris and README.macos have been added.  README.posix-bc
has been renamed to README.bs2000.  These are installed as L<perlaix>,
L<perlsolaris>, L<perlmacos>, and L<perlbs2000> respectively.

The following pod documents are brand new:

    perlclib	Internal replacements for standard C library functions
    perldebtut	Perl debugging tutorial
    perlebcdic	Considerations for running Perl on EBCDIC platforms
    perlnewmod	Perl modules: preparing a new module for distribution
    perlrequick	Perl regular expressions quick start
    perlretut	Perl regular expressions tutorial
    perlutil	utilities packaged with the Perl distribution

The F<INSTALL> file has been expanded to cover various issues, such as
64-bit support.

A longer list of contributors has been added to the source distribution.
See the file C<AUTHORS>.

Numerous other changes have been made to the included documentation and FAQs.

=head2 Bundled modules

The following modules have been added.

=over

=item B::Concise

Walks Perl syntax tree, printing concise info about ops.  See L<B::Concise>.

=item File::Temp

Returns name and handle of a temporary file safely.  See L<File::Temp>.

=item Pod::LaTeX