Retract 11635: close 20011113.110, reopen 20010809.028.

[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.

=head1 Security Vulnerability Closed

A potential security vulnerability in the optional suidperl component
of Perl has been identified.  suidperl is neither built nor installed
by default.  As of September the 2nd, 2000, the only known vulnerable
platform is Linux, most likely all Linux distributions.  CERT and
various vendors have been alerted about the vulnerability.

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
the Perl 5.7.0 release, so that particular vulnerability isn't there
anymore.  However, further security vulnerabilities are,
unfortunately, always possible.  The suidperl code is being reviewed
and if deemed too risky to continue to be supported, it may be
completely removed from future releases.  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 Incompatible Changes

=over 4

=item *

Arrays now always interpolate into double-quoted strings:
constructs like "foo@bar" now always assume C<@bar> is an array,
whether or not the compiler has seen use of C<@bar>.

=item *

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

=item *

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

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

=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 (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 *

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

=item *

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

=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 *

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', ...).

=back

=head1 Core Enhancements

=over 4

=item *

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

=item *

my __PACKAGE__ $obj now works.

=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 *

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

=item *

prototype(\&) is now available.

=item *

There is now an UNTIE method.

=back

=head1 Modules and Pragmata

=head2 New Modules

=over 4

=item *

File::Temp allows one to create temporary files and directories in an
easy, portable, and secure way.

=item *

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.

=back

=head2 Updated And Improved Modules and Pragmata

=over 4

=item *

The following independently supported modules have been updated to
newer versions from CPAN: CGI, CPAN, DB_File, File::Spec, Getopt::Long,
the podlators bundle, Pod::LaTeX, Pod::Parser, Term::ANSIColor, Test.

=item *

Bug fixes and minor enhancements have been applied to B::Deparse,
Data::Dumper, IO::Poll, IO::Socket::INET, Math::BigFloat,
Math::Complex, Math::Trig, Net::protoent, the re pragma, SelfLoader,
Sys::SysLog, Test::Harness, Text::Wrap, UNIVERSAL, and the warnings
pragma.

=item *

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

=item *

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

=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 *

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

=item *

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

=item *

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

=item *

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

=item *

The Shell module now has an OO interface.

=back

=head1 Utility Changes

=over 4

=item *

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

=item *

Perlbug is now much more robust.  It also sends the bug report to
perl.org, not perl.com.

=item *

The perlcc utility has been rewritten and its user interface (that is,
command line) is much more like that of the UNIX C compiler, cc.

=item *

The xsubpp utility for extension writers now understands POD
documentation embedded in the *.xs files.

=back

=head1 New Documentation

=over 4

=item *

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

=item *

perldebtut is a Perl debugging tutorial.

=item *

perlebcdic contains considerations for running Perl on EBCDIC platforms.
Note that unfortunately EBCDIC platforms that used to supported back in
Perl 5.005 are still unsupported by Perl 5.7.0; the plan, however, is to
bring them back to the fold.  

=item *

perlnewmod tells about writing and submitting a new module.

=item *

perlposix-bc explains using Perl on the POSIX-BC platform
(an EBCDIC mainframe platform).

=item *

perlretut is a regular expression tutorial.

=item *

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

=item *

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

=back

=head1 Performance Enhancements

=over 4

=item *

map() that changes the size of the list should now work faster.

=item *

sort() has been changed to use 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).

=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.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.)

=back

=head1 Selected Bug Fixes

=over 4

=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 *

C<*foo{FORMAT}> now works.

=item *

Lexical warnings now propagating correctly between scopes.

=item *

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

=item *

Fixed numerous memory leaks, especially in eval "".

=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 *

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

=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 *

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

=item *

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

=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 *

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

=item *

sort() arguments are now compiled in the right wantarray context
(they were accidentally using the context of the sort() itself).

=item *

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

=item *

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

=item *

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

=item *

Several Unicode fixes (but still not perfect).

=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 3.0.1.

=item *

chr() for values greater than 127 now create utf8 when under use
utf8.

=item *

Comparing with utf8 data does not magically upgrade non-utf8 data into
utf8.

=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--in
theory.

=item *

The C<tr///> operator now works I<slightly> better but is still rather
broken.  Note that the C<tr///CU> functionality has been removed (but
see pack('U0', ...)).

=item *

vec() now refuses to deal with characters >255.

=item *

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

=back

=item *

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

=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 perlvar for details).

=item *

Cygwin

Numerous updates; currently synchronised with Cygwin 1.1.4.

=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

Long doubles should now work (see INSTALL).

=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.

=item *

Windows

=over 8

=item *

accept() no longer leaks memory.

=item *

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

=item *

New %ENV entries now propagate to subprocesses.

=item *

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

=item *

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

=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 *

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

=item *

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

=item *

Better UNC path handling under ithreads.

=item *

wait() and waitpid() now work much better.

=item *

winsock handle leak fixed.

=back

=back

=head1 New or Changed Diagnostics

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.

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 <main::STDIN>. 

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.

=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() to the publicised API.

=item *

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

=item *

Added is_utf8_char(), is_utf8_string(), bytes_to_utf8(), and utf8_to_bytes().

=item *

Now xsubs can have attributes just like subs.

=back

=head1 Known Problems

=head2 Unicode Support Still Far From Perfect

We're working on it.  Stay tuned.

=head2 EBCDIC Still A Lost Platform

The plan is to bring them back.

=head2 Building Extensions Can Fail Because Of Largefiles

Certain extensions like mod_perl and BSD::Resource 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 ftmp-security tests warn 'system possibly insecure'

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

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

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 Long Doubles Still Don't Work In Solaris

The experimental long double support is still very much so in Solaris.
(Other platforms like Linux and Tru64 are beginning to solidify in
this area.)

=head2 Linux With Sfio Fails op/misc Test 48

No known fix.

=head2 Storable tests fail in some platforms

If any Storable tests fail the use of Storable is not advisable.

=over 4

=item *

Many Storable tests fail on AIX configured with 64 bit integers.

So far unidentified problems break Storable in AIX if Perl is
configured to use 64 bit integers.  AIX in 32-bit mode works and
other 64-bit platforms work with Storable.

=item *

DOS DJGPP may hang when testing Storable.

=item *

st-06compat fails in UNICOS and UNICOS/mk.

This means that you cannot read old (pre-Storable-0.7) Storable images
made in other platforms.

=item *

st-store.t and st-retrieve may fail with Compaq C 6.2 on OpenVMS Alpha 7.2.

=back

=head2 Threads Are Still Experimental

Multithreading is still an experimental feature.  Some platforms
emit the following message for lib/thr5005

    #
    # This is a KNOWN FAILURE, and one of the reasons why threading
    # is still an experimental feature.  It is here to stop people
    # from deploying threads in production. ;-)
    #

and another known thread-related warning is

   pragma/overload......Unbalanced saves: 3 more saves than restores
   panic: magic_mutexfree during global destruction.
   ok
   lib/selfloader.......Unbalanced saves: 3 more saves than restores
   panic: magic_mutexfree during global destruction.
   ok
   lib/st-dclone........Unbalanced saves: 3 more saves than restores
   panic: magic_mutexfree during global destruction.
   ok

=head2 The Compiler Suite Is Still Experimental

The compiler suite is slowly getting better but is nowhere near
working order yet.  The backend part that has seen perhaps the most
progress is the bytecode compiler.

=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 April 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
all the Perl 5.7 releases (and will be gone also from the maintenance
release 5.6.1), so that particular vulnerability isn't there anymore.
However, further security vulnerabilities are, unfortunately, always
possible.  The suidperl code is being reviewed and if deemed too risky
to continue to be supported, it may be completely removed from future
releases.  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 Incompatible Changes

=over 4

=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 *

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

=back

=head1 Core Enhancements

=head2 AUTOLOAD Is Now Lvaluable

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

=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.

=item *

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

=item *

Formats now support zero-padded decimal fields.

=item *

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 into often slightly faster and always less lossy
arithmetics. (Previously Perl always preferred floating point numbers
in its math.)

=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.

=item *

Unicode in general should be now much more usable.  Unicode can be
used in hash keys, Unicode in regular expressions should work now,
Unicode in tr/// should work now (though tr/// seems to be a
particularly tricky to get right, so you have been warned)

=item *

The Unicode Character Database coming with Perl has been upgraded
to Unicode 3.1.  For more information, see http://www.unicode.org/,
and http://www.unicode.org/unicode/reports/tr27/

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

=item *

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.)

=back

=head2 Signals Are Now Safe

Perl used to be fragile in that signals arriving at inopportune moments
could corrupt Perl's internal state.

=head1 Modules and Pragmata

=head2 New Modules

=over 4

=item *

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

See L<B::Concise> for more information.

=item *

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

See L<Class::ISA> for more information.

=item *

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

=item *

Digest, a frontend module for calculating digests (checksums),
from Gisle Aas, has been added.

See L<Digest> for more information.

=item *

Digest::MD5 for calculating MD5 digests (checksums), by Gisle Aas,
has been added.

    use Digest::MD5 'md5_hex';

    $digest = md5_hex("Thirsty Camel");

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

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

See L<Digest::MD5> for more information.

=item *

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.

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

See L<Encode> for more information.

=item *

Filter::Simple is an easy-to-use frontend to Filter::Util::Call,
from Damian Conway.

    # 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"

See L<Filter::Simple> for more information.

=item *

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

=item *

Locale::Constants, Locale::Country, Locale::Currency, and 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> for more information.

=item *

MIME::Base64, by Gisle Aas, allows you to encode data in base64.

    use MIME::Base64;

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

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

See L<MIME::Base64> for more information.

=item *

MIME::QuotedPrint, by Gisle Aas, allows you to encode data in
quoted-printable encoding.

    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> for more information.

=item *

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

=item *

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

    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> for more information.

=item *

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

=item *

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> for more information.

=item *

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

    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> for more information.

=item *

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

=item *

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 *

B::Deparse should be now more robust.  It still far from providing a full
round trip for any random piece of Perl code, though, and is under active
development: expect more robustness in 5.7.2.

=item *

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

=item *

Math::BigFloat has undergone much fixing, and in addition the fmod()
function now supports modulus operations.

(The fixed Math::BigFloat module is also available in CPAN for those
who can't upgrade their Perl: http://www.cpan.org/authors/id/J/JP/JPEACOCK/)

=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 *

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 *

Net::Ping has been enhanced.  There is now "external" protocol which
uses Net::Ping::External module which runs external ping(1) and parses
the output.  An alpha version of Net::Ping::External is available in
CPAN and in 5.7.2 the Net::Ping::External may be integrated to Perl.

=item *

The C<open> pragma allows layers other than ":raw" and ":crlf" when
using PerlIO.

=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 *

The Test module has been significantly enhanced.  Its use is
greatly recommended for module writers.

=item *

The 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

The following modules have been upgraded from the versions at CPAN:
CPAN, CGI, DB_File, File::Temp, Getopt::Long, Pod::Man, Pod::Text,
Storable, Text-Tabs+Wrap.

=head1 Performance Enhancements

=over 4

=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 Utility Changes

=over 4

=item *

h2xs now produces template README.

=item *

s2p has been completely rewritten in Perl.  (It is in fact a full
implementation of sed in Perl.)

=item *

xsubpp now supports OUT keyword.

=back

=head1 New Documentation

=head2 perlclib

Internal replacements for standard C library functions.
(Interesting only for extension writers and Perl core hackers.)

=head2 perliol

Internals of PerlIO with layers.

=head2 README.aix

Documentation on compiling Perl on AIX has been added.  AIX has
several different C compilers and getting the right patch level
is essential.  On install README.aix will be installed as L<perlaix>.

=head2 README.bs2000

Documentation on compiling Perl on the POSIX-BC platform (an EBCDIC
mainframe environment) has been added.

This was formerly known as README.posix-bc but the name was considered
to be too confusing (it has nothing to do with the POSIX module or the
POSIX standard).  On install README.bs2000 will be installed as L<perlbs2000>.

=head2 README.macos

In perl 5.7.1 (and in the 5.6.1) the MacPerl sources have been
synchronised with the standard Perl sources.  To compile MacPerl
some additional steps are required, and this file documents those
steps.  On install README.macos will be installed as L<perlmacos>.

=head2 README.mpeix

The README.mpeix has been podified, which means that this information
about compiling and using Perl on the MPE/iX miniframe platform will
be installed as L<perlmpeix>.

=head2 README.solaris

README.solaris has been created and Solaris wisdom from elsewhere
in the Perl documentation has been collected there.  On install
README.solaris will be installed as L<perlsolaris>.

=head2 README.vos

The README.vos has been podified, which means that this information
about compiling and using Perl on the Stratus VOS miniframe platform
will be installed as L<perlvos>.

=head2 Porting/repository.pod

Documentation on how to use the Perl source repository has been added.

=head1 Installation and Configuration Improvements

=over 4

=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 *

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 *

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

=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

=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 *

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

=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 *

NCR MP-RAS is now supported.

=item *

NonStop-UX is now supported.

=item *

Amdahl UTS is now supported.

=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

=head2 Generic Improvements

=over 4

=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 *

Some new Configure symbols, useful for extension writers:

=over 8

=item d_cmsghdr

For struct cmsghdr.

=item d_fcntl_can_lock

Whether fcntl() can be used for file locking.

=item d_fsync

=item d_getitimer

=item d_getpagsz

For getpagesize(), though you should prefer POSIX::sysconf(_SC_PAGE_SIZE))

=item d_msghdr_s

For struct msghdr.

=item need_va_copy

Whether one needs to use Perl_va_copy() to copy varargs.

=item d_readv

=item d_recvmsg

=item d_sendmsg

=item sig_size

The number of elements in an array needed to hold all the available signals.

=item d_sockatmark

=item d_strtoq

=item d_u32align

Whether one needs to access character data aligned by U32 sized pointers.

=item d_ualarm

=item d_usleep

=back

=item *

Removed Configure symbols: the PDP-11 memory model settings: huge,
large, medium, models.

=item *

SOCKS support is now much more robust.

=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.

=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 *

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

=item *

The order of DESTROYs has been made more predictable.

=item *

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

=item *

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

=item *

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

=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 *

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

=item *

Tie::ARRAY SPLICE method was broken.

=item *

vec() now tries to work with characters <= 255 when possible, but it leaves
higher character values in place.  In that case, if vec() was used to modify
the string, it is no longer considered to be utf8-encoded.

=back

=head2 Platform Specific Changes and Fixes

=over 4

=item *

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

=item *

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

=item *

Windows

=over 8

=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 *

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 *

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

=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 binary distribution).

=back

=back

=head1 New or Changed Diagnostics

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.

=over 4

=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.

=back

=head1 Changed Internals

=over 4

=item *

Some new APIs: ptr_table_clear(), ptr_table_free(), sv_setref_uv().
For the full list of the available APIs see L<perlapi>.

=item *

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

=item *

Perl now uses system malloc instead of Perl malloc on all 64-bit
platforms, and even in some not-always-64-bit platforms like AIX,
IRIX, and Solaris.  This change breaks backward compatibility but
Perl's malloc has problems with large address spaces and also the
speed of vendors' malloc is generally better in large address space
machines (Perl's malloc is mostly tuned for space).

=back

=head1 New Tests

Many new tests have been added.  The most notable is probably the
lib/1_compile: it is very notable because running it takes quite a
long time -- it test compiles all the Perl modules in the distribution.
Please be patient.

=head1 Known Problems

Note that unlike other sections in this document (which describe
changes since 5.7.0) this section is cumulative containing known
problems for all the 5.7 releases.

=head2 AIX 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.

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

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

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

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 Test lib/posix Subtest 9 Fails In LP64-Configured HP-UX

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 lib/b test 19

The test fails on various platforms (PA64 and IA64 are known), but the
exact cause is still being investigated.

=head2 Linux With Sfio Fails op/misc Test 48

No known fix.

=head2 sigaction test 13 in VMS

The test is known to fail; whether it's because of VMS of because
of faulty test is not known.

=head2 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 else 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

The subtests 19 and 20 of lib/thr5005.t test 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. (Note that support for 5.005-style threading remains
experimental.)

=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 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 The Compiler Suite Is Still Experimental

The compiler suite is slowly getting better but is nowhere near
working order yet.

=head1 Security Vulnerability Closed

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

A security vulnerability affecting all Perl versions prior to 5.6.1
was found in August 2000.  The vulnerability does not affect default
installations and as far as is known affects only the Linux platform.

You should upgrade your Perl to 5.6.1 as soon as possible.  Patches
for earlier releases exist but using the patches require full
recompilation from the source code anyway, so 5.6.1 is your best
choice.

See http://www.cpan.org/src/5.0/sperl-2000-08-05/sperl-2000-08-05.txt
for more information.

=head1 Incompatible Changes

=head2 64-bit platforms and malloc

If your pointers are 64 bits wide, the Perl malloc is no more being
used because it simply does not work with 8-byte pointers.  Also,
usually the system malloc on such platforms are much better optimized
for such large memory models than the Perl malloc.

=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 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 Different Definition of the Unicode Character Classes \p{In...}

As suggested by the Unicode consortium, the Unicode character classes
now prefer I<scripts> as opposed to I<blocks> (as defined by Unicode);
in Perl, when the C<\p{In....}> and the C<\p{In....}> regular expression
constructs are used.  This has changed the definition of some of those
character classes.

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 256 characters based on the Unicode
numbering.

In general this change results in more inclusive Unicode character
classes, but changes to the other direction also do take place:
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>).

Changes in the character class semantics may have happened if a script
and a block happen to have the same name, for example C<Hebrew>.
In such cases the script wins and C<\p{InHebrew}> now means the script
definition of Hebrew.  The block definition in still available,
though, by appending C<Block> to the name: C<\p{InHebrewBlock}> means
what C<\p{InHebrew}> meant in perl 5.6.0.  For the full list
of affected character classes, see L<perlunicode/Blocks>.

=head2 Deprecations

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.

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

The suidperl is also considered to be too much a risk to continue
maintaining and the suidperl code is likely to be removed in a future
release.

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.

The chdir(undef) and chdir('') behaviors to match chdir() has been
deprecated.  In future versions, chdir(undef) and chdir('') will
simply fail.

=head1 Core Enhancements

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.

=over 4

=item *

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

=item *

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

=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 *

Lvalue subroutines can now return C<undef> in list context.

=item *

The C<op_clear> and C<op_null> are now exported.

=item *

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

=item *

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

=item *

The Perl parser has been stress tested using both random input and
Markov chain input.

=item *

C<eval "v200"> now works.

=item *

VMS now works under PerlIO.

=item *

END blocks are now run even if you exit/die in a BEGIN block.
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>.

=back

=head1 Modules and Pragmata

=head2 New Modules and Distributions

=over 4

=item *

L<Attribute::Handlers> - Simpler definition of attribute handlers

=item *

L<ExtUtils::Constant> - generate XS code to import C header constants

=item *

L<I18N::Langinfo> - query locale information

=item *

L<I18N::LangTags> - functions for dealing with RFC3066-style language tags

=item *

L<libnet> - a collection of perl5 modules related to network programming

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

=item *

L<List::Util> - selection of general-utility list subroutines

=item *

L<Locale::Maketext> - framework for localization

=item *

L<Memoize> - Make your functions faster by trading space for time

=item *

L<NEXT> - pseudo-class for method redispatch

=item *

L<Scalar::Util> - selection of general-utility scalar subroutines

=item *

L<Test::More> - yet another framework for writing test scripts

=item *

L<Test::Simple> - Basic utilities for writing tests

=item *

L<Time::HiRes> - high resolution ualarm, usleep, and gettimeofday

=item *

L<Time::Piece> - Object Oriented time objects

(Previously known as L<Time::Object>.)

=item *

L<Time::Seconds> - a simple API to convert seconds to other date values

=item *

L<UnicodeCD> - Unicode Character Database

=back

=head2 Updated And Improved Modules and Pragmata

=over 4

=item *

L<B::Deparse> module 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 *

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

=item *

L<Cwd> extension is now (even) faster.

=item *

L<DB_File> extension has been updated to version 1.77.

=item *

L<Fcntl>, L<Socket>, and L<Sys::Syslog> have been rewritten to use the
new-style constant dispatch section (see L<ExtUtils::Constant>).

=item *

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

=item *

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

=item *

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

=item *

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

=back

=head1 Utility Changes

=over 4

=item *

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

=item *

L<h2ph> now supports C trigraphs.

=item *

L<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 *

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

=item *

The F<Pod::Html> (and thusly L<pod2html>) now allows specifying
a cache directory.

=back

=head1 New Documentation

=over 4

=item *

L<Locale::Maketext::TPJ13> is an article about software localization,
originally published in The Perl Journal #13, republished here with
kind permission.

=item *

More README.$PLATFORM files have been converted into pod, which also
means that they also be installed as perl$PLATFORM documentation
files.  The new files are L<perlapollo>, L<perlbeos>, L<perldgux>,
L<perlhurd>, L<perlmint>, L<perlnetware>, L<perlplan9>, L<perlqnx>,
and L<perltru64>.

=item *

The F<Todo> and F<Todo-5.6> files have been merged into L<perltodo>.

=item *

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

=back

=head1 Installation and Configuration Improvements

=head2 New Or Improved Platforms

=over 4

=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 *

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

=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 *

Several MacOS (Classic) portability patches have been applied.  We
hope to get a fully working port by 5.8.0.  (The remaining problems
relate to the changed IO model of Perl.)  See L<perlmacos>.

=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 *

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

=item *

The Amdahl UTS UNIX mainframe platform is now supported.

=back

=head2 Generic Improvements

=over 4

=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 *

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 *

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>).

=item *

The C<B::Deparse> compiler backend has been so significantly improved
that almost the whole Perl test suite passes after being deparsed.  A
make target has been added to help in further testing: C<make test.deparse>.

=back

=head1 Selected Bug Fixes

=over 5

=item *

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

=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 *

L<dprofpp> -R didn't work.

=item *

PERL5OPT with embedded spaces didn't work.

=item *

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

=back

=head2 Platform Specific Changes and Fixes

=over 4

=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.

=back

=head1 New or Changed Diagnostics

=over 4

=item *

In the regular expression diagnostics the C<E<lt>E<lt> HERE> marker
introduced in 5.7.0 has been changed to be C<E<lt>-- HERE> since too
many people found the C<E<lt>E<lt>> to be too similar to here-document
starters.

=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->{bar}> has been
deprecated for a while.  Now you will get an optional warning.

=back

=head1 Source Code Enhancements

=head2 MAGIC constants

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

=head2 Better commented code

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

=head2 Regex pre-/post-compilation items matched up

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.

=head2 gcc -Wall

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

=head1 New Tests

Several new tests have been added, especially for the F<lib> subsection.

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

Note that unlike other sections in this document (which describe
changes since 5.7.0) this section is cumulative containing known
problems for all the 5.7 releases.

=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 is
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 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.>

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.

  lib/autouse.t                 4
  t/lib/thr5005.t               19-20

=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 UTS

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

=head2 VMS

Rather many tests are failing in VMS but that actually more tests
succeed in VMS than they used to, it's just that there are many,
many more tests than there used to be.

Here are the known failures from some compiler/platform combinations.

DEC C V5.3-006 on OpenVMS VAX V6.2
 
  [-.ext.list.util.t]tainted..............FAILED on test 3
  [-.ext.posix]sigaction..................FAILED on test 7
  [-.ext.time.hires]hires.................FAILED on test 14
  [-.lib.file.find]taint..................FAILED on test 17
  [-.lib.math.bigint.t]bigintpm...........FAILED on test 1183
  [-.lib.test.simple.t]exit...............FAILED on test 1
  [.lib]vmsish............................FAILED on test 13
  [.op]sprintf............................FAILED on test 12
  Failed 8/399 tests, 91.23% okay.

DEC C V6.0-001 on OpenVMS Alpha V7.2-1 and
Compaq C V6.2-008 on OpenVMS Alpha V7.1

  [-.ext.list.util.t]tainted..............FAILED on test 3 
  [-.lib.file.find]taint..................FAILED on test 17
  [-.lib.test.simple.t]exit...............FAILED on test 1
  [.lib]vmsish............................FAILED on test 13
  Failed 4/399 tests, 92.48% okay.

Compaq C V6.4-005 on OpenVMS Alpha 7.2.1

  [-.ext.b]showlex........................FAILED on test 1
  [-.ext.list.util.t]tainted..............FAILED on test 3
  [-.lib.file.find]taint..................FAILED on test 17 
  [-.lib.test.simple.t]exit...............FAILED on test 1
  [.lib]vmsish............................FAILED on test 13
  [.op]misc...............................FAILED on test 49
  Failed 6/401 tests, 92.77% okay.

=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 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 Variable Attributes are not Currently Usable for Tieing

This limitation will hopefully be fixed in future.  (Subroutine
attributes work fine for tieing, see L<Attribute::Handlers>).

=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 The Compiler Suite Is Still Experimental

The compiler suite is slowly getting better but is nowhere near
working order yet.

=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).

=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/perl/, 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