|
perl581delta - what is new for perl v5.8.1
This document describes differences between the 5.8.0 release and
the 5.8.1 release.
If you are upgrading from an earlier release such as 5.6.1, first read
the the perl58delta manpage, which describes differences between 5.6.0 and
5.8.0.
In case you are wondering about 5.6.1, it was bug-fix-wise rather
identical to the development release 5.7.1. Confused? This timeline
hopefully helps a bit: it lists the new major releases, their maintenance
releases, and the development releases.
New Maintenance Development
5.6.0 2000-Mar-22
5.7.0 2000-Sep-02
5.6.1 2001-Apr-08
5.7.1 2001-Apr-09
5.7.2 2001-Jul-13
5.7.3 2002-Mar-05
5.8.0 2002-Jul-18
5.8.1 2003-Sep-25
Mainly due to security reasons, the "random ordering" of hashes
has been made even more random. Previously while the order of hash
elements from keys(), values(), and each() was essentially random,
it was still repeatable. Now, however, the order varies between
different runs of Perl.
Perl has never guaranteed any ordering of the hash keys, and the
ordering has already changed several times during the lifetime of
Perl 5. Also, the ordering of hash keys has always been, and
continues to be, affected by the insertion order.
The added randomness may affect applications.
One possible scenario is when output of an application has included
hash data. For example, if you have used the Data::Dumper module to
dump data into different files, and then compared the files to see
whether the data has changed, now you will have false positives since
the order in which hashes are dumped will vary. In general the cure
is to sort the keys (or the values); in particular for Data::Dumper to
use the Sortkeys option. If some particular order is really
important, use tied hashes: for example the Tie::IxHash module
which by default preserves the order in which the hash elements
were added.
More subtle problem is reliance on the order of "global destruction".
That is what happens at the end of execution: Perl destroys all data
structures, including user data. If your destructors (the DESTROY
subroutines) have assumed any particular ordering to the global
destruction, there might be problems ahead. For example, in a
destructor of one object you cannot assume that objects of any other
class are still available, unless you hold a reference to them.
If the environment variable PERL_DESTRUCT_LEVEL is set to a non-zero
value, or if Perl is exiting a spawned thread, it will also destruct
the ordinary references and the symbol tables that are no longer in use.
You can't call a class method or an ordinary function on a class that
has been collected that way.
The hash randomisation is certain to reveal hidden assumptions about
some particular ordering of hash elements, and outright bugs: it
revealed a few bugs in the Perl core and core modules.
To disable the hash randomisation in runtime, set the environment
variable PERL_HASH_SEED to 0 (zero) before running Perl (for more
information see PERL_HASH_SEED in the perlrun manpage), or to disable the feature
completely in compile time, compile with -DNO_HASH_SEED (see INSTALL).
See Algorithmic Complexity Attacks in the perlsec manpage for the original
rationale behind this change.
In Perl 5.8.0 all filehandles, including the standard filehandles,
were implicitly set to be in Unicode UTF-8 if the locale settings
indicated the use of UTF-8. This feature caused too many problems,
so the feature was turned off and redesigned: see Core Enhancements.
The version strings or v-strings (see Version Strings in the perldata manpage)
feature introduced in Perl 5.6.0 has been a source of some confusion--
especially when the user did not want to use it, but Perl thought it
knew better. Especially troublesome has been the feature that before
a "=>" a version string (a "v" followed by digits) has been interpreted
as a v-string instead of a string literal. In other words:
%h = ( v65 => 42 );
has meant since Perl 5.6.0
%h = ( 'A' => 42 );
(at least in platforms of ASCII progeny) Perl 5.8.1 restores the
more natural interpretation
%h = ( 'v65' => 42 );
The multi-number v-strings like v65.66 and 65.66.67 still continue to
be v-strings in Perl 5.8.
The -C switch has changed in an incompatible way. The old semantics
of this switch only made sense in Win32 and only in the "use utf8"
universe in 5.6.x releases, and do not make sense for the Unicode
implementation in 5.8.0. Since this switch could not have been used
by anyone, it has been repurposed. The behavior that this switch
enabled in 5.6.x releases may be supported in a transparent,
data-dependent fashion in a future release.
For the new life of this switch, see UTF-8 no longer default under UTF-8 locales, and -C in the perlrun manpage.
Perl 5.8.1 uses the /d switch when running the cmd.exe shell
internally for system(), backticks, and when opening pipes to external
programs. The extra switch disables the execution of AutoRun commands
from the registry, which is generally considered undesirable when
running external programs. If you wish to retain compatibility with
the older behavior, set PERL5SHELL in your environment to cmd /x/c.
In Perl 5.8.0 many Unicode features were introduced. One of them
was found to be of more nuisance than benefit: the automagic
(and silent) "UTF-8-ification" of filehandles, including the
standard filehandles, if the user's locale settings indicated
use of UTF-8.
For example, if you had en_US.UTF-8 as your locale, your STDIN and
STDOUT were automatically "UTF-8", in other words an implicit
binmode(..., ":utf8") was made. This meant that trying to print, say,
chr(0xff), ended up printing the bytes 0xc3 0xbf. Hardly what
you had in mind unless you were aware of this feature of Perl 5.8.0.
The problem is that the vast majority of people weren't: for example
in RedHat releases 8 and 9 the default locale setting is UTF-8, so
all RedHat users got UTF-8 filehandles, whether they wanted it or not.
The pain was intensified by the Unicode implementation of Perl 5.8.0
(still) having nasty bugs, especially related to the use of s/// and
tr///. (Bugs that have been fixed in 5.8.1)
Therefore a decision was made to backtrack the feature and change it
from implicit silent default to explicit conscious option. The new
Perl command line option -C and its counterpart environment
variable PERL_UNICODE can now be used to control how Perl and Unicode
interact at interfaces like I/O and for example the command line
arguments. See -C in the perlrun manpage and PERL_UNICODE in the perlrun manpage for more
information.
In Perl 5.8.0 the so-called "safe signals" were introduced. This
means that Perl no longer handles signals immediately but instead
"between opcodes", when it is safe to do so. The earlier immediate
handling easily could corrupt the internal state of Perl, resulting
in mysterious crashes.
However, the new safer model has its problems too. Because now an
opcode, a basic unit of Perl execution, is never interrupted but
instead let to run to completion, certain operations that can take a
long time now really do take a long time. For example, certain
network operations have their own blocking and timeout mechanisms, and
being able to interrupt them immediately would be nice.
Therefore perl 5.8.1 introduces a "backdoor" to restore the pre-5.8.0
(pre-5.7.3, really) signal behaviour. Just set the environment variable
PERL_SIGNALS to unsafe, and the old immediate (and unsafe)
signal handling behaviour returns. See PERL_SIGNALS in the perlrun manpage
and Deferred Signals (Safe Signals) in the perlipc manpage.
In completely unrelated news, you can now use safe signals with
POSIX::SigAction. See POSIX::SigAction in the POSIX manpage.
Formerly, the indices passed to FETCH, STORE, EXISTS, and
DELETE methods in tied array class were always non-negative. If
the actual argument was negative, Perl would call FETCHSIZE implicitly
and add the result to the index before passing the result to the tied
array method. This behaviour is now optional. If the tied array class
contains a package variable named $NEGATIVE_INDICES which is set to
a true value, negative values will be passed to FETCH, STORE,
EXISTS, and DELETE unchanged.
The syntaxes
local ${$x}
local @{$x}
local %{$x}
now do localise variables, given that the $x is a valid variable name.
The copy of the Unicode Character Database included in Perl 5.8 has
been updated to 4.0.0 from 3.2.0. This means for example that the
Unicode character properties are as in Unicode 4.0.0.
There is one new feature deprecation. Perl 5.8.0 forgot to add
some deprecation warnings, these warnings have now been added.
Finally, a reminder of an impending feature removal.
Pseudo-hashes were deprecated in Perl 5.8.0 and will be removed in
Perl 5.10.0, see the perl58delta manpage for details. Each attempt to access
pseudo-hashes will trigger the warning Pseudo-hashes are deprecated.
If you really want to continue using pseudo-hashes but not to see the
deprecation warnings, use:
no warnings 'deprecated';
Or you can continue to use the the fields manpage pragma, but please don't
expect the data structures to be pseudohashes any more.
5.005-style threads (activated by use Thread;) were deprecated in
Perl 5.8.0 and will be removed after Perl 5.8, see the perl58delta manpage for
details. Each 5.005-style thread creation will trigger the warning
5.005 threads are deprecated. If you really want to continue
using the 5.005 threads but not to see the deprecation warnings, use:
no warnings 'deprecated';
The $* variable controlling multi-line matching has been deprecated
and will be removed after 5.8. The variable has been deprecated for a
long time, and a deprecation warning Use of $* is deprecated is given,
now the variable will just finally be removed. The functionality has
been supplanted by the /s and /m modifiers on pattern matching.
If you really want to continue using the $*-variable but not to see
the deprecation warnings, use:
no warnings 'deprecated';
map in void context is no longer expensive. map is now context
aware, and will not construct a list if called in void context.
If a socket gets closed by the server while printing to it, the client
now gets a SIGPIPE. While this new feature was not planned, it fell
naturally out of PerlIO changes, and is to be considered an accidental
feature.
PerlIO::get_layers(FH) returns the names of the PerlIO layers
active on a filehandle.
PerlIO::via layers can now have an optional UTF8 method to
indicate whether the layer wants to "auto-:utf8" the stream.
utf8::is_utf8() has been added as a quick way to test whether
a scalar is encoded internally in UTF-8 (Unicode).
The following modules and pragmata have been updated since Perl 5.8.0:
- base
- B::Bytecode
-
In much better shape than it used to be. Still far from perfect, but
maybe worth a try.
- B::Concise
- B::Deparse
- Benchmark
-
An optional feature, :hireswallclock, now allows for high
resolution wall clock times (uses Time::HiRes).
- ByteLoader
-
See B::Bytecode.
- bytes
-
Now has bytes::substr.
- CGI
- charnames
-
One can now have custom character name aliases.
- CPAN
-
There is now a simple command line frontend to the CPAN.pm
module called cpan.
- Data::Dumper
-
A new option, Pair, allows choosing the separator between hash keys
and values.
- DB_File
- Devel::PPPort
- Digest::MD5
- Encode
-
Significant updates on the encoding pragma functionality
(tr/// and the DATA filehandle, formats).
-
If a filehandle has been marked as to have an encoding, unmappable
characters are detected already during input, not later (when the
corrupted data is being used).
-
The ISO 8859-6 conversion table has been corrected (the 0x30..0x39
erroneously mapped to U+0660..U+0669, instead of U+0030..U+0039). The
GSM 03.38 conversion did not handle escape sequences correctly. The
UTF-7 encoding has been added (making Encode feature-complete with
Unicode::String).
- fields
- libnet
- Math::BigInt
-
A lot of bugs have been fixed since v1.60, the version included in Perl
v5.8.0. Especially noteworthy are the bug in Calc that caused div and mod to
fail for some large values, and the fixes to the handling of bad inputs.
-
Some new features were added, e.g. the broot() method, you can now pass
parameters to config() to change some settings at runtime, and it is now
possible to trap the creation of NaN and infinity.
-
As usual, some optimizations took place and made the math overall a tad
faster. In some cases, quite a lot faster, actually. Especially alternative
libraries like Math::BigInt::GMP benefit from this. In addition, a lot of the
quite clunky routines like fsqrt() and flog() are now much much faster.
- MIME::Base64
- NEXT
-
Diamond inheritance now works.
- Net::Ping
- PerlIO::scalar
-
Reading from non-string scalars (like the special variables, see
the perlvar manpage) now works.
- podlators
- Pod::LaTeX
- PodParsers
- Pod::Perldoc
-
Complete rewrite. As a side-effect, no longer refuses to startup when
run by root.
- Scalar::Util
-
New utilities: refaddr, isvstring, looks_like_number, set_prototype.
- Storable
-
Can now store code references (via B::Deparse, so not foolproof).
- strict
-
Earlier versions of the strict pragma did not check the parameters
implicitly passed to its "import" (use) and "unimport" (no) routine.
This caused the false idiom such as:
-
use strict qw(@ISA);
@ISA = qw(Foo);
-
This however (probably) raised the false expectation that the strict
refs, vars and subs were being enforced (and that @ISA was somehow
"declared"). But the strict refs, vars, and subs are not enforced
when using this false idiom.
-
Starting from Perl 5.8.1, the above will cause an error to be
raised. This may cause programs which used to execute seemingly
correctly without warnings and errors to fail when run under 5.8.1.
This happens because
-
use strict qw(@ISA);
-
will now fail with the error:
-
Unknown 'strict' tag(s) '@ISA'
-
The remedy to this problem is to replace this code with the correct idiom:
-
use strict;
use vars qw(@ISA);
@ISA = qw(Foo);
- Term::ANSIcolor
- Test::Harness
-
Now much more picky about extra or missing output from test scripts.
- Test::More
- Test::Simple
- Text::Balanced
- Time::HiRes
-
Use of nanosleep(), if available, allows mixing subsecond sleeps with
alarms.
- threads
-
Several fixes, for example for join() problems and memory
leaks. In some platforms (like Linux) that use glibc the minimum memory
footprint of one ithread has been reduced by several hundred kilobytes.
- threads::shared
-
Many memory leaks have been fixed.
- Unicode::Collate
- Unicode::Normalize
- Win32::GetFolderPath
- Win32::GetOSVersion
-
Now returns extra information.
The h2xs utility now produces a more modern layout:
Foo-Bar/lib/Foo/Bar.pm instead of Foo/Bar/Bar.pm.
Also, the boilerplate test is now called t/Foo-Bar.t
instead of t/1.t.
The Perl debugger (lib/perl5db.pl) has now been extensively
documented and bugs found while documenting have been fixed.
perldoc has been rewritten from scratch to be more robust and
featureful.
perlcc -B works now at least somewhat better, while perlcc -c
is rather more broken. (The Perl compiler suite as a whole continues
to be experimental.)
perl573delta has been added to list the differences between the
(now quite obsolete) development releases 5.7.2 and 5.7.3.
perl58delta has been added: it is the perldelta of 5.8.0, detailing
the differences between 5.6.0 and 5.8.0.
perlartistic has been added: it is the Artistic License in pod format,
making it easier for modules to refer to it.
perlcheat has been added: it is a Perl cheat sheet.
perlgpl has been added: it is the GNU General Public License in pod
format, making it easier for modules to refer to it.
perlmacosx has been added to tell about the installation and use
of Perl in Mac OS X.
perlos400 has been added to tell about the installation and use
of Perl in OS/400 PASE.
perlreref has been added: it is a regular expressions quick reference.
The UNIX standard Perl location, /usr/bin/perl, is no longer
overwritten by default if it exists. This change was very prudent
because so many UNIX vendors already provide a /usr/bin/perl,
but simultaneously many system utilities may depend on that
exact version of Perl, so better not to overwrite it.
One can now specify installation directories for site and vendor man
and HTML pages, and site and vendor scripts. See INSTALL.
One can now specify a destination directory for Perl installation
by specifying the DESTDIR variable for make install. (This feature
is slightly different from the previous Configure -Dinstallprefix=....)
See INSTALL.
gcc versions 3.x introduced a new warning that caused a lot of noise
during Perl compilation: gcc -Ialreadyknowndirectory (warning:
changing search order). This warning has now been avoided by
Configure weeding out such directories before the compilation.
One can now build subsets of Perl core modules by using the
Configure flags -Dnoextensions=... and -Donlyextensions=...,
see INSTALL.
In Cygwin Perl can now be built with threads (Configure -Duseithreads).
This works with both Cygwin 1.3.22 and Cygwin 1.5.3.
In newer FreeBSD releases Perl 5.8.0 compilation failed because of
trying to use malloc.h, which in FreeBSD is just a dummy file, and
a fatal error to even try to use. Now malloc.h is not used.
Perl is now known to build also in Hitachi HI-UXMPP.
Perl is now known to build again in LynxOS.
Mac OS X now installs with Perl version number embedded in
installation directory names for easier upgrading of user-compiled
Perl, and the installation directories in general are more standard.
In other words, the default installation no longer breaks the
Apple-provided Perl. On the other hand, with Configure -Dprefix=/usr
you can now really replace the Apple-supplied Perl (please be careful).
Mac OS X now builds Perl statically by default. This change was done
mainly for faster startup times. The Apple-provided Perl is still
dynamically linked and shared, and you can enable the sharedness for
your own Perl builds by Configure -Duseshrplib.
Perl has been ported to IBM's OS/400 PASE environment. The best way
to build a Perl for PASE is to use an AIX host as a cross-compilation
environment. See README.os400.
Yet another cross-compilation option has been added: now Perl builds
on OpenZaurus, an Linux distribution based on Mandrake + Embedix for
the Sharp Zaurus PDA. See the Cross/README file.
Tru64 when using gcc 3 drops the optimisation for toke.c to -O2
because of gigantic memory use with the default -O3.
Tru64 can now build Perl with the newer Berkeley DBs.
Building Perl on WinCE has been much enhanced, see README.ce
and README.perlce.
There have been many fixes in the area of anonymous subs, lexicals and
closures. Although this means that Perl is now more "correct", it is
possible that some existing code will break that happens to rely on
the faulty behaviour. In practice this is unlikely unless your code
contains a very complex nesting of anonymous subs, evals and lexicals.
If an input filehandle is marked :utf8 and Perl sees illegal UTF-8
coming in when doing <FH>, if warnings are enabled a warning is
immediately given - instead of being silent about it and Perl being
unhappy about the broken data later. (The :encoding(utf8) layer
also works the same way.)
binmode(SOCKET, ":utf8") only worked on the input side, not on the
output side of the socket. Now it works both ways.
For threaded Perls certain system database functions like getpwent()
and getgrent() now grow their result buffer dynamically, instead of
failing. This means that at sites with lots of users and groups the
functions no longer fail by returning only partial results.
Perl 5.8.0 had accidentally broken the capability for users
to define their own uppercase<->lowercase Unicode mappings
(as advertised by the Camel). This feature has been fixed and
is also documented better.
In 5.8.0 this
$some_unicode .= <FH>;
didn't work correctly but instead corrupted the data. This has now
been fixed.
Tied methods like FETCH etc. may now safely access tied values, i.e.
resulting in a recursive call to FETCH etc. Remember to break the
recursion, though.
At startup Perl blocks the SIGFPE signal away since there isn't much
Perl can do about it. Previously this blocking was in effect also for
programs executed from within Perl. Now Perl restores the original
SIGFPE handling routine, whatever it was, before running external
programs.
Linenumbers in Perl scripts may now be greater than 65536, or 2**16.
(Perl scripts have always been able to be larger than that, it's just
that the linenumber for reported errors and warnings have "wrapped
around".) While scripts that large usually indicate a need to rethink
your code a bit, such Perl scripts do exist, for example as results
from generated code. Now linenumbers can go all the way to
4294967296, or 2**32.
Linux
HP-UX
VMS
-
Configuration now tests for the presence of poll(), and IO::Poll
now uses the vendor-supplied function if detected.
-
A rare access violation at Perl start-up could occur if the Perl image was
installed with privileges or if there was an identifier with the
subsystem attribute set in the process's rightslist. Either of these
circumstances triggered tainting code that contained a pointer bug.
The faulty pointer arithmetic has been fixed.
-
The length limit on values (not keys) in the %ENV hash has been raised
from 255 bytes to 32640 bytes (except when the PERL_ENV_TABLES setting
overrides the default use of logical names for %ENV). If it is
necessary to access these long values from outside Perl, be aware that
they are implemented using search list logical names that store the
value in pieces, each 255-byte piece (up to 128 of them) being an
element in the search list. When doing a lookup in %ENV from within
Perl, the elements are combined into a single value. The existing
VMS-specific ability to access individual elements of a search list
logical name via the $ENV{'foo;N'} syntax (where N is the search list
index) is unimpaired.
-
The piping implementation now uses local rather than global DCL
symbols for inter-process communication.
-
File::Find could become confused when navigating to a relative
directory whose name collided with a logical name. This problem has
been corrected by adding directory syntax to relative path names, thus
preventing logical name translation.
Win32
-
A memory leak in the fork() emulation has been fixed.
-
The return value of the ioctl() built-in function was accidentally
broken in 5.8.0. This has been corrected.
-
The internal message loop executed by perl during blocking operations
sometimes interfered with messages that were external to Perl.
This often resulted in blocking operations terminating prematurely or
returning incorrect results, when Perl was executing under environments
that could generate Windows messages. This has been corrected.
-
Pipes and sockets are now automatically in binary mode.
-
The four-argument form of select() did not preserve $! (errno) properly
when there were errors in the underlying call. This is now fixed.
-
The "CR CR LF" problem of has been fixed, binmode(FH, ":crlf")
is now effectively a no-op.
All the warnings related to pack() and unpack() were made more
informative and consistent.
The old version
A thread exited while %d other threads were still running
was misleading because the "other&quo | 
