perl581delta.1

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.\" ========================================================================
.\"
.IX Title "PERL581DELTA 1"
.TH PERL581DELTA 1 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
perl581delta \- what is new for perl v5.8.1
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This document describes differences between the 5.8.0 release and
the 5.8.1 release.
.PP
If you are upgrading from an earlier release such as 5.6.1, first read
the perl58delta, which describes differences between 5.6.0 and
5.8.0.
.PP
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.
.PP
.Vb 1
\&          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
.Ve
.SH "Incompatible Changes"
.IX Header "Incompatible Changes"
.Sh "Hash Randomisation"
.IX Subsection "Hash Randomisation"
Mainly due to security reasons, the \*(L"random ordering\*(R" of hashes
has been made even more random.  Previously while the order of hash
elements from \fIkeys()\fR, \fIvalues()\fR, and \fIeach()\fR was essentially random,
it was still repeatable.  Now, however, the order varies between
different runs of Perl.
.PP
\&\fBPerl has never guaranteed any ordering of the hash keys\fR, 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.
.PP
The added randomness may affect applications.
.PP
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 \f(CW\*(C`Sortkeys\*(C'\fR 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.
.PP
More subtle problem is reliance on the order of \*(L"global destruction\*(R".
That is what happens at the end of execution: Perl destroys all data
structures, including user data.  If your destructors (the \s-1DESTROY\s0
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 \s-1PERL_DESTRUCT_LEVEL\s0 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.
.PP
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.
.PP
To disable the hash randomisation in runtime, set the environment
variable \s-1PERL_HASH_SEED\s0 to 0 (zero) before running Perl (for more
information see \*(L"\s-1PERL_HASH_SEED\s0\*(R" in perlrun), or to disable the feature
completely in compile time, compile with \f(CW\*(C`\-DNO_HASH_SEED\*(C'\fR (see \fI\s-1INSTALL\s0\fR).
.PP
See \*(L"Algorithmic Complexity Attacks\*(R" in perlsec for the original
rationale behind this change.
.Sh "\s-1UTF\-8\s0 On Filehandles No Longer Activated By Locale"
.IX Subsection "UTF-8 On Filehandles No Longer Activated By Locale"
In Perl 5.8.0 all filehandles, including the standard filehandles,
were implicitly set to be in Unicode \s-1UTF\-8\s0 if the locale settings
indicated the use of \s-1UTF\-8\s0.  This feature caused too many problems,
so the feature was turned off and redesigned: see \*(L"Core Enhancements\*(R".
.ie n .Sh "Single-number v\-strings are no longer v\-strings before ""=>"""
.el .Sh "Single-number v\-strings are no longer v\-strings before ``=>''"
.IX Subsection "Single-number v-strings are no longer v-strings before =>"
The version strings or v\-strings (see \*(L"Version Strings\*(R" in perldata)
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 \*(L"=>\*(R" a version string (a \*(L"v\*(R" followed by digits) has been interpreted
as a v\-string instead of a string literal.  In other words:
.PP
.Vb 1
\&        %h = ( v65 => 42 );
.Ve
.PP
has meant since Perl 5.6.0
.PP
.Vb 1
\&        %h = ( \*(AqA\*(Aq => 42 );
.Ve
.PP
(at least in platforms of \s-1ASCII\s0 progeny)  Perl 5.8.1 restores the
more natural interpretation
.PP
.Vb 1
\&        %h = ( \*(Aqv65\*(Aq => 42 );
.Ve
.PP
The multi-number v\-strings like v65.66 and 65.66.67 still continue to
be v\-strings in Perl 5.8.
.Sh "(Win32) The \-C Switch Has Been Repurposed"
.IX Subsection "(Win32) The -C Switch Has Been Repurposed"
The \-C switch has changed in an incompatible way.  The old semantics
of this switch only made sense in Win32 and only in the \*(L"use utf8\*(R"
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.
.PP
For the new life of this switch, see \*(L"\s-1UTF\-8\s0 no longer default under
\&\s-1UTF\-8\s0 locales\*(R", and \*(L"\-C\*(R" in perlrun.
.Sh "(Win32) The /d Switch Of cmd.exe"
.IX Subsection "(Win32) The /d Switch Of cmd.exe"
Perl 5.8.1 uses the /d switch when running the cmd.exe shell
internally for \fIsystem()\fR, 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 \s-1PERL5SHELL\s0 in your environment to \f(CW\*(C`cmd /x/c\*(C'\fR.
.SH "Core Enhancements"
.IX Header "Core Enhancements"
.Sh "\s-1UTF\-8\s0 no longer default under \s-1UTF\-8\s0 locales"
.IX Subsection "UTF-8 no longer default under UTF-8 locales"
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) \*(L"UTF\-8\-ification\*(R" of filehandles, including the
standard filehandles, if the user's locale settings indicated
use of \s-1UTF\-8\s0.
.PP
For example, if you had \f(CW\*(C`en_US.UTF\-8\*(C'\fR as your locale, your \s-1STDIN\s0 and
\&\s-1STDOUT\s0 were automatically \*(L"\s-1UTF\-8\s0\*(R", in other words an implicit
binmode(..., \*(L":utf8\*(R") was made.  This meant that trying to print, say,
\&\fIchr\fR\|(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 \fBdefault\fR locale setting is \s-1UTF\-8\s0, so
all RedHat users got \s-1UTF\-8\s0 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)