PERL5100DELTA

NAME

DESCRIPTION

Many of the bug fixes in 5.10.0 were already seen in the 5.8.X maintenance releases; they are not duplicated here and are documented in the set of man pages named perl58[1-8]?delta.  

Core Enhancements

The feature pragma

Currently the following new features are available: "switch" (adds a switch statement), "say" (adds a "say" built-in function), and "state" (adds a "state" keyword for declaring ``static'' variables). Those features are described in their own sections of this document.

The "feature" pragma is also implicitly loaded when you require a minimal perl version (with the "use VERSION" construct) greater than, or equal to, 5.9.5. See feature for details.  

New -E command-line switch

Defined-or operator

    $a // $b

is merely equivalent to

   defined $a ? $a : $b

and the statement

   $c //= $d;

can now be used instead of

   $c = $d unless defined $c;

The "//" operator has the same precedence and associativity as "||". Special care has been taken to ensure that this operator Do What You Mean while not breaking old code, but some edge cases involving the empty regular expression may now parse differently. See perlop for details.  

Switch and Smart Match operator

    given ($foo) {
        when (/^abc/) { $abc = 1; }
        when (/^def/) { $def = 1; }
        when (/^xyz/) { $xyz = 1; }
        default { $nothing = 1; }
    }

A more complete description of how Perl matches the switch variable against the "when" conditions is given in ``Switch statements'' in perlsyn.

This kind of match is called smart match, and it's also possible to use it outside of switch statements, via the new "~~" operator. See ``Smart matching in detail'' in perlsyn.

This feature was contributed by Robin Houston.  

Regular expressions

Recursive Patterns

It is now possible to write recursive patterns without using the "(??{})" construct. This new way is more efficient, and in many cases easier to read.

Each capturing parenthesis can now be treated as an independent pattern that can be entered by using the "(?PARNO)" syntax ("PARNO" standing for ``parenthesis number''). For example, the following pattern will match nested balanced angle brackets:

    /
     ^                      # start of line
     (                      # start capture buffer 1
        <                   #   match an opening angle bracket
        (?:                 #   match one of:
            (?>             #     don't backtrack over the inside of this group
                [^<>]+      #       one or more non angle brackets
            )               #     end non backtracking group
        |                   #     ... or ...
            (?1)            #     recurse to bracket 1 and try it again
        )*                  #   0 or more times.
        >                   #   match a closing angle bracket
     )                      # end capture buffer one
     $                      # end of line
    /x

PCRE users should note that Perl's recursive regex feature allows backtracking into a recursed pattern, whereas in PCRE the recursion is atomic or ``possessive'' in nature. As in the example above, you can add (?>) to control this selectively. (Yves Orton)

Named Capture Buffers

It is now possible to name capturing parenthesis in a pattern and refer to the captured contents by name. The naming syntax is "(?<NAME>....)". It's possible to backreference to a named buffer with the "\k<NAME>" syntax. In code, the new magical hashes "%+" and "%-" can be used to access the contents of the capture buffers.

Thus, to replace all doubled chars with a single copy, one could write

    s/(?<letter>.)\k<letter>/$+{letter}/g

Only buffers with defined contents will be ``visible'' in the "%+" hash, so it's possible to do something like

    foreach my $name (keys %+) {
        print "content of buffer '$name' is $+{$name}\n";
    }

The "%-" hash is a bit more complete, since it will contain array refs holding values from all capture buffers similarly named, if there should be many of them.

"%+" and "%-" are implemented as tied hashes through the new module "Tie::Hash::NamedCapture".

Users exposed to the .NET regex engine will find that the perl implementation differs in that the numerical ordering of the buffers is sequential, and not ``unnamed first, then named''. Thus in the pattern

   /(A)(?<B>B)(C)(?<D>D)/

$1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer would expect. This is considered a feature. :-) (Yves Orton)

Possessive Quantifiers

Perl now supports the ``possessive quantifier'' syntax of the ``atomic match'' pattern. Basically a possessive quantifier matches as much as it can and never gives any back. Thus it can be used to control backtracking. The syntax is similar to non-greedy matching, except instead of using a '?' as the modifier the '+' is used. Thus "?+", "*+", "++", "{min,max}+" are now legal quantifiers. (Yves Orton)

Backtracking control verbs

The regex engine now supports a number of special-purpose backtrack control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL) and (*ACCEPT). See perlre for their descriptions. (Yves Orton)

Relative backreferences

A new syntax "\g{N}" or "\gN" where ``N'' is a decimal integer allows a safer form of back-reference notation as well as allowing relative backreferences. This should make it easier to generate and embed patterns that contain backreferences. See ``Capture buffers'' in perlre. (Yves Orton)

\K escape

The functionality of Jeff Pinyan's module Regexp::Keep has been added to the core. In regular expressions you can now use the special escape "\K" as a way to do something like floating length positive lookbehind. It is also useful in substitutions like:

  s/(foo)bar/$1/g

that can now be converted to

  s/foo\Kbar//g

which is much more efficient. (Yves Orton)

Vertical and horizontal whitespace, and linebreak

Regular expressions now recognize the "\v" and "\h" escapes that match vertical and horizontal whitespace, respectively. "\V" and "\H" logically match their complements.

"\R" matches a generic linebreak, that is, vertical whitespace, plus the multi-character sequence "\x0D\x0A".

say()

Lexical $_

    my $_;

The operations that default on $_ will use the lexically-scoped version of $_ when it exists, instead of the global $_.

In a "map" or a "grep" block, if $_ was previously my'ed, then the $_ inside the block is lexical as well (and scoped to the block).

In a scope where $_ has been lexicalized, you can still have access to the global version of $_ by using $::_, or, more simply, by overriding the lexical declaration with "our $_". (Rafael Garcia-Suarez)  

The _ prototype

This has a small incompatible consequence: the prototype() function has been adjusted to return "_" for some built-ins in appropriate cases (for example, "prototype('CORE::rmdir')"). (Rafael Garcia-Suarez)  

UNITCHECK blocks

"CHECK" and "INIT" blocks, while useful for some specialized purposes, are always executed at the transition between the compilation and the execution of the main program, and thus are useless whenever code is loaded at runtime. On the other hand, "UNITCHECK" blocks are executed just after the unit which defined them has been compiled. See perlmod for more information. (Alex Gough)  

New Pragma, mro

Note that, due to changes in the implementation of class hierarchy search, code that used to undef the *ISA glob will most probably break. Anyway, undef'ing *ISA had the side-effect of removing the magic on the @ISA array and should not have been done in the first place. Also, the cache *::ISA::CACHE:: no longer exists; to force reset the @ISA cache, you now need to use the "mro" API, or more simply to assign to @ISA (e.g. with "@ISA = @ISA").  

readdir() may return a short filename on Windows

Similarly, $^X, @INC, and $ENV{PATH} are preprocessed at startup to make sure all paths are valid in the ANSI codepage (if possible).

The Win32::GetLongPathName() function now returns the UTF-8 encoded correct long file name instead of using replacement characters to force the name into the ANSI codepage. The new Win32::GetANSIPathName() function can be used to turn a long pathname into a short one only if the long one cannot be represented in the ANSI codepage.

Many other functions in the "Win32" module have been improved to accept UTF-8 encoded arguments. Please see Win32 for details.  

readpipe() is now overridable

Default argument for readline()

state() variables

To use state variables, one needs to enable them by using

    use feature 'state';

or by using the "-E" command-line switch in one-liners. See ``Persistent variables via state()'' in perlsub.  

Stacked filetest operators

UNIVERSAL::DOES()

See ``$obj->DOES( ROLE )'' in UNIVERSAL.  

Formats

Byte-order modifiers for pack() and unpack()

no VERSION

chdir, chmod and chown on filehandles

OS groups

Recursive sort subs

Exceptions in constant folding

Source filters in @INC

New internal variables

${^RE_DEBUG_FLAGS}

This variable controls what debug flags are in effect for the regular expression engine when running under "use re "debug"". See re for details.

${^CHILD_ERROR_NATIVE}

This variable gives the native status returned by the last pipe close, backtick command, successful call to wait() or waitpid(), or from the system() operator. See perlrun for details. (Contributed by Gisle Aas.)

${^RE_TRIE_MAXBUF}

See ``Trie optimisation of literal string alternations''.

${^WIN32_SLOPPY_STAT}

See ``Sloppy stat on Windows''.

Miscellaneous

"mkdir()" without arguments now defaults to $_.

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

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

UCD 5.0.0

MAD

kill() on Windows

Incompatible Changes

Packing and UTF-8 strings

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

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

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

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

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

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

Byte/character count feature in unpack()

The $* and $# variables have been removed

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

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

substr() lvalues are no longer fixed-length

Parsing of -f _

:unique

Effect of pragmas in eval

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

chdir FOO

Handling of .pmc files

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

$^V is now a version object instead of a v-string

@- and @+ in patterns

$AUTOLOAD can now be tainted

Tainting and printf

undef and signal handlers

strictures and dereferencing in defined()

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

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

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

(?p{}) has been removed

Pseudo-hashes have been removed

Removal of the bytecode compiler and of perlcc

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

Removal of the JPL

Recursive inheritance detected earlier

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

Modules and Pragmata

Upgrading individual core modules

Pragmata Changes

feature

The new pragma "feature" is used to enable new features that might break old code. See "The "feature" pragma" above.

mro

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

Scoping of the sort pragma

The "sort" pragma is now lexically scoped. Its effect used to be global.

Scoping of bignum, bigint, bigrat

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

base

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

strict and warnings

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

version

The "version" module provides support for version objects.

warnings

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

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

less

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

New modules

*

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

*

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

*

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

*

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

*

"IO::Zlib" is an "IO::"-style interface to "Compress::Zlib".

*

"Archive::Tar" is a module to manipulate "tar" archives.

*

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

*

"ExtUtils::CBuilder" and "ExtUtils::ParseXS" have been added.

*

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

*

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

*

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

*

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

*

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

*

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

*

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

*

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

*

"Term::UI" simplifies the task to ask questions at a terminal prompt.

*

"Object::Accessor" provides an interface to create per-object accessors.

*

"Module::Pluggable" is a simple framework to create modules that accept pluggable sub-modules.

*

"Module::Load::Conditional" provides simple ways to query and possibly load installed modules.

*

"Time::Piece" provides an object oriented interface to time functions, overriding the built-ins localtime() and gmtime().

*

"IPC::Cmd" helps to find and run external commands, possibly interactively.

*

"File::Fetch" provide a simple generic file fetching mechanism.

*

"Log::Message" and "Log::Message::Simple" are used by the log facility of "CPANPLUS".

*

"Archive::Extract" is a generic archive extraction mechanism for .tar (plain, gziped or bzipped) or .zip files.

*

"CPANPLUS" provides an API and a command-line tool to access the CPAN mirrors.

*

"Pod::Escapes" provides utilities that are useful in decoding Pod E<...> sequences.

*

"Pod::Simple" is now the backend for several of the Pod-related modules included with Perl.

Selected Changes to Core Modules

Attribute::Handlers

"Attribute::Handlers" can now report the caller's file and line number. (David Feldman)

All interpreted attributes are now passed as array references. (Damian Conway)

B::Lint

"B::Lint" is now based on "Module::Pluggable", and so can be extended with plugins. (Joshua ben Jore)

B

It's now possible to access the lexical pragma hints ("%^H") by using the method B::COP::hints_hash(). It returns a "B::RHE" object, which in turn can be used to get a hash reference via the method B::RHE::HASH(). (Joshua ben Jore)

Thread

As the old 5005thread threading model has been removed, in favor of the ithreads scheme, the "Thread" module is now a compatibility wrapper, to be used in old code only. It has been removed from the default list of dynamic extensions.

Utility Changes

perl -d

The Perl debugger can now save all debugger commands for sourcing later; notably, it can now emulate stepping backwards, by restarting and rerunning all bar the last command from a saved command history.

It can also display the parent inheritance tree of a given class, with the "i" command.

ptar

"ptar" is a pure perl implementation of "tar" that comes with "Archive::Tar".

ptardiff

"ptardiff" is a small utility used to generate a diff between the contents of a tar archive and a directory tree. Like "ptar", it comes with "Archive::Tar".

shasum

"shasum" is a command-line utility, used to print or to check SHA digests. It comes with the new "Digest::SHA" module.

corelist

The "corelist" utility is now installed with perl (see ``New modules'' above).

h2ph and h2xs

"h2ph" and "h2xs" have been made more robust with regard to ``modern'' C code.

"h2xs" implements a new option "--use-xsloader" to force use of "XSLoader" even in backwards compatible modules.

The handling of authors' names that had apostrophes has been fixed.

Any enums with negative values are now skipped.

perlivp

"perlivp" no longer checks for *.ph files by default. Use the new "-a" option to run all tests.

find2perl

"find2perl" now assumes "-print" as a default action. Previously, it needed to be specified explicitly.

Several bugs have been fixed in "find2perl", regarding "-exec" and "-eval". Also the options "-path", "-ipath" and "-iname" have been added.

config_data

"config_data" is a new utility that comes with "Module::Build". It provides a command-line interface to the configuration of Perl modules that use Module::Build's framework of configurability (that is, *::ConfigData modules that contain local configuration information for their parent modules.)

cpanp

"cpanp", the CPANPLUS shell, has been added. ("cpanp-run-perl", a helper for CPANPLUS operation, has been added too, but isn't intended for direct use).

cpan2dist

"cpan2dist" is a new utility that comes with CPANPLUS. It's a tool to create distributions (or packages) from CPAN modules.

pod2html

The output of "pod2html" has been enhanced to be more customizable via CSS. Some formatting problems were also corrected. (Jari Aalto)

New Documentation

The new perlglossary manpage is a glossary of terms used in the Perl documentation, technical and otherwise, kindly provided by O'Reilly Media, Inc.

The perlreguts manpage, courtesy of Yves Orton, describes internals of the Perl regular expression engine.

The perlreapi manpage describes the interface to the perl interpreter used to write pluggable regular expression engines (by var Arnfjo.r- Bjarmason).

The perlunitut manpage is an tutorial for programming with Unicode and string encodings in Perl, courtesy of Juerd Waalboer.

A new manual page, perlunifaq (the Perl Unicode FAQ), has been added (Juerd Waalboer).

The perlcommunity manpage gives a description of the Perl community on the Internet and in real life. (Edgar ``Trizor'' Bering)

The CORE manual page documents the "CORE::" namespace. (Tels)

The long-existing feature of "/(?{...})/" regexps setting $_ and pos() is now documented.  

Performance Enhancements

In-place sorting

Likewise, "reverse sort ..." is now optimized to sort in reverse, avoiding the generation of a temporary intermediate list.  

Lexical array access

XS-assisted SWASHGET

Constant subroutines

Several of the core modules have been converted to use this feature for their system dependent constants - as a result "use POSIX;" now takes about 200K less memory.  

PERL_DONT_CREATE_GVSV

Weak references are cheaper

sort() enhancements

Memory optimisations

UTF-8 cache optimisation

Sloppy stat on Windows

Regular expressions optimisations

Engine de-recursivised

The regular expression engine is no longer recursive, meaning that patterns that used to overflow the stack will either die with useful explanations, or run to completion, which, since they were able to blow the stack before, will likely take a very long time to happen. If you were experiencing the occasional stack overflow (or segfault) and upgrade to discover that now perl apparently hangs instead, look for a degenerate regex. (Dave Mitchell)

Single char char-classes treated as literals

Classes of a single character are now treated the same as if the character had been used as a literal, meaning that code that uses char-classes as an escaping mechanism will see a speedup. (Yves Orton)

Trie optimisation of literal string alternations

Alternations, where possible, are optimised into more efficient matching structures. String literal alternations are merged into a trie and are matched simultaneously. This means that instead of O(N) time for matching N alternations at a given point, the new code performs in O(1) time. A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune this optimization. (Yves Orton)

Note: Much code exists that works around perl's historic poor performance on alternations. Often the tricks used to do so will disable the new optimisations. Hopefully the utility modules used for this purpose will be educated about these new optimisations.

Aho-Corasick start-point optimisation

When a pattern starts with a trie-able alternation and there aren't better optimisations available, the regex engine will use Aho-Corasick matching to find the start point. (Yves Orton)

Installation and Configuration Improvements

Configuration improvements

-Dusesitecustomize

Run-time customization of @INC can be enabled by passing the "-Dusesitecustomize" flag to Configure. When enabled, this will make perl run $sitelibexp/sitecustomize.pl before anything else. This script can then be set up to add additional entries to @INC.

Relocatable installations

There is now Configure support for creating a relocatable perl tree. If you Configure with "-Duserelocatableinc", then the paths in @INC (and everything else in %Config) can be optionally located via the path of the perl executable.

That means that, if the string ".../" is found at the start of any path, it's substituted with the directory of $^X. So, the relocation can be configured on a per-directory basis, although the default with "-Duserelocatableinc" is that everything is relocated. The initial install is done to the original configured prefix.

strlcat() and strlcpy()

The configuration process now detects whether strlcat() and strlcpy() are available. When they are not available, perl's own version is used (from Russ Allbery's public domain implementation). Various places in the perl interpreter now use them. (Steve Peters)

d_pseudofork and d_printf_format_null

A new configuration variable, available as $Config{d_pseudofork} in the Config module, has been added, to distinguish real fork() support from fake pseudofork used on Windows platforms.

A new configuration variable, "d_printf_format_null", has been added, to see if printf-like formats are allowed to be NULL.

Configure help

"Configure -h" has been extended with the most commonly used options.

Compilation improvements

Parallel build

Parallel makes should work properly now, although there may still be problems if "make test" is instructed to run in parallel.

Borland's compilers support

Building with Borland's compilers on Win32 should work more smoothly. In particular Steve Hay has worked to side step many warnings emitted by their compilers and at least one C compiler internal error.

Static build on Windows

Perl extensions on Windows now can be statically built into the Perl DLL.

Also, it's now possible to build a "perl-static.exe" that doesn't depend on the Perl DLL on Win32. See the Win32 makefiles for details. (Vadim Konovalov)

ppport.h files

All ppport.h files in the XS modules bundled with perl are now autogenerated at build time. (Marcus Holland-Moritz)

C++ compatibility

Efforts have been made to make perl and the core XS modules compilable with various C++ compilers (although the situation is not perfect with some of the compilers on some of the platforms tested.)

Support for Microsoft 64-bit compiler

Support for building perl with Microsoft's 64-bit compiler has been improved. (ActiveState)

Visual C++

Perl can now be compiled with Microsoft Visual C++ 2005 (and 2008 Beta 2).

Win32 builds

All win32 builds (MS-Win, WinCE) have been merged and cleaned up.

Installation improvements

Module auxiliary files

README files and changelogs for CPAN modules bundled with perl are no longer installed.

New Improved Platforms

Many improvements have been made towards making Perl work correctly on z/OS.

Perl has been reported to work on DragonFlyBSD and MidnightBSD.

Perl has also been reported to work on NexentaOS ( http://www.gnusolaris.org/ ).

The VMS port has been improved. See perlvms.

Support for Cray XT4 Catamount/Qk has been added. See hints/catamount.sh in the source code distribution for more information.

Vendor patches have been merged for RedHat and Gentoo.

DynaLoader::dl_unload_file() now works on Windows.  

Selected Bug Fixes

strictures in regexp-eval blocks

"strict" wasn't in effect in regexp-eval blocks ("/(?{...})/").

Calling CORE::require()

CORE::require() and CORE::do() were always parsed as require() and do() when they were overridden. This is now fixed.

Subscripts of slices

You can now use a non-arrowed form for chained subscripts after a list slice, like in:

    ({foo => "bar"})[0]{foo}

This used to be a syntax error; a "->" was required.

no warnings 'category' works correctly with -w

Previously when running with warnings enabled globally via "-w", selective disabling of specific warning categories would actually turn off all warnings. This is now fixed; now "no warnings 'io';" will only turn off warnings in the "io" class. Previously it would erroneously turn off all warnings.

threads improvements

Several memory leaks in ithreads were closed. Also, ithreads were made less memory-intensive.

"threads" is now a dual-life module, also available on CPAN. It has been expanded in many ways. A kill() method is available for thread signalling. One can get thread status, or the list of running or joinable threads.

A new "threads->exit()" method is used to exit from the application (this is the default for the main thread) or from the current thread only (this is the default for all other threads). On the other hand, the exit() built-in now always causes the whole application to terminate. (Jerry D. Hedden)

chr() and negative values

chr() on a negative value now gives "\x{FFFD}", the Unicode replacement character, unless when the "bytes" pragma is in effect, where the low eight bits of the value are used.

PERL5SHELL and tainting

On Windows, the PERL5SHELL environment variable is now checked for taintedness. (Rafael Garcia-Suarez)

Using *FILE{IO}

"stat()" and "-X" filetests now treat *FILE{IO} filehandles like *FILE filehandles. (Steve Peters)

Overloading and reblessing

Overloading now works when references are reblessed into another class. Internally, this has been implemented by moving the flag for ``overloading'' from the reference to the referent, which logically is where it should always have been. (Nicholas Clark)

Overloading and UTF-8

A few bugs related to UTF-8 handling with objects that have stringification overloaded have been fixed. (Nicholas Clark)

eval memory leaks fixed

Traditionally, "eval 'syntax error'" has leaked badly. Many (but not all) of these leaks have now been eliminated or reduced. (Dave Mitchell)

Random device on Windows

In previous versions, perl would read the file /dev/urandom if it existed when seeding its random number generator. That file is unlikely to exist on Windows, and if it did would probably not contain appropriate data, so perl no longer tries to read it on Windows. (Alex Davies)

PERLIO_DEBUG

The "PERLIO_DEBUG" environment variable no longer has any effect for setuid scripts and for scripts run with -T.

Moreover, with a thread-enabled perl, using "PERLIO_DEBUG" could lead to an internal buffer overflow. This has been fixed.

PerlIO::scalar and read-only scalars

PerlIO::scalar will now prevent writing to read-only scalars. Moreover, seek() is now supported with PerlIO::scalar-based filehandles, the underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)

study() and UTF-8

study() never worked for UTF-8 strings, but could lead to false results. It's now a no-op on UTF-8 data. (Yves Orton)

Critical signals

The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an ``unsafe'' manner (contrary to other signals, that are deferred until the perl interpreter reaches a reasonably stable state; see ``Deferred Signals (Safe Signals)'' in perlipc). (Rafael)

@INC-hook fix

When a module or a file is loaded through an @INC-hook, and when this hook has set a filename entry in %INC, __FILE__ is now set for this module accordingly to the contents of that %INC entry. (Rafael)

-t switch fix

The "-w" and "-t" switches can now be used together without messing up which categories of warnings are activated. (Rafael)

Duping UTF-8 filehandles

Duping a filehandle which has the ":utf8" PerlIO layer set will now properly carry that layer on the duped filehandle. (Rafael)

Localisation of hash elements

Localizing a hash element whose key was given as a variable didn't work correctly if the variable was changed while the local() was in effect (as in "local $h{$x}; ++$x"). (Bo Lindbergh)

New or Changed Diagnostics

Use of uninitialized value

Perl will now try to tell you the name of the variable (if any) that was undefined.

Deprecated use of my() in false conditional

A new deprecation warning, Deprecated use of my() in false conditional, has been added, to warn against the use of the dubious and deprecated construct

    my $x if 0;

See perldiag. Use "state" variables instead.

!=~ should be !~

A new warning, "!=~ should be !~", is emitted to prevent this misspelling of the non-matching operator.

Newline in left-justified string

The warning Newline in left-justified string has been removed.

Too late for -T option

The error Too late for ``-T'' option has been reformulated to be more descriptive.

%s variable %s masks earlier declaration

This warning is now emitted in more consistent cases; in short, when one of the declarations involved is a "my" variable:

    my $x;   my $x;     # warns
    my $x;  our $x;     # warns
    our $x;  my $x;     # warns

On the other hand, the following:

    our $x; our $x;

now gives a ""our" variable %s redeclared" warning.

readdir()/closedir()/etc. attempted on invalid dirhandle

These new warnings are now emitted when a dirhandle is used but is either closed or not really a dirhandle.

Opening dirhandle/filehandle %s also as a file/directory

Two deprecation warnings have been added: (Rafael)

    Opening dirhandle %s also as a file
    Opening filehandle %s also as a directory

Use of -P is deprecated

Perl's command-line switch "-P" is now deprecated.

v-string in use/require is non-portable

Perl will warn you against potential backwards compatibility problems with the "use VERSION" syntax.

perl -V

"perl -V" has several improvements, making it more useable from shell scripts to get the value of configuration variables. See perlrun for details.

Changed Internals

When compiling the perl core with gcc, as many gcc warning flags are turned on as is possible on the platform. (This quest for cleanliness doesn't extend to XS code because we cannot guarantee the tidiness of code we didn't write.) Similar strictness flags have been added or tightened for various other C compilers.  

Reordering of SVt_* constants

Elimination of SVt_PVBM

New type SVt_BIND

Removal of CPP symbols

Less space is used by ops

New parser

Also, Dave Mitchell improved the lexer debugging output under "-DT".  

Use of const

Mathoms

AvFLAGS has been removed

av_* changes

$^H and %^H

B:: modules inheritance changed

Anonymous hash and array constructors

Known Problems

Stacked filetest operators won't work when the "filetest" pragma is in effect, because they rely on the stat() buffer "_" being populated, and filetest bypasses stat().  

UTF-8 problems

Platform Specific Problems

Reporting Bugs

If you believe you have an unreported bug, please run the 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 "perl -V", will be sent off to perlbug@perl.org to be analysed by the Perl porting team.  

SEE ALSO

The INSTALL file for how to build Perl.

The README file for general stuff.

The Artistic and Copying files for copyright information.