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NAME
       perl5100delta - what is new for perl 5.10.0

DESCRIPTION
       This document describes the differences between the 5.8.8
       release and the 5.10.0 release.

       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
       The "feature" pragma is used to enable new syntax that
       would break Perl's backwards-compatibility with older
       releases of the language. It's a lexical pragma, like
       "strict" or "warnings".

       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
       -E is equivalent to -e, but it implicitly enables all
       optional features (like "use feature ":5.10"").

   Defined-or operator
       A new operator "//" (defined-or) has been implemented.
       The following expression:

           $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



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       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
       Perl 5 now has a switch statement. It's available when
       "use feature 'switch'" is in effect. This feature
       introduces three new keywords, "given", "when", and
       "default":

           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



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                $                      # 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



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           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()"
       say() is a new built-in, only available when "use feature
       'say'" is in effect, that is similar to print(), but that
       implicitly appends a newline to the printed string. See
       "say" in perlfunc. (Robin Houston)





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   Lexical $_
       The default variable $_ can now be lexicalized, by
       declaring it like any other lexical variable, with a
       simple

           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
       A new prototype character has been added. "_" is
       equivalent to "$" but defaults to $_ if the corresponding
       argument isn't supplied (both "$" and "_" denote a
       scalar). Due to the optional nature of the argument, you
       can only use it at the end of a prototype, or before a
       semicolon.

       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
       "UNITCHECK", a new special code block has been introduced,
       in addition to "BEGIN", "CHECK", "INIT" and "END".

       "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"
       A new pragma, "mro" (for Method Resolution Order) has been
       added. It permits to switch, on a per-class basis, the
       algorithm that perl uses to find inherited methods in case
       of a multiple inheritance hierarchy. The default MRO
       hasn't changed (DFS, for Depth First Search). Another MRO
       is available: the C3 algorithm. See mro for more
       information.  (Brandon Black)



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       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
       The readdir() function may return a "short filename" when
       the long filename contains characters outside the ANSI
       codepage.  Similarly Cwd::cwd() may return a short
       directory name, and glob() may return short names as well.
       On the NTFS file system these short names can always be
       represented in the ANSI codepage.  This will not be true
       for all other file system drivers; e.g. the FAT filesystem
       stores short filenames in the OEM codepage, so some files
       on FAT volumes remain unaccessible through the ANSI APIs.

       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
       The built-in function readpipe() is now overridable.
       Overriding it permits also to override its operator
       counterpart, "qx//" (a.k.a. "``").  Moreover, it now
       defaults to $_ if no argument is provided. (Rafael Garcia-
       Suarez)

   Default argument for readline()
       readline() now defaults to *ARGV if no argument is
       provided. (Rafael Garcia-Suarez)

   state() variables
       A new class of variables has been introduced. State
       variables are similar to "my" variables, but are declared
       with the "state" keyword in place of "my". They're visible
       only in their lexical scope, but their value is
       persistent: unlike "my" variables, they're not undefined
       at scope entry, but retain their previous value. (Rafael
       Garcia-Suarez, Nicholas Clark)



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       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 Private Variables" in perlsub.

   Stacked filetest operators
       As a new form of syntactic sugar, it's now possible to
       stack up filetest operators. You can now write "-f -w -x
       $file" in a row to mean "-x $file && -w _ && -f _". See
       "-X" in perlfunc.

   UNIVERSAL::DOES()
       The "UNIVERSAL" class has a new method, "DOES()". It has
       been added to solve semantic problems with the "isa()"
       method. "isa()" checks for inheritance, while "DOES()" has
       been designed to be overridden when module authors use
       other types of relations between classes (in addition to
       inheritance). (chromatic)

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

   Formats
       Formats were improved in several ways. A new field, "^*",
       can be used for variable-width, one-line-at-a-time text.
       Null characters are now handled correctly in picture
       lines. Using "@#" and "~~" together will now produce a
       compile-time error, as those format fields are
       incompatible.  perlform has been improved, and
       miscellaneous bugs fixed.

   Byte-order modifiers for pack() and unpack()
       There are two new byte-order modifiers, ">" (big-endian)
       and "<" (little-endian), that can be appended to most
       pack() and unpack() template characters and groups to
       force a certain byte-order for that type or group.  See
       "pack" in perlfunc and perlpacktut for details.

   "no VERSION"
       You can now use "no" followed by a version number to
       specify that you want to use a version of perl older than
       the specified one.

   "chdir", "chmod" and "chown" on filehandles
       "chdir", "chmod" and "chown" can now work on filehandles
       as well as filenames, if the system supports respectively
       "fchdir", "fchmod" and "fchown", thanks to a patch
       provided by Gisle Aas.

   OS groups
       $( and $) now return groups in the order where the OS
       returns them, thanks to Gisle Aas. This wasn't previously
       the case.



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   Recursive sort subs
       You can now use recursive subroutines with sort(), thanks
       to Robin Houston.

   Exceptions in constant folding
       The constant folding routine is now wrapped in an
       exception handler, and if folding throws an exception
       (such as attempting to evaluate 0/0), perl now retains the
       current optree, rather than aborting the whole program.
       Without this change, programs would not compile if they
       had expressions that happened to generate exceptions, even
       though those expressions were in code that could never be
       reached at runtime. (Nicholas Clark, Dave Mitchell)

   Source filters in @INC
       It's possible to enhance the mechanism of subroutine hooks
       in @INC by adding a source filter on top of the filehandle
       opened and returned by the hook. This feature was planned
       a long time ago, but wasn't quite working until now. See
       "require" in perlfunc for details. (Nicholas Clark)

   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 perlvar 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
       "unpack()" now defaults to unpacking the $_ variable.

       "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.



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   UCD 5.0.0
       The copy of the Unicode Character Database included in
       Perl 5 has been updated to version 5.0.0.

   MAD
       MAD, which stands for Miscellaneous Attribute Decoration,
       is a still-in-development work leading to a Perl 5 to Perl
       6 converter. To enable it, it's necessary to pass the
       argument "-Dmad" to Configure. The obtained perl isn't
       binary compatible with a regular perl 5.10, and has space
       and speed penalties; moreover not all regression tests
       still pass with it. (Larry Wall, Nicholas Clark)

   kill() on Windows
       On Windows platforms, "kill(-9, $pid)" now kills a process
       tree.  (On UNIX, this delivers the signal to all processes
       in the same process group.)

Incompatible Changes
   Packing and UTF-8 strings
       The semantics of pack() and unpack() regarding
       UTF-8-encoded data has been changed. Processing is now by
       default character per character instead of byte per byte
       on the underlying encoding. Notably, code that used things
       like "pack("a*", $string)" to see through the encoding of
       string will now simply get back the original $string.
       Packed strings can also get upgraded during processing
       when you store upgraded characters. You can get the old
       behaviour by using "use bytes".

       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



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       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()
       A new unpack() template character, ".", returns the number
       of bytes or characters (depending on the selected encoding
       mode, see above) read so far.

   The $* and $# variables have been removed
       $*, which was deprecated in favor of the "/s" and "/m"
       regexp modifiers, has 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
       The lvalues returned by the three argument form of
       substr() used to be a "fixed length window" on the
       original string. In some cases this could cause surprising
       action at distance or other undefined behaviour. Now the
       length of the window adjusts itself to the length of the
       string assigned to it.

   Parsing of "-f _"
       The identifier "_" is now forced to be a bareword after a
       filetest operator. This solves a number of misparsing
       issues when a global "_" subroutine is defined.

   ":unique"
       The ":unique" attribute has been made a no-op, since its
       current implementation was fundamentally flawed and not
       threadsafe.

   Effect of pragmas in eval
       The compile-time value of the "%^H" hint variable can now
       propagate into eval("")uated code. This makes it more
       useful to implement lexical pragmas.

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

   chdir FOO
       A bareword argument to chdir() is now recognized as a file
       handle.  Earlier releases interpreted the bareword as a



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       directory name.  (Gisle Aas)

   Handling of .pmc files
       An old feature of perl was that before "require" or "use"
       look for a file with a .pm extension, they will first look
       for a similar filename with a .pmc extension. If this file
       is found, it will be loaded in place of any potentially
       existing file ending in a .pm extension.

       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
       $^V can still be used with the %vd format in printf, but
       any character-level operations will now access the string
       representation of the "version" object and not the
       ordinals of a v-string.  Expressions like "substr($^V, 0,
       2)" or "split //, $^V" no longer work and must be
       rewritten.

   @- and @+ in patterns
       The special arrays "@-" and "@+" are no longer
       interpolated in regular expressions. (Sadahiro Tomoyuki)

   $AUTOLOAD can now be tainted
       If you call a subroutine by a tainted name, and if it
       defers to an AUTOLOAD function, then $AUTOLOAD will be
       (correctly) tainted.  (Rick Delaney)

   Tainting and printf
       When perl is run under taint mode, "printf()" and
       "sprintf()" will now reject any tainted format argument.
       (Rafael Garcia-Suarez)

   undef and signal handlers
       Undefining or deleting a signal handler via "undef
       $SIG{FOO}" is now equivalent to setting it to 'DEFAULT'.
       (Rafael Garcia-Suarez)

   strictures and dereferencing in defined()
       "use strict 'refs'" was ignoring taking a hard reference
       in an argument to defined(), as in :

           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)"



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       are discouraged constructs anyway.)  (Nicholas Clark)

   "(?p{})" has been removed
       The regular expression construct "(?p{})", which was
       deprecated in perl 5.8, has been removed. Use "(??{})"
       instead. (Rafael Garcia-Suarez)

   Pseudo-hashes have been removed
       Support for pseudo-hashes has been removed from Perl 5.9.
       (The "fields" pragma remains here, but uses an alternate
       implementation.)

   Removal of the bytecode compiler and of perlcc
       "perlcc", the byteloader and the supporting modules (B::C,
       B::CC, B::Bytecode, etc.) are no longer distributed with
       the perl sources. Those experimental tools have never
       worked reliably, and, due to the lack of volunteers to
       keep them in line with the perl interpreter developments,
       it was decided to remove them instead of shipping a broken
       version of those.  The last version of those modules can
       be found with perl 5.9.4.

       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
       The JPL (Java-Perl Lingo) has been removed from the perl
       sources tarball.

   Recursive inheritance detected earlier
       Perl will now immediately throw an exception if you modify
       any package's @ISA in such a way that it would cause
       recursive inheritance.

       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
       Even more core modules are now also available separately
       through the CPAN.  If you wish to update one of these
       modules, you don't need to wait for a new perl release.
       From within the cpan shell, running the 'r' command will
       report on modules with upgrades available.  See "perldoc
       CPAN" for more information.

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




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       "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
       o   "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.

       o   "Module::CoreList", by Richard Clamp, is a small handy



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           module that tells you what versions of core modules
           ship with any versions of Perl 5. It comes with a
           command-line frontend, "corelist".

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

       o   "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).

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

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

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

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

       o   "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.

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

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

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

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

       o   "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.

       o   "Locale::Maketext::Simple", needed by CPANPLUS, is a
           simple wrapper around "Locale::Maketext::Lexicon".



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           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.

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

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

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

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

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

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

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

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

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

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

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

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

       o   "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)




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       "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



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           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 perlpragma manpage documents how to write one's own
       lexical pragmas in pure Perl (something that is possible
       starting with 5.9.4).

       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



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       engines (by var Arnfjoer` 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
       Sorting arrays in place ("@a = sort @a") is now optimized
       to avoid making a temporary copy of the array.

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

   Lexical array access
       Access to elements of lexical arrays via a numeric
       constant between 0 and 255 is now faster. (This used to be
       only the case for global arrays.)

   XS-assisted SWASHGET
       Some pure-perl code that perl was using to retrieve
       Unicode properties and transliteration mappings has been
       reimplemented in XS.

   Constant subroutines
       The interpreter internals now support a far more memory
       efficient form of inlineable constants. Storing a
       reference to a constant value in a symbol table is
       equivalent to a full typeglob referencing a constant
       subroutine, but using about 400 bytes less memory. This
       proxy constant subroutine is automatically upgraded to a
       real typeglob with subroutine if necessary.  The approach
       taken is analogous to the existing space optimisation for
       subroutine stub declarations, which are stored as plain
       scalars in place of the full typeglob.

       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.




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   "PERL_DONT_CREATE_GVSV"
       The new compilation flag "PERL_DONT_CREATE_GVSV",
       introduced as an option in perl 5.8.8, is turned on by
       default in perl 5.9.3. It prevents perl from creating an
       empty scalar with every new typeglob. See perl589delta for
       details.

   Weak references are cheaper
       Weak reference creation is now O(1) rather than O(n),
       courtesy of Nicholas Clark. Weak reference deletion
       remains O(n), but if deletion only happens at program
       exit, it may be skipped completely.

   sort() enhancements
       Salvador Fandin~o provided improvements to reduce the
       memory usage of "sort" and to speed up some cases.

   Memory optimisations
       Several internal data structures (typeglobs, GVs, CVs,
       formats) have been restructured to use less memory.
       (Nicholas Clark)

   UTF-8 cache optimisation
       The UTF-8 caching code is now more efficient, and used
       more often.  (Nicholas Clark)

   Sloppy stat on Windows
       On Windows, perl's stat() function normally opens the file
       to determine the link count and update attributes that may
       have been changed through hard links. Setting
       ${^WIN32_SLOPPY_STAT} to a true value speeds up stat() by
       not performing this operation. (Jan Dubois)

   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



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           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)





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       "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).





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       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 Or Improved Platforms
       Perl has been reported to work on Symbian OS. See
       perlsymbian for more information.

       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



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           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



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           /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



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           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




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       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
       In general, the source code of perl has been refactored,
       tidied up, and optimized in many places. Also, memory
       management and allocation has been improved in several
       points.

       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
       The relative ordering of constants that define the various
       types of "SV" have changed; in particular, "SVt_PVGV" has
       been moved before "SVt_PVLV", "SVt_PVAV", "SVt_PVHV" and
       "SVt_PVCV".  This is unlikely to make any difference
       unless you have code that explicitly makes assumptions
       about that ordering. (The inheritance hierarchy of "B::*"
       objects has been changed to reflect this.)

   Elimination of SVt_PVBM
       Related to this, the internal type "SVt_PVBM" has been
       been removed. This dedicated type of "SV" was used by the
       "index" operator and parts of the regexp engine to
       facilitate fast Boyer-Moore matches. Its use internally
       has been replaced by "SV"s of type "SVt_PVGV".

   New type SVt_BIND
       A new type "SVt_BIND" has been added, in readiness for the
       project to implement Perl 6 on 5. There deliberately is no
       implementation yet, and they cannot yet be created or
       destroyed.

   Removal of CPP symbols
       The C preprocessor symbols "PERL_PM_APIVERSION" and
       "PERL_XS_APIVERSION", which were supposed to give the
       version number of the oldest perl binary-compatible (resp.
       source-compatible) with the present one, were not used,
       and sometimes had misleading values. They have been
       removed.



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   Less space is used by ops
       The "BASEOP" structure now uses less space. The "op_seq"
       field has been removed and replaced by a single bit bit-
       field "op_opt". "op_type" is now 9 bits long.
       (Consequently, the "B::OP" class doesn't provide an "seq"
       method anymore.)

   New parser
       perl's parser is now generated by bison (it used to be
       generated by byacc.) As a result, it seems to be a bit
       more robust.

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

   Use of "const"
       Andy Lester supplied many improvements to determine which
       function parameters and local variables could actually be
       declared "const" to the C compiler. Steve Peters provided
       new *_set macros and reworked the core to use these rather
       than assigning to macros in LVALUE context.

   Mathoms
       A new file, mathoms.c, has been added. It contains
       functions that are no longer used in the perl core, but
       that remain available for binary or source compatibility
       reasons. However, those functions will not be compiled in
       if you add "-DNO_MATHOMS" in the compiler flags.

   "AvFLAGS" has been removed
       The "AvFLAGS" macro has been removed.

   "av_*" changes
       The "av_*()" functions, used to manipulate arrays, no
       longer accept null "AV*" parameters.

   $^H and %^H
       The implementation of the special variables $^H and %^H
       has changed, to allow implementing lexical pragmas in pure
       Perl.

   B:: modules inheritance changed
       The inheritance hierarchy of "B::" modules has changed;
       "B::NV" now inherits from "B::SV" (it used to inherit from
       "B::IV").

   Anonymous hash and array constructors
       The anonymous hash and array constructors now take 1 op in
       the optree instead of 3, now that pp_anonhash and
       pp_anonlist return a reference to an hash/array when the
       op is flagged with OPf_SPECIAL. (Nicholas Clark)

Known Problems
       There's still a remaining problem in the implementation of



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       the lexical $_: it doesn't work inside "/(?{...})/"
       blocks. (See the TODO test in t/op/mydef.t.)

       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
       The handling of Unicode still is unclean in several
       places, where it's dependent on whether a string is
       internally flagged as UTF-8. This will be made more
       consistent in perl 5.12, but that won't be possible
       without a certain amount of backwards incompatibility.

Platform Specific Problems
       When compiled with g++ and thread support on Linux, it's
       reported that the $! stops working correctly. This is
       related to the fact that the glibc provides two
       strerror_r(3) implementation, and perl selects the wrong
       one.

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://rt.perl.org/rt3/ .  There may also be information
       at http://www.perl.org/ , the Perl Home Page.

       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 Changes file and the perl590delta to perl595delta man
       pages for exhaustive details on what changed.

       The INSTALL file for how to build Perl.

       The README file for general stuff.

       The Artistic and Copying files for copyright information.













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