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

           $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

   Switch and Smart Match operator
       Perl 5 now has a switch statement. It's available when "use feature

       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

           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


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


           $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

       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:


           that can now be converted to


           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".

       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)

       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
       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

   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)

       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.

       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 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

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

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

   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

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

           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.)

           See "Trie optimisation of literal string alternations".

           See "Sloppy stat on Windows".

       "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.

   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

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 range 0..255, and not respect the string

       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

   The $* and $# variables have been removed
       $*, which was deprecated in favor of the "/s" and "/m" regexp
       modifiers, has been removed.

   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.

       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

       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 directory name.  (Gisle

   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

   @- 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

   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
       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
       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

   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.

   warnings::enabled and warnings::warnif changed to favor users of modules
       The behaviour in 5.10.x favors the person using the module; The
       behaviour in 5.8.x favors the module writer;

       Assume the following code:

         main calls Foo::Bar::baz()
         Foo::Bar inherits from Foo::Base
         Foo::Bar::baz() calls Foo::Base::_bazbaz()
         Foo::Base::_bazbaz() calls: warnings::warnif('substr', 'some warning

       On 5.8.x, the code warns when Foo::Bar contains "use warnings;" It does
       not matter if Foo::Base or main have warnings enabled to disable the
       "perldoc CPAN" for more information.

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

           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

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

           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)

           The "version" module provides support for version objects.

           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" 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   "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

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

       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". 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

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

       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

       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" 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" 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)

           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" is a pure perl implementation of "tar" that comes with

           "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" is a command-line utility, used to print or to check SHA

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

           Any enums with negative values are now skipped.

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

           "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

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

           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 engines (by var Arnfjoer`

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

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

   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.

       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)

           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

       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
           Run-time customization of @INC can be enabled by passing the
           "-Dusesitecustomize" flag to Configure. When enabled, this will
           make perl run $sitelibexp/ 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)

   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

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

       Many improvements have been made towards making Perl work correctly on

       Perl has been reported to work on DragonFlyBSD and MidnightBSD.
       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

       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)

           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.

       "-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)
           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

       "%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
       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
       Related to this, the internal type "SVt_PVBM" has 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.

   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.

       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

       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 .  There may also be information at , 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 to be analysed by
       the Perl porting team.

       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.

perl v5.14.2                      2011-09-26                  PERL5100DELTA(1)
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