This document describes differences between the 5.9.4 and the 5.9.5
       development releases. See perl590delta, perl591delta, perl592delta,
       perl593delta and perl594delta for the differences between 5.8.0 and

Incompatible Changes
   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)

   strictures and array/hash dereferencing in defined()
       "defined @$foo" and "defined %$bar" are now subject to "strict 'refs'"
       (that is, $foo and $bar shall be proper references there.)  (Nicholas

       (However, "defined(@foo)" and "defined(%bar)" are discouraged
       constructs anyway.)

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

   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 Linguo) 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
           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

           Note, users experienced with PCRE will find that the Perl
           implementation of this feature differs from the PCRE one in that it
           is possible to backtrack into a recursed pattern, whereas in PCRE
           the recursion is atomic or "possessive" in nature. (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, one could write


           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

           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

           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. You can now use in regular expressions 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 "_" prototype
       A new prototype character has been added. "_" is equivalent to "$" (it
       denotes a scalar), but defaults to $_ if the corresponding argument
       isn't supplied. 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)

   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
       readline() now defaults to *ARGV if no argument is provided. (Rafael)

   UCD 5.0.0
       The copy of the Unicode Character Database included in Perl 5.9 has
       been updated to version 5.0.0.

   Smart match
       The smart match operator ("~~") is now available by default (you don't
       need to enable it with "use feature" any longer). (Michael G Schwern)

   Implicit loading of "feature"
       The "feature" pragma is now implicitly loaded when you require a
       minimal perl version (with the "use VERSION" construct) greater than,
       or equal to, 5.9.5.

Modules and Pragmas
   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.

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

       Many bugs have been fixed; noteworthy are comparisons with NaN, which
       no longer warn about undef values.

       The following things are new:

           The config() method now also supports the calling-style
           "config('lib')" in addition to "config()->{'lib'}".

           Upon import, using "lib => 'Foo'" now warns if the low-level
           library cannot be found. To suppress the warning, you can use "try
           => 'Foo'" instead. To convert the warning into a die, use "only =>
           'Foo'" instead.

       roundmode common
           A rounding mode of "common" is now supported.

       Also, support for the following methods has been added:

       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
           functions, overriding the built-ins localtime() and gmtime().

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

       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.

   Module changes
           The "assertions" pragma, its submodules "assertions::activate" and
           "assertions::compat" and the -A command-line switch have been
           removed.  The interface was not judged mature enough for inclusion
           in a stable release.

           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)

           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)

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

           "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
       "cpanp", the CPANPLUS shell, has been added. ("cpanp-run-perl", an
       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 manpage, perlunifaq
       A new manual page, perlunifaq (the Perl Unicode FAQ), has been added
       (Juerd Waalboer).

Installation and Configuration Improvements
   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.)

   Visual C++
       Perl now can be compiled with Microsoft Visual C++ 2005.

   Static build on Win32
       It's now possible to build a "perl-static.exe" that doesn't depend on
       to see if printf-like formats are allowed to be NULL.

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

       Much less 'Whoa there' messages.

   64bit systems
       Better detection of 64bit(only) systems, and setting all the (library)
       paths accordingly.

       Perl has been reported to work on MidnightBSD.

       Support for Cray XT4 Catamount/Qk has been added.

       Vendor patches have been merged for RedHat and GenToo.

Selected Bug Fixes
       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

       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)

       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)

       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)

       The "-w" and "-t" switches can now be used together without messing up
       what categories of warnings are activated or not. (Rafael)

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

       Localizing an 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
       Two deprecation warnings have been added: (Rafael)

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

Changed Internals
       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 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                   PERL595DELTA(1)
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