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perl595delta (1)


perl595delta - what is new for perl v5.9.5


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Perl Programmers Reference Guide                  PERL595DELTA(1)

     perl595delta - what is new for perl v5.9.5

     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 5.9.4.

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'.

  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 Clark)

     (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

  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).

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  Removal of the JPL
     The JPL (Java-Perl Linguo) 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.

Core Enhancements
  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

         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

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         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

         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

         "%+" 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


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

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

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

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     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

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

  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 execution of the main program, and thus

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     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)

  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)

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

  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.

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     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:

     bpi(), bcos(), bsin(), batan(), batan2()
     bexp(), bnok()
     from_hex(), from_oct(), and from_bin()

     In addition, the default math-backend (Calc (Perl) and
     FastCalc (XS)) now support storing numbers in parts with 9
     digits instead of 7 on Perls with either 64bit integer or
     long double support. This means math operations scale better
     and are thus faster for really big numbers.

  New Core Modules
     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 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

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         time functions, overriding the built-ins localtime() and

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

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

     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

     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

         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 "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

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         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

     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.)

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  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 "perl59.dll" on Win32. See the Win32 makefiles for
     details.  (Vadim Konovalov)

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

  "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

     "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 Hietaniemi)

     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)

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     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.

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

     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

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
     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).

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.

     See attributes(5) for descriptions of the following

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     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
     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.

     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

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