perl5100delta - what is new for perl 5.10.0


   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
   '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

   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

           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


       $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".

   Optional pre-match and post-match captures with the /p flag
       There is a new flag "/p" for regular expressions.  Using this makes
       the engine preserve a copy of the part of the matched string before
       the matching substring to the new special variable "${^PREMATCH}",
       the part after the matching substring to "${^POSTMATCH}", and the
       matched substring itself to "${^MATCH}".

       Perl is still able to store these substrings to the special
       variables "$`", "$'", $&, but using these variables anywhere in the
       program adds a penalty to all regular expression matches, whereas
       if you use the "/p" flag and the new special variables instead, you
       pay only for the regular expressions where the flag is used.

       For more detail on the new variables, see perlvar; for the use of
       the regular expression flag, see perlop and perlre.

   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)

   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)

   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

   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
   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.

   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.

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

   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

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.

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

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

   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.

   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
   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)" 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
   warning one has to modify Foo::Bar.

   On 5.10.0 and newer, the code warns when main contains "use warnings;"
   It does not matter if Foo::Base or Foo::Bar have warnings enabled to
   disable the warning one has to modify main.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

   Selected Changes to Core Modules
       "Attribute::Handlers" 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
       digests. It comes with the new "Digest::SHA" module.

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

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

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

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

       Any enums with negative values are now skipped.

       "perlivp" 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 Arnfjr

   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

   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 Fandio 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

   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)

   "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

   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.

   Perl has also been reported to work on NexentaOS ( ).

   The VMS port has been improved. See perlvms.

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

   Vendor patches have been merged for RedHat and Gentoo.

   DynaLoader::dl_unload_file() now works on Windows.

Selected Bug Fixes

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

   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)
       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

   "%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
   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 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
   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

Known Problems

   There's still a remaining problem in the implementation of the lexical
   $_: it doesn't work inside "/(?{...})/" blocks. (See the TODO test in

   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.


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