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perl5100delta (1)


perl5100delta - what is new for perl 5.10.0


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Perl Programmers Reference Guide                 PERL5100DELTA(1)

     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

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

     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

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

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

         $a // $b

     is merely equivalent to

        defined $a ? $a : $b

     and the statement

        $c //= $d;

     can now be used instead of

        $c = $d unless defined $c;

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     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 details.

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

         given ($foo) {
             when (/^abc/) { $abc = 1; }
             when (/^def/) { $def = 1; }
             when (/^xyz/) { $xyz = 1; }
             default { $nothing = 1; }

     A more complete description of how Perl matches the switch
     variable against the "when" conditions is given in "Switch
     statements" in perlsyn.

     This kind of match is called smart match, and it's also
     possible to use it outside of switch statements, via the new
     "~~" operator. See "Smart matching in detail" in perlsyn.

     This feature was contributed by Robin Houston.

  Regular expressions
     Recursive Patterns
         It is now possible to write recursive patterns without
         using the "(??{})" construct. This new way is more
         efficient, and in many cases easier to read.

         Each capturing parenthesis can now be treated as an
         independent pattern that can be entered by using the
         "(?PARNO)" syntax ("PARNO" standing for "parenthesis
         number"). For example, the following pattern will match
         nested balanced angle brackets:

              ^                      # start of line
              (                      # start capture buffer 1
                 <                   #   match an opening angle bracket
                 (?:                 #   match one of:
                     (?>             #     don't backtrack over the inside of this group
                         [^<>]+      #       one or more non angle brackets
                     )               #     end non backtracking group
                 |                   #     ... or ...
                     (?1)            #     recurse to bracket 1 and try it again
                 )*                  #   0 or more times.
                 >                   #   match a closing angle bracket

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              )                      # 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

         Thus, to replace all doubled chars with a single copy,
         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

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         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)

     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

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

     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

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     "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.

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     (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-

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

  state() variables
     A new class of variables has been introduced. State
     variables are similar to "my" variables, but are declared
     with the "state" keyword in place of "my". They're visible

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     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

     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 fixed.

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

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

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

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     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 Houston.

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

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

  New internal variables
         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 $_.

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     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 group.)

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

     To be consistent with pack(), the "C0" in unpack() templates
     indicates that the data is to be processed in character
     mode, i.e. character by character; on the contrary, "U0" in
     unpack() indicates UTF-8 mode, where the packed string is
     processed in its UTF-8-encoded Unicode form on a byte by
     byte basis. This is reversed with regard to perl 5.8.X, but
     now consistent between pack() and unpack().

     Moreover, "C0" and "U0" can also be used in pack() templates
     to specify respectively character and byte modes.

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     "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 encoding).

     In practice, that means that pack formats are now encoding-
     neutral, except "C".

     For consistency, "A" in unpack() format now trims all
     Unicode whitespace from the end of the string. Before perl
     5.9.2, it used to strip only the classical ASCII space

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

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

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

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

  substr() lvalues are no longer fixed-length
     The lvalues returned by the three argument form of substr()
     used to be a "fixed length window" on the original string.
     In some cases this could cause surprising action at distance
     or other undefined behaviour. Now the length of the window
     adjusts itself to the length of the string assigned to it.

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

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

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

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

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

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

     Previously, .pmc files were loaded only if more recent than
     the matching .pm file. Starting with 5.9.4, they'll be
     always loaded if they exist.

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

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

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

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

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

  strictures and dereferencing in defined()
     "use strict 'refs'" was ignoring taking a hard reference in

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     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

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

     However the B compiler framework stays supported in the perl
     core, as with the more useful modules it has permitted
     (among others, B::Deparse and B::Concise).

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

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

     Previously, the exception would not occur until Perl
     attempted to make use of the recursive inheritance while
     resolving a method or doing a "$foo->isa($bar)" lookup.

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  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

     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

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"

         This new pragma enables to change the algorithm used to
         resolve inherited methods. See "New Pragma, "mro""

     Scoping of the "sort" pragma
         The "sort" pragma is now lexically scoped. Its effect
         used to be global.

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


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         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

         The "warnings" pragma doesn't load "Carp" anymore. That
         means that code that used "Carp" routines without having
         loaded it at compile time might need to be adjusted;
         typically, the following (faulty) code won't work
         anymore, and will require parentheses to be added after
         the function name:

             use warnings;
             require Carp;
             Carp::confess 'argh';

         "less" now does something useful (or at least it tries
         to). In fact, it has been turned into a lexical pragma.
         So, in your modules, you can now test whether your users
         have requested to use less CPU, or less memory, less
         magic, or maybe even less fat. See less for more.
         (Joshua ben Jore)

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

     o   "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".

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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     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

     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.

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

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

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

         All interpreted attributes are now passed as array
         references. (Damian Conway)

         "B::Lint" is now based on "Module::Pluggable", and so
         can be extended with plugins. (Joshua ben Jore)

     "B" It's now possible to access the lexical pragma hints
         ("%^H") by using the method B::COP::hints_hash(). It
         returns a "B::RHE" object, which in turn can be used to
         get a hash reference via the method B::RHE::HASH().
         (Joshua ben Jore)

         As the old 5005thread threading model has been removed,

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         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 "Archive::Tar".

         "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"

         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.

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         Several bugs have been fixed in "find2perl", regarding
         "-exec" and "-eval". Also the options "-path", "-ipath"
         and "-iname" have been added.

         "config_data" is a new utility that comes with
         "Module::Build". It provides a command-line interface to
         the configuration of Perl modules that use
         Module::Build's framework of configurability (that is,
         *::ConfigData modules that contain local configuration
         information for their parent modules.)

         "cpanp", the CPANPLUS shell, has been added.
         ("cpanp-run-perl", a helper for CPANPLUS operation, has
         been added too, but isn't intended for direct use).

         "cpan2dist" is a new utility that comes with CPANPLUS.
         It's a tool to create distributions (or packages) from
         CPAN modules.

         The output of "pod2html" has been enhanced to be more
         customizable via CSS. Some formatting problems were also
         corrected. (Jari Aalto)

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

     The new perlglossary manpage is a glossary of terms used in
     the Perl documentation, technical and otherwise, kindly
     provided by O'Reilly Media, Inc.

     The perlreguts manpage, courtesy of Yves Orton, describes
     internals of the Perl regular expression engine.

     The perlreapi manpage describes the interface to the perl
     interpreter used to write pluggable regular expression
     engines (by var Arnfjoer` Bjarmason).

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

     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"

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     The CORE manual page documents the "CORE::" namespace.

     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

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

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

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

     Several of the core modules have been converted to use this
     feature for their system dependent constants - as a result
     "use POSIX;" now takes about 200K less memory.

     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

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     O(n), but if deletion only happens at program exit, it may
     be skipped completely.

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

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

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

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

  Regular expressions optimisations
     Engine de-recursivised
         The regular expression engine is no longer recursive,
         meaning that patterns that used to overflow the stack
         will either die with useful explanations, or run to
         completion, which, since they were able to blow the
         stack before, will likely take a very long time to
         happen. If you were experiencing the occasional stack
         overflow (or segfault) and upgrade to discover that now
         perl apparently hangs instead, look for a degenerate
         regex. (Dave Mitchell)

     Single char char-classes treated as literals
         Classes of a single character are now treated the same
         as if the character had been used as a literal, meaning
         that code that uses char-classes as an escaping
         mechanism will see a speedup. (Yves Orton)

     Trie optimisation of literal string alternations
         Alternations, where possible, are optimised into more
         efficient matching structures. String literal
         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

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         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

     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

     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.

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     Configure help
         "Configure -h" has been extended with the most commonly
         used options.

  Compilation improvements
     Parallel build
         Parallel makes should work properly now, although there
         may still be problems if "make test" is instructed to
         run in parallel.

     Borland's compilers support
         Building with Borland's compilers on Win32 should work
         more smoothly. In particular Steve Hay has worked to
         side step many warnings emitted by their compilers and
         at least one C compiler internal error.

     Static build on Windows
         Perl extensions on Windows now can be statically built
         into the Perl DLL.

         Also, it's now possible to build a "perl-static.exe"
         that doesn't depend on the Perl DLL on Win32. See the
         Win32 makefiles for details.  (Vadim Konovalov)

     ppport.h files
         All ppport.h files in the XS modules bundled with perl
         are now autogenerated at build time. (Marcus Holland-

     C++ compatibility
         Efforts have been made to make perl and the core XS
         modules compilable with various C++ compilers (although
         the situation is not perfect with some of the compilers
         on some of the platforms tested.)

     Support for Microsoft 64-bit compiler
         Support for building perl with Microsoft's 64-bit
         compiler has been improved. (ActiveState)

     Visual C++
         Perl can now be compiled with Microsoft Visual C++ 2005
         (and 2008 Beta 2).

     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.

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

     Many improvements have been made towards making Perl work
     correctly on z/OS.

     Perl has been reported to work on DragonFlyBSD and

     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.

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

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

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

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

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

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

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

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

     Random device on Windows
         In previous versions, perl would read the file
         /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)


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         The "PERLIO_DEBUG" environment variable no longer has
         any effect for setuid scripts and for scripts run with

         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

     Critical signals
         The signals SIGILL, SIGBUS and SIGSEGV are now always
         delivered in an "unsafe" manner (contrary to other
         signals, that are deferred until the perl interpreter
         reaches a reasonably stable state; see "Deferred Signals
         (Safe Signals)" in perlipc). (Rafael)

     @INC-hook fix
         When a module or a file is loaded through an @INC-hook,
         and when this hook has set a filename entry in %INC,
         __FILE__ is now set for this module accordingly to the
         contents of that %INC entry. (Rafael)

     "-t" switch fix
         The "-w" and "-t" switches can now be used together
         without messing up which categories of warnings are
         activated. (Rafael)

     Duping UTF-8 filehandles
         Duping a filehandle which has the ":utf8" PerlIO layer
         set will now properly carry that layer on the duped
         filehandle. (Rafael)

     Localisation of hash elements
         Localizing a hash element whose key was given as a
         variable didn't work correctly if the variable was
         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.

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     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

     Too late for "-T" option
         The error Too late for "-T" option has been reformulated
         to be more descriptive.

     "%s" variable %s masks earlier declaration
         This warning is now emitted in more consistent cases; in
         short, when one of the declarations involved is a "my"

             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.

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     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

     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

  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.)

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  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

     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

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

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

     Stacked filetest operators won't work when the "filetest"
     pragma is in effect, because they rely on the stat() buffer
     "_" being populated, and filetest bypasses stat().

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  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

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

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