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perl5110delta (1)


perl5110delta - what is new for perl v5.11.0


Please see following description for synopsis


Perl Programmers Reference Guide                 PERL5110DELTA(1)

     perl5110delta - what is new for perl v5.11.0

     This document describes differences between the 5.10.0
     release and the 5.11.0 development release.

Incompatible Changes
  Unicode interpretation of \w, \d, \s, and the POSIX character
     classes redefined.
     Previous versions of Perl tried to map POSIX style character
     class definitions onto Unicode property names so that
     patterns would "dwim" when matches were made against latin-1
     or unicode strings. This proved to be a mistake, breaking
     character class negation, causing forward compatibility
     problems (as Unicode keeps updating their property
     definitions and adding new characters), and other problems.

     Therefore we have now defined a new set of artificial
     "unicode" property names which will be used to do unicode
     matching of patterns using POSIX style character classes and
     perl short-form escape character classes like \w and \d.

     The key change here is that \d will no longer match every
     digit in the unicode standard (there are thousands) nor will
     \w match every word character in the standard, instead they
     will match precisely their POSIX or Perl definition.

     Those needing to match based on Unicode properties can
     continue to do so by using the \p{} syntax to match
     whichever property they like, including the new artificial

     NOTE: This is a backwards incompatible no-warning change in
     behaviour. If you are upgrading and you process large
     volumes of text look for POSIX and Perl style character
     classes and change them to the relevent property name (by
     removing the word 'Posix' from the current name).

     The following table maps the POSIX character class names,
     the escapes and the old and new Unicode property mappings:

         POSIX  Esc  Class               New-Property  ! Old-Property
         alnum       [0-9A-Za-z]         IsPosixAlnum  ! IsAlnum
         alpha       [A-Za-z]            IsPosixAlpha  ! IsAlpha
         ascii       [\000-\177]         IsASCII       = IsASCII
         blank       [\011 ]             IsPosixBlank  !
         cntrl       [\0-\37\177]        IsPosixCntrl  ! IsCntrl
         digit   \d  [0-9]               IsPosixDigit  ! IsDigit
         graph       [!-~]               IsPosixGraph  ! IsGraph
         lower       [a-z]               IsPosixLower  ! IsLower

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         print       [ -~]               IsPosixPrint  ! IsPrint
         punct       [!-/:-@[-`{-~]      IsPosixPunct  ! IsPunct
         space       [\11-\15 ]          IsPosixSpace  ! IsSpace
                 \s  [\11\12\14\15 ]     IsPerlSpace   ! IsSpacePerl
         upper       [A-Z]               IsPosixUpper  ! IsUpper
         word    \w  [0-9A-Z_a-z]        IsPerlWord    ! IsWord
         xdigit      [0-9A-Fa-f]         IsXDigit      = IsXDigit

     If you wish to build perl with the old mapping you may do so
     by setting


     in regcomp.h, and then setting


     to true your enviornment when testing.

  @INC reorganization
     In @INC, ARCHLIB and PRIVLIB now occur after after the
     current version's site_perl and vendor_perl.

  Switch statement changes
     The handling of complex expressions by the "given"/"when"
     switch statement has been enhanced. These enhancements are
     also available in 5.10.1 and subsequent 5.10 releases. There
     are two new cases where "when" now interprets its argument
     as a boolean, instead of an expression to be used in a smart

     flip-flop operators
         The ".." and "..." flip-flop operators are now evaluated
         in boolean context, following their usual semantics; see
         "Range Operators" in perlop.

         Note that, as in perl 5.10.0, "when (1..10)" will not
         work to test whether a given value is an integer between
         1 and 10; you should use "when ([1..10])" instead (note
         the array reference).

         However, contrary to 5.10.0, evaluating the flip-flop
         operators in boolean context ensures it can now be
         useful in a "when()", notably for implementing bistable
         conditions, like in:

             when (/^=begin/ .. /^=end/) {
               # do something

     defined-or operator
         A compound expression involving the defined-or operator,

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         as in "when (expr1 // expr2)", will be treated as
         boolean if the first expression is boolean. (This just
         extends the existing rule that applies to the regular or
         operator, as in "when (expr1 || expr2)".)

     The next section details more changes brought to the
     semantics to the smart match operator, that naturally also
     modify the behaviour of the switch statements where smart
     matching is implicitly used.  These changers were also made
     for the 5.10.1 release, and will remain in subsequent 5.10

  Smart match changes
     Changes to type-based dispatch

     The smart match operator "~~" is no longer commutative. The
     behaviour of a smart match now depends primarily on the type
     of its right hand argument. Moreover, its semantics have
     been adjusted for greater consistency or usefulness in
     several cases. While the general backwards compatibility is
     maintained, several changes must be noted:

     o   Code references with an empty prototype are no longer
         treated specially.  They are passed an argument like the
         other code references (even if they choose to ignore

     o   "%hash ~~ sub {}" and "@array ~~ sub {}" now test that
         the subroutine returns a true value for each key of the
         hash (or element of the array), instead of passing the
         whole hash or array as a reference to the subroutine.

     o   Due to the commutativity breakage, code references are
         no longer treated specially when appearing on the left
         of the "~~" operator, but like any vulgar scalar.

     o   "undef ~~ %hash" is always false (since "undef" can't be
         a key in a hash). No implicit conversion to "" is done
         (as was the case in perl 5.10.0).

     o   "$scalar ~~ @array" now always distributes the smart
         match across the elements of the array. It's true if one
         element in @array verifies "$scalar ~~ $element". This
         is a generalization of the old behaviour that tested
         whether the array contained the scalar.

     The full dispatch table for the smart match operator is
     given in "Smart matching in detail" in perlsyn.

     Smart match and overloading

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     According to the rule of dispatch based on the rightmost
     argument type, when an object overloading "~~" appears on
     the right side of the operator, the overload routine will
     always be called (with a 3rd argument set to a true value,
     see overload.) However, when the object will appear on the
     left, the overload routine will be called only when the
     rightmost argument is a simple scalar. This way
     distributivity of smart match across arrays is not broken,
     as well as the other behaviours with complex types
     (coderefs, hashes, regexes). Thus, writers of overloading
     routines for smart match mostly need to worry only with
     comparing against a scalar, and possibly with
     stringification overloading; the other common cases will be
     automatically handled consistently.

     "~~" will now refuse to work on objects that do not overload
     it (in order to avoid relying on the object's underlying
     structure). (However, if the object overloads the
     stringification or the numification operators, and if
     overload fallback is active, it will be used instead, as

  Labels can't be keywords
     Labels used as targets for the "goto", "last", "next" or
     "redo" statements cannot be keywords anymore. This
     restriction will prevent potential confusion between the
     "goto LABEL" and "goto EXPR" syntaxes: for example, a
     statement like "goto print" would jump to a label whose name
     would be the return value of "print()", (usually 1), instead
     of a label named "print". Moreover, the other control flow
     statements would just ignore any keyword passed to them as a
     label name. Since such labels cannot be defined anymore,
     this kind of error will be avoided.

  Other incompatible changes
     o   The semantics of "use feature :5.10*" have changed
         slightly.  See "Modules and Pragmata" for more

     o   It is now a run-time error to use the smart match
         operator "~~" with an object that has no overload
         defined for it. (This way "~~" will not break
         encapsulation by matching against the object's internal
         representation as a reference.)

     o   The version control system used for the development of
         the perl interpreter has been switched from Perforce to
         git.  This is mainly an internal issue that only affects
         people actively working on the perl core; but it may
         have minor external visibility, for example in some of
         details of the output of "perl -V". See perlrepository
         for more information.

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     o   The internal structure of the "ext/" directory in the
         perl source has been reorganised. In general, a module
         "Foo::Bar" whose source was stored under ext/Foo/Bar/ is
         now located under ext/Foo-Bar/. Also, nearly all dual-
         life modules have been moved from lib/ to ext/. This is
         purely a source tarball change, and should make no
         difference to the compilation or installation of perl,
         unless you have a very customised build process that
         explicitly relies on this structure, or which hard-codes
         the "nonxs_ext" Configure parameter. Specifically, this
         change does not by default alter the location of any
         files in the final installation.

     o   As part of the "Test::Harness" 2.x to 3.x upgrade, the
         experimental "Test::Harness::Straps" module has been
         removed.  See "Updated Modules" for more details.

     o   As part of the "ExtUtils::MakeMaker" upgrade, the
         "ExtUtils::MakeMaker::bytes" and
         "ExtUtils::MakeMaker::vmsish" modules have been removed
         from this distribution.

     o   "Module::CoreList" no longer contains the %:patchlevel

     o   This one is actually a change introduced in 5.10.0, but
         it was missed from that release's perldelta, so it is
         mentioned here instead.

         A bugfix related to the handling of the "/m" modifier
         and "qr" resulted in a change of behaviour between 5.8.x
         and 5.10.0:

             # matches in 5.8.x, doesn't match in 5.10.0
             $re = qr/^bar/; "foo\nbar" =~ /$re/m;

     o   "length undef" now returns undef.

     o   Unsupported private C API functions are now declared
         "static" to prevent leakage to Perl's public API.

     o   To support the bootstrapping process, miniperl no longer
         builds with UTF-8 support in the regexp engine.

         This allows a build to complete with PERL_UNICODE set
         and a UTF-8 locale.  Without this there's a
         bootstrapping problem, as miniperl can't load the UTF-8
         components of the regexp engine, because they're not yet

     o   miniperl's @INC is now restricted to just -I..., the
         split of $ENV{PERL5LIB}, and "."

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     o   A space or a newline is now required after a "#line XXX"

     o   Tied filehandles now have an additional method EOF which
         provides the EOF type

     o   To better match all other flow control statements,
         "foreach" may no longer be used as an attribute.

Core Enhancements
  Unicode Character Database 5.1.0
     The copy of the Unicode Character Database included in Perl
     5.11.0 has been updated to 5.1.0 from 5.0.0. See
     for the notable changes.

  A proper interface for pluggable Method Resolution Orders
     As of Perl 5.11.0 there is a new interface for plugging and
     using method resolution orders other than the default
     (linear depth first search).  The C3 method resolution order
     added in 5.10.0 has been re-implemented as a plugin, without
     changing its Perl-space interface. See perlmroapi for more

  The "overloading" pragma
     This pragma allows you to lexically disable or enable
     overloading for some or all operations. (Yuval Kogman)

  "\N" regex escape
     A new regex escape has been added, "\N". It will match any
     character that is not a newline, independently from the
     presence or absence of the single line match modifier "/s".
     (If "\N" is followed by an opening brace and by a letter,
     perl will still assume that a Unicode character name is
     coming, so compatibility is preserved.) (Rafael Garcia-

  Implicit strictures
     Using the "use VERSION" syntax with a version number greater
     or equal to 5.11.0 will also lexically enable strictures
     just like "use strict" would do (in addition to enabling
     features.) So, the following:

         use 5.11.0;

     will now imply:

         use strict;
         use feature ':5.11';

  Parallel tests
     The core distribution can now run its regression tests in

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     parallel on Unix-like platforms. Instead of running "make
     test", set "TEST_JOBS" in your environment to the number of
     tests to run in parallel, and run "make test_harness". On a
     Bourne-like shell, this can be done as

         TEST_JOBS=3 make test_harness  # Run 3 tests in parallel

     An environment variable is used, rather than parallel make
     itself, because TAP::Harness needs to be able to schedule
     individual non-conflicting test scripts itself, and there is
     no standard interface to "make" utilities to interact with
     their job schedulers.

     Note that currently some test scripts may fail when run in
     parallel (most notably "ext/IO/t/io_dir.t"). If necessary
     run just the failing scripts again sequentially and see if
     the failures go away.

  The "..." operator
     A new operator, "...", nicknamed the Yada Yada operator, has
     been added.  It is intended to mark placeholder code, that
     is not yet implemented.  See "Yada Yada Operator" in perlop.

  DTrace support
     Some support for DTrace has been added. See "DTrace support"
     in INSTALL.

  Support for "configure_requires" in CPAN module metadata
     Both "CPAN" and "CPANPLUS" now support the
     "configure_requires" keyword in the META.yml metadata file
     included in most recent CPAN distributions.  This allows
     distribution authors to specify configuration prerequisites
     that must be installed before running Makefile.PL or

     See the documentation for "ExtUtils::MakeMaker" or
     "Module::Build" for more on how to specify
     "configure_requires" when creating a distribution for CPAN.

  "each" is now more flexible
     The "each" function can now operate on arrays.

  Y2038 compliance
     Perl's core time-related functions are now Y2038 compliant.
     (With 29 years to spare!)

  $, flexibility
     The variable $, may now be tied.

  // in where clauses
     // now behaves like || in when clauses

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  Enabling warnings from your shell environment
     You can now set "-W" from the "PERL5OPT" environment

  "delete local"
     "delete local" now allows you to locally delete a hash

  New support for Abstract namespace sockets
     Abstract namespace sockets are Linux-specific socket type
     that live in AF_UNIX family, slightly abusing it to be able
     to use arbitrary character arrays as addresses: They start
     with nul byte and are not terminated by nul byte, but with
     the length passed to the socket() system call.

Modules and Pragmata
  Dual-lifed modules moved
     Dual-lifed modules maintained primarily in the Perl core now
     live in dist/.  Dual-lifed modules maintained primarily on
     CPAN now live in cpan/

     In previous releases of Perl, it was customary to enumerate
     all module changes in this section of the "perldelta" file.
     From 5.11.0 forward only notable updates (such as new or
     deprecated modules ) will be listed in this section. For a
     complete reference to the versions of modules shipped in a
     given release of perl, please see Module::CoreList.

  New Modules and Pragmata
         This is a new lexically-scoped alternative for the
         "Fatal" module.  The bundled version is 2.06_01. Note
         that in this release, using a string eval when "autodie"
         is in effect can cause the autodie behaviour to leak
         into the surrounding scope. See "BUGS" in autodie for
         more details.

         This has been added to the core (version 2.020).

         This pragma establishes an ISA relationship with base
         classes at compile time. It provides the key feature of
         "base" without the feature creep.

         This has been added to the core (version 1.39).

  Pragmata Changes
         See "The "overloading" pragma" above.

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         The "attrs" pragma has been removed. It had been marked
         as deprecated since 5.6.0.

         The Unicode NameAliases.txt database file has been
         added. This has the effect of adding some extra "\N"
         character names that formerly wouldn't have been
         recognised; for example, "\N{LATIN CAPITAL LETTER GHA}".

         The meaning of the ":5.10" and ":5.10.X" feature bundles
         has changed slightly. The last component, if any (i.e.
         "X") is simply ignored.  This is predicated on the
         assumption that new features will not, in general, be
         added to maintenance releases. So ":5.10" and ":5.10.X"
         have identical effect. This is a change to the behaviour
         documented for 5.10.0.

         Upgraded from version 1.00 to 1.01. Performance for
         single inheritance is 40% faster - see "Performance
         Enhancements" below.

         "mro" is now implemented as an XS extension. The
         documented interface has not changed. Code relying on
         the implementation detail that some "mro::" methods
         happened to be available at all times gets to "keep both

  Updated Modules
         Upgraded from version 6.42 to 6.55_02.

         Note that "ExtUtils::MakeMaker::bytes" and
         "ExtUtils::MakeMaker::vmsish" have been removed from
         this distribution.

         Upgraded from version 2.64 to 3.17.

         Note that one side-effect of the 2.x to 3.x upgrade is
         that the experimental "Test::Harness::Straps" module
         (and its supporting "Assert", "Iterator", "Point" and
         "Results" modules) have been removed. If you still need
         this, then they are available in the (unmaintained)
         "Test-Harness-Straps" distribution on CPAN.

         Upgraded from version 1.04 to 1.05.

         "UNIVERSAL->import()" is now deprecated.

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Utility Changes
         Now looks in "include-fixed" too, which is a recent
         addition to gcc's search path.

         No longer incorrectly treats enum values like macros
         (Daniel Burr).

         Now handles C++ style constants ("//") properly in
         enums. (A patch from Rainer Weikusat was used; Daniel
         Burr also proposed a similar fix).
         "LVALUE" subroutines now work under the debugger.

         The debugger now correctly handles proxy constant
         subroutines, and subroutine stubs.

         perlbug now uses %Module::CoreList::bug_tracker to print
         out upstream bug tracker URLs.

         Where the user names a module that their bug report is
         about, and we know the URL for its upstream bug tracker,
         provide a message to the user explaining that the core
         copies the CPAN version directly, and provide the URL
         for reporting the bug directly to upstream.

         Perl 5.11.0 added a new utility perlthanks, which is a
         variant of perlbug, but for sending non-bug-reports to
         the authors and maintainers of Perl. Getting nothing but
         bug reports can become a bit demoralising: we'll see if
         this changes things.

New Documentation
         This contains instructions on how to build perl for the
         Haiku platform.

         This describes the new interface for pluggable Method
         Resolution Orders.

         This document, by Richard Foley, provides an
         introduction to the use of performance and optimization
         techniques which can be used with particular reference
         to perl programs.


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         This describes how to access the perl source using the
         git version control system.

Changes to Existing Documentation
     The various large Changes* files (which listed every change
     made to perl over the last 18 years) have been removed, and
     replaced by a small file, also called Changes, which just
     explains how that same information may be extracted from the
     git version control system.

     The file Porting/patching.pod has been deleted, as it mainly
     described interacting with the old Perforce-based
     repository, which is now obsolete.  Information still
     relevant has been moved to perlrepository.

     perlapi, perlintern, perlmodlib and perltoc are now all
     generated at build time, rather than being shipped as part
     of the release.

     o   Documented -X overloading.

     o   Documented that "when()" treats specially most of the
         filetest operators

     o   Documented when as a syntax modifier

     o   Eliminated "Old Perl threads tutorial", which describes
         5005 threads.

         pod/perlthrtut.pod is the same material reworked for

     o   Correct previous documentation: v-strings are not

         With version objects, we need them to use MODULE VERSION
         syntax.  This patch removes the deprecation note.

     o   Added security contact information to perlsec

Performance Enhancements
     o   A new internal cache means that "isa()" will often be

     o   The implementation of "C3" Method Resolution Order has
         been optimised - linearisation for classes with single
         inheritance is 40% faster. Performance for multiple
         inheritance is unchanged.

     o   Under "use locale", the locale-relevant information is
         now cached on read-only values, such as the list
         returned by "keys %hash". This makes operations such as

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         "sort keys %hash" in the scope of "use locale" much

     o   Empty "DESTROY" methods are no longer called.

     o   Faster "Perl_sv_utf8_upgrade()"

     o   Speed up "keys" on empty hash

Installation and Configuration Improvements
  ext/ reorganisation
     The layout of directories in ext has been revised.
     Specifically, all extensions are now flat, and at the top
     level, with "/" in pathnames replaced by "-", so that
     ext/Data/Dumper/ is now ext/Data-Dumper/, etc.  The names of
     the extensions as specified to Configure, and as reported by
     %Config::Config under the keys "dynamic_ext",
     "known_extensions", "nonxs_ext" and "static_ext" have not
     changed, and still use "/". Hence this change will not have
     any affect once perl is installed. "Safe" has been split out
     from being part of "Opcode", and "mro" is now an extension
     in its own right.

     Nearly all dual-life modules have been moved from lib to
     ext, and will now appear as known "nonxs_ext". This will
     made no difference to the structure of an installed perl,
     nor will the modules installed differ, unless you run
     Configure with options to specify an exact list of
     extensions to build. In this case, you will rapidly become
     aware that you need to add to your list, because various
     modules needed to complete the build, such as
     "ExtUtils::ParseXS", have now become extensions, and without
     them the build will fail well before it attempts to run the
     regression tests.

  Configuration improvements
     If "vendorlib" and "vendorarch" are the same, then they are
     only added to @INC once.

     $Config{usedevel} and the C-level "PERL_USE_DEVEL" are now
     defined if perl is built with  "-Dusedevel".

     Configure will enable use of "-fstack-protector", to provide
     protection against stack-smashing attacks, if the compiler
     supports it.

     Configure will now determine the correct prototypes for re-
     entrant functions, and for "gconvert", if you are using a
     C++ compiler rather than a C compiler.

     On Unix, if you build from a tree containing a git
     repository, the configuration process will note the commit

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     hash you have checked out, for display in the output of
     "perl -v" and "perl -V". Unpushed local commits are
     automatically added to the list of local patches displayed
     by "perl -V".

  Compilation improvements
     As part of the flattening of ext, all extensions on all
     platforms are built by This replaces the Unix-
     specific ext/util/make_ext, VMS-specific and
     Win32-specific win32/

  Platform Specific Changes
     AIX Removed libbsd for AIX 5L and 6.1. Only "flock()" was
         used from libbsd.

         Removed libgdbm for AIX 5L and 6.1. The libgdbm is
         delivered as an optional package with the AIX Toolbox.
         Unfortunately the 64 bit version is broken.

         Hints changes mean that AIX 4.2 should work again.

         On Cygwin we now strip the last number from the DLL.
         This has been the behaviour in the build for
         years. The hints files have been updated.

         Support for Apollo DomainOS was removed in Perl 5.11.0

         The hints files now identify the correct threading
         libraries on FreeBSD 7 and later.

         We now work around a bizarre preprocessor bug in the
         Irix 6.5 compiler: "cc -E -" unfortunately goes into K&R
         mode, but "cc -E file.c" doesn't.

         Patches from the Haiku maintainers have been merged in.
         Perl should now build on Haiku.

         Support for Tenon Intersystems MachTen Unix layer for
         MacOS Classic was removed in Perl 5.11.0

         Support for Atari MiNT was removed in Perl 5.11.0.

     MirOS BSD
         Perl should now build on MirOS BSD.

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         Hints now supports versions 5.*.

     Stratus VOS
         Various changes from Stratus have been merged in.

         There is now support for Symbian S60 3.2 SDK and S60 5.0

         Improved message window handling means that "alarm" and
         "kill" messages will no longer be dropped under race

     VMS Reads from the in-memory temporary files of
         "PerlIO::scalar" used to fail if $/ was set to a numeric
         reference (to indicate record-style reads).  This is now

         VMS now supports "getgrgid".

         Many improvements and cleanups have been made to the VMS
         file name handling and conversion code.

         Enabling the "PERL_VMS_POSIX_EXIT" logical name now
         encodes a POSIX exit status in a VMS condition value for
         better interaction with GNV's bash shell and other
         utilities that depend on POSIX exit values.  See "$?" in
         perlvms for details.

         "File::Copy" now detects Unix compatibility mode on VMS.

Selected Bug Fixes
     o   "-I" on shebang line now adds directories in front of
         @INC as documented, and as does "-I" when specified on
         the command-line.

     o   "kill" is now fatal when called on non-numeric process
         identifiers.  Previously, an 'undef' process identifier
         would be interpreted as a request to kill process "0",
         which would terminate the current process group on POSIX
         systems.  Since process identifiers are always integers,
         killing a non-numeric process is now fatal.

     o   5.10.0 inadvertently disabled an optimisation, which
         caused a measurable performance drop in list assignment,
         such as is often used to assign function parameters from
         @_. The optimisation has been re-instated, and the
         performance regression fixed.

     o   Fixed memory leak on "while (1) { map 1, 1 }" [RT

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     o   Some potential coredumps in PerlIO fixed [RT

     o   The debugger now works with lvalue subroutines.

     o   The debugger's "m" command was broken on modules that
         defined constants [RT #61222].

     o   "crypt" and string complement could return tainted
         values for untainted arguments [RT #59998].

     o   The "-i".suffix command-line switch now recreates the
         file using restricted permissions, before changing its
         mode to match the original file. This eliminates a
         potential race condition [RT #60904].

     o   On some Unix systems, the value in $? would not have the
         top bit set ("$? & 128") even if the child core dumped.

     o   Under some circumstances, $^R could incorrectly become
         undefined [RT #57042].

     o   In the XS API, various hash functions, when passed a
         pre-computed hash where the key is UTF-8, might result
         in an incorrect lookup.

     o   XS code including XSUB.h before perl.h gave a compile-
         time error [RT #57176].

     o   "$object->isa('Foo')" would report false if the package
         "Foo" didn't exist, even if the object's @ISA contained

     o   Various bugs in the new-to 5.10.0 mro code, triggered by
         manipulating @ISA, have been found and fixed.

     o   Bitwise operations on references could crash the
         interpreter, e.g.  "$x=\$y; $x |= "foo"" [RT #54956].

     o   Patterns including alternation might be sensitive to the
         internal UTF-8 representation, e.g.

             my $byte = chr(192);
             my $utf8 = chr(192); utf8::upgrade($utf8);
             $utf8 =~ /$byte|X}/i;       # failed in 5.10.0

     o   Within UTF8-encoded Perl source files (i.e. where "use
         utf8" is in effect), double-quoted literal strings could
         be corrupted where a "\xNN", "\0NNN" or "\N{}" is
         followed by a literal character with ordinal value

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         greater than 255 [RT #59908].

     o   "B::Deparse" failed to correctly deparse various
         constructs: "readpipe STRING" [RT #62428],
         "CORE::require(STRING)" [RT #62488], "sub foo(_)" [RT

     o   Using "setpgrp" with no arguments could corrupt the perl

     o   The block form of "eval" is now specifically trappable
         by "Safe" and "ops".  Previously it was erroneously
         treated like string "eval".

     o   In 5.10.0, the two characters "[~" were sometimes parsed
         as the smart match operator ("~~") [RT #63854].

     o   In 5.10.0, the "*" quantifier in patterns was sometimes
         treated as "{0,32767}" [RT #60034, #60464]. For example,
         this match would fail:

             ("ab" x 32768) =~ /^(ab)*$/

     o   "shmget" was limited to a 32 bit segment size on a 64
         bit OS [RT #63924].

     o   Using "next" or "last" to exit a "given" block no longer
         produces a spurious warning like the following:

             Exiting given via last at line 123

     o   On Windows, '.\foo' and '..\foo'  were treated
         differently than './foo' and '../foo' by "do" and
         "require" [RT #63492].

     o   Assigning a format to a glob could corrupt the format;

              *bar=*foo{FORMAT}; # foo format now bad

     o   Attempting to coerce a typeglob to a string or number
         could cause an assertion failure. The correct error
         message is now generated, "Can't coerce GLOB to $type".

     o   Under "use filetest 'access'", "-x" was using the wrong
         access mode. This has been fixed [RT #49003].

     o   "length" on a tied scalar that returned a Unicode value
         would not be correct the first time. This has been

     o   Using an array "tie" inside in array "tie" could SEGV.

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         This has been fixed. [RT #51636]

     o   A race condition inside "PerlIOStdio_close()" has been
         identified and fixed. This used to cause various
         threading issues, including SEGVs.

     o   In "unpack", the use of "()" groups in scalar context
         was internally placing a list on the interpreter's
         stack, which manifested in various ways, including
         SEGVs.  This is now fixed [RT #50256].

     o   Magic was called twice in "substr", "\&$x", "tie $x, $m"
         and "chop".  These have all been fixed.

     o   A 5.10.0 optimisation to clear the temporary stack
         within the implicit loop of "s///ge" has been reverted,
         as it turned out to be the cause of obscure bugs in
         seemingly unrelated parts of the interpreter [commit

     o   The line numbers for warnings inside "elsif" are now

     o   The ".." operator now works correctly with ranges whose
         ends are at or close to the values of the smallest and
         largest integers.

     o   "binmode STDIN, ':raw'" could lead to segmentation
         faults on some platforms.  This has been fixed [RT

     o   An off-by-one error meant that "index $str, ..." was
         effectively being executed as "index "$str\0", ...".
         This has been fixed [RT #53746].

     o   Various leaks associated with named captures in regexes
         have been fixed [RT #57024].

     o   A weak reference to a hash would leak. This was
         affecting "DBI" [RT #56908].

     o   Using (?|) in a regex could cause a segfault [RT

     o   Use of a UTF-8 "tr//" within a closure could cause a
         segfault [RT #61520].

     o   Calling "Perl_sv_chop()" or otherwise upgrading an SV
         could result in an unaligned 64-bit access on the SPARC
         architecture [RT #60574].

     o   In the 5.10.0 release, "inc_version_list" would

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         incorrectly list "5.10.*" after "5.8.*"; this affected
         the @INC search order [RT #67628].

     o   In 5.10.0, "pack "a*", $tainted_value" returned a non-
         tainted value [RT #52552].

     o   In 5.10.0, "printf" and "sprintf" could produce the
         fatal error "panic: utf8_mg_pos_cache_update" when
         printing UTF-8 strings [RT #62666].

     o   In the 5.10.0 release, a dynamically created "AUTOLOAD"
         method might be missed (method cache issue) [RT

     o   In the 5.10.0 release, a combination of "use feature"
         and "//ee" could cause a memory leak [RT #63110].

     o   "-C" on the shebang ("#!") line is once more permitted
         if it is also specified on the command line. "-C" on the
         shebang line used to be a silent no-op if it was not
         also on the command line, so perl 5.10.0 disallowed it,
         which broke some scripts. Now perl checks whether it is
         also on the command line and only dies if it is not [RT

     o   In 5.10.0, certain types of re-entrant regular
         expression could crash, or cause the following assertion
         failure [RT #60508]:

             Assertion rx->sublen >= (s - rx->subbeg) + i failed

     o   Previously missing files from Unicode 5.1 Character
         Database are now included.

     o   "TMPDIR" is now honored when opening an anonymous
         temporary file

New or Changed Diagnostics
     "panic: sv_chop %s"
         This new fatal error occurs when the C routine
         "Perl_sv_chop()" was passed a position that is not
         within the scalar's string buffer. This could be caused
         by buggy XS code, and at this point recovery is not

     "Can't locate package %s for the parents of %s"
         This warning has been removed. In general, it only got
         produced in conjunction with other warnings, and
         removing it allowed an ISA lookup optimisation to be

     "v-string in use/require is non-portable"

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         This warning has been removed.

     "Deep recursion on subroutine "%s""
         It is now possible to change the depth threshold for
         this warning from the default of 100, by recompiling the
         perl binary, setting the C pre-processor macro
         "PERL_SUB_DEPTH_WARN" to the desired value.

Changed Internals
     o   TODO: "SVt_RV" is gone. RVs are now stored in IVs

     o   TODO: REGEXPs are first class

     o   TODO: OOK is reworked, such that an OOKed scalar is PV
         not PVIV

     o   The J.R.R. Tolkien quotes at the head of C source file
         have been checked and proper citations added, thanks to
         a patch from Tom Christiansen.

     o   "Perl_vcroak()" now accepts a null first argument. In
         addition, a full audit was made of the "not NULL"
         compiler annotations, and those for several other
         internal functions were corrected.

     o   New macros "dSAVEDERRNO", "dSAVE_ERRNO", "SAVE_ERRNO",
         "RESTORE_ERRNO" have been added to formalise the
         temporary saving of the "errno" variable.

     o   The function "Perl_sv_insert_flags" has been added to
         augment "Perl_sv_insert".

     o   The function "Perl_newSV_type(type)" has been added,
         equivalent to "Perl_newSV()" followed by

     o   The function "Perl_newSVpvn_flags()" has been added,
         equivalent to "Perl_newSVpvn()" and then performing the
         action relevant to the flag.

         Two flag bits are currently supported.

             This will call "SvUTF8_on()" for you. (Note that
             this does not convert an sequence of ISO 8859-1
             characters to UTF-8). A wrapper, "newSVpvn_utf8()"
             is available for this.

             Call "Perl_sv_2mortal()" on the new SV.

         There is also a wrapper that takes constant strings,

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     o   The function "Perl_croak_xs_usage" has been added as a
         wrapper to "Perl_croak".

     o   The functions "PerlIO_find_layer" and
         "PerlIO_list_alloc" are now exported.

     o   "PL_na" has been exterminated from the core code,
         replaced by local STRLEN temporaries, or "*_nolen()"
         calls. Either approach is faster than "PL_na", which is
         a pointer deference into the interpreter structure under
         ithreads, and a global variable otherwise.

     o   "Perl_mg_free()" used to leave freed memory accessible
         via "SvMAGIC()" on the scalar. It now updates the linked
         list to remove each piece of magic as it is freed.

     o   Under ithreads, the regex in "PL_reg_curpm" is now
         reference counted. This eliminates a lot of hackish
         workarounds to cope with it not being reference counted.

     o   "Perl_mg_magical()" would sometimes incorrectly turn on
         "SvRMAGICAL()".  This has been fixed.

     o   The public IV and NV flags are now not set if the string
         value has trailing "garbage". This behaviour is
         consistent with not setting the public IV or NV flags if
         the value is out of range for the type.

     o   SV allocation tracing has been added to the diagnostics
         enabled by "-Dm".  The tracing can alternatively output
         via the "PERL_MEM_LOG" mechanism, if that was enabled
         when the perl binary was compiled.

     o   Smartmatch resolution tracing has been added as a new
         diagnostic. Use "-DM" to enable it.

     o   A new debugging flag "-DB" now dumps subroutine
         definitions, leaving "-Dx" for its original purpose of
         dumping syntax trees.

     o   Uses of "Nullav", "Nullcv", "Nullhv", "Nullop", "Nullsv"
         etc have been replaced by "NULL" in the core code, and
         non-dual-life modules, as "NULL" is clearer to those
         unfamiliar with the core code.

     o   A macro MUTABLE_PTR(p) has been added, which on (non-
         pedantic) gcc will not cast away "const", returning a
         "void *". Macros "MUTABLE_SV(av)", "MUTABLE_SV(cv)" etc
         build on this, casting to "AV *" etc without casting
         away "const". This allows proper compile-time auditing

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         of "const" correctness in the core, and helped picked up
         some errors (now fixed).

     o   Macros "mPUSHs()" and "mXPUSHs()" have been added, for
         pushing SVs on the stack and mortalizing them.

     o   Use of the private structure "mro_meta" has changed
         slightly. Nothing outside the core should be accessing
         this directly anyway.

     o   A new tool, Porting/ has been added, that
         allows you to view how a C preprocessor macro would be
         expanded when compiled.  This is handy when trying to
         decode the macro hell that is the perl guts.

New Tests
     Many modules updated from CPAN incorporate new tests.

     Several tests that have the potential to hang forever if
     they fail now incorporate a "watchdog" functionality that
     will kill them after a timeout, which helps ensure that
     "make test" and "make test_harness" run to completion
     automatically. (Jerry Hedden).

     Some core-specific tests have been added:

         Check that the debugger can retain source lines from

         Check that bad layers fail.

         Check that PerlIO layers are not leaking.

         Check that certain special forms of open work.

         General PerlIO tests.

         Check that there is no unexpected interaction between
         the internal types "PVBM" and "PVGV".

         Check that mro works properly in the presence of aliased

         Tests for "dbmopen" and "dbmclose".

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         Tests for the interaction of "index" and threads.

         Tests for the interaction of esoteric patterns and

         Test that "qr" doesn't leak.

         Tests for the interaction of regex recursion and

         Tests for the interaction of patterns with embedded
         "qr//" and threads.

         Tests for Unicode properties in regular expressions.

         Tests for the interaction of Unicode properties and

         Test the tied methods of "Tie::Hash::NamedCapture".

         Check that POSIX character classes behave consistently.

         Check that exportable "re" functions in universal.c

         Check that "setpgrp" works.

         Tests for the interaction of "substr" and threads.

         Check that upgrading and assigning scalars works.

         Check that Unicode in the lexer works.

         Check that Unicode and "tie" work.

Known Problems
     This is a list of some significant unfixed bugs, which are

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     regressions from either 5.10.0 or 5.8.x.

     o   "List::Util::first" misbehaves in the presence of a
         lexical $_ (typically introduced by "my $_" or
         implicitly by "given"). The variable which gets set for
         each iteration is the package variable $_, not the
         lexical $_ [RT #67694].

         A similar issue may occur in other modules that provide
         functions which take a block as their first argument,

             foo { ... $_ ...} list

     o   The "charnames" pragma may generate a run-time error
         when a regex is interpolated [RT #56444]:

             use charnames ':full';
             my $r1 = qr/\N{THAI CHARACTER SARA I}/;
             "foo" =~ $r1;    # okay
             "foo" =~ /$r1+/; # runtime error

         A workaround is to generate the character outside of the

             my $a = "\N{THAI CHARACTER SARA I}";
             my $r1 = qr/$a/;

     o   Some regexes may run much more slowly when run in a
         child thread compared with the thread the pattern was
         compiled into [RT #55600].

     The following items are now deprecated.

     o   "Switch" is buggy and should be avoided. From perl
         5.11.0 onwards, it is intended that any use of the core
         version of this module will emit a warning, and that the
         module will eventually be removed from the core
         (probably in perl 5.14.0). See "Switch statements" in
         perlsyn for its replacement.

     o   The following modules will be removed from the core
         distribution in a future release, and should be
         installed from CPAN instead. Distributions on CPAN which
         require these should add them to their prerequisites.
         The core versions of these modules warnings will issue a
         deprecation warning.

         o   "Class::ISA"

         o   "Pod::Plainer"

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         o   "Shell"

         Currently support to install from CPAN without a force
         is "TODO" in CPAN and CPANPLUS. This will be addressed
         before 5.12.0 ships.

     o   "suidperl" has been removed. It used to provide a
         mechanism to emulate setuid permission bits on systems
         that don't support it properly.

     o   Deprecate assignment to $[

     o   Remove attrs, which has been deprecated since

     o   Deprecate use of the attribute :locked on subroutines.

     o   Deprecate using "locked" with the attributes pragma.

     o   Deprecate using "unique" with the attributes pragma.

     o   warn if ++ or -- are unable to change the value because
         it's beyond the limit of representation

         This uses a new warnings category: "imprecision".

     o   Make lc/uc/lcfirst/ucfirst warn when passed undef.

     o   Show constant in "Useless use of a constant in void

     o   Make the new warning report undef constants as undef

     o   Add a new warning, "Prototype after '%s'"

     o   Tweak the "Illegal character in prototype" warning so
         it's more precise when reporting illegal characters
         after _

     o   Unintended interpolation of $\ in regex

     o   Make overflow warnings in gmtime/localtime only occur
         when warnings are on

     o   Improve mro merging error messages.

         They are now very similar to those produced by

     o   Amelioration of the error message "Unrecognized
         character %s in column %d"

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         Changes the error message to "Unrecognized character %s;
         marked by <-- HERE after %s<-- HERE near column %d".
         This should make it a little simpler to spot and correct
         the suspicious character.

     o   Explicitely point to $. when it causes an uninitialized
         warning for ranges in scalar context

     o   Deprecated numerous Perl 4-era libraries:
,,,,,,,,,,,,,,,,,,,,,,,,,,,, and are all now deprecated. Using
         them will incur a warning.

     Some of the work in this release was funded by a TPF grant
     funded by Dijkmat BV, The Netherlands.

     Steffen Mueller and David Golden in particular helped
     getting CPAN modules polished and synchronised with their
     in-core equivalents.

     Craig Berry was tireless in getting maint to run under VMS,
     no matter how many times we broke it for him.

     The other core committers contributed most of the changes,
     and applied most of the patches sent in by the hundreds of
     contributors listed in AUTHORS.

     Much of the work of categorizing changes in this perldelta
     file was contributed by the following porters using

     Nicholas Clark, leon, shawn, alexm, rjbs, rafl, Pedro Melo,
     brunorc, anonymous, X, Tom Hukins, anonymous, Jesse,
     dagolden, Moritz Onken, Mark Fowler, chorny, anonymous, tmtm

     Finally, thanks to Larry Wall, without whom none of this
     would be necessary.

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.

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     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.

     If the bug you are reporting has security implications,
     which make it inappropriate to send to a publicly archived
     mailing list, then please send it to This points to a closed
     subscription unarchived mailing list, which includes all the
     core committers, who be able to help assess the impact of
     issues, figure out a resolution, and help co-ordinate the
     release of patches to mitigate or fix the problem across all
     platforms on which Perl is supported. Please only use this
     address for security issues in the Perl core, not for
     modules independently distributed on CPAN.

     See attributes(5) for descriptions of the following

     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
     The Changes file for an explanation of how to view
     exhaustive details on what changed.

     The INSTALL file for how to build Perl.

     The README file for general stuff.

     The Artistic and Copying files for copyright information.

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

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

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