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riddles in the dark

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Gurusamy Sarathy
April 8, 2001 22:46
riddles in the dark
Message ID:

    `What have I got in my pocket?' he said aloud.  He was talking to
     himself, but Gollum thought it was a riddle, and he was frightfully

    `Not fair! not fair!' he hissed.  `It isn't fair, my precious, is it,
     to ask us what it's got in its nassty little pocketses?'

     Bilbo seeing what had happened and having nothing better to ask
     stuck to his question, `What have I got in my pocket?' he said

    `S-s-s-s-s,' hissed Gollum.  `It must give us three guesseses,
     my precious, three guesseses.'

                                --Riddles in the Dark,
				  The Hobbit, J R R Tolkien

Gee, I'm sure most of you should know in a single guess by now.  :-)
Here's are a couple of hints:

A special thanks to Jarkko for all his help in making this release
happen when it did, extra special thanks to anyone who ever sent
in anything that ended up in there, and extra extra special apologies
to anyone who sent in stuff for 5.6.1 that I had to bump off as
being 5.6.2 material.


    perldelta - what's new for perl v5.6.x

    This document describes differences between the 5.005 release and the
    5.6.1 release.

Summary of changes between 5.6.0 and 5.6.1
    This section contains a summary of the changes between the 5.6.0 release
    and the 5.6.1 release. More details about the changes mentioned here may
    be found in the Changes files that accompany the Perl source
    distribution. See the perlhack manpage for pointers to online resources
    where you can inspect the individual patches described by these changes.

  Security Issues

    suidperl will not run /bin/mail anymore, because some platforms have a
    /bin/mail that is vulnerable to buffer overflow attacks.

    Note that suidperl is neither built nor installed by default in any
    recent version of perl. Use of suidperl is highly discouraged. If you
    think you need it, try alternatives such as sudo first. See

  Core bug fixes

    This is not an exhaustive list. It is intended to cover only the
    significant user-visible changes.

        A bug in the caching mechanism used by "UNIVERSAL::isa()" that
        affected has been fixed. The bug has existed since the 5.005
        releases, but wasn't tickled by in those releases.

    Memory leaks
        Various cases of memory leaks and attempts to access uninitialized
        memory have been cured. See the section on "Known Problems" below
        for further issues.

    Numeric conversions
        Numeric conversions did not recognize changes in the string value
        properly in certain circumstances.

        In other situations, large unsigned numbers (those above 2**31)
        could sometimes lose their unsignedness, causing bogus results in
        arithmetic operations.

        Integer modulus on large unsigned integers sometimes returned
        incorrect values.

        Perl 5.6.0 generated "not a number" warnings on certain conversions
        where previous versions didn't.

        These problems have all been rectified.

        Infinity is now recognized as a number.

        In Perl 5.6.0, qw(a\\b) produced a string with two backslashes
        instead of one, in a departure from the behavior in previous
        versions. The older behavior has been reinstated.

        caller() could cause core dumps in certain situations. Carp was
        sometimes affected by this problem.

    Bugs in regular expressions
        Pattern matches on overloaded values are now handled correctly.

        Perl 5.6.0 parsed m/\x{ab}/ incorrectly, leading to spurious
        warnings. This has been corrected.

        The RE engine found in Perl 5.6.0 accidentally pessimised certain
        kinds of simple pattern matches. These are now handled better.

        Regular expression debug output (whether through "use re 'debug'" or
        via "-Dr") now looks better.

        Multi-line matches like ""a\nxb\n" =~ /(?!\A)x/m" were flawed. The
        bug has been fixed.

        Use of $& could trigger a core dump under some situations. This is
        now avoided.

        Match variables $1 et al., weren't being unset when a pattern match
        was backtracking, and the anomaly showed up inside "/...(?{ ...
        }).../" etc. These variables are now tracked correctly.

        pos() did not return the correct value within s///ge in earlier
        versions. This is now handled correctly.

    "slurp" mode
        readline() on files opened in "slurp" mode could return an extra ""
        at the end in certain situations. This has been corrected.

    Autovivification of symbolic references to special variables
        Autovivification of symbolic references of special variables
        described in the perlvar manpage (as in "${$num}") was accidentally
        disabled. This works again now.

    Lexical warnings
        Lexical warnings now propagate correctly into "eval "..."".

        "use warnings qw(FATAL all)" did not work as intended. This has been

        Lexical warnings could leak into other scopes in some situations.
        This is now fixed.

        warnings::enabled() now reports the state of $^W correctly if the
        caller isn't using lexical warnings.

    Spurious warnings and errors
        Perl 5.6.0 could emit spurious warnings about redefinition of
        dl_error() when statically building extensions into perl. This has
        been corrected.

        "our" variables could result in bogus "Variable will not stay
        shared" warnings. This is now fixed.

        "our" variables of the same name declared in two sibling blocks
        resulted in bogus warnings about "redeclaration" of the variables.
        The problem has been corrected.

        Compatibility of the builtin glob() with old csh-based glob has been
        improved with the addition of GLOB_ALPHASORT option. See

        File::Glob::glob() has been renamed to File::Glob::bsd_glob()
        because the name clashes with the builtin glob(). The older name is
        still available for compatibility, but is deprecated.

        Spurious syntax errors generated in certain situations, when glob()
        caused File::Glob to be loaded for the first time, have been fixed.

        Some cases of inconsistent taint propagation (such as within hash
        values) have been fixed.

        The tainting behavior of sprintf() has been rationalized. It does
        not taint the result of floating point formats anymore, making the
        behavior consistent with that of string interpolation.

        Arguments to sort() weren't being provided the right wantarray()
        context. The comparison block is now run in scalar context, and the
        arguments to be sorted are always provided list context.

        sort() is also fully reentrant, in the sense that the sort function
        can itself call sort(). This did not work reliably in previous

    #line directives
        #line directives now work correctly when they appear at the very
        beginning of "eval "..."".

    Subroutine prototypes
        The (\&) prototype now works properly.

        map() could get pathologically slow when the result list it
        generates is larger than the source list. The performance has been
        improved for common scenarios.

        Debugger exit code now reflects the script exit code.

        Condition ""0"" in breakpoints is now treated correctly.

        The "d" command now checks the line number.

        "$." is no longer corrupted by the debugger.

        All debugger output now correctly goes to the socket if RemotePort
        is set.

        PERL5OPT can be set to more than one switch group. Previously, it
        used to be limited to one group of options only.

        chop(@list) in list context returned the characters chopped in
        reverse order. This has been reversed to be in the right order.

    Unicode support
        Unicode support has seen a large number of incremental improvements,
        but continues to be highly experimental. It is not expected to be
        fully supported in the 5.6.x maintenance releases.

        substr(), join(), repeat(), reverse(), quotemeta() and string
        concatenation were all handling Unicode strings incorrectly in Perl
        5.6.0. This has been corrected.

        Support for "tr///CU" and "tr///UC" etc., have been removed since we
        realized the interface is broken. For similar functionality, see the
        pack entry in the perlfunc manpage.

        The Unicode Character Database has been updated to version 3.0.1
        with additions made available to the public as of August 30, 2000.

        The Unicode character classes \p{Blank} and \p{SpacePerl} have been
        added. "Blank" is like C isblank(), that is, it contains only
        "horizontal whitespace" (the space character is, the newline isn't),
        and the "SpacePerl" is the Unicode equivalent of "\s" (\p{Space}
        isn't, since that includes the vertical tabulator character, whereas
        "\s" doesn't.)

        If you are experimenting with Unicode support in perl, the
        development versions of Perl may have more to offer. In particular,
        I/O layers are now available in the development track, but not in
        the maintenance track, primarily to do backward compatibility
        issues. Unicode support is also evolving rapidly on a daily basis in
        the development track--the maintenance track only reflects the most
        conservative of these changes.

    64-bit support
        Support for 64-bit platforms has been improved, but continues to be
        experimental. The level of support varies greatly among platforms.

        The B Compiler and its various backends have had many incremental
        improvements, but they continue to remain highly experimental. Use
        in production environments is discouraged.

        The perlcc tool has been rewritten so that the user interface is
        much more like that of a C compiler.

        The perlbc tools has been removed. Use "perlcc -B" instead.

    Lvalue subroutines
        There have been various bugfixes to support lvalue subroutines
        better. However, the feature still remains experimental.

        IO::Socket::INET failed to open the specified port if the service
        name was not known. It now correctly uses the supplied port number
        as is.

        File::Find now chdir()s correctly when chasing symbolic links.

        xsubpp now tolerates embedded POD sections.

    "no Module;"
        "no Module;" does not produce an error even if Module does not have
        an unimport() method. This parallels the behavior of "use" vis-a-vis

        A large number of tests have been added.

  Core features

    untie() will now call an UNTIE() hook if it exists. See the perltie
    manpage for details.

    The "-DT" command line switch outputs copious tokenizing information.
    See the perlrun manpage.

    Arrays are now always interpolated in double-quotish strings.
    Previously, """" used to be a fatal error at compile time, if
    an array "@bar" was not used or declared. This transitional behavior was
    intended to help migrate perl4 code, and is deemed to be no longer
    useful. See the section on "Arrays now always interpolate into
    double-quoted strings".

    keys(), each(), pop(), push(), shift(), splice() and unshift() can all
    be overridden now.

    "my __PACKAGE__ $obj" now does the expected thing.

  Configuration issues

    On some systems (IRIX and Solaris among them) the system malloc is
    demonstrably better. While the defaults haven't been changed in order to
    retain binary compatibility with earlier releases, you may be better off
    building perl with "Configure -Uusemymalloc ..." as discussed in the
    INSTALL file.

    "Configure" has been enhanced in various ways:

    *   Minimizes use of temporary files.

    *   By default, does not link perl with libraries not used by it, such
        as the various dbm libraries. SunOS 4.x hints preserve behavior on
        that platform.

    *   Support for pdp11-style memory models has been removed due to

    *   Building outside the source tree is supported on systems that have
        symbolic links. This is done by running

            sh /path/to/source/Configure -Dmksymlinks ...
            make all test install

        in a directory other than the perl source directory. See INSTALL.

    *   "Configure -S" can be run non-interactively.


    README.aix, README.solaris and README.macos have been added.
    README.posix-bc has been renamed to README.bs2000. These are installed
    as the perlaix manpage, the perlsolaris manpage, the perlmacos manpage,
    and the perlbs2000 manpage respectively.

    The following pod documents are brand new:

        perlclib    Internal replacements for standard C library functions
        perldebtut  Perl debugging tutorial
        perlebcdic  Considerations for running Perl on EBCDIC platforms
        perlnewmod  Perl modules: preparing a new module for distribution
        perlrequick Perl regular expressions quick start
        perlretut   Perl regular expressions tutorial
        perlutil    utilities packaged with the Perl distribution

    The INSTALL file has been expanded to cover various issues, such as
    64-bit support.

    A longer list of contributors has been added to the source distribution.
    See the file "AUTHORS".

    Numerous other changes have been made to the included documentation and

  Bundled modules

    The following modules have been added.

        Walks Perl syntax tree, printing concise info about ops. See the
        B::Concise manpage.

        Returns name and handle of a temporary file safely. See the
        File::Temp manpage.

        Converts Pod data to formatted LaTeX. See the Pod::LaTeX manpage.

        Converts POD data to formatted overstrike text. See the
        Pod::Text::Overstrike manpage.

    The following modules have been upgraded.

    CGI CGI v2.752 is now included.

        CPAN v1.59_54 is now included.

        Various bugfixes have been added.

        DB_File v1.75 supports newer Berkeley DB versions, among other

        Devel::Peek has been enhanced to support dumping of memory
        statistics, when perl is built with the included malloc().

        File::Find now supports pre and post-processing of the files in
        order to sort() them, etc.

        Getopt::Long v2.25 is included.

        Various bug fixes have been included.

        IPC::Open3 allows use of numeric file descriptors.

        The fmod() function supports modulus operations. Various bug fixes
        have also been included.

        Math::Complex handles inf, NaN etc., better.

        ping() could fail on odd number of data bytes, and when the echo
        service isn't running. This has been corrected.

        A memory leak has been fixed.

        Version 1.13 of the Pod::Parser suite is included.

        Pod::Text and related modules have been upgraded to the versions in
        podlators suite v2.08.

        On dosish platforms, some keys went missing because of lack of
        support for files with "holes". A workaround for the problem has
        been added.

        Various bug fixes have been included.

        Now supports Tie::RefHash::Nestable to automagically tie hashref

        Various bug fixes have been included.

  Platform-specific improvements

    The following new ports are now available.

    Perl now builds under Amdahl UTS.

    Perl has also been verified to build under Amiga OS.

    Support for EPOC has been much improved. See README.epoc.

    Building perl with -Duseithreads or -Duse5005threads now works under
    HP-UX 10.20 (previously it only worked under 10.30 or later). You will
    need a thread library package installed. See README.hpux.

    Long doubles should now work under Linux.

    MacOS Classic is now supported in the mainstream source package. See

    Support for MPE/iX has been updated. See README.mpeix.

    Support for OS/2 has been improved. See "os2/Changes" and README.os2.

    Dynamic loading on z/OS (formerly OS/390) has been improved. See

    Support for VMS has seen many incremental improvements, including better
    support for operators like backticks and system(), and better %ENV
    handling. See "README.vms" and the perlvms manpage.

    Support for Stratus VOS has been improved. See "vos/Changes" and

    Support for Windows has been improved.

    *   fork() emulation has been improved in various ways, but still
        continues to be experimental. See the perlfork manpage for known
        bugs and caveats.

    *   %SIG has been enabled under USE_ITHREADS, but its use is completely
        unsupported under all configurations.

    *   Borland C++ v5.5 is now a supported compiler that can build Perl.
        However, the generated binaries continue to be incompatible with
        those generated by the other supported compilers (GCC and Visual

    *   Non-blocking waits for child processes (or pseudo-processes) are
        supported via "waitpid($pid, &POSIX::WNOHANG)".

    *   A memory leak in accept() has been fixed.

    *   wait(), waitpid() and backticks now return the correct exit status
        under Windows 9x.

    *   Trailing new %ENV entries weren't propagated to child processes.
        This is now fixed.

    *   Current directory entries in %ENV are now correctly propagated to
        child processes.

    *   Duping socket handles with open(F, ">&MYSOCK") now works under
        Windows 9x.

    *   The makefiles now provide a single switch to bulk-enable all the
        features enabled in ActiveState ActivePerl (a popular binary

    *   Win32::GetCwd() correctly returns C:\ instead of C: when at the
        drive root. Other bugs in chdir() and Cwd::cwd() have also been

    *   fork() correctly returns undef and sets EAGAIN when it runs out of
        pseudo-process handles.

    *   ExtUtils::MakeMaker now uses $ENV{LIB} to search for libraries.

    *   UNC path handling is better when perl is built to support fork().

    *   A handle leak in socket handling has been fixed.

    *   send() works from within a pseudo-process.

    Unless specifically qualified otherwise, the remainder of this document
    covers changes between the 5.005 and 5.6.0 releases.

Core Enhancements
  Interpreter cloning, threads, and concurrency

    Perl 5.6.0 introduces the beginnings of support for running multiple
    interpreters concurrently in different threads. In conjunction with the
    perl_clone() API call, which can be used to selectively duplicate the
    state of any given interpreter, it is possible to compile a piece of
    code once in an interpreter, clone that interpreter one or more times,
    and run all the resulting interpreters in distinct threads.

    On the Windows platform, this feature is used to emulate fork() at the
    interpreter level. See the perlfork manpage for details about that.

    This feature is still in evolution. It is eventually meant to be used to
    selectively clone a subroutine and data reachable from that subroutine
    in a separate interpreter and run the cloned subroutine in a separate
    thread. Since there is no shared data between the interpreters, little
    or no locking will be needed (unless parts of the symbol table are
    explicitly shared). This is obviously intended to be an easy-to-use
    replacement for the existing threads support.

    Support for cloning interpreters and interpreter concurrency can be
    enabled using the -Dusethreads Configure option (see win32/Makefile for
    how to enable it on Windows.) The resulting perl executable will be
    functionally identical to one that was built with -Dmultiplicity, but
    the perl_clone() API call will only be available in the former.

    -Dusethreads enables the cpp macro USE_ITHREADS by default, which in
    turn enables Perl source code changes that provide a clear separation
    between the op tree and the data it operates with. The former is
    immutable, and can therefore be shared between an interpreter and all of
    its clones, while the latter is considered local to each interpreter,
    and is therefore copied for each clone.

    Note that building Perl with the -Dusemultiplicity Configure option is
    adequate if you wish to run multiple independent interpreters
    concurrently in different threads. -Dusethreads only provides the
    additional functionality of the perl_clone() API call and other support
    for running cloned interpreters concurrently.

        NOTE: This is an experimental feature.  Implementation details are
        subject to change.

  Lexically scoped warning categories

    You can now control the granularity of warnings emitted by perl at a
    finer level using the "use warnings" pragma. the warnings manpage and
    the perllexwarn manpage have copious documentation on this feature.

  Unicode and UTF-8 support

    Perl now uses UTF-8 as its internal representation for character
    strings. The "utf8" and "bytes" pragmas are used to control this support
    in the current lexical scope. See the perlunicode manpage, the utf8
    manpage and the bytes manpage for more information.

    This feature is expected to evolve quickly to support some form of I/O
    disciplines that can be used to specify the kind of input and output
    data (bytes or characters). Until that happens, additional modules from
    CPAN will be needed to complete the toolkit for dealing with Unicode.

        NOTE: This should be considered an experimental feature.  Implementation
        details are subject to change.

  Support for interpolating named characters

    The new "\N" escape interpolates named characters within strings. For
    example, ""Hi! \N{WHITE SMILING FACE}"" evaluates to a string with a
    Unicode smiley face at the end.

  "our" declarations

    An "our" declaration introduces a value that can be best understood as a
    lexically scoped symbolic alias to a global variable in the package that
    was current where the variable was declared. This is mostly useful as an
    alternative to the "vars" pragma, but also provides the opportunity to
    introduce typing and other attributes for such variables. See the our
    entry in the perlfunc manpage.

  Support for strings represented as a vector of ordinals

    Literals of the form "v1.2.3.4" are now parsed as a string composed of
    characters with the specified ordinals. This is an alternative, more
    readable way to construct (possibly Unicode) strings instead of
    interpolating characters, as in ""\x{1}\x{2}\x{3}\x{4}"". The leading
    "v" may be omitted if there are more than two ordinals, so "1.2.3" is
    parsed the same as "v1.2.3".

    Strings written in this form are also useful to represent version
    "numbers". It is easy to compare such version "numbers" (which are
    really just plain strings) using any of the usual string comparison
    operators "eq", "ne", "lt", "gt", etc., or perform bitwise string
    operations on them using "|", "&", etc.

    In conjunction with the new "$^V" magic variable (which contains the
    perl version as a string), such literals can be used as a readable way
    to check if you're running a particular version of Perl:

        # this will parse in older versions of Perl also
        if ($^V and $^V gt v5.6.0) {
            # new features supported

    "require" and "use" also have some special magic to support such
    literals. They will be interpreted as a version rather than as a module

        require v5.6.0;             # croak if $^V lt v5.6.0
        use v5.6.0;                 # same, but croaks at compile-time

    Alternatively, the "v" may be omitted if there is more than one dot:

        require 5.6.0;
        use 5.6.0;

    Also, "sprintf" and "printf" support the Perl-specific format flag "%v"
    to print ordinals of characters in arbitrary strings:

        printf "v%vd", $^V;         # prints current version, such as "v5.5.650"
        printf "%*vX", ":", $addr;  # formats IPv6 address
        printf "%*vb", " ", $bits;  # displays bitstring

    See the section on "Scalar value constructors" in the perldata manpage
    for additional information.

  Improved Perl version numbering system

    Beginning with Perl version 5.6.0, the version number convention has
    been changed to a "dotted integer" scheme that is more commonly found in
    open source projects.

    Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc.
    The next development series following v5.6.0 will be numbered v5.7.x,
    beginning with v5.7.0, and the next major production release following
    v5.6.0 will be v5.8.0.

    The English module now sets $PERL_VERSION to $^V (a string value) rather
    than "$]" (a numeric value). (This is a potential incompatibility. Send
    us a report via perlbug if you are affected by this.)

    The v1.2.3 syntax is also now legal in Perl. See the Support for strings
    represented as a vector of ordinals entry elsewhere in this document for
    more on that.

    To cope with the new versioning system's use of at least three
    significant digits for each version component, the method used for
    incrementing the subversion number has also changed slightly. We assume
    that versions older than v5.6.0 have been incrementing the subversion
    component in multiples of 10. Versions after v5.6.0 will increment them
    by 1. Thus, using the new notation, 5.005_03 is the "same" as v5.5.30,
    and the first maintenance version following v5.6.0 will be v5.6.1 (which
    should be read as being equivalent to a floating point value of
    5.006_001 in the older format, stored in "$]").

  New syntax for declaring subroutine attributes

    Formerly, if you wanted to mark a subroutine as being a method call or
    as requiring an automatic lock() when it is entered, you had to declare
    that with a "use attrs" pragma in the body of the subroutine. That can
    now be accomplished with declaration syntax, like this:

        sub mymethod : locked method ;
        sub mymethod : locked method {

        sub othermethod :locked :method ;
        sub othermethod :locked :method {

    (Note how only the first ":" is mandatory, and whitespace surrounding
    the ":" is optional.) and have been updated to keep the attributes
    with the stubs they provide. See the attributes manpage.

  File and directory handles can be autovivified

    Similar to how constructs such as "$x->[0]" autovivify a reference,
    handle constructors (open(), opendir(), pipe(), socketpair(), sysopen(),
    socket(), and accept()) now autovivify a file or directory handle if the
    handle passed to them is an uninitialized scalar variable. This allows
    the constructs such as "open(my $fh, ...)" and "open(local $fh,...)" to
    be used to create filehandles that will conveniently be closed
    automatically when the scope ends, provided there are no other
    references to them. This largely eliminates the need for typeglobs when
    opening filehandles that must be passed around, as in the following

        sub myopen {
            open my $fh, "@_"
                 or die "Can't open '@_': $!";
            return $fh;

            my $f = myopen("</etc/motd");
            print <$f>;
            # $f implicitly closed here

  open() with more than two arguments

    If open() is passed three arguments instead of two, the second argument
    is used as the mode and the third argument is taken to be the file name.
    This is primarily useful for protecting against unintended magic
    behavior of the traditional two-argument form. See the open entry in the
    perlfunc manpage.

  64-bit support

    Any platform that has 64-bit integers either

            (1) natively as longs or ints
            (2) via special compiler flags
            (3) using long long or int64_t

    is able to use "quads" (64-bit integers) as follows:

    *   constants (decimal, hexadecimal, octal, binary) in the code

    *   arguments to oct() and hex()

    *   arguments to print(), printf() and sprintf() (flag prefixes ll, L,

    *   printed as such

    *   pack() and unpack() "q" and "Q" formats

    *   in basic arithmetics: + - * / % (NOTE: operating close to the limits
        of the integer values may produce surprising results)

    *   in bit arithmetics: & | ^ ~ << >> (NOTE: these used to be forced to
        be 32 bits wide but now operate on the full native width.)

    *   vec()

    Note that unless you have the case (a) you will have to configure and
    compile Perl using the -Duse64bitint Configure flag.

        NOTE: The Configure flags -Duselonglong and -Duse64bits have been
        deprecated.  Use -Duse64bitint instead.

    There are actually two modes of 64-bitness: the first one is achieved
    using Configure -Duse64bitint and the second one using Configure
    -Duse64bitall. The difference is that the first one is minimal and the
    second one maximal. The first works in more places than the second.

    The "use64bitint" does only as much as is required to get 64-bit
    integers into Perl (this may mean, for example, using "long longs")
    while your memory may still be limited to 2 gigabytes (because your
    pointers could still be 32-bit). Note that the name "64bitint" does not
    imply that your C compiler will be using 64-bit "int"s (it might, but it
    doesn't have to): the "use64bitint" means that you will be able to have
    64 bits wide scalar values.

    The "use64bitall" goes all the way by attempting to switch also integers
    (if it can), longs (and pointers) to being 64-bit. This may create an
    even more binary incompatible Perl than -Duse64bitint: the resulting
    executable may not run at all in a 32-bit box, or you may have to
    reboot/reconfigure/rebuild your operating system to be 64-bit aware.

    Natively 64-bit systems like Alpha and Cray need neither -Duse64bitint
    nor -Duse64bitall.

    Last but not least: note that due to Perl's habit of always using
    floating point numbers, the quads are still not true integers. When
    quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
    -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they are
    silently promoted to floating point numbers, after which they will start
    losing precision (in their lower digits).

        NOTE: 64-bit support is still experimental on most platforms.
        Existing support only covers the LP64 data model.  In particular, the
        LLP64 data model is not yet supported.  64-bit libraries and system
        APIs on many platforms have not stabilized--your mileage may vary.

  Large file support

    If you have filesystems that support "large files" (files larger than 2
    gigabytes), you may now also be able to create and access them from

        NOTE: The default action is to enable large file support, if
        available on the platform.

    If the large file support is on, and you have a Fcntl constant
    O_LARGEFILE, the O_LARGEFILE is automatically added to the flags of

    Beware that unless your filesystem also supports "sparse files" seeking
    to umpteen petabytes may be inadvisable.

    Note that in addition to requiring a proper file system to do large
    files you may also need to adjust your per-process (or your per-system,
    or per-process-group, or per-user-group) maximum filesize limits before
    running Perl scripts that try to handle large files, especially if you
    intend to write such files.

    Finally, in addition to your process/process group maximum filesize
    limits, you may have quota limits on your filesystems that stop you
    (your user id or your user group id) from using large files.

    Adjusting your process/user/group/file system/operating system limits is
    outside the scope of Perl core language. For process limits, you may try
    increasing the limits using your shell's limits/limit/ulimit command
    before running Perl. The BSD::Resource extension (not included with the
    standard Perl distribution) may also be of use, it offers the
    getrlimit/setrlimit interface that can be used to adjust process
    resource usage limits, including the maximum filesize limit.

  Long doubles

    In some systems you may be able to use long doubles to enhance the range
    and precision of your double precision floating point numbers (that is,
    Perl's numbers). Use Configure -Duselongdouble to enable this support
    (if it is available).

  "more bits"

    You can "Configure -Dusemorebits" to turn on both the 64-bit support and
    the long double support.

  Enhanced support for sort() subroutines

    Perl subroutines with a prototype of "($$)", and XSUBs in general, can
    now be used as sort subroutines. In either case, the two elements to be
    compared are passed as normal parameters in @_. See the sort entry in
    the perlfunc manpage.

    For unprototyped sort subroutines, the historical behavior of passing
    the elements to be compared as the global variables $a and $b remains

  "sort $coderef @foo" allowed

    sort() did not accept a subroutine reference as the comparison function
    in earlier versions. This is now permitted.

  File globbing implemented internally

    Perl now uses the File::Glob implementation of the glob() operator
    automatically. This avoids using an external csh process and the
    problems associated with it.

        NOTE: This is currently an experimental feature.  Interfaces and
        implementation are subject to change.

  Support for CHECK blocks

    In addition to "BEGIN", "INIT", "END", "DESTROY" and "AUTOLOAD",
    subroutines named "CHECK" are now special. These are queued up during
    compilation and behave similar to END blocks, except they are called at
    the end of compilation rather than at the end of execution. They cannot
    be called directly.

  POSIX character class syntax [: :] supported

    For example to match alphabetic characters use /[[:alpha:]]/. See the
    perlre manpage for details.

  Better pseudo-random number generator

    In 5.005_0x and earlier, perl's rand() function used the C library
    rand(3) function. As of 5.005_52, Configure tests for drand48(),
    random(), and rand() (in that order) and picks the first one it finds.

    These changes should result in better random numbers from rand().

  Improved "qw//" operator

    The "qw//" operator is now evaluated at compile time into a true list
    instead of being replaced with a run time call to "split()". This
    removes the confusing misbehaviour of "qw//" in scalar context, which
    had inherited that behaviour from split().


        $foo = ($bar) = qw(a b c); print "$foo|$bar\n";

    now correctly prints "3|a", instead of "2|a".

  Better worst-case behavior of hashes

    Small changes in the hashing algorithm have been implemented in order to
    improve the distribution of lower order bits in the hashed value. This
    is expected to yield better performance on keys that are repeated

  pack() format 'Z' supported

    The new format type 'Z' is useful for packing and unpacking
    null-terminated strings. See the section on "pack" in the perlfunc

  pack() format modifier '!' supported

    The new format type modifier '!' is useful for packing and unpacking
    native shorts, ints, and longs. See the section on "pack" in the
    perlfunc manpage.

  pack() and unpack() support counted strings

    The template character '/' can be used to specify a counted string type
    to be packed or unpacked. See the section on "pack" in the perlfunc

  Comments in pack() templates

    The '#' character in a template introduces a comment up to end of the
    line. This facilitates documentation of pack() templates.

  Weak references

    In previous versions of Perl, you couldn't cache objects so as to allow
    them to be deleted if the last reference from outside the cache is
    deleted. The reference in the cache would hold a reference count on the
    object and the objects would never be destroyed.

    Another familiar problem is with circular references. When an object
    references itself, its reference count would never go down to zero, and
    it would not get destroyed until the program is about to exit.

    Weak references solve this by allowing you to "weaken" any reference,
    that is, make it not count towards the reference count. When the last
    non-weak reference to an object is deleted, the object is destroyed and
    all the weak references to the object are automatically undef-ed.

    To use this feature, you need the WeakRef package from CPAN, which
    contains additional documentation.

        NOTE: This is an experimental feature.  Details are subject to change.  

  Binary numbers supported

    Binary numbers are now supported as literals, in s?printf formats, and

        $answer = 0b101010;
        printf "The answer is: %b\n", oct("0b101010");

  Lvalue subroutines

    Subroutines can now return modifiable lvalues. See the section on
    "Lvalue subroutines" in the perlsub manpage.

        NOTE: This is an experimental feature.  Details are subject to change.

  Some arrows may be omitted in calls through references

    Perl now allows the arrow to be omitted in many constructs involving
    subroutine calls through references. For example, "$foo[10]->('foo')"
    may now be written "$foo[10]('foo')". This is rather similar to how the
    arrow may be omitted from "$foo[10]->{'foo'}". Note however, that the
    arrow is still required for "foo(10)->('bar')".

  Boolean assignment operators are legal lvalues

    Constructs such as "($a ||= 2) += 1" are now allowed.

  exists() is supported on subroutine names

    The exists() builtin now works on subroutine names. A subroutine is
    considered to exist if it has been declared (even if implicitly). See
    the exists entry in the perlfunc manpage for examples.

  exists() and delete() are supported on array elements

    The exists() and delete() builtins now work on simple arrays as well.
    The behavior is similar to that on hash elements.

    exists() can be used to check whether an array element has been
    initialized. This avoids autovivifying array elements that don't exist.
    If the array is tied, the EXISTS() method in the corresponding tied
    package will be invoked.

    delete() may be used to remove an element from the array and return it.
    The array element at that position returns to its uninitialized state,
    so that testing for the same element with exists() will return false. If
    the element happens to be the one at the end, the size of the array also
    shrinks up to the highest element that tests true for exists(), or 0 if
    none such is found. If the array is tied, the DELETE() method in the
    corresponding tied package will be invoked.

    See the exists entry in the perlfunc manpage and the delete entry in the
    perlfunc manpage for examples.

  Pseudo-hashes work better

    Dereferencing some types of reference values in a pseudo-hash, such as
    "$ph->{foo}[1]", was accidentally disallowed. This has been corrected.

    When applied to a pseudo-hash element, exists() now reports whether the
    specified value exists, not merely if the key is valid.

    delete() now works on pseudo-hashes. When given a pseudo-hash element or
    slice it deletes the values corresponding to the keys (but not the keys
    themselves). See the section on "Pseudo-hashes: Using an array as a
    hash" in the perlref manpage.

    Pseudo-hash slices with constant keys are now optimized to array lookups
    at compile-time.

    List assignments to pseudo-hash slices are now supported.

    The "fields" pragma now provides ways to create pseudo-hashes, via
    fields::new() and fields::phash(). See the fields manpage.

        NOTE: The pseudo-hash data type continues to be experimental.
        Limiting oneself to the interface elements provided by the
        fields pragma will provide protection from any future changes.

  Automatic flushing of output buffers

    fork(), exec(), system(), qx//, and pipe open()s now flush buffers of
    all files opened for output when the operation was attempted. This
    mostly eliminates confusing buffering mishaps suffered by users unaware
    of how Perl internally handles I/O.

    This is not supported on some platforms like Solaris where a suitably
    correct implementation of fflush(NULL) isn't available.

  Better diagnostics on meaningless filehandle operations

    Constructs such as "open(<FH>)" and "close(<FH>)" are compile time
    errors. Attempting to read from filehandles that were opened only for
    writing will now produce warnings (just as writing to read-only
    filehandles does).

  Where possible, buffered data discarded from duped input filehandle

    "open(NEW, "<&OLD")" now attempts to discard any data that was
    previously read and buffered in "OLD" before duping the handle. On
    platforms where doing this is allowed, the next read operation on "NEW"
    will return the same data as the corresponding operation on "OLD".
    Formerly, it would have returned the data from the start of the
    following disk block instead.

  eof() has the same old magic as <>

    "eof()" would return true if no attempt to read from "<>" had yet been
    made. "eof()" has been changed to have a little magic of its own, it now
    opens the "<>" files.

  binmode() can be used to set :crlf and :raw modes

    binmode() now accepts a second argument that specifies a discipline for
    the handle in question. The two pseudo-disciplines ":raw" and ":crlf"
    are currently supported on DOS-derivative platforms. See the section on
    "binmode" in the perlfunc manpage and the open manpage.

  "-T" filetest recognizes UTF-8 encoded files as "text"

    The algorithm used for the "-T" filetest has been enhanced to correctly
    identify UTF-8 content as "text".

  system(), backticks and pipe open now reflect exec() failure

    On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
    etc., are implemented via fork() and exec(). When the underlying exec()
    fails, earlier versions did not report the error properly, since the
    exec() happened to be in a different process.

    The child process now communicates with the parent about the error in
    launching the external command, which allows these constructs to return
    with their usual error value and set $!.

  Improved diagnostics

    Line numbers are no longer suppressed (under most likely circumstances)
    during the global destruction phase.

    Diagnostics emitted from code running in threads other than the main
    thread are now accompanied by the thread ID.

    Embedded null characters in diagnostics now actually show up. They used
    to truncate the message in prior versions.

    $foo::a and $foo::b are now exempt from "possible typo" warnings only if
    sort() is encountered in package "foo".

    Unrecognized alphabetic escapes encountered when parsing quote
    constructs now generate a warning, since they may take on new semantics
    in later versions of Perl.

    Many diagnostics now report the internal operation in which the warning
    was provoked, like so:

        Use of uninitialized value in concatenation (.) at (eval 1) line 1.
        Use of uninitialized value in print at (eval 1) line 1.

    Diagnostics that occur within eval may also report the file and line
    number where the eval is located, in addition to the eval sequence
    number and the line number within the evaluated text itself. For

        Not enough arguments for scalar at (eval 4)[newlib/] line 2, at EOF

  Diagnostics follow STDERR

    Diagnostic output now goes to whichever file the "STDERR" handle is
    pointing at, instead of always going to the underlying C runtime
    library's "stderr".

  More consistent close-on-exec behavior

    On systems that support a close-on-exec flag on filehandles, the flag is
    now set for any handles created by pipe(), socketpair(), socket(), and
    accept(), if that is warranted by the value of $^F that may be in
    effect. Earlier versions neglected to set the flag for handles created
    with these operators. See the pipe entry in the perlfunc manpage, the
    socketpair entry in the perlfunc manpage, the socket entry in the
    perlfunc manpage, the accept entry in the perlfunc manpage, and the
    section on "$^F" in the perlvar manpage.

  syswrite() ease-of-use

    The length argument of "syswrite()" has become optional.

  Better syntax checks on parenthesized unary operators

    Expressions such as:

        print defined(&foo,&bar,&baz);
        print uc("foo","bar","baz");

    used to be accidentally allowed in earlier versions, and produced
    unpredictable behaviour. Some produced ancillary warnings when used in
    this way; others silently did the wrong thing.

    The parenthesized forms of most unary operators that expect a single
    argument now ensure that they are not called with more than one
    argument, making the cases shown above syntax errors. The usual
    behaviour of:

        print defined &foo, &bar, &baz;
        print uc "foo", "bar", "baz";
        undef $foo, &bar;

    remains unchanged. See the perlop manpage.

  Bit operators support full native integer width

    The bit operators (& | ^ ~ << >>) now operate on the full native
    integral width (the exact size of which is available in
    $Config{ivsize}). For example, if your platform is either natively
    64-bit or if Perl has been configured to use 64-bit integers, these
    operations apply to 8 bytes (as opposed to 4 bytes on 32-bit platforms).
    For portability, be sure to mask off the excess bits in the result of
    unary "~", e.g., "~$x & 0xffffffff".

  Improved security features

    More potentially unsafe operations taint their results for improved

    The "passwd" and "shell" fields returned by the getpwent(), getpwnam(),
    and getpwuid() are now tainted, because the user can affect their own
    encrypted password and login shell.

    The variable modified by shmread(), and messages returned by msgrcv()
    (and its object-oriented interface IPC::SysV::Msg::rcv) are also
    tainted, because other untrusted processes can modify messages and
    shared memory segments for their own nefarious purposes.

  More functional bareword prototype (*)

    Bareword prototypes have been rationalized to enable them to be used to
    override builtins that accept barewords and interpret them in a special
    way, such as "require" or "do".

    Arguments prototyped as "*" will now be visible within the subroutine as
    either a simple scalar or as a reference to a typeglob. See the
    Prototypes entry in the perlsub manpage.

  "require" and "do" may be overridden

    "require" and "do 'file'" operations may be overridden locally by
    importing subroutines of the same name into the current package (or
    globally by importing them into the CORE::GLOBAL:: namespace).
    Overriding "require" will also affect "use", provided the override is
    visible at compile-time. See the section on "Overriding Built-in
    Functions" in the perlsub manpage.

  $^X variables may now have names longer than one character

    Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax error.
    Now variable names that begin with a control character may be
    arbitrarily long. However, for compatibility reasons, these variables
    *must* be written with explicit braces, as "${^XY}" for example.
    "${^XYZ}" is synonymous with ${"\cXYZ"}. Variable names with more than
    one control character, such as "${^XY^Z}", are illegal.

    The old syntax has not changed. As before, `^X' may be either a literal
    control-X character or the two-character sequence `caret' plus `X'. When
    braces are omitted, the variable name stops after the control character.
    Thus ""$^XYZ"" continues to be synonymous with "$^X . "YZ"" as before.

    As before, lexical variables may not have names beginning with control
    characters. As before, variables whose names begin with a control
    character are always forced to be in package `main'. All such variables
    are reserved for future extensions, except those that begin with "^_",
    which may be used by user programs and are guaranteed not to acquire
    special meaning in any future version of Perl.

  New variable $^C reflects "-c" switch

    "$^C" has a boolean value that reflects whether perl is being run in
    compile-only mode (i.e. via the "-c" switch). Since BEGIN blocks are
    executed under such conditions, this variable enables perl code to
    determine whether actions that make sense only during normal running are
    warranted. See the perlvar manpage.

  New variable $^V contains Perl version as a string

    "$^V" contains the Perl version number as a string composed of
    characters whose ordinals match the version numbers, i.e. v5.6.0. This
    may be used in string comparisons.

    See "Support for strings represented as a vector of ordinals" for an

  Optional Y2K warnings

    If Perl is built with the cpp macro "PERL_Y2KWARN" defined, it emits
    optional warnings when concatenating the number 19 with another number.

    This behavior must be specifically enabled when running Configure. See

  Arrays now always interpolate into double-quoted strings

    In double-quoted strings, arrays now interpolate, no matter what. The
    behavior in earlier versions of perl 5 was that arrays would interpolate
    into strings if the array had been mentioned before the string was
    compiled, and otherwise Perl would raise a fatal compile-time error. In
    versions 5.000 through 5.003, the error was

            Literal @example now requires backslash

    In versions 5.004_01 through 5.6.0, the error was

            In string, @example now must be written as \@example

    The idea here was to get people into the habit of writing
    ""fred\"" when they wanted a literal "@" sign, just as they
    have always written ""Give me back my \$5"" when they wanted a literal
    "$" sign.

    Starting with 5.6.1, when Perl now sees an "@" sign in a double-quoted
    string, it *always* attempts to interpolate an array, regardless of
    whether or not the array has been used or declared already. The fatal
    error has been downgraded to an optional warning:

            Possible unintended interpolation of @example in string

    This warns you that """" is going to turn into
    "" if you don't backslash the "@". See for more details about the
    history here.

Modules and Pragmata

        While used internally by Perl as a pragma, this module also provides
        a way to fetch subroutine and variable attributes. See the
        attributes manpage.

    B   The Perl Compiler suite has been extensively reworked for this
        release. More of the standard Perl testsuite passes when run under
        the Compiler, but there is still a significant way to go to achieve
        production quality compiled executables.

            NOTE: The Compiler suite remains highly experimental.  The
            generated code may not be correct, even when it manages to execute
            without errors.

        Overall, Benchmark results exhibit lower average error and better
        timing accuracy.

        You can now run tests for *n* seconds instead of guessing the right
        number of tests to run: e.g., timethese(-5, ...) will run each code
        for at least 5 CPU seconds. Zero as the "number of repetitions"
        means "for at least 3 CPU seconds". The output format has also
        changed. For example:

           use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})

        will now output something like this:

           Benchmark: running a, b, each for at least 5 CPU seconds...
                    a:  5 wallclock secs ( 5.77 usr +  0.00 sys =  5.77 CPU) @ 200551.91/s (n=1156516)
                    b:  4 wallclock secs ( 5.00 usr +  0.02 sys =  5.02 CPU) @ 159605.18/s (n=800686)

        New features: "each for at least N CPU seconds...", "wallclock
        secs", and the "@ operations/CPU second (n=operations)".

        timethese() now returns a reference to a hash of Benchmark objects
        containing the test results, keyed on the names of the tests.

        timethis() now returns the iterations field in the Benchmark result
        object instead of 0.

        timethese(), timethis(), and the new cmpthese() (see below) can also
        take a format specifier of 'none' to suppress output.

        A new function countit() is just like timeit() except that it takes
        a TIME instead of a COUNT.

        A new function cmpthese() prints a chart comparing the results of
        each test returned from a timethese() call. For each possible pair
        of tests, the percentage speed difference (iters/sec or
        seconds/iter) is shown.

        For other details, see the Benchmark manpage.

        The ByteLoader is a dedicated extension to generate and run Perl
        bytecode. See the ByteLoader manpage.

        References can now be used.

        The new version also allows a leading underscore in constant names,
        but disallows a double leading underscore (as in "__LINE__"). Some
        other names are disallowed or warned against, including BEGIN, END,
        etc. Some names which were forced into main:: used to fail silently
        in some cases; now they're fatal (outside of main::) and an optional
        warning (inside of main::). The ability to detect whether a constant
        had been set with a given name has been added.

        See the constant manpage.

        This pragma implements the "\N" string escape. See the charnames

        A "Maxdepth" setting can be specified to avoid venturing too deeply
        into deep data structures. See the Data::Dumper manpage.

        The XSUB implementation of Dump() is now automatically called if the
        "Useqq" setting is not in use.

        Dumping "qr//" objects works correctly.

    DB  "DB" is an experimental module that exposes a clean abstraction to
        Perl's debugging API.

        DB_File can now be built with Berkeley DB versions 1, 2 or 3. See

        Devel::DProf, a Perl source code profiler has been added. See the
        Devel::DProf manpage and the dprofpp manpage.

        The Devel::Peek module provides access to the internal
        representation of Perl variables and data. It is a data debugging
        tool for the XS programmer.

        The Dumpvalue module provides screen dumps of Perl data.

        DynaLoader now supports a dl_unload_file() function on platforms
        that support unloading shared objects using dlclose().

        Perl can also optionally arrange to unload all extension shared
        objects loaded by Perl. To enable this, build Perl with the
        Configure option "-Accflags=-DDL_UNLOAD_ALL_AT_EXIT". (This maybe
        useful if you are using Apache with mod_perl.)

        $PERL_VERSION now stands for "$^V" (a string value) rather than for
        "$]" (a numeric value).

    Env Env now supports accessing environment variables like PATH as array

        More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
        large file (more than 4GB) access (NOTE: the O_LARGEFILE is
        automatically added to sysopen() flags if large file support has
        been configured, as is the default), Free/Net/OpenBSD locking
        behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the
        combined mask of O_RDONLY, O_WRONLY, and O_RDWR. The
        seek()/sysseek() constants SEEK_SET, SEEK_CUR, and SEEK_END are
        available via the ":seek" tag. The chmod()/stat() S_IF* constants
        and S_IS* functions are available via the ":mode" tag.

        A compare_text() function has been added, which allows custom
        comparison functions. See the File::Compare manpage.

        File::Find now works correctly when the wanted() function is either
        autoloaded or is a symbolic reference.

        A bug that caused File::Find to lose track of the working directory
        when pruning top-level directories has been fixed.

        File::Find now also supports several other options to control its
        behavior. It can follow symbolic links if the "follow" option is
        specified. Enabling the "no_chdir" option will make File::Find skip
        changing the current directory when walking directories. The
        "untaint" flag can be useful when running with taint checks enabled.

        See the File::Find manpage.

        This extension implements BSD-style file globbing. By default, it
        will also be used for the internal implementation of the glob()
        operator. See the File::Glob manpage.

        New methods have been added to the File::Spec module: devnull()
        returns the name of the null device (/dev/null on Unix) and tmpdir()
        the name of the temp directory (normally /tmp on Unix). There are
        now also methods to convert between absolute and relative filenames:
        abs2rel() and rel2abs(). For compatibility with operating systems
        that specify volume names in file paths, the splitpath(),
        splitdir(), and catdir() methods have been added.

        The new File::Spec::Functions modules provides a function interface
        to the File::Spec module. Allows shorthand

            $fullname = catfile($dir1, $dir2, $file);

        instead of

            $fullname = File::Spec->catfile($dir1, $dir2, $file);

        Getopt::Long licensing has changed to allow the Perl Artistic
        License as well as the GPL. It used to be GPL only, which got in the
        way of non-GPL applications that wanted to use Getopt::Long.

        Getopt::Long encourages the use of Pod::Usage to produce help
        messages. For example:

            use Getopt::Long;
            use Pod::Usage;
            my $man = 0;
            my $help = 0;
            GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
            pod2usage(1) if $help;
            pod2usage(-exitstatus => 0, -verbose => 2) if $man;


            =head1 NAME

            sample - Using GetOpt::Long and Pod::Usage

            =head1 SYNOPSIS

            sample [options] [file ...]

               -help            brief help message
               -man             full documentation

            =head1 OPTIONS

            =over 8

            =item B<-help>

            Print a brief help message and exits.

            =item B<-man>

            Prints the manual page and exits.


            =head1 DESCRIPTION

            B<This program> will read the given input file(s) and do something
            useful with the contents thereof.


        See the Pod::Usage manpage for details.

        A bug that prevented the non-option call-back <> from being
        specified as the first argument has been fixed.

        To specify the characters < and > as option starters, use ><. Note,
        however, that changing option starters is strongly deprecated.

    IO  write() and syswrite() will now accept a single-argument form of the
        call, for consistency with Perl's syswrite().

        You can now create a TCP-based IO::Socket::INET without forcing a
        connect attempt. This allows you to configure its options (like
        making it non-blocking) and then call connect() manually.

        A bug that prevented the IO::Socket::protocol() accessor from ever
        returning the correct value has been corrected.

        IO::Socket::connect now uses non-blocking IO instead of alarm() to
        do connect timeouts.

        IO::Socket::accept now uses select() instead of alarm() for doing

        IO::Socket::INET->new now sets $! correctly on failure. $@ is still
        set for backwards compatibility.

    JPL Java Perl Lingo is now distributed with Perl. See jpl/README for
        more information.

    lib "use lib" now weeds out any trailing duplicate entries. "no lib"
        removes all named entries.

        The bitwise operations "<<", ">>", "&", "|", and "~" are now
        supported on bigints.

        The accessor methods Re, Im, arg, abs, rho, and theta can now also
        act as mutators (accessor $z->Re(), mutator $z->Re(3)).

        The class method "display_format" and the corresponding object
        method "display_format", in addition to accepting just one argument,
        now can also accept a parameter hash. Recognized keys of a parameter
        hash are ""style"", which corresponds to the old one parameter case,
        and two new parameters: ""format"", which is a printf()-style format
        string (defaults usually to ""%.15g"", you can revert to the default
        by setting the format string to "undef") used for both parts of a
        complex number, and ""polar_pretty_print"" (defaults to true), which
        controls whether an attempt is made to try to recognize small
        multiples and rationals of pi (2pi, pi/2) at the argument (angle) of
        a polar complex number.

        The potentially disruptive change is that in list context both
        methods now *return the parameter hash*, instead of only the value
        of the ""style"" parameter.

        A little bit of radial trigonometry (cylindrical and spherical),
        radial coordinate conversions, and the great circle distance were

    Pod::Parser, Pod::InputObjects
        Pod::Parser is a base class for parsing and selecting sections of
        pod documentation from an input stream. This module takes care of
        identifying pod paragraphs and commands in the input and hands off
        the parsed paragraphs and commands to user-defined methods which are
        free to interpret or translate them as they see fit.

        Pod::InputObjects defines some input objects needed by Pod::Parser,
        and for advanced users of Pod::Parser that need more about a command
        besides its name and text.

        As of release 5.6.0 of Perl, Pod::Parser is now the officially
        sanctioned "base parser code" recommended for use by all pod2xxx
        translators. Pod::Text (pod2text) and Pod::Man (pod2man) have
        already been converted to use Pod::Parser and efforts to convert
        Pod::HTML (pod2html) are already underway. For any questions or
        comments about pod parsing and translating issues and utilities,
        please use the mailing list.

        For further information, please see the Pod::Parser manpage and the
        Pod::InputObjects manpage.

    Pod::Checker, podchecker
        This utility checks pod files for correct syntax, according to the
        perlpod manpage. Obvious errors are flagged as such, while warnings
        are printed for mistakes that can be handled gracefully. The
        checklist is not complete yet. See the Pod::Checker manpage.

    Pod::ParseUtils, Pod::Find
        These modules provide a set of gizmos that are useful mainly for pod
        translators. Pod::Find traverses directory structures and returns
        found pod files, along with their canonical names (like
        "File::Spec::Unix"). Pod::ParseUtils contains Pod::List (useful for
        storing pod list information), Pod::Hyperlink (for parsing the
        contents of "L<>" sequences) and Pod::Cache (for caching information
        about pod files, e.g., link nodes).

    Pod::Select, podselect
        Pod::Select is a subclass of Pod::Parser which provides a function
        named "podselect()" to filter out user-specified sections of raw pod
        documentation from an input stream. podselect is a script that
        provides access to Pod::Select from other scripts to be used as a
        filter. See the Pod::Select manpage.

    Pod::Usage, pod2usage
        Pod::Usage provides the function "pod2usage()" to print usage
        messages for a Perl script based on its embedded pod documentation.
        The pod2usage() function is generally useful to all script authors
        since it lets them write and maintain a single source (the pods) for
        documentation, thus removing the need to create and maintain
        redundant usage message text consisting of information already in
        the pods.

        There is also a pod2usage script which can be used from other kinds
        of scripts to print usage messages from pods (even for non-Perl
        scripts with pods embedded in comments).

        For details and examples, please see the Pod::Usage manpage.

    Pod::Text and Pod::Man
        Pod::Text has been rewritten to use Pod::Parser. While pod2text() is
        still available for backwards compatibility, the module now has a
        new preferred interface. See the Pod::Text manpage for the details.
        The new Pod::Text module is easily subclassed for tweaks to the
        output, and two such subclasses (Pod::Text::Termcap for
        man-page-style bold and underlining using termcap information, and
        Pod::Text::Color for markup with ANSI color sequences) are now

        pod2man has been turned into a module, Pod::Man, which also uses
        Pod::Parser. In the process, several outstanding bugs related to
        quotes in section headers, quoting of code escapes, and nested lists
        have been fixed. pod2man is now a wrapper script around this module.

        An EXISTS method has been added to this module (and sdbm_exists()
        has been added to the underlying sdbm library), so one can now call
        exists on an SDBM_File tied hash and get the correct result, rather
        than a runtime error.

        A bug that may have caused data loss when more than one disk block
        happens to be read from the database in a single FETCH() has been

        Sys::Syslog now uses XSUBs to access facilities from syslog.h so it
        no longer requires to exist.

        Sys::Hostname now uses XSUBs to call the C library's gethostname()
        or uname() if they exist.

        Term::ANSIColor is a very simple module to provide easy and readable
        access to the ANSI color and highlighting escape sequences,
        supported by most ANSI terminal emulators. It is now included

        The timelocal() and timegm() functions used to silently return bogus
        results when the date fell outside the machine's integer range. They
        now consistently croak() if the date falls in an unsupported range.

        The error return value in list context has been changed for all
        functions that return a list of values. Previously these functions
        returned a list with a single element "undef" if an error occurred.
        Now these functions return the empty list in these situations. This
        applies to the following functions:


        The remaining functions are unchanged and continue to return "undef"
        on error even in list context.

        The Win32::SetLastError(ERROR) function has been added as a
        complement to the Win32::GetLastError() function.

        The new Win32::GetFullPathName(FILENAME) returns the full absolute
        pathname for FILENAME in scalar context. In list context it returns
        a two-element list containing the fully qualified directory name and
        the filename. See the Win32 manpage.

        The XSLoader extension is a simpler alternative to DynaLoader. See
        the XSLoader manpage.

    DBM Filters
        A new feature called "DBM Filters" has been added to all the DBM
        modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
        DBM Filters add four new methods to each DBM module:


        These can be used to filter key-value pairs before the pairs are
        written to the database or just after they are read from the
        database. See the perldbmfilter manpage for further information.


    "use attrs" is now obsolete, and is only provided for
    backward-compatibility. It's been replaced by the "sub : attributes"
    syntax. See the section on "Subroutine Attributes" in the perlsub
    manpage and the attributes manpage.

    Lexical warnings pragma, "use warnings;", to control optional warnings.
    See the perllexwarn manpage.

    "use filetest" to control the behaviour of filetests ("-r" "-w" ...).
    Currently only one subpragma implemented, "use filetest 'access';", that
    uses access(2) or equivalent to check permissions instead of using
    stat(2) as usual. This matters in filesystems where there are ACLs
    (access control lists): the stat(2) might lie, but access(2) knows

    The "open" pragma can be used to specify default disciplines for handle
    constructors (e.g. open()) and for qx//. The two pseudo-disciplines
    ":raw" and ":crlf" are currently supported on DOS-derivative platforms
    (i.e. where binmode is not a no-op). See also the section on "binmode()
    can be used to set :crlf and :raw modes".

Utility Changes

    "dprofpp" is used to display profile data generated using
    "Devel::DProf". See the dprofpp manpage.


    The "find2perl" utility now uses the enhanced features of the File::Find
    module. The -depth and -follow options are supported. Pod documentation
    is also included in the script.


    The "h2xs" tool can now work in conjunction with "C::Scan" (available
    from CPAN) to automatically parse real-life header files. The "-M",
    "-a", "-k", and "-o" options are new.


    "perlcc" now supports the C and Bytecode backends. By default, it
    generates output from the simple C backend rather than the optimized C

    Support for non-Unix platforms has been improved.


    "perldoc" has been reworked to avoid possible security holes. It will
    not by default let itself be run as the superuser, but you may still use
    the -U switch to try to make it drop privileges first.

  The Perl Debugger

    Many bug fixes and enhancements were added to, the Perl
    debugger. The help documentation was rearranged. New commands include "<
    ?", "> ?", and "{ ?" to list out current actions, "man *docpage*" to run
    your doc viewer on some perl docset, and support for quoted options. The
    help information was rearranged, and should be viewable once again if
    you're using less as your pager. A serious security hole was
    plugged--you should immediately remove all older versions of the Perl
    debugger as installed in previous releases, all the way back to perl3,
    from your system to avoid being bitten by this.

Improved Documentation
    Many of the platform-specific README files are now part of the perl
    installation. See the perl manpage for the complete list.

        The official list of public Perl API functions.

        A tutorial for beginners on object-oriented Perl.

        An introduction to using the Perl Compiler suite.

        A howto document on using the DBM filter facility.

        All material unrelated to running the Perl debugger, plus all
        low-level guts-like details that risked crushing the casual user of
        the debugger, have been relocated from the old manpage to the next
        entry below.

        This new manpage contains excessively low-level material not related
        to the Perl debugger, but slightly related to debugging Perl itself.
        It also contains some arcane internal details of how the debugging
        process works that may only be of interest to developers of Perl

        Notes on the fork() emulation currently available for the Windows

        An introduction to writing Perl source filters.

        Some guidelines for hacking the Perl source code.

        A list of internal functions in the Perl source code. (List is
        currently empty.)

        Introduction and reference information about lexically scoped
        warning categories.

        Detailed information about numbers as they are represented in Perl.

        A tutorial on using open() effectively.

        A tutorial that introduces the essentials of references.

        A tutorial on managing class data for object modules.

        Discussion of the most often wanted features that may someday be
        supported in Perl.

        An introduction to Unicode support features in Perl.

Performance enhancements
  Simple sort() using { $a <=> $b } and the like are optimized

    Many common sort() operations using a simple inlined block are now
    optimized for faster performance.

  Optimized assignments to lexical variables

    Certain operations in the RHS of assignment statements have been
    optimized to directly set the lexical variable on the LHS, eliminating
    redundant copying overheads.

  Faster subroutine calls

    Minor changes in how subroutine calls are handled internally provide
    marginal improvements in performance.

  delete(), each(), values() and hash iteration are faster

    The hash values returned by delete(), each(), values() and hashes in a
    list context are the actual values in the hash, instead of copies. This
    results in significantly better performance, because it eliminates
    needless copying in most situations.

Installation and Configuration Improvements
  -Dusethreads means something different

    The -Dusethreads flag now enables the experimental interpreter-based
    thread support by default. To get the flavor of experimental threads
    that was in 5.005 instead, you need to run Configure with "-Dusethreads

    As of v5.6.0, interpreter-threads support is still lacking a way to
    create new threads from Perl (i.e., "use Thread;" will not work with
    interpreter threads). "use Thread;" continues to be available when you
    specify the -Duse5005threads option to Configure, bugs and all.

        NOTE: Support for threads continues to be an experimental feature.
        Interfaces and implementation are subject to sudden and drastic changes.

  New Configure flags

    The following new flags may be enabled on the Configure command line by
    running Configure with "-Dflag".

        usethreads useithreads      (new interpreter threads: no Perl API yet)
        usethreads use5005threads   (threads as they were in 5.005)

        use64bitint                 (equal to now deprecated 'use64bits')

        usesocks                    (only SOCKS v5 supported)

  Threadedness and 64-bitness now more daring

    The Configure options enabling the use of threads and the use of
    64-bitness are now more daring in the sense that they no more have an
    explicit list of operating systems of known threads/64-bit capabilities.
    In other words: if your operating system has the necessary APIs and
    datatypes, you should be able just to go ahead and use them, for threads
    by Configure -Dusethreads, and for 64 bits either explicitly by
    Configure -Duse64bitint or implicitly if your system has 64-bit wide
    datatypes. See also the section on "64-bit support".

  Long Doubles

    Some platforms have "long doubles", floating point numbers of even
    larger range than ordinary "doubles". To enable using long doubles for
    Perl's scalars, use -Duselongdouble.


    You can enable both -Duse64bitint and -Duselongdouble with
    -Dusemorebits. See also the section on "64-bit support".


    Some platforms support system APIs that are capable of handling large
    files (typically, files larger than two gigabytes). Perl will try to use
    these APIs if you ask for -Duselargefiles.

    See the section on "Large file support" for more information.


    You can use "Configure -Uinstallusrbinperl" which causes installperl to
    skip installing perl also as /usr/bin/perl. This is useful if you prefer
    not to modify /usr/bin for some reason or another but harmful because
    many scripts assume to find Perl in /usr/bin/perl.

  SOCKS support

    You can use "Configure -Dusesocks" which causes Perl to probe for the
    SOCKS proxy protocol library (v5, not v4). For more information on
    SOCKS, see:

  "-A" flag

    You can "post-edit" the Configure variables using the Configure "-A"
    switch. The editing happens immediately after the platform specific
    hints files have been processed but before the actual configuration
    process starts. Run "Configure -h" to find out the full "-A" syntax.

  Enhanced Installation Directories

    The installation structure has been enriched to improve the support for
    maintaining multiple versions of perl, to provide locations for
    vendor-supplied modules, scripts, and manpages, and to ease maintenance
    of locally-added modules, scripts, and manpages. See the section on
    Installation Directories in the INSTALL file for complete details. For
    most users building and installing from source, the defaults should be

    If you previously used "Configure -Dsitelib" or "-Dsitearch" to set
    special values for library directories, you might wish to consider using
    the new "-Dsiteprefix" setting instead. Also, if you wish to re-use a file from an earlier version of perl, you should be sure to
    check that Configure makes sensible choices for the new directories. See
    INSTALL for complete details.

  gcc automatically tried if 'cc' does not seem to be working

    In many platforms the vendor-supplied 'cc' is too stripped-down to build
    Perl (basically, the 'cc' doesn't do ANSI C). If this seems to be the
    case and the 'cc' does not seem to be the GNU C compiler 'gcc', an
    automatic attempt is made to find and use 'gcc' instead.

Platform specific changes
  Supported platforms

    *   The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the
        Thread extension.

    *   GNU/Hurd is now supported.

    *   Rhapsody/Darwin is now supported.

    *   EPOC is now supported (on Psion 5).

    *   The cygwin port (formerly cygwin32) has been greatly improved.


    *   Perl now works with djgpp 2.02 (and 2.03 alpha).

    *   Environment variable names are not converted to uppercase any more.

    *   Incorrect exit codes from backticks have been fixed.

    *   This port continues to use its own builtin globbing (not

  OS390 (OpenEdition MVS)

    Support for this EBCDIC platform has not been renewed in this release.
    There are difficulties in reconciling Perl's standardization on UTF-8 as
    its internal representation for characters with the EBCDIC character
    set, because the two are incompatible.

    It is unclear whether future versions will renew support for this
    platform, but the possibility exists.


    Numerous revisions and extensions to configuration, build, testing, and
    installation process to accommodate core changes and VMS-specific

    Expand %ENV-handling code to allow runtime mapping to logical names, CLI
    symbols, and CRTL environ array.

    Extension of subprocess invocation code to accept filespecs as command

    Add to Perl command line processing the ability to use default file
    types and to recognize Unix-style "2>&1".

    Expansion of File::Spec::VMS routines, and integration into

    Extension of ExtUtils::MM_VMS to handle complex extensions more

    Barewords at start of Unix-syntax paths may be treated as text rather
    than only as logical names.

    Optional secure translation of several logical names used internally by

    Miscellaneous bugfixing and porting of new core code to VMS.

    Thanks are gladly extended to the many people who have contributed VMS
    patches, testing, and ideas.


    Perl can now emulate fork() internally, using multiple interpreters
    running in different concurrent threads. This support must be enabled at
    build time. See the perlfork manpage for detailed information.

    When given a pathname that consists only of a drivename, such as "A:",
    opendir() and stat() now use the current working directory for the drive
    rather than the drive root.

    The builtin XSUB functions in the Win32:: namespace are documented. See
    the Win32 manpage.

    $^X now contains the full path name of the running executable.

    A Win32::GetLongPathName() function is provided to complement
    Win32::GetFullPathName() and Win32::GetShortPathName(). See the Win32

    POSIX::uname() is supported.

    system(1,...) now returns true process IDs rather than process handles.
    kill() accepts any real process id, rather than strictly return values
    from system(1,...).

    For better compatibility with Unix, "kill(0, $pid)" can now be used to
    test whether a process exists.

    The "Shell" module is supported.

    Better support for building Perl under in Windows 95 has
    been added.

    Scripts are read in binary mode by default to allow ByteLoader (and the
    filter mechanism in general) to work properly. For compatibility, the
    DATA filehandle will be set to text mode if a carriage return is
    detected at the end of the line containing the __END__ or __DATA__
    token; if not, the DATA filehandle will be left open in binary mode.
    Earlier versions always opened the DATA filehandle in text mode.

    The glob() operator is implemented via the "File::Glob" extension, which
    supports glob syntax of the C shell. This increases the flexibility of
    the glob() operator, but there may be compatibility issues for programs
    that relied on the older globbing syntax. If you want to preserve
    compatibility with the older syntax, you might want to run perl with
    "-MFile::DosGlob". For details and compatibility information, see the
    File::Glob manpage.

Significant bug fixes
  <HANDLE> on empty files

    With "$/" set to "undef", "slurping" an empty file returns a string of
    zero length (instead of "undef", as it used to) the first time the
    HANDLE is read after "$/" is set to "undef". Further reads yield

    This means that the following will append "foo" to an empty file (it
    used to do nothing):

        perl -0777 -pi -e 's/^/foo/' empty_file

    The behaviour of:

        perl -pi -e 's/^/foo/' empty_file

    is unchanged (it continues to leave the file empty).

  "eval '...'" improvements

    Line numbers (as reflected by caller() and most diagnostics) within
    "eval '...'" were often incorrect where here documents were involved.
    This has been corrected.

    Lexical lookups for variables appearing in "eval '...'" within functions
    that were themselves called within an "eval '...'" were searching the
    wrong place for lexicals. The lexical search now correctly ends at the
    subroutine's block boundary.

    The use of "return" within "eval {...}" caused $@ not to be reset
    correctly when no exception occurred within the eval. This has been

    Parsing of here documents used to be flawed when they appeared as the
    replacement expression in "eval 's/.../.../e'". This has been fixed.

  All compilation errors are true errors

    Some "errors" encountered at compile time were by necessity generated as
    warnings followed by eventual termination of the program. This enabled
    more such errors to be reported in a single run, rather than causing a
    hard stop at the first error that was encountered.

    The mechanism for reporting such errors has been reimplemented to queue
    compile-time errors and report them at the end of the compilation as
    true errors rather than as warnings. This fixes cases where error
    messages leaked through in the form of warnings when code was compiled
    at run time using "eval STRING", and also allows such errors to be
    reliably trapped using "eval "..."".

  Implicitly closed filehandles are safer

    Sometimes implicitly closed filehandles (as when they are localized, and
    Perl automatically closes them on exiting the scope) could inadvertently
    set $? or $!. This has been corrected.

  Behavior of list slices is more consistent

    When taking a slice of a literal list (as opposed to a slice of an array
    or hash), Perl used to return an empty list if the result happened to be
    composed of all undef values.

    The new behavior is to produce an empty list if (and only if) the
    original list was empty. Consider the following example:

        @a = (1,undef,undef,2)[2,1,2];

    The old behavior would have resulted in @a having no elements. The new
    behavior ensures it has three undefined elements.

    Note in particular that the behavior of slices of the following cases
    remains unchanged:

        @a = ()[1,2];
        @a = (getpwent)[7,0];
        @a = (anything_returning_empty_list())[2,1,2];
        @a = @b[2,1,2];
        @a = @c{'a','b','c'};

    See the perldata manpage.

  "(\$)" prototype and "$foo{a}"

    A scalar reference prototype now correctly allows a hash or array
    element in that slot.

  "goto &sub" and AUTOLOAD

    The "goto &sub" construct works correctly when "&sub" happens to be

  "-bareword" allowed under "use integer"

    The autoquoting of barewords preceded by "-" did not work in prior
    versions when the "integer" pragma was enabled. This has been fixed.

  Failures in DESTROY()

    When code in a destructor threw an exception, it went unnoticed in
    earlier versions of Perl, unless someone happened to be looking in $@
    just after the point the destructor happened to run. Such failures are
    now visible as warnings when warnings are enabled.

  Locale bugs fixed

    printf() and sprintf() previously reset the numeric locale back to the
    default "C" locale. This has been fixed.

    Numbers formatted according to the local numeric locale (such as using a
    decimal comma instead of a decimal dot) caused "isn't numeric" warnings,
    even while the operations accessing those numbers produced correct
    results. These warnings have been discontinued.

  Memory leaks

    The "eval 'return sub {...}'" construct could sometimes leak memory.
    This has been fixed.

    Operations that aren't filehandle constructors used to leak memory when
    used on invalid filehandles. This has been fixed.

    Constructs that modified "@_" could fail to deallocate values in "@_"
    and thus leak memory. This has been corrected.

  Spurious subroutine stubs after failed subroutine calls

    Perl could sometimes create empty subroutine stubs when a subroutine was
    not found in the package. Such cases stopped later method lookups from
    progressing into base packages. This has been corrected.

  Taint failures under "-U"

    When running in unsafe mode, taint violations could sometimes cause
    silent failures. This has been fixed.

  END blocks and the "-c" switch

    Prior versions used to run BEGIN and END blocks when Perl was run in
    compile-only mode. Since this is typically not the expected behavior,
    END blocks are not executed anymore when the "-c" switch is used, or if
    compilation fails.

    See the section on "Support for CHECK blocks" for how to run things when
    the compile phase ends.

  Potential to leak DATA filehandles

    Using the "__DATA__" token creates an implicit filehandle to the file
    that contains the token. It is the program's responsibility to close it
    when it is done reading from it.

    This caveat is now better explained in the documentation. See the
    perldata manpage.

New or Changed Diagnostics
    "%s" variable %s masks earlier declaration in same %s
        (W misc) A "my" or "our" variable has been redeclared in the current
        scope or statement, effectively eliminating all access to the
        previous instance. This is almost always a typographical error. Note
        that the earlier variable will still exist until the end of the
        scope or until all closure referents to it are destroyed.

    "my sub" not yet implemented
        (F) Lexically scoped subroutines are not yet implemented. Don't try
        that yet.

    "our" variable %s redeclared
        (W misc) You seem to have already declared the same global once
        before in the current lexical scope.

    '!' allowed only after types %s
        (F) The '!' is allowed in pack() and unpack() only after certain
        types. See the pack entry in the perlfunc manpage.

    / cannot take a count
        (F) You had an unpack template indicating a counted-length string,
        but you have also specified an explicit size for the string. See the
        pack entry in the perlfunc manpage.

    / must be followed by a, A or Z
        (F) You had an unpack template indicating a counted-length string,
        which must be followed by one of the letters a, A or Z to indicate
        what sort of string is to be unpacked. See the pack entry in the
        perlfunc manpage.

    / must be followed by a*, A* or Z*
        (F) You had a pack template indicating a counted-length string,
        Currently the only things that can have their length counted are a*,
        A* or Z*. See the pack entry in the perlfunc manpage.

    / must follow a numeric type
        (F) You had an unpack template that contained a '#', but this did
        not follow some numeric unpack specification. See the pack entry in
        the perlfunc manpage.

    /%s/: Unrecognized escape \\%c passed through
        (W regexp) You used a backslash-character combination which is not
        recognized by Perl. This combination appears in an interpolated
        variable or a "'"-delimited regular expression. The character was
        understood literally.

    /%s/: Unrecognized escape \\%c in character class passed through
        (W regexp) You used a backslash-character combination which is not
        recognized by Perl inside character classes. The character was
        understood literally.

    /%s/ should probably be written as "%s"
        (W syntax) You have used a pattern where Perl expected to find a
        string, as in the first argument to "join". Perl will treat the true
        or false result of matching the pattern against $_ as the string,
        which is probably not what you had in mind.

    %s() called too early to check prototype
        (W prototype) You've called a function that has a prototype before
        the parser saw a definition or declaration for it, and Perl could
        not check that the call conforms to the prototype. You need to
        either add an early prototype declaration for the subroutine in
        question, or move the subroutine definition ahead of the call to get
        proper prototype checking. Alternatively, if you are certain that
        you're calling the function correctly, you may put an ampersand
        before the name to avoid the warning. See the perlsub manpage.

    %s argument is not a HASH or ARRAY element
        (F) The argument to exists() must be a hash or array element, such


    %s argument is not a HASH or ARRAY element or slice
        (F) The argument to delete() must be either a hash or array element,
        such as:


        or a hash or array slice, such as:

            @foo[$bar, $baz, $xyzzy]
            @{$ref->[12]}{"susie", "queue"}

    %s argument is not a subroutine name
        (F) The argument to exists() for "exists &sub" must be a subroutine
        name, and not a subroutine call. "exists &sub()" will generate this

    %s package attribute may clash with future reserved word: %s
        (W reserved) A lowercase attribute name was used that had a
        package-specific handler. That name might have a meaning to Perl
        itself some day, even though it doesn't yet. Perhaps you should use
        a mixed-case attribute name, instead. See the attributes manpage.

    (in cleanup) %s
        (W misc) This prefix usually indicates that a DESTROY() method
        raised the indicated exception. Since destructors are usually called
        by the system at arbitrary points during execution, and often a vast
        number of times, the warning is issued only once for any number of
        failures that would otherwise result in the same message being

        Failure of user callbacks dispatched using the "G_KEEPERR" flag
        could also result in this warning. See the G_KEEPERR entry in the
        perlcall manpage.

    <> should be quotes
        (F) You wrote "require <file>" when you should have written "require

    Attempt to join self
        (F) You tried to join a thread from within itself, which is an
        impossible task. You may be joining the wrong thread, or you may
        need to move the join() to some other thread.

    Bad evalled substitution pattern
        (F) You've used the /e switch to evaluate the replacement for a
        substitution, but perl found a syntax error in the code to evaluate,
        most likely an unexpected right brace '}'.

    Bad realloc() ignored
        (S) An internal routine called realloc() on something that had never
        been malloc()ed in the first place. Mandatory, but can be disabled
        by setting environment variable "PERL_BADFREE" to 1.

    Bareword found in conditional
        (W bareword) The compiler found a bareword where it expected a
        conditional, which often indicates that an || or && was parsed as
        part of the last argument of the previous construct, for example:

            open FOO || die;

        It may also indicate a misspelled constant that has been interpreted
        as a bareword:

            use constant TYPO => 1;
            if (TYOP) { print "foo" }

        The "strict" pragma is useful in avoiding such errors.

    Binary number > 0b11111111111111111111111111111111 non-portable
        (W portable) The binary number you specified is larger than 2**32-1
        (4294967295) and therefore non-portable between systems. See the
        perlport manpage for more on portability concerns.

    Bit vector size > 32 non-portable
        (W portable) Using bit vector sizes larger than 32 is non-portable.

    Buffer overflow in prime_env_iter: %s
        (W internal) A warning peculiar to VMS. While Perl was preparing to
        iterate over %ENV, it encountered a logical name or symbol
        definition which was too long, so it was truncated to the string

    Can't check filesystem of script "%s"
        (P) For some reason you can't check the filesystem of the script for

    Can't declare class for non-scalar %s in "%s"
        (S) Currently, only scalar variables can declared with a specific
        class qualifier in a "my" or "our" declaration. The semantics may be
        extended for other types of variables in future.

    Can't declare %s in "%s"
        (F) Only scalar, array, and hash variables may be declared as "my"
        or "our" variables. They must have ordinary identifiers as names.

    Can't ignore signal CHLD, forcing to default
        (W signal) Perl has detected that it is being run with the SIGCHLD
        signal (sometimes known as SIGCLD) disabled. Since disabling this
        signal will interfere with proper determination of exit status of
        child processes, Perl has reset the signal to its default value.
        This situation typically indicates that the parent program under
        which Perl may be running (e.g., cron) is being very careless.

    Can't modify non-lvalue subroutine call
        (F) Subroutines meant to be used in lvalue context should be
        declared as such, see the section on "Lvalue subroutines" in the
        perlsub manpage.

    Can't read CRTL environ
        (S) A warning peculiar to VMS. Perl tried to read an element of %ENV
        from the CRTL's internal environment array and discovered the array
        was missing. You need to figure out where your CRTL misplaced its
        environ or define PERL_ENV_TABLES (see the perlvms manpage) so that
        environ is not searched.

    Can't remove %s: %s, skipping file
        (S) You requested an inplace edit without creating a backup file.
        Perl was unable to remove the original file to replace it with the
        modified file. The file was left unmodified.

    Can't return %s from lvalue subroutine
        (F) Perl detected an attempt to return illegal lvalues (such as
        temporary or readonly values) from a subroutine used as an lvalue.
        This is not allowed.

    Can't weaken a nonreference
        (F) You attempted to weaken something that was not a reference. Only
        references can be weakened.

    Character class [:%s:] unknown
        (F) The class in the character class [: :] syntax is unknown. See
        the perlre manpage.

    Character class syntax [%s] belongs inside character classes
        (W unsafe) The character class constructs [: :], [= =], and [. .] go
        *inside* character classes, the [] are part of the construct, for
        example: /[012[:alpha:]345]/. Note that [= =] and [. .] are not
        currently implemented; they are simply placeholders for future

    Constant is not %s reference
        (F) A constant value (perhaps declared using the "use constant"
        pragma) is being dereferenced, but it amounts to the wrong type of
        reference. The message indicates the type of reference that was
        expected. This usually indicates a syntax error in dereferencing the
        constant value. See the section on "Constant Functions" in the
        perlsub manpage and the constant manpage.

    constant(%s): %s
        (F) The parser found inconsistencies either while attempting to
        define an overloaded constant, or when trying to find the character
        name specified in the "\N{...}" escape. Perhaps you forgot to load
        the corresponding "overload" or "charnames" pragma? See the
        charnames manpage and the overload manpage.

    CORE::%s is not a keyword
        (F) The CORE:: namespace is reserved for Perl keywords.

    defined(@array) is deprecated
        (D) defined() is not usually useful on arrays because it checks for
        an undefined *scalar* value. If you want to see if the array is
        empty, just use "if (@array) { # not empty }" for example.

    defined(%hash) is deprecated
        (D) defined() is not usually useful on hashes because it checks for
        an undefined *scalar* value. If you want to see if the hash is
        empty, just use "if (%hash) { # not empty }" for example.

    Did not produce a valid header
        See Server error.

    (Did you mean "local" instead of "our"?)
        (W misc) Remember that "our" does not localize the declared global
        variable. You have declared it again in the same lexical scope,
        which seems superfluous.

    Document contains no data
        See Server error.

    entering effective %s failed
        (F) While under the "use filetest" pragma, switching the real and
        effective uids or gids failed.

    false [] range "%s" in regexp
        (W regexp) A character class range must start and end at a literal
        character, not another character class like "\d" or "[:alpha:]". The
        "-" in your false range is interpreted as a literal "-". Consider
        quoting the "-", "\-". See the perlre manpage.

    Filehandle %s opened only for output
        (W io) You tried to read from a filehandle opened only for writing.
        If you intended it to be a read/write filehandle, you needed to open
        it with "+<" or "+>" or "+>>" instead of with "<" or nothing. If you
        intended only to read from the file, use "<". See the open entry in
        the perlfunc manpage.

    flock() on closed filehandle %s
        (W closed) The filehandle you're attempting to flock() got itself
        closed some time before now. Check your logic flow. flock() operates
        on filehandles. Are you attempting to call flock() on a dirhandle by
        the same name?

    Global symbol "%s" requires explicit package name
        (F) You've said "use strict vars", which indicates that all
        variables must either be lexically scoped (using "my"), declared
        beforehand using "our", or explicitly qualified to say which package
        the global variable is in (using "::").

    Hexadecimal number > 0xffffffff non-portable
        (W portable) The hexadecimal number you specified is larger than
        2**32-1 (4294967295) and therefore non-portable between systems. See
        the perlport manpage for more on portability concerns.

    Ill-formed CRTL environ value "%s"
        (W internal) A warning peculiar to VMS. Perl tried to read the
        CRTL's internal environ array, and encountered an element without
        the "=" delimiter used to separate keys from values. The element is

    Ill-formed message in prime_env_iter: |%s|
        (W internal) A warning peculiar to VMS. Perl tried to read a logical
        name or CLI symbol definition when preparing to iterate over %ENV,
        and didn't see the expected delimiter between key and value, so the
        line was ignored.

    Illegal binary digit %s
        (F) You used a digit other than 0 or 1 in a binary number.

    Illegal binary digit %s ignored
        (W digit) You may have tried to use a digit other than 0 or 1 in a
        binary number. Interpretation of the binary number stopped before
        the offending digit.

    Illegal number of bits in vec
        (F) The number of bits in vec() (the third argument) must be a power
        of two from 1 to 32 (or 64, if your platform supports that).

    Integer overflow in %s number
        (W overflow) The hexadecimal, octal or binary number you have
        specified either as a literal or as an argument to hex() or oct() is
        too big for your architecture, and has been converted to a floating
        point number. On a 32-bit architecture the largest hexadecimal,
        octal or binary number representable without overflow is 0xFFFFFFFF,
        037777777777, or 0b11111111111111111111111111111111 respectively.
        Note that Perl transparently promotes all numbers to a floating
        point representation internally--subject to loss of precision errors
        in subsequent operations.

    Invalid %s attribute: %s
        The indicated attribute for a subroutine or variable was not
        recognized by Perl or by a user-supplied handler. See the attributes

    Invalid %s attributes: %s
        The indicated attributes for a subroutine or variable were not
        recognized by Perl or by a user-supplied handler. See the attributes

    invalid [] range "%s" in regexp
        The offending range is now explicitly displayed.

    Invalid separator character %s in attribute list
        (F) Something other than a colon or whitespace was seen between the
        elements of an attribute list. If the previous attribute had a
        parenthesised parameter list, perhaps that list was terminated too
        soon. See the attributes manpage.

    Invalid separator character %s in subroutine attribute list
        (F) Something other than a colon or whitespace was seen between the
        elements of a subroutine attribute list. If the previous attribute
        had a parenthesised parameter list, perhaps that list was terminated
        too soon.

    leaving effective %s failed
        (F) While under the "use filetest" pragma, switching the real and
        effective uids or gids failed.

    Lvalue subs returning %s not implemented yet
        (F) Due to limitations in the current implementation, array and hash
        values cannot be returned in subroutines used in lvalue context. See
        the section on "Lvalue subroutines" in the perlsub manpage.

    Method %s not permitted
        See Server error.

    Missing %sbrace%s on \N{}
        (F) Wrong syntax of character name literal "\N{charname}" within
        double-quotish context.

    Missing command in piped open
        (W pipe) You used the "open(FH, "| command")" or "open(FH, "command
        |")" construction, but the command was missing or blank.

    Missing name in "my sub"
        (F) The reserved syntax for lexically scoped subroutines requires
        that they have a name with which they can be found.

    No %s specified for -%c
        (F) The indicated command line switch needs a mandatory argument,
        but you haven't specified one.

    No package name allowed for variable %s in "our"
        (F) Fully qualified variable names are not allowed in "our"
        declarations, because that doesn't make much sense under existing
        semantics. Such syntax is reserved for future extensions.

    No space allowed after -%c
        (F) The argument to the indicated command line switch must follow
        immediately after the switch, without intervening spaces.

    no UTC offset information; assuming local time is UTC
        (S) A warning peculiar to VMS. Perl was unable to find the local
        timezone offset, so it's assuming that local system time is
        equivalent to UTC. If it's not, define the logical name
        SYS$TIMEZONE_DIFFERENTIAL to translate to the number of seconds
        which need to be added to UTC to get local time.

    Octal number > 037777777777 non-portable
        (W portable) The octal number you specified is larger than 2**32-1
        (4294967295) and therefore non-portable between systems. See the
        perlport manpage for more on portability concerns.

        See also the perlport manpage for writing portable code.

    panic: del_backref
        (P) Failed an internal consistency check while trying to reset a
        weak reference.

    panic: kid popen errno read
        (F) forked child returned an incomprehensible message about its

    panic: magic_killbackrefs
        (P) Failed an internal consistency check while trying to reset all
        weak references to an object.

    Parentheses missing around "%s" list
        (W parenthesis) You said something like

            my $foo, $bar = @_;

        when you meant

            my ($foo, $bar) = @_;

        Remember that "my", "our", and "local" bind tighter than comma.

    Possible unintended interpolation of %s in string
        (W ambiguous) It used to be that Perl would try to guess whether you
        wanted an array interpolated or a literal @. It no longer does this;
        arrays are now *always* interpolated into strings. This means that
        if you try something like:

                print "";

        and the array "@example" doesn't exist, Perl is going to print
        "", which is probably not what you wanted. To get a literal
        "@" sign in a string, put a backslash before it, just as you would
        to get a literal "$" sign.

    Possible Y2K bug: %s
        (W y2k) You are concatenating the number 19 with another number,
        which could be a potential Year 2000 problem.

    pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead
        (W deprecated) You have written something like this:

            sub doit
                use attrs qw(locked);

        You should use the new declaration syntax instead.

            sub doit : locked

        The "use attrs" pragma is now obsolete, and is only provided for
        backward-compatibility. See the section on "Subroutine Attributes"
        in the perlsub manpage.

    Premature end of script headers
        See Server error.

    Repeat count in pack overflows
        (F) You can't specify a repeat count so large that it overflows your
        signed integers. See the pack entry in the perlfunc manpage.

    Repeat count in unpack overflows
        (F) You can't specify a repeat count so large that it overflows your
        signed integers. See the unpack entry in the perlfunc manpage.

    realloc() of freed memory ignored
        (S) An internal routine called realloc() on something that had
        already been freed.

    Reference is already weak
        (W misc) You have attempted to weaken a reference that is already
        weak. Doing so has no effect.

    setpgrp can't take arguments
        (F) Your system has the setpgrp() from BSD 4.2, which takes no
        arguments, unlike POSIX setpgid(), which takes a process ID and
        process group ID.

    Strange *+?{} on zero-length expression
        (W regexp) You applied a regular expression quantifier in a place
        where it makes no sense, such as on a zero-width assertion. Try
        putting the quantifier inside the assertion instead. For example,
        the way to match "abc" provided that it is followed by three
        repetitions of "xyz" is "/abc(?=(?:xyz){3})/", not

    switching effective %s is not implemented
        (F) While under the "use filetest" pragma, we cannot switch the real
        and effective uids or gids.

    This Perl can't reset CRTL environ elements (%s)
    This Perl can't set CRTL environ elements (%s=%s)
        (W internal) Warnings peculiar to VMS. You tried to change or delete
        an element of the CRTL's internal environ array, but your copy of
        Perl wasn't built with a CRTL that contained the setenv() function.
        You'll need to rebuild Perl with a CRTL that does, or redefine
        PERL_ENV_TABLES (see the perlvms manpage) so that the environ array
        isn't the target of the change to %ENV which produced the warning.

    Too late to run %s block
        (W void) A CHECK or INIT block is being defined during run time
        proper, when the opportunity to run them has already passed. Perhaps
        you are loading a file with "require" or "do" when you should be
        using "use" instead. Or perhaps you should put the "require" or "do"
        inside a BEGIN block.

    Unknown open() mode '%s'
        (F) The second argument of 3-argument open() is not among the list
        of valid modes: "<", ">", ">>", "+<", "+>", "+>>", "-|", "|-".

    Unknown process %x sent message to prime_env_iter: %s
        (P) An error peculiar to VMS. Perl was reading values for %ENV
        before iterating over it, and someone else stuck a message in the
        stream of data Perl expected. Someone's very confused, or perhaps
        trying to subvert Perl's population of %ENV for nefarious purposes.

    Unrecognized escape \\%c passed through
        (W misc) You used a backslash-character combination which is not
        recognized by Perl. The character was understood literally.

    Unterminated attribute parameter in attribute list
        (F) The lexer saw an opening (left) parenthesis character while
        parsing an attribute list, but the matching closing (right)
        parenthesis character was not found. You may need to add (or remove)
        a backslash character to get your parentheses to balance. See the
        attributes manpage.

    Unterminated attribute list
        (F) The lexer found something other than a simple identifier at the
        start of an attribute, and it wasn't a semicolon or the start of a
        block. Perhaps you terminated the parameter list of the previous
        attribute too soon. See the attributes manpage.

    Unterminated attribute parameter in subroutine attribute list
        (F) The lexer saw an opening (left) parenthesis character while
        parsing a subroutine attribute list, but the matching closing
        (right) parenthesis character was not found. You may need to add (or
        remove) a backslash character to get your parentheses to balance.

    Unterminated subroutine attribute list
        (F) The lexer found something other than a simple identifier at the
        start of a subroutine attribute, and it wasn't a semicolon or the
        start of a block. Perhaps you terminated the parameter list of the
        previous attribute too soon.

    Value of CLI symbol "%s" too long
        (W misc) A warning peculiar to VMS. Perl tried to read the value of
        an %ENV element from a CLI symbol table, and found a resultant
        string longer than 1024 characters. The return value has been
        truncated to 1024 characters.

    Version number must be a constant number
        (P) The attempt to translate a "use Module n.n LIST" statement into
        its equivalent "BEGIN" block found an internal inconsistency with
        the version number.

New tests
        Compatibility tests for "sub : attrs" vs the older "use attrs".

        Tests for new environment scalar capability (e.g., "use Env

        Tests for new environment array capability (e.g., "use Env

        IO constants (SEEK_*, _IO*).

        Directory-related IO methods (new, read, close, rewind, tied

        INET sockets with multi-homed hosts.

        IO poll().

        UNIX sockets.

        Regression tests for "my ($x,@y,%z) : attrs" and <sub : attrs>.

        File test operators.

        Verify operations that access pad objects (lexicals and

        Verify "exists &sub" operations.

Incompatible Changes
  Perl Source Incompatibilities

    Beware that any new warnings that have been added or old ones that have
    been enhanced are not considered incompatible changes.

    Since all new warnings must be explicitly requested via the "-w" switch
    or the "warnings" pragma, it is ultimately the programmer's
    responsibility to ensure that warnings are enabled judiciously.

    CHECK is a new keyword
        All subroutine definitions named CHECK are now special. See
        "/"Support for CHECK blocks"" for more information.

    Treatment of list slices of undef has changed
        There is a potential incompatibility in the behavior of list slices
        that are comprised entirely of undefined values. See the section on
        "Behavior of list slices is more consistent".

    Format of $English::PERL_VERSION is different
        The English module now sets $PERL_VERSION to $^V (a string value)
        rather than "$]" (a numeric value). This is a potential
        incompatibility. Send us a report via perlbug if you are affected by

        See the section on "Improved Perl version numbering system" for the
        reasons for this change.

    Literals of the form "1.2.3" parse differently
        Previously, numeric literals with more than one dot in them were
        interpreted as a floating point number concatenated with one or more
        numbers. Such "numbers" are now parsed as strings composed of the
        specified ordinals.

        For example, "print 97.98.99" used to output "97.9899" in earlier
        versions, but now prints "abc".

        See the section on "Support for strings represented as a vector of

    Possibly changed pseudo-random number generator
        Perl programs that depend on reproducing a specific set of
        pseudo-random numbers may now produce different output due to
        improvements made to the rand() builtin. You can use "sh Configure
        -Drandfunc=rand" to obtain the old behavior.

        See the section on "Better pseudo-random number generator".

    Hashing function for hash keys has changed
        Even though Perl hashes are not order preserving, the apparently
        random order encountered when iterating on the contents of a hash is
        actually determined by the hashing algorithm used. Improvements in
        the algorithm may yield a random order that is different from that
        of previous versions, especially when iterating on hashes.

        See the section on "Better worst-case behavior of hashes" for
        additional information.

    "undef" fails on read only values
        Using the "undef" operator on a readonly value (such as $1) has the
        same effect as assigning "undef" to the readonly value--it throws an

    Close-on-exec bit may be set on pipe and socket handles
        Pipe and socket handles are also now subject to the close-on-exec
        behavior determined by the special variable $^F.

        See the section on "More consistent close-on-exec behavior".

    Writing ""$$1"" to mean ""${$}1"" is unsupported
        Perl 5.004 deprecated the interpretation of "$$1" and similar within
        interpolated strings to mean "$$ . "1"", but still allowed it.

        In Perl 5.6.0 and later, ""$$1"" always means ""${$1}"".

    delete(), each(), values() and "\(%h)"
        operate on aliases to values, not copies

        delete(), each(), values() and hashes (e.g. "\(%h)") in a list
        context return the actual values in the hash, instead of copies (as
        they used to in earlier versions). Typical idioms for using these
        constructs copy the returned values, but this can make a significant
        difference when creating references to the returned values. Keys in
        the hash are still returned as copies when iterating on a hash.

        See also the section on "delete(), each(), values() and hash
        iteration are faster".

    vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS
        vec() generates a run-time error if the BITS argument is not a valid
        power-of-two integer.

    Text of some diagnostic output has changed
        Most references to internal Perl operations in diagnostics have been
        changed to be more descriptive. This may be an issue for programs
        that may incorrectly rely on the exact text of diagnostics for
        proper functioning.

    "%@" has been removed
        The undocumented special variable "%@" that used to accumulate
        "background" errors (such as those that happen in DESTROY()) has
        been removed, because it could potentially result in memory leaks.

    Parenthesized not() behaves like a list operator
        The "not" operator now falls under the "if it looks like a function,
        it behaves like a function" rule.

        As a result, the parenthesized form can be used with "grep" and
        "map". The following construct used to be a syntax error before, but
        it works as expected now:

            grep not($_), @things;

        On the other hand, using "not" with a literal list slice may not
        work. The following previously allowed construct:

            print not (1,2,3)[0];

        needs to be written with additional parentheses now:

            print not((1,2,3)[0]);

        The behavior remains unaffected when "not" is not followed by

    Semantics of bareword prototype "(*)" have changed
        The semantics of the bareword prototype "*" have changed. Perl 5.005
        always coerced simple scalar arguments to a typeglob, which wasn't
        useful in situations where the subroutine must distinguish between a
        simple scalar and a typeglob. The new behavior is to not coerce
        bareword arguments to a typeglob. The value will always be visible
        as either a simple scalar or as a reference to a typeglob.

        See the section on "More functional bareword prototype (*)".

    Semantics of bit operators may have changed on 64-bit platforms
        If your platform is either natively 64-bit or if Perl has been
        configured to used 64-bit integers, i.e., $Config{ivsize} is 8,
        there may be a potential incompatibility in the behavior of bitwise
        numeric operators (& | ^ ~ << >>). These operators used to strictly
        operate on the lower 32 bits of integers in previous versions, but
        now operate over the entire native integral width. In particular,
        note that unary "~" will produce different results on platforms that
        have different $Config{ivsize}. For portability, be sure to mask off
        the excess bits in the result of unary "~", e.g., "~$x &

        See the section on "Bit operators support full native integer

    More builtins taint their results
        As described in the section on "Improved security features", there
        may be more sources of taint in a Perl program.

        To avoid these new tainting behaviors, you can build Perl with the
        Configure option "-Accflags=-DINCOMPLETE_TAINTS". Beware that the
        ensuing perl binary may be insecure.

  C Source Incompatibilities

        Release 5.005 grandfathered old global symbol names by providing
        preprocessor macros for extension source compatibility. As of
        release 5.6.0, these preprocessor definitions are not available by
        default. You need to explicitly compile perl with "-DPERL_POLLUTE"
        to get these definitions. For extensions still using the old
        symbols, this option can be specified via MakeMaker:

            perl Makefile.PL POLLUTE=1

        This new build option provides a set of macros for all API functions
        such that an implicit interpreter/thread context argument is passed
        to every API function. As a result of this, something like
        "sv_setsv(foo,bar)" amounts to a macro invocation that actually
        translates to something like "Perl_sv_setsv(my_perl,foo,bar)". While
        this is generally expected to not have any significant source
        compatibility issues, the difference between a macro and a real
        function call will need to be considered.

        This means that there is a source compatibility issue as a result of
        this if your extensions attempt to use pointers to any of the Perl
        API functions.

        Note that the above issue is not relevant to the default build of
        Perl, whose interfaces continue to match those of prior versions
        (but subject to the other options described here).

        See the section on "The Perl API" in the perlguts manpage for
        detailed information on the ramifications of building Perl with this

            NOTE: PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
            with one of -Dusethreads, -Dusemultiplicity, or both.  It is not
            intended to be enabled by users at this time.

        Enabling Perl's malloc in release 5.005 and earlier caused the
        namespace of the system's malloc family of functions to be usurped
        by the Perl versions, since by default they used the same names.
        Besides causing problems on platforms that do not allow these
        functions to be cleanly replaced, this also meant that the system
        versions could not be called in programs that used Perl's malloc.
        Previous versions of Perl have allowed this behaviour to be
        suppressed with the HIDEMYMALLOC and EMBEDMYMALLOC preprocessor

        As of release 5.6.0, Perl's malloc family of functions have default
        names distinct from the system versions. You need to explicitly
        compile perl with "-DPERL_POLLUTE_MALLOC" to get the older
        behaviour. HIDEMYMALLOC and EMBEDMYMALLOC have no effect, since the
        behaviour they enabled is now the default.

        Note that these functions do not constitute Perl's memory allocation
        API. See the section on "Memory Allocation" in the perlguts manpage
        for further information about that.

  Compatible C Source API Changes

        The cpp macros "PERL_REVISION", "PERL_VERSION", and
        "PERL_SUBVERSION" are now available by default from perl.h, and
        reflect the base revision, patchlevel, and subversion respectively.
        "PERL_REVISION" had no prior equivalent, while "PERL_VERSION" and
        "PERL_SUBVERSION" were previously available as "PATCHLEVEL" and

        The new names cause less pollution of the cpp namespace and reflect
        what the numbers have come to stand for in common practice. For
        compatibility, the old names are still supported when patchlevel.h
        is explicitly included (as required before), so there is no source
        incompatibility from the change.

  Binary Incompatibilities

    In general, the default build of this release is expected to be binary
    compatible for extensions built with the 5.005 release or its
    maintenance versions. However, specific platforms may have broken binary
    compatibility due to changes in the defaults used in hints files.
    Therefore, please be sure to always check the platform-specific README
    files for any notes to the contrary.

    The usethreads or usemultiplicity builds are not binary compatible with
    the corresponding builds in 5.005.

    On platforms that require an explicit list of exports (AIX, OS/2 and
    Windows, among others), purely internal symbols such as parser functions
    and the run time opcodes are not exported by default. Perl 5.005 used to
    export all functions irrespective of whether they were considered part
    of the public API or not.

    For the full list of public API functions, see the perlapi manpage.

Known Problems
  Localizing a tied hash element may leak memory

    As of the 5.6.1 release, there is a known leak when code such as this is

        use Tie::Hash;
        tie my %tie_hash => 'Tie::StdHash';


        local($tie_hash{Foo}) = 1; # leaks

  Known test failures

    64-bit builds
        Subtest #15 of lib/b.t may fail under 64-bit builds on platforms
        such as HP-UX PA64 and Linux IA64. The issue is still being

        The lib/io_multihomed test may hang in HP-UX if Perl has been
        configured to be 64-bit. Because other 64-bit platforms do not hang
        in this test, HP-UX is suspect. All other tests pass in 64-bit
        HP-UX. The test attempts to create and connect to "multihomed"
        sockets (sockets which have multiple IP addresses).

        Note that 64-bit support is still experimental.

    Failure of Thread tests
        The subtests 19 and 20 of lib/thr5005.t test are known to fail due
        to fundamental problems in the 5.005 threading implementation. These
        are not new failures--Perl 5.005_0x has the same bugs, but didn't
        have these tests. (Note that support for 5.005-style threading
        remains experimental.)

    NEXTSTEP 3.3 POSIX test failure
        In NEXTSTEP 3.3p2 the implementation of the strftime(3) in the
        operating system libraries is buggy: the %j format numbers the days
        of a month starting from zero, which, while being logical to
        programmers, will cause the subtests 19 to 27 of the lib/posix test
        may fail.

    Tru64 (aka Digital UNIX, aka DEC OSF/1) lib/sdbm test failure with gcc
        If compiled with gcc 2.95 the lib/sdbm test will fail (dump core).
        The cure is to use the vendor cc, it comes with the operating system
        and produces good code.

  EBCDIC platforms not fully supported

    In earlier releases of Perl, EBCDIC environments like OS390 (also known
    as Open Edition MVS) and VM-ESA were supported. Due to changes required
    by the UTF-8 (Unicode) support, the EBCDIC platforms are not supported
    in Perl 5.6.0.

    The 5.6.1 release improves support for EBCDIC platforms, but they are
    not fully supported yet.

  UNICOS/mk CC failures during Configure run

    In UNICOS/mk the following errors may appear during the Configure run:

            Guessing which symbols your C compiler and preprocessor define...
            CC-20 cc: ERROR File = try.c, Line = 3
              bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K
            4 errors detected in the compilation of "try.c".

    The culprit is the broken awk of UNICOS/mk. The effect is fortunately
    rather mild: Perl itself is not adversely affected by the error, only
    the h2ph utility coming with Perl, and that is rather rarely needed
    these days.

  Arrow operator and arrays

    When the left argument to the arrow operator "->" is an array, or the
    "scalar" operator operating on an array, the result of the operation
    must be considered erroneous. For example:


    These expressions will get run-time errors in some future release of

  Experimental features

    As discussed above, many features are still experimental. Interfaces and
    implementation of these features are subject to change, and in extreme
    cases, even subject to removal in some future release of Perl. These
    features include the following:

    64-bit support
    Lvalue subroutines
    Weak references
    The pseudo-hash data type
    The Compiler suite
    Internal implementation of file globbing
    The DB module
    The regular expression code constructs:
        "(?{ code })" and "(??{ code })"

Obsolete Diagnostics
    Character class syntax [: :] is reserved for future extensions
        (W) Within regular expression character classes ([]) the syntax
        beginning with "[:" and ending with ":]" is reserved for future
        extensions. If you need to represent those character sequences
        inside a regular expression character class, just quote the square
        brackets with the backslash: "\[:" and ":\]".

    Ill-formed logical name |%s| in prime_env_iter
        (W) A warning peculiar to VMS. A logical name was encountered when
        preparing to iterate over %ENV which violates the syntactic rules
        governing logical names. Because it cannot be translated normally,
        it is skipped, and will not appear in %ENV. This may be a benign
        occurrence, as some software packages might directly modify logical
        name tables and introduce nonstandard names, or it may indicate that
        a logical name table has been corrupted.

    In string, @%s now must be written as \@%s
        The description of this error used to say:

                (Someday it will simply assume that an unbackslashed @
                 interpolates an array.)

        That day has come, and this fatal error has been removed. It has
        been replaced by a non-fatal warning instead. See the Arrays now
        always interpolate into double-quoted strings entry elsewhere in
        this document for details.

    Probable precedence problem on %s
        (W) The compiler found a bareword where it expected a conditional,
        which often indicates that an || or && was parsed as part of the
        last argument of the previous construct, for example:

            open FOO || die;

    regexp too big
        (F) The current implementation of regular expressions uses shorts as
        address offsets within a string. Unfortunately this means that if
        the regular expression compiles to longer than 32767, it'll blow up.
        Usually when you want a regular expression this big, there is a
        better way to do it with multiple statements. See the perlre

    Use of "$$<digit>" to mean "${$}<digit>" is deprecated
        (D) Perl versions before 5.004 misinterpreted any type marker
        followed by "$" and a digit. For example, "$$0" was incorrectly
        taken to mean "${$}0" instead of "${$0}". This bug is (mostly) fixed
        in Perl 5.004.

        However, the developers of Perl 5.004 could not fix this bug
        completely, because at least two widely-used modules depend on the
        old meaning of "$$0" in a string. So Perl 5.004 still interprets
        "$$<digit>" in the old (broken) way inside strings; but it generates
        this message as a warning. And in Perl 5.005, this special treatment
        will cease.

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. There may also be
    information at, the Perl Home Page.

    If you believe you have an unreported bug, please run the perlbug
    program included with your release. Be sure to trim your bug down to a
    tiny but sufficient test case. Your bug report, along with the output of
    "perl -V", will be sent off to to be analysed by the
    Perl porting team.

    The Changes file 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.

    Written by Gurusamy Sarathy <>, with many
    contributions from The Perl Porters.

    Send omissions or corrections to <>.

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