perl561delta - what's new for perl v5.6.1


   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 perlhack 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 "Known Problems" below for further

   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.

   qw(a\	)
       In Perl 5.6.0, qw(a\	) 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 perlvar (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 corrected.

       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 "pack" in perlfunc.

       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 "import".

       A large number of tests have been added.

   Core features
   untie() will now call an UNTIE() hook if it exists.  See perltie for

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

   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 "Arrays now always interpolate into double-quoted

   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 perlaix, perlsolaris, perlmacos, and perlbs2000 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

       Returns name and handle of a temporary file safely.  See

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

       Converts POD data to formatted overstrike text.  See

   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.

   Mac OS 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 perlvms.

   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 perlfork for known bugs and

   *   %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 perlfork 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.  warnings and perllexwarn
   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 perlunicode, utf8 and bytes
   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

       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 "our" in perlfunc.

   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 name:

       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 "Scalar value constructors" in perldata 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

   The v1.2.3 syntax is also now legal in Perl.  See "Support for strings
   represented as a vector of ordinals" 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 attributes.

   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 example:

       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 "open" in perlfunc.

   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

   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 "sort" in

   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
   perlre 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 "pack" in perlfunc.

   pack() format modifier '!' supported
   The new format type modifier '!' is useful for packing and unpacking
   native shorts, ints, and longs.  See "pack" in perlfunc.

   pack() and unpack() support counted strings
   The template character '/' can be used to specify a counted string type
   to be packed or unpacked.  See "pack" in 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 Devel::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 "Lvalue
   subroutines" in perlsub.

       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
   "exists" in perlfunc 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 "exists" in perlfunc and "delete" in perlfunc 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 "Pseudo-hashes: Using an array as a hash" in

   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 fields.

       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 "binmode" in
   perlfunc and open.

   "-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 $^F that may be in
   effect.  Earlier versions neglected to set the flag for handles created
   with these operators.  See "pipe" in perlfunc, "socketpair" in
   perlfunc, "socket" in perlfunc, "accept" in perlfunc, and "$^F" in

   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 perlop.

   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
   "Prototypes" in perlsub.

   "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 "Overriding Built-in Functions" in

   $^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 perlvar.

   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

   @- and @+ provide starting/ending offsets of regex submatches
   The new magic variables @- and @+ provide the starting and ending
   offsets, respectively, of $&, $1, $2, etc.  See perlvar for details.

Modules and Pragmata

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

   B   The Perl Compiler suite has been extensively reworked for this
       release.  More of the standard Perl test suite 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 Benchmark.

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

       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 constant.

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

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

       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
       Devel::DProf and dprofpp.

       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 File::Compare.

       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

       See File::Find.

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

       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 Pod::Usage 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 Pod::Parser and

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

   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 Pod::Select.

   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 Pod::Usage.

   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 Pod::Text 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 standard.

       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

       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 standard.

       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 Win32.

       The XSLoader extension is a simpler alternative to DynaLoader.  See

   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 perldbmfilter 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 "Subroutine Attributes" in perlsub and attributes.

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

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

Utility Changes

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

   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 perl 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 debuggers.

       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 "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 "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 "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 perlfork 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 Win32.

   $^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 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 File::Glob.

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 perldata.

   "(\$)" 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 "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

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

   "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 "pack" in perlfunc.

   / 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
       "pack" in perlfunc.

   / 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 "pack" in perlfunc.

   / 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 "pack" in perlfunc.

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

   /%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 perlsub.

   %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 error.

   %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 attributes.

   (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 repeated.

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

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

   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
       perlport 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 nosuid.

   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 "Lvalue subroutines" in perlsub.

   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 perlvms) 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

   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 "Constant Functions" in perlsub and

   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 charnames
       and overload.

   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 perlre.

   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 "open" in

   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 perlport 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 ignored.

   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 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 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 attributes.

   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 "Lvalue subroutines" in perlsub.

   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
       perlport for more on portability concerns.

       See also perlport 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 "Subroutine Attributes" in perlsub.

   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 "pack" in perlfunc.

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

   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 perlvms) 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 attributes.

   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 attributes.

   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

   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 "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 this.

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

   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 "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 "Better worst-case behavior of hashes" for additional

   "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 exception.

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

   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 "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 & 0xffffffff".

       See "Bit operators support full native integer width".

   More builtins taint their results
       As described in "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

       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 "Background and PERL_IMPLICIT_CONTEXT" in perlguts for detailed
       information on the ramifications of building Perl with this option.

           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 "Memory Allocation" in perlguts 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 perlapi.

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 executed:

       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

       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 "Arrays now
       always interpolate into double-quoted strings" 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 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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