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PERL56DELTA(1)                        Perl Programmers Reference Guide                        PERL56DELTA(1)



NAME
       perl56delta - what's new for perl v5.6.0

DESCRIPTION
       This document describes differences between the 5.005 release and the 5.6.0 release.

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 Unicode.

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

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

   "our" declarations
       An "our" declaration introduces a value that can be best understood as a lexically scoped symbolic
       alias to a global variable in the package that was current where the variable was declared.  This is
       mostly useful as an alternative to the "vars" pragma, but also provides the opportunity to introduce
       typing and other attributes for such variables.  See "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, but this particular usage
       should be avoided because it leads to misleading error messages under versions of Perl which don't
       support vector strings.  Using a true version number will ensure correct behavior in all versions of
       Perl:

           require 5.006;    # run time check for v5.6
           use 5.006_001;    # compile time check for v5.6.1

       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 this.)

       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.)

       AutoSplit.pm and SelfLoader.pm 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, q)

       •   printed as such

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

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

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

       •   vec()

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

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

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

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

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

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

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

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

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

           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 sysopen().

       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 perlfunc.

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

   "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().

       Thus:

           $foo = ($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 sequences.

   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 "oct()":

           $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 perlref.

       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 example:

           Not enough arguments for scalar at (eval 4)[newlib/perl5db.pl:1411] 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 perlvar.

   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");
           undef($foo,&bar);

       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 security.

       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 perlsub.

   $^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 example.

   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 INSTALL and README.Y2K.

   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\@example.com" 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 "fred@example.com" is going to turn into "fred.com" if you don't backslash the
       "@".  See http://perl.plover.com/at-error.html for more details about the history here.

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

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

       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.

       Benchmark
           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.

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

       constant
           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.

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

       Data::Dumper
           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
           DB_File can now be built with Berkeley DB versions 1, 2 or 3.  See "ext/DB_File/Changes".

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

       Devel::Peek
           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.

       Dumpvalue
           The Dumpvalue module provides screen dumps of Perl data.

       DynaLoader
           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.)

       English
           $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 variables.

       Fcntl
           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.

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

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

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

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

           See File::Find.

       File::Glob
           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.

       File::Spec
           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.

       File::Spec::Functions
           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
           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;

               __END__

               =head1 NAME

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

               =head1 SYNOPSIS

               sample [options] [file ...]

                Options:
                  -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.

               =back

               =head1 DESCRIPTION

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

               =cut

           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 timeouts.

           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.

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

       Math::Complex
           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.

       Math::Trig
           A little bit of radial trigonometry (cylindrical and spherical), radial coordinate conversions,
           and the great circle distance were added.

       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 pod-people@perl.org mailing list.

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

       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 module.

       SDBM_File
           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 fixed.

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

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

       Term::ANSIColor
           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.

       Time::Local
           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.

       Win32
           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:

               Win32::FsType
               Win32::GetOSVersion

           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.

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

       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:

               filter_store_key
               filter_store_value
               filter_fetch_key
               filter_fetch_value

           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.

   Pragmata
       "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 better.

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

   find2perl
       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.

   h2xs
       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
       "perlcc" now supports the C and Bytecode backends.  By default, it generates output from the simple C
       backend rather than the optimized C backend.

       Support for non-Unix platforms has been improved.

   perldoc
       "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 perl5db.pl, 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.

       perlapi.pod
           The official list of public Perl API functions.

       perlboot.pod
           A tutorial for beginners on object-oriented Perl.

       perlcompile.pod
           An introduction to using the Perl Compiler suite.

       perldbmfilter.pod
           A howto document on using the DBM filter facility.

       perldebug.pod
           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.

       perldebguts.pod
           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.

       perlfork.pod
           Notes on the fork() emulation currently available for the Windows platform.

       perlfilter.pod
           An introduction to writing Perl source filters.

       perlhack.pod
           Some guidelines for hacking the Perl source code.

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

       perllexwarn.pod
           Introduction and reference information about lexically scoped warning categories.

       perlnumber.pod
           Detailed information about numbers as they are represented in Perl.

       perlopentut.pod
           A tutorial on using open() effectively.

       perlreftut.pod
           A tutorial that introduces the essentials of references.

       perltootc.pod
           A tutorial on managing class data for object modules.

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

       perlunicode.pod
           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 -Duse5005threads".

       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".

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

           use64bitint                 (equal to now deprecated 'use64bits')
           use64bitall

           uselongdouble
           usemorebits
           uselargefiles
           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.

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

   -Duselargefiles
       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.

   installusrbinperl
       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:

           http://www.socks.nec.com/

   "-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 fine.

       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 config.sh 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.

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.

   DOS
       •   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 File::Glob).

   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.

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

       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 "verbs".

       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 ExtUtils::MM_VMS.

       Extension of ExtUtils::MM_VMS to handle complex extensions more flexibly.

       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 Perl.

       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.

   Win32
       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 command.com 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
       "undef".

       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 fixed.

       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 autoloaded.

   "-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 perldata.

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

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

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

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

       /%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 as:

               $foo{$bar}
               $ref->{"susie"}[12]

       %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:

               $foo{$bar}
               $ref->{"susie"}[12]

           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 shown.

       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 perlre.

       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 extensions.

       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.

       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 perlfunc.

       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 usersupplied
           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 usersupplied
           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 errno.

       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 "fred@example.com";

           and the array @example doesn't exist, Perl is going to print "fred.com", 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 "/abc(?=xyz){3}/".

       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 balance.

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

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

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

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

       lib/env
           Tests for new environment scalar capability (e.g., "use Env qw($BAR);").

       lib/env-array
           Tests for new environment array capability (e.g., "use Env qw(@PATH);").

       lib/io_const
           IO constants (SEEK_*, _IO*).

       lib/io_dir
           Directory-related IO methods (new, read, close, rewind, tied delete).

       lib/io_multihomed
           INET sockets with multi-homed hosts.

       lib/io_poll
           IO poll().

       lib/io_unix
           UNIX sockets.

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

       op/filetest
           File test operators.

       op/lex_assign
           Verify operations that access pad objects (lexicals and temporaries).

       op/exists_sub
           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 information.

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

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

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

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

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

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

               grep not($_), @things;

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

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

           needs to be written with additional parentheses now:

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

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

       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
       "PERL_POLLUTE"
           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

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

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

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

           See "The Perl API" 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.

       "PERL_POLLUTE_MALLOC"
           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 definitions.

           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
       "PATCHLEVEL" is now "PERL_VERSION"
           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 "SUBVERSION".

           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
   Thread test failures
       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.

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

   In 64-bit HP-UX the lib/io_multihomed test may hang
       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).

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

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

   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:

           @x->[2]
           scalar(@x)->[2]

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

   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:

       Threads
       Unicode
       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 http://www.perl.com/perl/ , 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 perlbug@perl.org to be analysed by the Perl porting team.

SEE ALSO
       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.

HISTORY
       Written by Gurusamy Sarathy <gsar@activestate.com>, with many contributions from The Perl Porters.

       Send omissions or corrections to <perlbug@perl.org>.



perl v5.12.5                                     2012-11-03                                   PERL56DELTA(1)