perl56delta(1) - phpMan

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:

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

       o   arguments to oct() and hex()

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

       o   printed as such

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

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

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

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

       o   GNU/Hurd is now supported.

       o   Rhapsody/Darwin is now supported.

       o   EPOC is now supported (on Psion 5).

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

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

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

       o   Incorrect exit codes from backticks have been fixed.

       o   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 handler.  See attributes.

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

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

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

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

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

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

       Method %s not permitted
           See Server error.

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

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

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

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

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

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

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

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

           See also perlport for writing portable code.

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

       panic: kid popen errno read
           (F) forked child returned an incomprehensible message about its 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 AT 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 "Background and PERL_IMPLICIT_CONTEXT" in perlguts for detailed information on the
           ramifications of building Perl with this option.

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

       "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 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 AT 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 AT activestate.com>, with many contributions from The Perl
       Porters.

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

perl v5.34.0                                2025-04-08                             PERL56DELTA(1)

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