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NAME    [Toc]    [Back]

       perl56delta - what's new for perl v5.6.0

DESCRIPTION    [Toc]    [Back]

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

Core Enhancements    [Toc]    [Back]

       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

       -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 inde-
       pendent 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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       The new "scape interpolates named characters within
       strings.  For example, "Hi! HITE 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    [Toc]    [Back]

       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 "".  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

           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

       Improved Perl version numbering system    [Toc]    [Back]

       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

       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    [Toc]    [Back]

       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

       File and directory handles can be autovivified    [Toc]    [Back]

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

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

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

       open() with more than two arguments

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

       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

       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

           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,
       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
           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    [Toc]    [Back]

       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    [Toc]    [Back]

       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

       "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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       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

       Improved "qw//" operator

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


           $foo = ($bar) = qw(a b c); print "$foo|$bar0;

       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

       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()

       Weak references    [Toc]    [Back]

       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: %b0, oct("0b101010");

       Lvalue subroutines    [Toc]    [Back]

       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    [Toc]    [Back]

       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

       Boolean assignment operators are legal lvalues    [Toc]    [Back]

       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

       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

       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

       Pseudo-hashes work better    [Toc]    [Back]

       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 pseudohash
 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

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

       Automatic flushing of output buffers    [Toc]    [Back]

       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

       Better diagnostics on meaningless filehandle operations    [Toc]    [Back]

       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

       "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 pseudodisciplines
 ":raw" and ":crlf" are currently supported on
       DOS-derivative platforms.  See "binmode" in perlfunc and

       "-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() fail-

       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    [Toc]    [Back]

       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

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       Expressions such as:

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

       used to be accidentally allowed in earlier versions, and
       produced unpredictable behaviour.  Some produced ancillary
       warnings when used in this way; others silently did the
       wrong thing.
       The parenthesized forms of most unary operators that
       expect a single argument now ensure that they are not
       called with more than one argument, making the cases shown
       above syntax errors.  The usual behaviour of:

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

       remains unchanged.  See perlop.

       Bit operators support full native integer width    [Toc]    [Back]

       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    [Toc]    [Back]

       More potentially unsafe operations taint their results for
       improved security.

       The "passwd" and "shell" fields returned by the getp-
       went(), 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

       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 ${"       syntax  error.
Now variable names that begin with a control
 character may be arbitrarily long.  However, for compatibility
 reasons, these variables must be written with
       explicit braces, as "${^XY}" for example.  "${^XYZ}" is
       synonymous with ${"       one control character,  such  as
"${^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

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       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 "
       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

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

Modules and Pragmata    [Toc]    [Back]


           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 testsuite
           passes when run under the Compiler, but there is still
           a significant way to go to achieve production quality
           compiled executables.

               NOTE: The Compiler suite remains highly experimental.  The
               generated  code  may  not be correct, even when it
manages to execute
               without errors.
           Overall, Benchmark results exhibit lower average error
           and better timing accuracy.

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

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

           will now output something like this:

              Benchmark:  running  a,  b, each for at least 5 CPU
                       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

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

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

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

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

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

           For other details, see Benchmark.

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

           References can now be used.

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

           See constant.

           This pragma implements the "tring escape.  See

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

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

           Dumping "qr//" objects works correctly.

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

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

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

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

           The Dumpvalue module provides screen dumps of Perl

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

           Perl can also optionally arrange to unload all extension
 shared objects loaded by Perl.  To enable this,
           build Perl with the Configure option
           "-Accflags=-DDL_UNLOAD_ALL_AT_EXIT".  (This maybe useful
 if you are using Apache with mod_perl.)
           $PERL_VERSION now stands for $^V (a string value)
           rather than for $] (a numeric value).

       Env Env now supports accessing environment variables like
           PATH as array variables.

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

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

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

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

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

           See File::Find.

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

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

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

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

           instead of

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

           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|?' => elp, man => an) or  pod2usage(2);
               pod2usage(1) if $help;
               pod2usage(-exitstatus  =>  0,  -verbose  =>  2) if


               =head1 NAME

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

               =head1 SYNOPSIS

               sample [options] [file ...]

                  -help            brief help message
                  -man             full documentation

               =head1 OPTIONS

               =over 8

               =item B<-help>

               Print a brief help message and exits.
               =item B<-man>

               Prints the manual page and exits.


               =head1 DESCRIPTION

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


           See Pod::Usage for details.

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

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

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

           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

           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.

           The bitwise operations "<<", ">>", "&", "|", and "~"
           are now supported on bigints.
           The accessor methods Re, Im, arg, abs, rho, and theta
           can now also act as mutators (accessor $z->Re(), mutator

           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

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

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

           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

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

           For further information, please see Pod::Parser and

       Pod::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 usag

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