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         perldelta - what's new for perl v5.6.0


         This document describes differences between the 5.005
         release and this one.

    Core Enhancements

         Interpreter cloning, threads, and concurrency
         Perl 5.005_63 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
         On the Windows platform, this feature is used to emulate
         fork() at the interpreter level.  See the perlfork manpage
         for details about that.
         This feature is still in evolution.  It is eventually meant
         to be used to selectively clone a subroutine and data
         reachable from that subroutine in a separate interpreter and
         run the cloned subroutine in a separate thread.  Since there
         is no shared data between the interpreters, little or no
         locking will be needed (unless parts of the symbol table are
         explicitly shared).  This is obviously intended to be an
         easy-to-use replacement for the existing threads support.
         Support for cloning interpreters and interpreter concurrency
         can be enabled using the -Dusethreads Configure option (see
         win32/Makefile for how to enable it on Windows.)  The
         resulting perl executable will be functionally identical to
         one that was built with -Dmultiplicity, but the perl_clone()
         API call will only be available in the former.
         -Dusethreads enables the cpp macro USE_ITHREADS by default,
         which in turn enables Perl source code changes that provide
         a clear separation between the op tree and the data it
         operates with.  The former is immutable, and can therefore
         be shared between an interpreter and all of its clones,
         while the latter is considered local to each interpreter,
         and is therefore copied for each clone.
         Note that building Perl with the -Dusemultiplicity Configure
         option is adequate if you wish to run multiple independent
         interpreters concurrently in different threads.
         -Dusethreads only provides the additional functionality of
         the perl_clone() API call and other support for running
         cloned interpreters concurrently.
             NOTE: This is an experimental feature.  Implementation details are
             subject to change.
         Lexically scoped warning categories
         You can now control the granularity of warnings emitted by
         perl at a finer level using the `use warnings' pragma.  the
         warnings manpage and the perllexwarn manpage have copious
         documentation on this feature.
         Unicode and UTF-8 support
         Perl now uses UTF-8 as its internal representation for
         character strings.  The `utf8' and `bytes' pragmas are used
         to control this support in the current lexical scope.  See
         the perlunicode manpage, the utf8 manpage and the bytes
         manpage for more information.
         This feature is expected to evolve quickly to support some
         form of I/O disciplines that can be used to specify the kind
         of input and output data (bytes or characters).  Until that
         happens, additional modules from CPAN will be needed to
         complete the toolkit for dealing with Unicode.
             NOTE: This should be considered an experimental feature.  Implementation
             details are subject to change.
         Support for interpolating named characters
         The new `\N' escape interpolates named characters within
         strings.  For example, `"Hi! \N{WHITE SMILING FACE}"'
         evaluates to a string with a unicode smiley face at the end.
         "our" declarations
         An "our" declaration introduces a value that can be best
         understood as a lexically scoped symbolic alias to a global
         variable in the package that was current where the variable
         was declared.  This is mostly useful as an alternative to
         the `vars' pragma, but also provides the opportunity to
         introduce typing and other attributes for such variables.
         See the our entry in the perlfunc manpage.
         Support for strings represented as a vector of ordinals
         Literals of the form `v1.2.3.4' are now parsed as a string
         composed of characters with the specified ordinals.  This is
         an alternative, more readable way to construct (possibly
         unicode) strings instead of interpolating characters, as in
         `"\x{1}\x{2}\x{3}\x{4}"'.  The leading `v' may be omitted if
         there are more than two ordinals, so `1.2.3' is parsed the
         same as `v1.2.3'.
         Strings written in this form are also useful to represent
         version "numbers".  It is easy to compare such version
         "numbers" (which are really just plain strings) using any of
         the usual string comparison operators `eq', `ne', `lt',
         `gt', etc., or perform bitwise string operations on them
         using `|', `&', etc.
         In conjunction with the new `$^V' magic variable (which
         contains the perl version as a string), such literals can be
         used as a readable way to check if you're running a
         particular version of Perl:
             # this will parse in older versions of Perl also
             if ($^V and $^V gt v5.6.0) {
                 # new features supported
         `require' and `use' also have some special magic to support
         such literals.  They will be interpreted as a version rather
         than as a module name:
             require v5.6.0;             # croak if $^V lt v5.6.0
             use v5.6.0;                 # same, but croaks at compile-time
         Alternatively, the `v' may be omitted if there is more than
         one dot:
             require 5.6.0;
             use 5.6.0;
         Also, `sprintf' and `printf' support the Perl-specific
         format flag `%v' to print ordinals of characters in
         arbitrary strings:
             printf "v%vd", $^V;         # prints current version, such as "v5.5.650"
             printf "%*vX", ":", $addr;  # formats IPv6 address
             printf "%*vb", " ", $bits;  # displays bitstring
         See the Scalar value constructors entry in the perldata
         manpage for additional information.
         Improved Perl version numbering system
         Beginning with Perl version 5.6.0, the version number
         convention has been changed to a "dotted integer" scheme
         that is more commonly found in open source projects.
         Maintenance versions of v5.6.0 will be released as v5.6.1,
         v5.6.2 etc.  The next development series following v5.6.0
         will be numbered v5.7.x, beginning with v5.7.0, and the next
         major production release following v5.6.0 will be v5.8.0.
         The English module now sets $PERL_VERSION to $^V (a string
         value) rather than `$]' (a numeric value).  (This is a
         potential incompatibility.  Send us a report via perlbug if
         you are affected by this.)
         The v1.2.3 syntax is also now legal in Perl.  See the
         Support for strings represented as a vector of ordinals
         entry elsewhere in this document for more on that.
         To cope with the new versioning system's use of at least
         three significant digits for each version component, the
         method used for incrementing the subversion number has also
         changed slightly.  We assume that versions older than v5.6.0
         have been incrementing the subversion component in multiples
         of 10.  Versions after v5.6.0 will increment them by 1.
         Thus, using the new notation, 5.005_03 is the "same" as
         v5.5.30, and the first maintenance version following v5.6.0
         will be v5.6.1 (which should be read as being equivalent to
         a floating point value of 5.006_001 in the older format,
         stored in `$]').
         New syntax for declaring subroutine attributes
         Formerly, if you wanted to mark a subroutine as being a
         method call or as requiring an automatic lock() when it is
         entered, you had to declare that with a `use attrs' pragma
         in the body of the subroutine.  That can now be accomplished
         with declaration syntax, like this:
             sub mymethod : locked method ;
             sub mymethod : locked method {
             sub othermethod :locked :method ;
             sub othermethod :locked :method {
         (Note how only the first `:' is mandatory, and whitespace
         surrounding the `:' is optional.)
     and have been updated to keep the
         attributes with the stubs they provide.  See the attributes
         File and directory handles can be autovivified
         Similar to how constructs such as `$x->[0]' autovivify a
         reference, handle constructors (open(), opendir(), pipe(),
         socketpair(), sysopen(), socket(), and accept()) now
         autovivify a file or directory handle if the handle passed
         to them is an uninitialized scalar variable.  This allows
         the constructs such as `open(my $fh, ...)' and `open(local
         $fh,...)'  to be used to create filehandles that will
         conveniently be closed automatically when the scope ends,
         provided there are no other references to them.  This
         largely eliminates the need for typeglobs when opening
         filehandles that must be passed around, as in the following
             sub myopen {
                 open my $fh, "@_"
                      or die "Can't open '@_': $!";
                 return $fh;
                 my $f = myopen("</etc/motd");
                 print <$f>;
                 # $f implicitly closed here
         open() with more than two arguments
         If open() is passed three arguments instead of two, the
         second argument is used as the mode and the third argument
         is taken to be the file name.  This is primarily useful for
         protecting against unintended magic behavior of the
         traditional two-argument form.  See the open entry in the
         perlfunc manpage.
         64-bit support
         Any platform that has 64-bit integers either
                 (1) natively as longs or ints
                 (2) via special compiler flags
                 (3) using long long or int64_t
         is able to use "quads" (64-bit integers) as follows:
         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 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
             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 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
         "more bits"
         You can "Configure -Dusemorebits" to turn on both the 64-bit
         support and the long double support.
         Enhanced support for sort() subroutines
         Perl subroutines with a prototype of `($$)', and XSUBs in
         general, can now be used as sort subroutines.  In either
         case, the two elements to be compared are passed as normal
         parameters in @_.  See the sort entry in the perlfunc
         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
         File globbing implemented internally
         Perl now uses the File::Glob implementation of the glob()
         operator automatically.  This avoids using an external csh
         process and the problems associated with it.
             NOTE: This is currently an experimental feature.  Interfaces and
             implementation are subject to change.
         Support for CHECK blocks
              In addition to `BEGIN', `INIT', `END', `DESTROY' and
              `AUTOLOAD', subroutines named `CHECK' are now special.
              These are queued up during compilation and behave
              similar to END blocks, except they are called at the
              end of compilation rather than at the end of execution.
              They cannot be called directly.
         POSIX character class syntax [: :] supported
         For example to match alphabetic characters use
         /[[:alpha:]]/.  See the perlre manpage for details.
         Better pseudo-random number generator
              In 5.005_0x and earlier, perl's rand() function used
              the C library rand(3) function.  As of 5.005_52,
              Configure tests for drand48(), random(), and rand() (in
              that order) and picks the first one it finds.
         These changes should result in better random numbers from
         Improved `qw//' operator
         The `qw//' operator is now evaluated at compile time into a
         true list instead of being replaced with a run time call to
         `split()'.  This removes the confusing misbehaviour of
         `qw//' in scalar context, which had inherited that behaviour
         from split().
             $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
         now correctly prints "3|a", instead of "2|a".
         Better worst-case behavior of hashes
              Small changes in the hashing algorithm have been
              implemented in order to improve the distribution of
              lower order bits in the hashed value.  This is expected
              to yield better performance on keys that are repeated
         pack() format 'Z' supported
         The new format type 'Z' is useful for packing and unpacking
         null-terminated strings.  See the pack entry in the perlfunc
         pack() format modifier '!' supported
         The new format type modifier '!' is useful for packing and
         unpacking native shorts, ints, and longs.  See the pack
         entry in the perlfunc manpage.
         pack() and unpack() support counted strings
         The template character '/' can be used to specify a counted
         string type to be packed or unpacked.  See the pack entry in
         the perlfunc manpage.
         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
         In previous versions of Perl, you couldn't cache objects so
         as to allow them to be deleted if the last reference from
         outside the cache is deleted.  The reference in the cache
         would hold a reference count on the object and the objects
         would never be destroyed.
         Another familiar problem is with circular references.  When
         an object references itself, its reference count would never
         go down to zero, and it would not get destroyed until the
         program is about to exit.
         Weak references solve this by allowing you to "weaken" any
         reference, that is, make it not count towards the reference
         count.  When the last non-weak reference to an object is
         deleted, the object is destroyed and all the weak references
         to the object are automatically undef-ed.
         To use this feature, you need the WeakRef package from CPAN,
         which contains additional documentation.
             NOTE: This is an experimental feature.  Details are subject to change.
         Binary numbers supported
         Binary numbers are now supported as literals, in s?printf
         formats, and `oct()':
             $answer = 0b101010;
             printf "The answer is: %b\n", oct("0b101010");
         Lvalue subroutines
         Subroutines can now return modifiable lvalues.  See the
         Lvalue subroutines entry in the perlsub manpage.
             NOTE: This is an experimental feature.  Details are subject to change.
         Some arrows may be omitted in calls through references
         Perl now allows the arrow to be omitted in many constructs
         involving subroutine calls through references.  For example,
         `$foo[10]->('foo')' may now be written `$foo[10]('foo')'.
         This is rather similar to how the arrow may be omitted from
         `$foo[10]->{'foo'}'.  Note however, that the arrow is still
         required for `foo(10)->('bar')'.
         Boolean assignment operators are legal lvalues
         Constructs such as `($a ||= 2) += 1' are now allowed.
         exists() is supported on subroutine names
         The exists() builtin now works on subroutine names.  A
         subroutine is considered to exist if it has been declared
         (even if implicitly).  See the exists entry in the perlfunc
         manpage for examples.
         exists() and delete() are supported on array elements
         The exists() and delete() builtins now work on simple arrays
         as well.  The behavior is similar to that on hash elements.
         exists() can be used to check whether an array element has
         been initialized.  This avoids autovivifying array elements
         that don't exist.  If the array is tied, the EXISTS() method
         in the corresponding tied package will be invoked.
         delete() may be used to remove an element from the array and
         return it.  The array element at that position returns to
         its unintialized state, so that testing for the same element
         with exists() will return false.  If the element happens to
         be the one at the end, the size of the array also shrinks up
         to the highest element that tests true for exists(), or 0 if
         none such is found.  If the array is tied, the DELETE()
         method in the corresponding tied package will be invoked.
         See the exists entry in the perlfunc manpage and the delete
         entry in the perlfunc manpage for examples.
         Pseudo-hashes work better
         Dereferencing some types of reference values in a pseudo-
         hash, such as `$ph->{foo}[1]', was accidentally disallowed.
         This has been corrected.
         When applied to a pseudo-hash element, exists() now reports
         whether the specified value exists, not merely if the key is
         delete() now works on pseudo-hashes.  When given a pseudo-
         hash element or slice it deletes the values corresponding to
         the keys (but not the keys themselves).  See the Pseudo-
         hashes: Using an array as a hash entry in the 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 the
         fields manpage.
             NOTE: The pseudo-hash data type continues to be experimental.
             Limiting oneself to the interface elements provided by the
             fields pragma will provide protection from any future changes.
         Automatic flushing of output buffers
         fork(), exec(), system(), qx//, and pipe open()s now flush
         buffers of all files opened for output when the operation
         was attempted.  This mostly eliminates confusing buffering
         mishaps suffered by users unaware of how Perl internally
         handles I/O.
         This is not supported on some platforms like Solaris where a
         suitably correct implementation of fflush(NULL) isn't
         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
         `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
         eof() has the same old magic as <>
         `eof()' would return true if no attempt to read from `<>'
         had yet been made.  `eof()' has been changed to have a
         little magic of its own, it now opens the `<>' files.
         binmode() can be used to set :crlf and :raw modes
         binmode() now accepts a second argument that specifies a
         discipline for the handle in question.  The two pseudo-
         disciplines ":raw" and ":crlf" are currently supported on
         DOS-derivative platforms.  See the binmode entry in the
         perlfunc manpage and the open manpage.
         `-T' filetest recognizes UTF-8 encoded files as "text"
         The algorithm used for the `-T' filetest has been enhanced
         to correctly identify UTF-8 content as "text".
         system(), backticks and pipe open now reflect exec() failure
         On Unix and similar platforms, system(), qx() and open(FOO,
         "cmd |") etc., are implemented via fork() and exec().  When
         the underlying exec() fails, earlier versions did not report
         the error properly, since the exec() happened to be in a
         different process.
         The child process now communicates with the parent about the
         error in launching the external command, which allows these
         constructs to return with their usual error value and set
         Improved diagnostics
         Line numbers are no longer suppressed (under most likely
         circumstances) during the global destruction phase.
         Diagnostics emitted from code running in threads other than
         the main thread are now accompanied by the thread ID.
         Embedded null characters in diagnostics now actually show
         up.  They used to truncate the message in prior versions.
         $foo::a and $foo::b are now exempt from "possible typo"
         warnings only if sort() is encountered in package `foo'.
         Unrecognized alphabetic escapes encountered when parsing
         quote constructs now generate a warning, since they may take
         on new semantics in later versions of Perl.
         Many diagnostics now report the internal operation in which
         the warning was provoked, like so:
             Use of uninitialized value in concatenation (.) at (eval 1) line 1.
             Use of uninitialized value in print at (eval 1) line 1.
         Diagnostics  that occur within eval may also report the file
         and line number where the eval is located, in addition to
         the eval sequence number and the line number within the
         evaluated text itself.  For example:
             Not enough arguments for scalar at (eval 4)[newlib/] line 2, at EOF
         Diagnostics follow STDERR
         Diagnostic output now goes to whichever file the `STDERR'
         handle is pointing at, instead of always going to the
         underlying C runtime library's `stderr'.
         More consistent close-on-exec behavior
              On systems that support a close-on-exec flag on
              filehandles, the flag is now set for any handles
              created by pipe(), socketpair(), socket(), and
              accept(), if that is warranted by the value of $^F that
              may be in effect.  Earlier versions neglected to set
              the flag for handles created with these operators.  See
              the pipe entry in the perlfunc manpage, the socketpair
              entry in the perlfunc manpage, the socket entry in the
              perlfunc manpage, the accept entry in the perlfunc
              manpage, and the section on "$^F" in the perlvar
         syswrite() ease-of-use
         The length argument of `syswrite()' has become optional.
         Better syntax checks on parenthesized unary operators
         Expressions such as:
             print defined(&foo,&bar,&baz);
             print uc("foo","bar","baz");
         used to be accidentally allowed in earlier versions, and
         produced unpredictable behaviour.  Some produced ancillary
         warnings when used in this way; others silently did the
         wrong thing.
         The parenthesized forms of most unary operators that expect
         a single argument now ensure that they are not called with
         more than one argument, making the cases shown above syntax
         errors.  The usual behaviour of:
             print defined &foo, &bar, &baz;
             print uc "foo", "bar", "baz";
             undef $foo, &bar;
         remains unchanged.  See the perlop manpage.
         Bit operators support full native integer width
         The bit operators (& | ^ ~ << >>) now operate on the full
         native integral width (the exact size of which is available
         in $Config{ivsize}).  For example, if your platform is
         either natively 64-bit or if Perl has been configured to use
         64-bit integers, these operations apply to 8 bytes (as
         opposed to 4 bytes on 32-bit platforms).  For portability,
         be sure to mask off the excess bits in the result of unary
         `~', e.g., `~$x & 0xffffffff'.
         Improved security features
         More potentially unsafe operations taint their results for
         improved 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 the Prototypes entry in the perlsub manpage.
         `require' and `do' may be overridden
         `require' and `do 'file'' operations may be overridden
         locally by importing subroutines of the same name into the
         current package (or globally by importing them into the
         CORE::GLOBAL:: namespace).  Overriding `require' will also
         affect `use', provided the override is visible at compile-
         time.  See the Overriding Built-in Functions entry in the
         perlsub manpage.
         $^X variables may now have names longer than one character
         Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a
         syntax error.  Now variable names that begin with a control
         character may be arbitrarily long.  However, for
         compatibility reasons, these variables must be written with
         explicit braces, as `${^XY}' for example.  `${^XYZ}' is
         synonymous with ${"\cXYZ"}.  Variable names with more than
         one control character, such as `${^XY^Z}', are illegal.
         The old syntax has not changed.  As before, `^X' may be
         either a literal control-X character or the two-character
         sequence `caret' plus `X'.  When braces are omitted, the
         variable name stops after the control character.  Thus
         `"$^XYZ"' continues to be synonymous with `$^X . "YZ"' as
         As before, lexical variables may not have names beginning
         with control characters.  As before, variables whose names
         begin with a control character are always forced to be in
         package `main'.  All such variables are reserved for future
         extensions, except those that begin with `^_', which may be
         used by user programs and are guaranteed not to acquire
         special meaning in any future version of Perl.
         New variable $^C reflects `-c' switch
         `$^C' has a boolean value that reflects whether perl is
         being run in compile-only mode (i.e. via the `-c' switch).
         Since BEGIN blocks are executed under such conditions, this
         variable enables perl code to determine whether actions that
         make sense only during normal running are warranted.  See
         the perlvar manpage.
         New variable $^V contains Perl version as a string
         `$^V' contains the Perl version number as a string composed
         of characters whose ordinals match the version numbers, i.e.
         v5.6.0.  This may be used in string comparisons.
         See `Support for strings represented as a vector of
         ordinals' for an 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.

    Modules and Pragmata

             While used internally by Perl as a pragma, this module
             also provides a way to fetch subroutine and variable
             attributes.  See the attributes manpage.
         B   The Perl Compiler suite has been extensively reworked
             for this release.  More of the standard Perl testsuite
             passes when run under the Compiler, but there is still a
             significant way to go to achieve production quality
             compiled executables.
                 NOTE: The Compiler suite remains highly experimental.  The
                 generated code may not be correct, even it manages to execute
                 without errors.
             Overall, Benchmark results exhibit lower average error
             and better timing accuracy.
             You can now run tests for n seconds instead of guessing
             the right number of tests to run: e.g., timethese(-5,
             ...) will run each code for at least 5 CPU seconds.
             Zero as the "number of repetitions" means "for at least
             3 CPU seconds".  The output format has also changed.
             For example:
                use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
             will now output something like this:
                Benchmark: running a, b, each for at least 5 CPU seconds...
                         a:  5 wallclock secs ( 5.77 usr +  0.00 sys =  5.77 CPU) @ 200551.91/s (n=1156516)
                         b:  4 wallclock secs ( 5.00 usr +  0.02 sys =  5.02 CPU) @ 159605.18/s (n=800686)
             New features: "each for at least N CPU seconds...",
             "wallclock secs", and the "@ operations/CPU second
             timethese() now returns a reference to a hash of
             Benchmark objects containing the test results, keyed on
             the names of the tests.
             timethis() now returns the iterations field in the
             Benchmark result object instead of 0.
             timethese(), timethis(), and the new cmpthese() (see
             below) can also take a format specifier of 'none' to
             suppress output.
             A new function countit() is just like timeit() except
             that it takes a TIME instead of a COUNT.
             A new function cmpthese() prints a chart comparing the
             results of each test returned from a timethese() call.
             For each possible pair of tests, the percentage speed
             difference (iters/sec or seconds/iter) is shown.
             For other details, see the Benchmark manpage.
             The ByteLoader is a dedicated extension to generate and
             run Perl bytecode.  See the ByteLoader manpage.
             References can now be used.
             The new version also allows a leading underscore in
             constant names, but disallows a double leading
             underscore (as in "__LINE__").  Some other names are
             disallowed or warned against, including BEGIN, END, etc.
             Some names which were forced into main:: used to fail
             silently in some cases; now they're fatal (outside of
             main::) and an optional warning (inside of main::).  The
             ability to detect whether a constant had been set with a
             given name has been added.
             See the constant manpage.
             This pragma implements the `\N' string escape.  See the
             charnames manpage.
             A `Maxdepth' setting can be specified to avoid venturing
             too deeply into deep data structures.  See the
             Data::Dumper manpage.
             The XSUB implementation of Dump() is now automatically
             called if the `Useqq' setting is not in use.
             Dumping `qr//' objects works correctly.
         DB  `DB' is an experimental module that exposes a clean
             abstraction to Perl's debugging API.
             DB_File can now be built with Berkeley DB versions 1, 2
             or 3.  See `ext/DB_File/Changes'.
             Devel::DProf, a Perl source code profiler has been
             added.  See the Devel::DProf manpage and the dprofpp
             The Devel::Peek module provides access to the internal
             representation of Perl variables and data.  It is a data
             debugging tool for the XS programmer.
             The Dumpvalue module provides screen dumps of Perl data.
             DynaLoader now supports a dl_unload_file() function on
             platforms that support unloading shared objects using
             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 the File::Compare
             File::Find now works correctly when the wanted()
             function is either autoloaded or is a symbolic
             A bug that caused File::Find to lose track of the
             working directory when pruning top-level directories has
             been fixed.
             File::Find now also supports several other options to
             control its behavior.  It can follow symbolic links if
             the `follow' option is specified.  Enabling the
             `no_chdir' option will make File::Find skip changing the
             current directory when walking directories.  The
             `untaint' flag can be useful when running with taint
             checks enabled.
             See the File::Find manpage.
             This extension implements BSD-style file globbing.  By
             default, it will also be used for the internal
             implementation of the glob() operator.  See the
             File::Glob manpage.
             New methods have been added to the File::Spec module:
             devnull() returns the name of the null device (/dev/null
             on Unix) and tmpdir() the name of the temp directory
             (normally /tmp on Unix).  There are now also methods to
             convert between absolute and relative filenames:
             abs2rel() and rel2abs().  For compatibility with
             operating systems that specify volume names in file
             paths, the splitpath(), splitdir(), and catdir() methods
             have been added.
             The new File::Spec::Functions modules provides a
             function interface to the File::Spec module.  Allows
                 $fullname = catfile($dir1, $dir2, $file);
             instead of
                 $fullname = File::Spec->catfile($dir1, $dir2, $file);
             Getopt::Long licensing has changed to allow the Perl
             Artistic License as well as the GPL. It used to be GPL
             only, which got in the way of non-GPL applications that
             wanted to use Getopt::Long.
             Getopt::Long encourages the use of Pod::Usage to produce
             help messages. For example:
                 use Getopt::Long;
                 use Pod::Usage;
                 my $man = 0;
                 my $help = 0;
                 GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
                 pod2usage(1) if $help;
                 pod2usage(-exitstatus => 0, -verbose => 2) if $man;
                 =head1 NAME
                 sample - Using GetOpt::Long and Pod::Usage
                 =head1 SYNOPSIS
                 sample [options] [file ...]
                    -help            brief help message
                    -man             full documentation
                 =head1 OPTIONS
                 =over 8
                 =item B<-help>
                 Print a brief help message and exits.
                 =item B<-man>
                 Prints the manual page and exits.
                 =head1 DESCRIPTION
                 B<This program> will read the given input file(s) and do someting
                 useful with the contents thereof.
             See the Pod::Usage manpage for details.
             A bug that prevented the non-option call-back <> from
             being specified as the first argument has been fixed.
             To specify the characters < and > as option starters,
             use ><. Note, however, that changing option starters is
             strongly deprecated.
         IO  write() and syswrite() will now accept a single-argument
             form of the call, for consistency with Perl's
             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:\fIs0: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 compatability.
         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 number.
             The potentially disruptive change is that in list
             context both methods now return the parameter hash,
             instead of only the value of the `"style"' parameter.
             A little bit of radial trigonometry (cylindrical and
             spherical), radial coordinate conversions, and the great
             circle distance were 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 mailing
             For further information, please see the Pod::Parser
             manpage and the Pod::InputObjects manpage.
         Pod::Checker, podchecker
             This utility checks pod files for correct syntax,
             according to the perlpod manpage.  Obvious errors are
             flagged as such, while warnings are printed for mistakes
             that can be handled gracefully.  The checklist is not
             complete yet.  See the Pod::Checker manpage.
         Pod::ParseUtils, Pod::Find
             These modules provide a set of gizmos that are useful
             mainly for pod translators.  Pod::Find traverses
             directory structures and returns found pod files, along
             with their canonical names (like `File::Spec::Unix').
             Pod::ParseUtils contains Pod::List (useful for storing
             pod list information), Pod::Hyperlink (for parsing the
             contents of `L<>' sequences) and Pod::Cache (for caching
             information about pod files, e.g., link nodes).
         Pod::Select, podselect
             Pod::Select is a subclass of Pod::Parser which provides
             a function named "podselect()" to filter out user-
             specified sections of raw pod documentation from an
             input stream. podselect is a script that provides access
             to Pod::Select from other scripts to be used as a
             filter.  See the Pod::Select manpage.
         Pod::Usage, pod2usage
             Pod::Usage provides the function "pod2usage()" to print
             usage messages for a Perl script based on its embedded
             pod documentation.  The pod2usage() function is
             generally useful to all script authors since it lets
             them write and maintain a single source (the pods) for
             documentation, thus removing the need to create and
             maintain redundant usage message text consisting of
             information already in the pods.
             There is also a pod2usage script which can be used from
             other kinds of scripts to print usage messages from pods
             (even for non-Perl scripts with pods embedded in
             For details and examples, please see the 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 the Pod::Text manpage for the details.
             The new Pod::Text module is easily subclassed for tweaks
             to the output, and two such subclasses
             (Pod::Text::Termcap for man-page-style bold and
             underlining using termcap information, and
             Pod::Text::Color for markup with ANSI color sequences)
             are now standard.
             pod2man has been turned into a module, Pod::Man, which
             also uses Pod::Parser.  In the process, several
             outstanding bugs related to quotes in section headers,
             quoting of code escapes, and nested lists have been
             fixed.  pod2man is now a wrapper script around this
             An EXISTS method has been added to this module (and
             sdbm_exists() has been added to the underlying sdbm
             library), so one can now call exists on an SDBM_File
             tied hash and get the correct result, rather than a
             runtime error.
             A bug that may have caused data loss when more than one
             disk block happens to be read from the database in a
             single FETCH() has been fixed.
             Sys::Syslog now uses XSUBs to access facilities from
             syslog.h so it no longer requires to exist.
             Sys::Hostname now uses XSUBs to call the C library's
             gethostname() or uname() if they exist.
             Term::ANSIColor is a very simple module to provide easy
             and readable access to the ANSI color and highlighting
             escape sequences, supported by most ANSI terminal
             emulators.  It is now included standard.
             The timelocal() and timegm() functions used to silently
             return bogus results when the date fell outside the
             machine's integer range.  They now consistently croak()
             if the date falls in an unsupported range.
             The error return value in list context has been changed
             for all functions that return a list of values.
             Previously these functions returned a list with a single
             element `undef' if an error occurred.  Now these
             functions return the empty list in these situations.
             This applies to the following functions:
             The remaining functions are unchanged and continue to
             return `undef' on error even in list context.
             The Win32::SetLastError(ERROR) function has been added
             as a complement to the Win32::GetLastError() function.
             The new Win32::GetFullPathName(FILENAME) returns the
             full absolute pathname for FILENAME in scalar context.
             In list context it returns a two-element list containing
             the fully qualified directory name and the filename.
             See the Win32 manpage.
             The XSLoader extension is a simpler alternative to
             DynaLoader.  See the XSLoader manpage.
         DBM Filters
             A new feature called "DBM Filters" has been added to all
             the DBM modules--DB_File, GDBM_File, NDBM_File,
             ODBM_File, and SDBM_File.  DBM Filters add four new
             methods to each DBM module:
             These can be used to filter key-value pairs before the
             pairs are written to the database or just after they are
             read from the database.  See the perldbmfilter manpage
             for further information.
         `use attrs' is now obsolete, and is only provided for
         backward-compatibility.  It's been replaced by the `sub :
         attributes' syntax.  See the Subroutine Attributes entry in
         the perlsub manpage and the attributes manpage.
         Lexical warnings pragma, `use warnings;', to control
         optional warnings.  See the perllexwarn manpage.
         `use filetest' to control the behaviour of filetests (`-r'
         `-w' ...).  Currently only one subpragma implemented, "use
         filetest 'access';", that uses access(2) or equivalent to
         check permissions instead of using stat(2) as usual.  This
         matters in filesystems where there are ACLs (access control
         lists): the stat(2) might lie, but access(2) knows 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 the binmode() can be used to set
         :crlf and :raw modes entry elsewhere in this document.

    Utility Changes

         `dprofpp' is used to display profile data generated using
         `Devel::DProf'.  See the dprofpp manpage.
         The `find2perl' utility now uses the enhanced features of
         the File::Find module.  The -depth and -follow options are
         supported.  Pod documentation is also included in the
         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
         `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' has been reworked to avoid possible security
         holes.  It will not by default let itself be run as the
         superuser, but you may still use the -U switch to try to
         make it drop privileges first.
         The Perl Debugger
         Many bug fixes and enhancements were added to,
         the Perl debugger.  The help documentation was rearranged.
         New commands include `< ?', `> ?', and `{ ?' to list out
         current actions, `man docpage' to run your doc viewer on
         some perl docset, and support for quoted options.  The help
         information was rearranged, and should be viewable once
         again if you're using less as your pager.  A serious
         security hole was plugged--you should immediately remove all
         older versions of the Perl debugger as installed in previous
         releases, all the way back to perl3, from your system to
         avoid being bitten by this.

    Improved Documentation

         Many of the platform-specific README files are now part of
         the perl installation.  See the perl manpage for the
         complete list.
             The official list of public Perl API functions.
             A tutorial for beginners on object-oriented Perl.
             An introduction to using the Perl Compiler suite.
             A howto document on using the DBM filter facility.
             All material unrelated to running the Perl debugger,
             plus all low-level guts-like details that risked
             crushing the casual user of the debugger, have been
             relocated from the old manpage to the next entry below.
             This new manpage contains excessively low-level material
             not related to the Perl debugger, but slightly related
             to debugging Perl itself.  It also contains some arcane
             internal details of how the debugging process works that
             may only be of interest to developers of Perl debuggers.
             Notes on the fork() emulation currently available for
             the Windows platform.
             An introduction to writing Perl source filters.
             Some guidelines for hacking the Perl source code.
             A list of internal functions in the Perl source code.
             (List is currently empty.)
             Introduction and reference information about lexically
             scoped warning categories.
             Detailed information about numbers as they are
             represented in Perl.
             A tutorial on using open() effectively.
             A tutorial that introduces the essentials of references.
             A tutorial on managing class data for object modules.
             Discussion of the most often wanted features that may
             someday be supported in Perl.
             An introduction to Unicode support features in Perl.

    Performance enhancements

         Simple sort() using { $a <=> $b } and the like are optimized
         Many common sort() operations using a simple inlined block
         are now optimized for faster performance.
         Optimized assignments to lexical variables
         Certain operations in the RHS of assignment statements have
         been optimized to directly set the lexical variable on the
         LHS, eliminating redundant copying overheads.
         Faster subroutine calls
         Minor changes in how subroutine calls are handled internally
         provide marginal improvements in performance.
         delete(), each(), values() and hash iteration are faster
              The hash values returned by delete(), each(), values()
              and hashes in a list context are the actual values in
              the hash, instead of copies.  This results in
              significantly better performance, because it eliminates
              needless copying in most situations.

    Installation and Configuration Improvements

         -Dusethreads means something different
         The -Dusethreads flag now enables the experimental
         interpreter-based thread support by default.  To get the
         flavor of experimental threads that was in 5.005 instead,
         you need to run Configure with "-Dusethreads
         As of v5.6.0, interpreter-threads support is still lacking a
         way to create new threads from Perl (i.e., `use Thread;'
         will not work with interpreter threads).  `use Thread;'
         continues to be available when you specify the
         -Duse5005threads option to Configure, bugs and all.
             NOTE: Support for threads continues to be an experimental feature.
             Interfaces and implementation are subject to sudden and drastic changes.
         New Configure flags
         The following new flags may be enabled on the Configure
         command line by running Configure with `-Dflag'.
             usethreads useithreads      (new interpreter threads: no Perl API yet)
             usethreads use5005threads   (threads as they were in 5.005)
             use64bitint                 (equal to now deprecated 'use64bits')
             usesocks                    (only SOCKS v5 supported)
         Threadedness and 64-bitness now more daring
         The Configure options enabling the use of threads and the
         use of 64-bitness are now more daring in the sense that they
         no more have an explicit list of operating systems of known
         threads/64-bit capabilities.  In other words: if your
         operating system has the necessary APIs and datatypes, you
         should be able just to go ahead and use them, for threads by
         Configure -Dusethreads, and for 64 bits either explicitly by
         Configure -Duse64bitint or implicitly if your system has
         64-bit wide datatypes.  See also the section on "64-bit
         Long Doubles
         Some platforms have "long doubles", floating point numbers
         of even larger range than ordinary "doubles".  To enable
         using long doubles for Perl's scalars, use -Duselongdouble.
         You can enable both -Duse64bitint and -Duselongdouble with
         -Dusemorebits.  See also the section on "64-bit support".
         Some platforms support system APIs that are capable of
         handling large files (typically, files larger than two
         gigabytes).  Perl will try to use these APIs if you ask for
         See the section on "Large file support" for more
         You can use "Configure -Uinstallusrbinperl" which causes
         installperl to skip installing perl also as /usr/bin/perl.
         This is useful if you prefer not to modify /usr/bin for some
         reason or another but harmful because many scripts assume to
         find Perl in /usr/bin/perl.
         SOCKS support
         You can use "Configure -Dusesocks" which causes Perl to
         probe for the SOCKS proxy protocol library (v5, not v4).
         For more information on SOCKS, see:
         `-A' flag
         You can "post-edit" the Configure variables using the
         Configure `-A' switch.  The editing happens immediately
         after the platform specific hints files have been processed
         but before the actual configuration process starts.  Run
         `Configure -h' to find out the full `-A' syntax.
         Enhanced Installation Directories
         The installation structure has been enriched to improve the
         support for maintaining multiple versions of perl, to
         provide locations for vendor-supplied modules, scripts, and
         manpages, and to ease maintenance of locally-added modules,
         scripts, and manpages.  See the section on Installation
         Directories in the INSTALL file for complete details.  For
         most users building and installing from source, the defaults
         should be 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 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   VM/ESA is now supported.
         o   Siemens BS2000 is now supported under the POSIX Shell.
         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 is now supported (on Psion 5).
         o   The cygwin port (formerly cygwin32) has been greatly
         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
         OS390 (OpenEdition MVS)
         Support for this EBCDIC platform has not been renewed in
         this release.  There are difficulties in reconciling Perl's
         standardization on UTF-8 as its internal representation for
         characters with the EBCDIC character set, because the two
         are incompatible.
         It is unclear whether future versions will renew support for
         this platform, but the possibility exists.
         Numerous revisions and extensions to configuration, build,
         testing, and installation process to accomodate 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
         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.
         Perl can now emulate fork() internally, using multiple
         interpreters running in different concurrent threads.  This
         support must be enabled at build time.  See the perlfork
         manpage for detailed information.
         When given a pathname that consists only of a drivename,
         such as `A:', opendir() and stat() now use the current
         working directory for the drive rather than the drive root.
         The builtin XSUB functions in the Win32:: namespace are
         documented.  See the Win32 manpage.
         $^X now contains the full path name of the running
         A Win32::GetLongPathName() function is provided to
         complement Win32::GetFullPathName() and
         Win32::GetShortPathName().  See the Win32 manpage.
         POSIX:\fIs0:uname() is supported.
         system(1,...) now returns true process IDs rather than
         process handles.  kill() accepts any real process id, rather
         than strictly return values from system(1,...).
         For better compatibility with Unix, `kill(0, $pid)' can now
         be used to test whether a process exists.
         The `Shell' module is supported.
         Better support for building Perl under in
         Windows 95 has been added.
         Scripts are read in binary mode by default to allow
         ByteLoader (and the filter mechanism in general) to work
         properly.  For compatibility, the DATA filehandle will be
         set to text mode if a carriage return is detected at the end
         of the line containing the __END__ or __DATA__ token; if
         not, the DATA filehandle will be left open in binary mode.
         Earlier versions always opened the DATA filehandle in text
         The glob() operator is implemented via the `File::Glob'
         extension, which supports glob syntax of the C shell.  This
         increases the flexibility of the glob() operator, but there
         may be compatibility issues for programs that relied on the
         older globbing syntax.  If you want to preserve
         compatibility with the older syntax, you might want to run
         perl with `-MFile::DosGlob'.  For details and compatibility
         information, see the File::Glob manpage.

    Significant bug fixes

         <HANDLE> on empty files
         With `$/' set to `undef', "slurping" an empty file returns a
         string of zero length (instead of `undef', as it used to)
         the first time the HANDLE is read after `$/' is set to
         `undef'.  Further reads yield `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
         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 neccessity
         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 $!.  This has been
         Behavior of list slices is more consistent
         When taking a slice of a literal list (as opposed to a slice
         of an array or hash), Perl used to return an empty list if
         the result happened to be composed of all undef values.
         The new behavior is to produce an empty list if (and only
         if) the original list was empty.  Consider the following
             @a = (1,undef,undef,2)[2,1,2];
         The old behavior would have resulted in @a having no
         elements.  The new behavior ensures it has three undefined
         Note in particular that the behavior of slices of the
         following cases remains unchanged:
             @a = ()[1,2];
             @a = (getpwent)[7,0];
             @a = (anything_returning_empty_list())[2,1,2];
             @a = @b[2,1,2];
             @a = @c{'a','b','c'};
         See the perldata manpage.
         `(\$)' prototype and `$foo{a}'
         A scalar reference prototype now correctly allows a hash or
         array element in that slot.
         `goto &sub' and AUTOLOAD
         The `goto &sub' construct works correctly when `&sub'
         happens to be 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
         Constructs that modified `@_' could fail to deallocate
         values in `@_' and thus leak memory.  This has been
         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.
         See the CHECK blocks entry elsewhere in this document for
         how to run things when the compile phase ends.
         Potential to leak DATA filehandles
         Using the `__DATA__' token creates an implicit filehandle to
         the file that contains the token.  It is the program's
         responsibility to close it when it is done reading from it.
         This caveat is now better explained in the documentation.
         See the perldata manpage.

    New or Changed Diagnostics

         "%s" variable %s masks earlier declaration in same %s
             (W misc) A "my" or "our" variable has been redeclared in
             the current scope or statement, effectively eliminating
             all access to the previous instance.  This is almost
             always a typographical error.  Note that the earlier
             variable will still exist until the end of the scope or
             until all closure referents to it are destroyed.
         "my sub" not yet implemented
             (F) Lexically scoped subroutines are not yet
             implemented.  Don't try that yet.
         "our" variable %s redeclared
             (W misc) You seem to have already declared the same
             global once before in the current lexical scope.
         '!' allowed only after types %s
             (F) The '!' is allowed in pack() and unpack() only after
             certain types.  See the pack entry in the perlfunc
         / cannot take a count
             (F) You had an unpack template indicating a counted-
             length string, but you have also specified an explicit
             size for the string.  See the pack entry in the perlfunc
         / must be followed by a, A or Z
             (F) You had an unpack template indicating a counted-
             length string, which must be followed by one of the
             letters a, A or Z to indicate what sort of string is to
             be unpacked.  See the pack entry in the perlfunc
         / must be followed by a*, A* or Z*
             (F) You had a pack template indicating a counted-length
             string, Currently the only things that can have their
             length counted are a*, A* or Z*.  See the pack entry in
             the perlfunc manpage.
         / must follow a numeric type
             (F) You had an unpack template that contained a '#', but
             this did not follow some numeric unpack specification.
             See the pack entry in the perlfunc manpage.
         /%s/: Unrecognized escape \\%c passed through
             (W regexp) You used a backslash-character combination
             which is not recognized by Perl.  This combination
             appears in an interpolated variable or a `''-delimited
             regular expression.  The character was understood
         /%s/: Unrecognized escape \\%c in character class passed through
             (W regexp) You used a backslash-character combination
             which is not recognized by Perl inside character
             classes.  The character was understood literally.
         /%s/ should probably be written as "%s"
             (W syntax) You have used a pattern where Perl expected
             to find a string, as in the first argument to `join'.
             Perl will treat the true or false result of matching the
             pattern against $_ as the string, which is probably not
             what you had in mind.
         %s() called too early to check prototype
             (W prototype) You've called a function that has a
             prototype before the parser saw a definition or
             declaration for it, and Perl could not check that the
             call conforms to the prototype.  You need to either add
             an early prototype declaration for the subroutine in
             question, or move the subroutine definition ahead of the
             call to get proper prototype checking.  Alternatively,
             if you are certain that you're calling the function
             correctly, you may put an ampersand before the name to
             avoid the warning.  See the perlsub manpage.
         %s argument is not a HASH or ARRAY element
             (F) The argument to exists() must be a hash or array
             element, such as:
         %s argument is not a HASH or ARRAY element or slice
             (F) The argument to delete() must be either a hash or
             array element, such as:
             or a hash or array slice, such as:
                 @foo[$bar, $baz, $xyzzy]
                 @{$ref->[12]}{"susie", "queue"}
         %s argument is not a subroutine name
             (F) The argument to exists() for `exists &sub' must be a
             subroutine name, and not a subroutine call.  `exists
             &sub()' will generate this error.
         %s package attribute may clash with future reserved word: %s
             (W reserved) A lowercase attribute name was used that
             had a package-specific handler.  That name might have a
             meaning to Perl itself some day, even though it doesn't
             yet.  Perhaps you should use a mixed-case attribute
             name, instead.  See the attributes manpage.
         (in cleanup) %s
             (W misc) This prefix usually indicates that a DESTROY()
             method raised the indicated exception.  Since
             destructors are usually called by the system at
             arbitrary points during execution, and often a vast
             number of times, the warning is issued only once for any
             number of failures that would otherwise result in the
             same message being repeated.
             Failure of user callbacks dispatched using the
             `G_KEEPERR' flag could also result in this warning.  See
             the G_KEEPERR entry in the perlcall manpage.
         <> should be quotes
             (F) You wrote `require <file>' when you should have
             written `require '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
         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-
             (W portable) The binary number you specified is larger
             than 2**32-1 (4294967295) and therefore non-portable
             between systems.  See the perlport manpage for more on
             portability concerns.
         Bit vector size > 32 non-portable
             (W portable) Using bit vector sizes larger than 32 is
         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 the Lvalue subroutines
             entry in the perlsub manpage.
         Can't read CRTL environ
             (S) A warning peculiar to VMS.  Perl tried to read an
             element of %ENV from the CRTL's internal environment
             array and discovered the array was missing.  You need to
             figure out where your CRTL misplaced its environ or
             define PERL_ENV_TABLES (see the perlvms manpage) so that
             environ is not searched.
         Can't remove %s: %s, skipping file
             (S) You requested an inplace edit without creating a
             backup file.  Perl was unable to remove the original
             file to replace it with the modified file.  The file was
             left unmodified.
         Can't return %s from lvalue subroutine
             (F) Perl detected an attempt to return illegal lvalues
             (such as temporary or readonly values) from a subroutine
             used as an lvalue.  This is not allowed.
         Can't weaken a nonreference
             (F) You attempted to weaken something that was not a
             reference.  Only references can be weakened.
         Character class [:%s:] unknown
             (F) The class in the character class [: :] syntax is
             unknown.  See the perlre manpage.
         Character class syntax [%s] belongs inside character classes
             (W unsafe) The character class constructs [: :], [= =],
             and [. .]  go inside character classes, the [] are part
             of the construct, for example: /[012[:alpha:]345]/.
             Note that [= =] and [. .]  are not currently
             implemented; they are simply placeholders for future
         Constant is not %s reference
             (F) A constant value (perhaps declared using the `use
             constant' pragma) is being dereferenced, but it amounts
             to the wrong type of reference.  The message indicates
             the type of reference that was expected. This usually
             indicates a syntax error in dereferencing the constant
             value.  See the Constant Functions entry in the perlsub
             manpage and the constant manpage.
         constant(%s): %s
             (F) The parser found inconsistencies either while
             attempting to define an overloaded constant, or when
             trying to find the character name specified in the
             `\N{...}' escape.  Perhaps you forgot to load the
             corresponding `overload' or `charnames' pragma?  See the
             charnames manpage and the overload manpage.
         CORE::%s is not a keyword
             (F) The CORE:: namespace is reserved for Perl keywords.
         defined(@array) is deprecated
             (D) defined() is not usually useful on arrays because it
             checks for an undefined scalar value.  If you want to
             see if the array is empty, just use `if (@array) { # not
             empty }' for example.
         defined(%hash) is deprecated
             (D) defined() is not usually useful on hashes because it
             checks for an undefined scalar value.  If you want to
             see if the hash is empty, just use `if (%hash) { # not
             empty }' for example.
         Did not produce a valid header
             See Server error.
         (Did you mean "local" instead of "our"?)
             (W misc) Remember that "our" does not localize the
             declared global variable.  You have declared it again in
             the same lexical scope, which seems superfluous.
         Document contains no data
             See Server error.
         entering effective %s failed
             (F) While under the `use filetest' pragma, switching the
             real and effective uids or gids failed.
         false [] range "%s" in regexp
             (W regexp) A character class range must start and end at
             a literal character, not another character class like
             `\d' or `[:alpha:]'.  The "-" in your false range is
             interpreted as a literal "-".  Consider quoting the "-",
             "\-".  See the perlre manpage.
         Filehandle %s opened only for output
             (W io) You tried to read from a filehandle opened only
             for writing.  If you intended it to be a read/write
             filehandle, you needed to open it with "+<" or "+>" or
             "+>>" instead of with "<" or nothing.  If you intended
             only to read from the file, use "<".  See the open entry
             in the perlfunc manpage.
         flock() on closed filehandle %s
             (W closed) The filehandle you're attempting to flock()
             got itself closed some time before now.  Check your
             logic flow.  flock() operates on filehandles.  Are you
             attempting to call flock() on a dirhandle by the same
         Global symbol "%s" requires explicit package name
             (F) You've said "use strict vars", which indicates that
             all variables must either be lexically scoped (using
             "my"), declared beforehand using "our", or explicitly
             qualified to say which package the global variable is in
             (using "::").
         Hexadecimal number > 0xffffffff non-portable
             (W portable) The hexadecimal number you specified is
             larger than 2**32-1 (4294967295) and therefore non-
             portable between systems.  See the perlport manpage for
             more on portability concerns.
         Ill-formed CRTL environ value "%s"
             (W internal) A warning peculiar to VMS.  Perl tried to
             read the CRTL's internal environ array, and encountered
             an element without the `=' delimiter used to spearate
             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
         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
         Invalid %s attribute: %s
             The indicated attribute for a subroutine or variable was
             not recognized by Perl or by a user-supplied handler.
             See the attributes manpage.
         Invalid %s attributes: %s
             The indicated attributes for a subroutine or variable
             were not recognized by Perl or by a user-supplied
             handler.  See the attributes manpage.
         invalid [] range "%s" in regexp
             The offending range is now explicitly displayed.
         Invalid separator character %s in attribute list
             (F) Something other than a colon or whitespace was seen
             between the elements of an attribute list.  If the
             previous attribute had a parenthesised parameter list,
             perhaps that list was terminated too soon.  See the
             attributes manpage.
         Invalid separator character %s in subroutine attribute list
             (F) Something other than a colon or whitespace was seen
             between the elements of a subroutine attribute list.  If
             the previous attribute had a parenthesised parameter
             list, perhaps that list was terminated too soon.
         leaving effective %s failed
             (F) While under the `use filetest' pragma, switching the
             real and effective uids or gids failed.
         Lvalue subs returning %s not implemented yet
             (F) Due to limitations in the current implementation,
             array and hash values cannot be returned in subroutines
             used in lvalue context.  See the Lvalue subroutines
             entry in the perlsub manpage.
         Method %s not permitted
             See Server error.
         Missing %sbrace%s on \N{}
             (F) Wrong syntax of character name literal
             `\N{charname}' within double-quotish context.
         Missing command in piped open
             (W pipe) You used the `open(FH, "| command")' or
             `open(FH, "command |")' construction, but the command
             was missing or blank.
         Missing name in "my sub"
             (F) The reserved syntax for lexically scoped subroutines
             requires that they have a name with which they can be
         No %s specified for -%c
             (F) The indicated command line switch needs a mandatory
             argument, but you haven't specified one.
         No package name allowed for variable %s in "our"
             (F) Fully qualified variable names are not allowed in
             "our" declarations, because that doesn't make much sense
             under existing semantics.  Such syntax is reserved for
             future extensions.
         No space allowed after -%c
             (F) The argument to the indicated command line switch
             must follow immediately after the switch, without
             intervening spaces.
         no UTC offset information; assuming local time is UTC
             (S) A warning peculiar to VMS.  Perl was unable to find
             the local timezone offset, so it's assuming that local
             system time is equivalent to UTC.  If it's not, define
             the logical name SYS$TIMEZONE_DIFFERENTIAL to translate
             to the number of seconds which need to be added to UTC
             to get local time.
         Octal number > 037777777777 non-portable
             (W portable) The octal number you specified is larger
             than 2**32-1 (4294967295) and therefore non-portable
             between systems.  See the perlport manpage for more on
             portability concerns.
             See also the perlport manpage for writing portable code.
         panic: del_backref
             (P) Failed an internal consistency check while trying to
             reset a weak reference.
         panic: kid popen errno read
             (F) forked child returned an incomprehensible message
             about its 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
         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 somehing like this:
                 sub doit
                     use attrs qw(locked);
             You should use the new declaration syntax instead.
                 sub doit : locked
             The `use attrs' pragma is now obsolete, and is only
             provided for backward-compatibility. See the Subroutine
             Attributes entry in the perlsub manpage.
         Premature end of script headers
             See Server error.
         Repeat count in pack overflows
             (F) You can't specify a repeat count so large that it
             overflows your signed integers.  See the pack entry in
             the perlfunc manpage.
         Repeat count in unpack overflows
             (F) You can't specify a repeat count so large that it
             overflows your signed integers.  See the unpack entry in
             the perlfunc manpage.
         realloc() of freed memory ignored
             (S) An internal routine called realloc() on something
             that had already been freed.
         Reference is already weak
             (W misc) You have attempted to weaken a reference that
             is already weak.  Doing so has no effect.
         setpgrp can't take arguments
             (F) Your system has the setpgrp() from BSD 4.2, which
             takes no arguments, unlike POSIX setpgid(), which takes
             a process ID and process group ID.
         Strange *+?{} on zero-length expression
             (W regexp) You applied a regular expression quantifier
             in a place where it makes no sense, such as on a zero-
             width assertion.  Try putting the quantifier inside the
             assertion instead.  For example, the way to match "abc"
             provided that it is followed by three repetitions of
             "xyz" is `/abc(?=(?:xyz){3})/', not `/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 the perlvms manpage) so that the
             environ array isn't the target of the change to %ENV
             which produced the warning.
         Too late to run %s block
             (W void) A CHECK or INIT block is being defined during
             run time proper, when the opportunity to run them has
             already passed.  Perhaps you are loading a file with
             `require' or `do' when you should be using `use'
             instead.  Or perhaps you should put the `require' or
             `do' inside a BEGIN block.
         Unknown open() mode '%s'
             (F) The second argument of 3-argument open() is not
             among the list of valid modes: `<', `>', `>>', `+<',
             `+>', `+>>', `-|', `|-'.
         Unknown process %x sent message to prime_env_iter: %s
             (P) An error peculiar to VMS.  Perl was reading values
             for %ENV before iterating over it, and someone else
             stuck a message in the stream of data Perl expected.
             Someone's very confused, or perhaps trying to subvert
             Perl's population of %ENV for nefarious purposes.
         Unrecognized escape \\%c passed through
             (W misc) You used a backslash-character combination
             which is not recognized by Perl.  The character was
             understood literally.
         Unterminated attribute parameter in attribute list
             (F) The lexer saw an opening (left) parenthesis
             character while parsing an attribute list, but the
             matching closing (right) parenthesis character was not
             found.  You may need to add (or remove) a backslash
             character to get your parentheses to balance.  See the
             attributes manpage.
         Unterminated attribute list
             (F) The lexer found something other than a simple
             identifier at the start of an attribute, and it wasn't a
             semicolon or the start of a block.  Perhaps you
             terminated the parameter list of the previous attribute
             too soon.  See the attributes manpage.
         Unterminated attribute parameter in subroutine attribute list
             (F) The lexer saw an opening (left) parenthesis
             character while parsing a subroutine attribute list, but
             the matching closing (right) parenthesis character was
             not found.  You may need to add (or remove) a backslash
             character to get your parentheses to balance.
         Unterminated subroutine attribute list
             (F) The lexer found something other than a simple
             identifier at the start of a subroutine attribute, and
             it wasn't a semicolon or the start of a block.  Perhaps
             you terminated the parameter list of the previous
             attribute too soon.
         Value of CLI symbol "%s" too long
             (W misc) A warning peculiar to VMS.  Perl tried to read
             the value of an %ENV element from a CLI symbol table,
             and found a resultant string longer than 1024
             characters.  The return value has been truncated to 1024
         Version number must be a constant number
             (P) The attempt to translate a `use Module n.n LIST'
             statement into its equivalent `BEGIN' block found an
             internal inconsistency with the version number.

    New tests

             Compatibility tests for `sub : attrs' vs the older `use
             Tests for new environment scalar capability (e.g., `use
             Env qw($BAR);').
             Tests for new environment array capability (e.g., `use
             Env qw(@PATH);').
             IO constants (SEEK_*, _IO*).
             Directory-related IO methods (new, read, close, rewind,
             tied delete).
             INET sockets with multi-homed hosts.
             IO poll().
             UNIX sockets.
             Regression tests for `my ($x,@y,%z) : attrs' and <sub :
             File test operators.
             Verify operations that access pad objects (lexicals and
             Verify `exists &sub' operations.

    Incompatible Changes

         Perl Source Incompatibilities
         Beware that any new warnings that have been added or old
         ones that have been enhanced are not considered incompatible
         Since all new warnings must be explicitly requested via the
         `-w' switch or the `warnings' pragma, it is ultimately the
         programmer's responsibility to ensure that warnings are
         enabled judiciously.
         CHECK is a new keyword
             All subroutine definitions named CHECK are now special.
             See `/"Support for CHECK blocks"' for more information.
         Treatment of list slices of undef has changed
             There is a potential incompatibility in the behavior of
             list slices that are comprised entirely of undefined
             values.  See the Behavior of list slices is more
             consistent entry elsewhere in this document.
         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 the Improved Perl version numbering system entry
         elsewhere in this document 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
             For example, `print 97.98.99' used to output `97.9899'
             in earlier versions, but now prints `abc'.
             See the Support for strings represented as a vector of
             ordinals entry elsewhere in this document.
         Possibly changed pseudo-random number generator
             Perl programs that depend on reproducing a specific set
             of pseudo-random numbers may now produce different
             output due to improvements made to the rand() builtin.
             You can use `sh Configure -Drandfunc=rand' to obtain the
             old behavior.
             See the Better pseudo-random number generator entry
             elsewhere in this document.
         Hashing function for hash keys has changed
             Even though Perl hashes are not order preserving, the
             apparently random order encountered when iterating on
             the contents of a hash is actually determined by the
             hashing algorithm used.  Improvements in the algorithm
             may yield a random order that is different from that of
             previous versions, especially when iterating on hashes.
             See the Better worst-case behavior of hashes entry
             elsewhere in this document 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 the More consistent close-on-exec behavior entry
             elsewhere in this document.
         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(), values() and `\(%h)' operate on aliases to values, not
             delete(), each(), values() and hashes in a list context
             return the actual values in the hash, instead of copies
             (as they used to in earlier versions).  Typical idioms
             for using these constructs copy the returned values, but
             this can make a significant difference when creating
             references to the returned values.  Keys in the hash are
             still returned as copies when iterating on a hash.
             See also the delete(), each(), values() and hash
             iteration are faster entry elsewhere in this document.
         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
         `%@' 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
                 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 the More functional bareword prototype (*) entry
             elsewhere in this document.
         Semantics of bit operators may have changed on 64-bit
         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 the Bit operators support full native integer width
         entry elsewhere in this document.
         More builtins taint their results
         As described in the Improved security features entry
         elsewhere in this document, there may be more sources of
         taint in a Perl program.
         To avoid these new tainting behaviors, you can build Perl
         with the Configure option `-Accflags=-DINCOMPLETE_TAINTS'.
         Beware that the ensuing perl binary may be insecure.
         C Source Incompatibilities
             Release 5.005 grandfathered old global symbol names by
             providing preprocessor macros for extension source
             compatibility.  As of release 5.6.0, these preprocessor
             definitions are not available by default.  You need to
             explicitly compile perl with `-DPERL_POLLUTE' to get
             these definitions.  For extensions still using the old
             symbols, this option can be specified via MakeMaker:
                 perl Makefile.PL POLLUTE=1
             This new build option provides a set of macros for all
             API functions such that an implicit interpreter/thread
             context argument is passed to every API function.  As a
             result of this, something like `sv_setsv(foo,bar)'
             amounts to a macro invocation that actually translates
             to something like `Perl_sv_setsv(my_perl,foo,bar)'.
             While this is generally expected to not have any
             significant source compatibility issues, the difference
             between a macro and a real function call will need to be
             This means that there is a source compatibility issue as
             a result of this if your extensions attempt to use
             pointers to any of the Perl API functions.
             Note that the above issue is not relevant to the default
             build of Perl, whose interfaces continue to match those
             of prior versions (but subject to the other options
             described here).
             See the The Perl API entry in the perlguts manpage for
             detailed information on the ramifications of building
             Perl with this option.
                 NOTE: PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
                 with one of -Dusethreads, -Dusemultiplicity, or both.  It is not
                 intended to be enabled by users at this time.
             Enabling Perl's malloc in release 5.005 and earlier
             caused the namespace of the system's malloc family of
             functions to be usurped by the Perl versions, since by
             default they used the same names.  Besides causing
             problems on platforms that do not allow these functions
             to be cleanly replaced, this also meant that the system
             versions could not be called in programs that used
             Perl's malloc.  Previous versions of Perl have allowed
             this behaviour to be suppressed with the HIDEMYMALLOC
             and EMBEDMYMALLOC preprocessor 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 the Memory Allocation entry
             in the perlguts manpage for further information about
         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
             The new names cause less pollution of the cpp namespace
             and reflect what the numbers have come to stand for in
             common practice.  For compatibility, the old names are
             still supported when patchlevel.h is explicitly included
             (as required before), so there is no source
             incompatibility from the change.
         Binary Incompatibilities
         In general, the default build of this release is expected to
         be binary compatible for extensions built with the 5.005
         release or its maintenance versions.  However, specific
         platforms may have broken binary compatibility due to
         changes in the defaults used in hints files.  Therefore,
         please be sure to always check the platform-specific README
         files for any notes to the contrary.
         The usethreads or usemultiplicity builds are not binary
         compatible with the corresponding builds in 5.005.
         On platforms that require an explicit list of exports (AIX,
         OS/2 and Windows, among others), purely internal symbols
         such as parser functions and the run time opcodes are not
         exported by default.  Perl 5.005 used to export all
         functions irrespective of whether they were considered part
         of the public API or not.
         For the full list of public API functions, see the perlapi

    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
         These expressions will get run-time errors in some future
         release of Perl.
         Windows 2000
         Windows 2000 is known to fail test 22 in lib/open3.t (cause
         unknown at this time).  That test passes under Windows NT.
         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
         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 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.
         Probable precedence problem on %s
             (W) The compiler found a bareword where it expected a
             conditional, which often indicates that an || or && was
             parsed as part of the last argument of the previous
             construct, for example:
                 open FOO || die;
         regexp too big
             (F) The current implementation of regular expressions
             uses shorts as address offsets within a string.
             Unfortunately this means that if the regular expression
             compiles to longer than 32767, it'll blow up.  Usually
             when you want a regular expression this big, there is a
             better way to do it with multiple statements.  See the
             perlre manpage.
         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

    Reporting Bugs

         If you find what you think is a bug, you might check the
         articles recently posted to the comp.lang.perl.misc
         newsgroup.  There may also be information at, the Perl Home Page.
         If you believe you have an unreported bug, please run the
         perlbug program included with your release.  Be sure to trim
         your bug down to a tiny but sufficient test case.  Your bug
         report, along with the output of `perl -V', will be sent off
         to to be analysed by the Perl porting team.


         The Changes file for exhaustive details on what changed.
         The INSTALL file for how to build Perl.
         The README file for general stuff.
         The Artistic and Copying files for copyright information.


         Written by Gurusamy Sarathy <>, with
         many contributions from The Perl Porters.
         Send omissions or corrections to <>.

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