MirOS Manual: perl56delta(1)


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

NAME

     perl56delta - what's new for perl v5.6.0

DESCRIPTION

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

Core Enhancements

     Interpreter cloning, threads, and concurrency

     Perl 5.6.0 introduces the beginnings of support for running
     multiple interpreters concurrently in different threads.  In
     conjunction with the perl_clone() API call, which can be
     used to selectively duplicate the state of any given inter-
     preter, it is possible to compile a piece of code once in an
     interpreter, clone that interpreter one or more times, and
     run all the resulting interpreters in distinct threads.

     On the Windows platform, this feature is used to emulate
     fork() at the interpreter level.  See perlfork for details
     about that.

     This feature is still in evolution.  It is eventually meant
     to be used to selectively clone a subroutine and data reach-
     able 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 lock-
     ing 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.

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         NOTE: This is an experimental feature.  Implementation details are
         subject to change.

     Lexically scoped warning categories

     You can now control the granularity of warnings emitted by
     perl at a finer level using the "use warnings" pragma.
     warnings and perllexwarn have copious documentation on this
     feature.

     Unicode and UTF-8 support

     Perl now uses UTF-8 as its internal representation for char-
     acter strings.  The "utf8" and "bytes" pragmas are used to
     control this support in the current lexical scope.  See per-
     lunicode, utf8 and bytes for more information.

     This feature is expected to evolve quickly to support some
     form of I/O disciplines that can be used to specify the kind
     of input and output data (bytes or characters).  Until that
     happens, additional modules from CPAN will be needed to com-
     plete the toolkit for dealing with Unicode.

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

     Support for interpolating named characters

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

     "our" declarations

     An "our" declaration introduces a value that can be best
     understood as a lexically scoped symbolic alias to a global
     variable in the package that was current where the variable
     was declared.  This is mostly useful as an alternative to
     the "vars" pragma, but also provides the opportunity to
     introduce typing and other attributes for such variables.
     See "our" in perlfunc.

     Support for strings represented as a vector of ordinals

     Literals of the form "v1.2.3.4" are now parsed as a string
     composed of characters with the specified ordinals.  This is
     an alternative, more readable way to construct (possibly
     unicode) strings instead of interpolating characters, as in
     "\x{1}\x{2}\x{3}\x{4}".  The leading "v" may be omitted if
     there are more than two ordinals, so 1.2.3 is parsed the
     same as "v1.2.3".

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     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 con-
     tains the perl version as a string), such literals can be
     used as a readable way to check if you're running a particu-
     lar version of Perl:

         # this will parse in older versions of Perl also
         if ($^V and $^V gt v5.6.0) {
             # new features supported
         }

     "require" and "use" also have some special magic to support
     such literals, but this particular usage should be avoided
     because it leads to misleading error messages under versions
     of Perl which don't support vector strings.  Using a true
     version number will ensure correct behavior in all versions
     of Perl:

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

     Also, "sprintf" and "printf" support the Perl-specific for-
     mat flag %v to print ordinals of characters in arbitrary
     strings:

         printf "v%vd", $^V;         # prints current version, such as "v5.5.650"
         printf "%*vX", ":", $addr;  # formats IPv6 address
         printf "%*vb", " ", $bits;  # displays bitstring

     See "Scalar value constructors" in perldata for additional
     information.

     Improved Perl version numbering system

     Beginning with Perl version 5.6.0, the version number con-
     vention 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 poten-
     tial incompatibility. Send us a report via perlbug if you

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     are affected by this.)

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

     To cope with the new versioning system's use of at least
     three significant digits for each version component, the
     method used for incrementing the subversion number has also
     changed slightly.  We assume that versions older than v5.6.0
     have been incrementing the subversion component in multiples
     of 10.  Versions after v5.6.0 will increment them by 1.
     Thus, using the new notation, 5.005_03 is the "same" as
     v5.5.30, and the first maintenance version following v5.6.0
     will be v5.6.1 (which should be read as being equivalent to
     a floating point value of 5.006_001 in the older format,
     stored in $]).

     New syntax for declaring subroutine attributes

     Formerly, if you wanted to mark a subroutine as being a
     method call or as requiring an automatic lock() when it is
     entered, you had to declare that with a "use attrs" pragma
     in the body of the subroutine. That can now be accomplished
     with declaration syntax, like this:

         sub mymethod : locked method;
         ...
         sub mymethod : locked method {
             ...
         }

         sub othermethod :locked :method;
         ...
         sub othermethod :locked :method {
             ...
         }

     (Note how only the first ":" is mandatory, and whitespace
     surrounding the ":" is optional.)

     AutoSplit.pm and SelfLoader.pm have been updated to keep the
     attributes with the stubs they provide.  See attributes.

     File and directory handles can be autovivified

     Similar to how constructs such as "$x->[0]" autovivify a
     reference, handle constructors (open(), opendir(), pipe(),
     socketpair(), sysopen(), socket(), and accept()) now auto-
     vivify 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

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     $fh,...)" to be used to create filehandles that will con-
     veniently be closed automatically when the scope ends, pro-
     vided there are no other references to them.  This largely
     eliminates the need for typeglobs when opening filehandles
     that must be passed around, as in the following example:

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

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

     open() with more than two arguments

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

     64-bit support

     Any platform that has 64-bit integers either

             (1) natively as longs or ints
             (2) via special compiler flags
             (3) using long long or int64_t

     is able to use "quads" (64-bit integers) as follows:

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

     +   arguments to oct() and hex()

     +   arguments to print(), printf() and sprintf() (flag pre-
         fixes ll, L, q)

     +   printed as such

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

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

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

     +   vec()

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

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

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

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

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

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

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

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

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     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 con-
     stant 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 filesys-
     tems that stop you (your user id or your user group id) from
     using large files.

     Adjusting your process/user/group/file system/operating sys-
     tem 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 Con-
     figure -Duselongdouble to enable this support (if it is
     available).

     "more bits"

     You can "Configure -Dusemorebits" to turn on both the 64-bit
     support and the long double support.

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     Enhanced support for sort() subroutines

     Perl subroutines with a prototype of "($$)", and XSUBs in
     general, can now be used as sort subroutines.  In either
     case, the two elements to be compared are passed as normal
     parameters in @_.  See "sort" in perlfunc.

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

     "sort $coderef @foo" allowed

     sort() did not accept a subroutine reference as the com-
     parison function in earlier versions.  This is now permit-
     ted.

     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 "AUTO-
     LOAD", subroutines named "CHECK" are now special.  These are
     queued up during compilation and behave similar to END
     blocks, except they are called at the end of compilation
     rather than at the end of execution.  They cannot be called
     directly.

     POSIX character class syntax [: :] supported

     For example to match alphabetic characters use
     /[[:alpha:]]/. See perlre for details.

     Better pseudo-random number generator

     In 5.005_0x and earlier, perl's rand() function used the C
     library rand(3) function.  As of 5.005_52, Configure tests
     for drand48(), random(), and rand() (in that order) and
     picks the first one it finds.

     These changes should result in better random numbers from
     rand().

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     Improved "qw//" operator

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

     Thus:

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

     now correctly prints "3|a", instead of "2|a".

     Better worst-case behavior of hashes

     Small changes in the hashing algorithm have been implemented
     in order to improve the distribution of lower order bits in
     the hashed value.  This is expected to yield better perfor-
     mance on keys that are repeated sequences.

     pack() format 'Z' supported

     The new format type 'Z' is useful for packing and unpacking
     null-terminated strings.  See "pack" in perlfunc.

     pack() format modifier '!' supported

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

     pack() and unpack() support counted strings

     The template character '/' can be used to specify a counted
     string type to be packed or unpacked.  See "pack" in perl-
     func.

     Comments in pack() templates

     The '#' character in a template introduces a comment up to
     end of the line.  This facilitates documentation of pack()
     templates.

     Weak references

     In previous versions of Perl, you couldn't cache objects so
     as to allow them to be deleted if the last reference from
     outside the cache is deleted.  The reference in the cache
     would hold a reference count on the object and the objects
     would never be destroyed.

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     Another familiar problem is with circular references.  When
     an object references itself, its reference count would never
     go down to zero, and it would not get destroyed until the
     program is about to exit.

     Weak references solve this by allowing you to "weaken" any
     reference, that is, make it not count towards the reference
     count. When the last non-weak reference to an object is
     deleted, the object is destroyed and all the weak references
     to the object are automatically undef-ed.

     To use this feature, you need the Devel::WeakRef package
     from CPAN, which contains additional documentation.

         NOTE: This is an experimental feature.  Details are subject to change.

     Binary numbers supported

     Binary numbers are now supported as literals, in s?printf
     formats, and "oct()":

         $answer = 0b101010;
         printf "The answer is: %b\n", oct("0b101010");

     Lvalue subroutines

     Subroutines can now return modifiable lvalues. See "Lvalue
     subroutines" in perlsub.

         NOTE: This is an experimental feature.  Details are subject to change.

     Some arrows may be omitted in calls through references

     Perl now allows the arrow to be omitted in many constructs
     involving subroutine calls through references.  For example,
     "$foo[10]->('foo')" may now be written "$foo[10]('foo')".
     This is rather similar to how the arrow may be omitted from
     "$foo[10]->{'foo'}".  Note however, that the arrow is still
     required for "foo(10)->('bar')".

     Boolean assignment operators are legal lvalues

     Constructs such as "($a ||= 2) += 1" are now allowed.

     exists() is supported on subroutine names

     The exists() builtin now works on subroutine names.  A sub-
     routine is considered to exist if it has been declared (even
     if implicitly). See "exists" in perlfunc for examples.

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     exists() and delete() are supported on array elements

     The exists() and delete() builtins now work on simple arrays
     as well. The behavior is similar to that on hash elements.

     exists() can be used to check whether an array element has
     been initialized.  This avoids autovivifying array elements
     that don't exist. If the array is tied, the EXISTS() method
     in the corresponding tied package will be invoked.

     delete() may be used to remove an element from the array and
     return it.  The array element at that position returns to
     its uninitialized state, so that testing for the same ele-
     ment with exists() will return false.  If the element hap-
     pens to be the one at the end, the size of the array also
     shrinks up to the highest element that tests true for
     exists(), or 0 if none such is found.  If the array is tied,
     the DELETE() method in the corresponding tied package will
     be invoked.

     See "exists" in perlfunc and "delete" in perlfunc for exam-
     ples.

     Pseudo-hashes work better

     Dereferencing some types of reference values in a
     pseudo-hash, such as "$ph->{foo}[1]", was accidentally
     disallowed.  This has been corrected.

     When applied to a pseudo-hash element, exists() now reports
     whether the specified value exists, not merely if the key is
     valid.

     delete() now works on pseudo-hashes.  When given a pseudo-
     hash element or slice it deletes the values corresponding to
     the keys (but not the keys themselves).  See "Pseudo-hashes:
     Using an array as a hash" in perlref.

     Pseudo-hash slices with constant keys are now optimized to
     array lookups at compile-time.

     List assignments to pseudo-hash slices are now supported.

     The "fields" pragma now provides ways to create
     pseudo-hashes, via fields::new() and fields::phash().  See
     fields.

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

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     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 avail-
     able.

     Better diagnostics on meaningless filehandle operations

     Constructs such as "open(<FH>)" and "close(<FH>)" are com-
     pile time errors.  Attempting to read from filehandles that
     were opened only for writing will now produce warnings (just
     as writing to read-only filehandles does).

     Where possible, buffered data discarded from duped input
     filehandle

     "open(NEW, "<&OLD")" now attempts to discard any data that
     was previously read and buffered in "OLD" before duping the
     handle. On platforms where doing this is allowed, the next
     read operation on "NEW" will return the same data as the
     corresponding operation on "OLD".  Formerly, it would have
     returned the data from the start of the following disk block
     instead.

     eof() has the same old magic as <>

     "eof()" would return true if no attempt to read from "<>"
     had yet been made.  "eof()" has been changed to have a lit-
     tle magic of its own, it now opens the "<>" files.

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

     binmode() now accepts a second argument that specifies a
     discipline for the handle in question.  The two pseudo-
     disciplines ":raw" and ":crlf" are currently supported on
     DOS-derivative platforms. See "binmode" in perlfunc and
     open.

     "-T" filetest recognizes UTF-8 encoded files as "text"

     The algorithm used for the "-T" filetest has been enhanced
     to correctly identify UTF-8 content as "text".

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     system(), backticks and pipe open now reflect exec() failure

     On Unix and similar platforms, system(), qx() and open(FOO,
     "cmd |") etc., are implemented via fork() and exec().  When
     the underlying exec() fails, earlier versions did not report
     the error properly, since the exec() happened to be in a
     different process.

     The child process now communicates with the parent about the
     error in launching the external command, which allows these
     constructs to return with their usual error value and set
     $!.

     Improved diagnostics

     Line numbers are no longer suppressed (under most likely
     circumstances) during the global destruction phase.

     Diagnostics emitted from code running in threads other than
     the main thread are now accompanied by the thread ID.

     Embedded null characters in diagnostics now actually show
     up.  They used to truncate the message in prior versions.

     $foo::a and $foo::b are now exempt from "possible typo"
     warnings only if sort() is encountered in package "foo".

     Unrecognized alphabetic escapes encountered when parsing
     quote constructs now generate a warning, since they may take
     on new semantics in later versions of Perl.

     Many diagnostics now report the internal operation in which
     the warning was provoked, like so:

         Use of uninitialized value in concatenation (.) at (eval 1) line 1.
         Use of uninitialized value in print at (eval 1) line 1.

     Diagnostics  that occur within eval may also report the file
     and line number where the eval is located, in addition to
     the eval sequence number and the line number within the
     evaluated text itself.  For example:

         Not enough arguments for scalar at (eval 4)[newlib/perl5db.pl:1411] line 2, at EOF

     Diagnostics follow STDERR

     Diagnostic output now goes to whichever file the "STDERR"
     handle is pointing at, instead of always going to the under-
     lying C runtime library's "stderr".

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     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(), sock-
     etpair(), socket(), and accept(), if that is warranted by
     the value of $^F that may be in effect.  Earlier versions
     neglected to set the flag for handles created with these
     operators.  See "pipe" in perlfunc, "socketpair" in perl-
     func, "socket" in perlfunc, "accept" in perlfunc, and "$^F"
     in perlvar.

     syswrite() ease-of-use

     The length argument of "syswrite()" has become optional.

     Better syntax checks on parenthesized unary operators

     Expressions such as:

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

     used to be accidentally allowed in earlier versions, and
     produced unpredictable behaviour.  Some produced ancillary
     warnings when used in this way; others silently did the
     wrong thing.

     The parenthesized forms of most unary operators that expect
     a single argument now ensure that they are not called with
     more than one argument, making the cases shown above syntax
     errors.  The usual behaviour of:

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

     remains unchanged.  See perlop.

     Bit operators support full native integer width

     The bit operators (& | ^ ~ << >>) now operate on the full
     native integral width (the exact size of which is available
     in $Config{ivsize}). For example, if your platform is either
     natively 64-bit or if Perl has been configured to use 64-bit
     integers, these operations apply to 8 bytes (as opposed to 4
     bytes on 32-bit platforms). For portability, be sure to mask
     off the excess bits in the result of unary "~", e.g., "~$x &
     0xffffffff".

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     Improved security features

     More potentially unsafe operations taint their results for
     improved security.

     The "passwd" and "shell" fields returned by the getpwent(),
     getpwnam(), and getpwuid() are now tainted, because the user
     can affect their own encrypted password and login shell.

     The variable modified by shmread(), and messages returned by
     msgrcv() (and its object-oriented interface
     IPC::SysV::Msg::rcv) are also tainted, because other
     untrusted processes can modify messages and shared memory
     segments for their own nefarious purposes.

     More functional bareword prototype (*)

     Bareword prototypes have been rationalized to enable them to
     be used to override builtins that accept barewords and
     interpret them in a special way, such as "require" or "do".

     Arguments prototyped as "*" will now be visible within the
     subroutine as either a simple scalar or as a reference to a
     typeglob. See "Prototypes" in perlsub.

     "require" and "do" may be overridden

     "require" and "do 'file'" operations may be overridden
     locally by importing subroutines of the same name into the
     current package (or globally by importing them into the
     CORE::GLOBAL:: namespace). Overriding "require" will also
     affect "use", provided the override is visible at
     compile-time. See "Overriding Built-in Functions" in perl-
     sub.

     $^X variables may now have names longer than one character

     Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a
     syntax error.  Now variable names that begin with a control
     character may be arbitrarily long.  However, for compatibil-
     ity reasons, these variables must be written with explicit
     braces, as "${^XY}" for example. "${^XYZ}" is synonymous
     with ${"\cXYZ"}.  Variable names with more than one control
     character, such as "${^XY^Z}", are illegal.

     The old syntax has not changed.  As before, `^X' may be
     either a literal control-X character or the two-character
     sequence `caret' plus `X'.  When braces are omitted, the
     variable name stops after the control character.  Thus
     "$^XYZ" continues to be synonymous with "$^X . "YZ"" as
     before.

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     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 spe-
     cial 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 vari-
     able enables perl code to determine whether actions that
     make sense only during normal running are warranted.  See
     perlvar.

     New variable $^V contains Perl version as a string

     $^V contains the Perl version number as a string composed of
     characters whose ordinals match the version numbers, i.e.
     v5.6.0. This may be used in string comparisons.

     See "Support for strings represented as a vector of ordi-
     nals" 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 Con-
     figure. See INSTALL and README.Y2K.

     Arrays now always interpolate into double-quoted strings

     In double-quoted strings, arrays now interpolate, no matter
     what.  The behavior in earlier versions of perl 5 was that
     arrays would interpolate into strings if the array had been
     mentioned before the string was compiled, and otherwise Perl
     would raise a fatal compile-time error. In versions 5.000
     through 5.003, the error was

             Literal @example now requires backslash

     In versions 5.004_01 through 5.6.0, the error was

             In string, @example now must be written as \@example

     The idea here was to get people into the habit of writing
     "fred\@example.com" when they wanted a literal "@" sign,

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     just as they have always written "Give me back my \$5" when
     they wanted a literal "$" sign.

     Starting with 5.6.1, when Perl now sees an "@" sign in a
     double-quoted string, it always attempts to interpolate an
     array, regardless of whether or not the array has been used
     or declared already.  The fatal error has been downgraded to
     an optional warning:

             Possible unintended interpolation of @example in string

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

     @- and @+ provide starting/ending offsets of regex matches

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

Modules and Pragmata

     Modules

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

     B   The Perl Compiler suite has been extensively reworked
         for this release.  More of the standard Perl testsuite
         passes when run under the Compiler, but there is still a
         significant way to go to achieve production quality com-
         piled executables.

             NOTE: The Compiler suite remains highly experimental.  The
             generated code may not be correct, even when it manages to execute
             without errors.

     Benchmark
         Overall, Benchmark results exhibit lower average error
         and better timing accuracy.

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

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

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         will now output something like this:

            Benchmark: running a, b, each for at least 5 CPU seconds...
                     a:  5 wallclock secs ( 5.77 usr +  0.00 sys =  5.77 CPU) @ 200551.91/s (n=1156516)
                     b:  4 wallclock secs ( 5.00 usr +  0.02 sys =  5.02 CPU) @ 159605.18/s (n=800686)

         New features: "each for at least N CPU seconds...",
         "wallclock secs", and the "@ operations/CPU second
         (n=operations)".

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

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

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

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

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

         For other details, see Benchmark.

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

     constant
         References can now be used.

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

         See constant.

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

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         charnames.

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

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

         Dumping "qr//" objects works correctly.

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

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

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

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

     Dumpvalue
         The Dumpvalue module provides screen dumps of Perl data.

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

         Perl can also optionally arrange to unload all extension
         shared objects loaded by Perl.  To enable this, build
         Perl with the Configure option
         "-Accflags=-DDL_UNLOAD_ALL_AT_EXIT".  (This maybe useful
         if you are using Apache with mod_perl.)

     English
         $PERL_VERSION now stands for $^V (a string value) rather
         than for $] (a numeric value).

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

     Fcntl
         More Fcntl constants added: F_SETLK64, F_SETLKW64,
         O_LARGEFILE for large file (more than 4GB) access (NOTE:
         the O_LARGEFILE is automatically added to sysopen()

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         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 com-
         bined mask of O_RDONLY, O_WRONLY, and O_RDWR.  The
         seek()/sysseek() constants SEEK_SET, SEEK_CUR, and
         SEEK_END are available via the ":seek" tag.  The
         chmod()/stat() S_IF* constants and S_IS* functions are
         available via the ":mode" tag.

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

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

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

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

         See File::Find.

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

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

     File::Spec::Functions
         The new File::Spec::Functions modules provides a func-
         tion interface to the File::Spec module.  Allows short-
         hand

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

         instead of

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

     Getopt::Long
         Getopt::Long licensing has changed to allow the Perl
         Artistic License as well as the GPL. It used to be GPL
         only, which got in the way of non-GPL applications that
         wanted to use Getopt::Long.

         Getopt::Long encourages the use of Pod::Usage to produce
         help messages. For example:

             use Getopt::Long;
             use Pod::Usage;
             my $man = 0;
             my $help = 0;
             GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
             pod2usage(1) if $help;
             pod2usage(-exitstatus => 0, -verbose => 2) if $man;

             __END__

             =head1 NAME

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

             =head1 SYNOPSIS

             sample [options] [file ...]

              Options:
                -help            brief help message
                -man             full documentation

             =head1 OPTIONS

             =over 8

             =item B<-help>

             Print a brief help message and exits.

             =item B<-man>

             Prints the manual page and exits.

             =back

             =head1 DESCRIPTION

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

             =cut

         See Pod::Usage for details.

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

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

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

         You can now create a TCP-based IO::Socket::INET without
         forcing a connect attempt.  This allows you to configure
         its options (like making it non-blocking) and then call
         connect() manually.

         A bug that prevented the IO::Socket::protocol() accessor
         from ever returning the correct value has been
         corrected.

         IO::Socket::connect now uses non-blocking IO instead of
         alarm() to do connect timeouts.

         IO::Socket::accept now uses select() instead of alarm()
         for doing timeouts.

         IO::Socket::INET->new now sets $! correctly on failure.
         $@ is still set for backwards compatibility.

     JPL Java Perl Lingo is now distributed with Perl.  See
         jpl/README for more information.

     lib "use lib" now weeds out any trailing duplicate entries.
         "no lib" removes all named entries.

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

     Math::Complex
         The accessor methods Re, Im, arg, abs, rho, and theta
         can now also act as mutators (accessor $z->Re(), mutator
         $z->Re(3)).

         The class method "display_format" and the corresponding

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         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 argu-
         ment (angle) of a polar complex number.

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

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

     Pod::Parser, Pod::InputObjects
         Pod::Parser is a base class for parsing and selecting
         sections of pod documentation from an input stream.
         This module takes care of identifying pod paragraphs and
         commands in the input and hands off the parsed para-
         graphs and commands to user-defined methods which are
         free to interpret or translate them as they see fit.

         Pod::InputObjects defines some input objects needed by
         Pod::Parser, and for advanced users of Pod::Parser that
         need more about a command besides its name and text.

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

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

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

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     Pod::ParseUtils, Pod::Find
         These modules provide a set of gizmos that are useful
         mainly for pod translators.  Pod::Find traverses direc-
         tory structures and returns found pod files, along with
         their canonical names (like "File::Spec::Unix").
         Pod::ParseUtils contains Pod::List (useful for storing
         pod list information), Pod::Hyperlink (for parsing the
         contents of "L<>" sequences) and Pod::Cache (for caching
         information about pod files, e.g., link nodes).

     Pod::Select, podselect
         Pod::Select is a subclass of Pod::Parser which provides
         a function named "podselect()" to filter out user-
         specified sections of raw pod documentation from an
         input stream. podselect is a script that provides access
         to Pod::Select from other scripts to be used as a
         filter. See Pod::Select.

     Pod::Usage, pod2usage
         Pod::Usage provides the function "pod2usage()" to print
         usage messages for a Perl script based on its embedded
         pod documentation.  The pod2usage() function is gen-
         erally useful to all script authors since it lets them
         write and maintain a single source (the pods) for docu-
         mentation, 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 com-
         ments).

         For details and examples, please see Pod::Usage.

     Pod::Text and Pod::Man
         Pod::Text has been rewritten to use Pod::Parser.  While
         pod2text() is still available for backwards compatibil-
         ity, the module now has a new preferred interface.  See
         Pod::Text for the details.  The new Pod::Text module is
         easily subclassed for tweaks to the output, and two such
         subclasses (Pod::Text::Termcap for man-page-style bold
         and underlining using termcap information, and
         Pod::Text::Color for markup with ANSI color sequences)
         are now standard.

         pod2man has been turned into a module, Pod::Man, which
         also uses Pod::Parser.  In the process, several out-
         standing bugs related to quotes in section headers,
         quoting of code escapes, and nested lists have been
         fixed.  pod2man is now a wrapper script around this
         module.

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     SDBM_File
         An EXISTS method has been added to this module (and
         sdbm_exists() has been added to the underlying sdbm
         library), so one can now call exists on an SDBM_File
         tied hash and get the correct result, rather than a run-
         time error.

         A bug that may have caused data loss when more than one
         disk block happens to be read from the database in a
         single FETCH() has been fixed.

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

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

     Term::ANSIColor
         Term::ANSIColor is a very simple module to provide easy
         and readable access to the ANSI color and highlighting
         escape sequences, supported by most ANSI terminal emula-
         tors.  It is now included standard.

     Time::Local
         The timelocal() and timegm() functions used to silently
         return bogus results when the date fell outside the
         machine's integer range.  They now consistently croak()
         if the date falls in an unsupported range.

     Win32
         The error return value in list context has been changed
         for all functions that return a list of values.  Previ-
         ously these functions returned a list with a single ele-
         ment "undef" if an error occurred.  Now these functions
         return the empty list in these situations.  This applies
         to the following functions:

             Win32::FsType
             Win32::GetOSVersion

         The remaining functions are unchanged and continue to
         return "undef" on error even in list context.

         The Win32::SetLastError(ERROR) function has been added
         as a complement to the Win32::GetLastError() function.

         The new Win32::GetFullPathName(FILENAME) returns the
         full absolute pathname for FILENAME in scalar context.
         In list context it returns a two-element list containing
         the fully qualified directory name and the filename.

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         See Win32.

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

     DBM Filters
         A new feature called "DBM Filters" has been added to all
         the DBM modules--DB_File, GDBM_File, NDBM_File,
         ODBM_File, and SDBM_File. DBM Filters add four new
         methods to each DBM module:

             filter_store_key
             filter_store_value
             filter_fetch_key
             filter_fetch_value

         These can be used to filter key-value pairs before the
         pairs are written to the database or just after they are
         read from the database. See perldbmfilter for further
         information.

     Pragmata

     "use attrs" is now obsolete, and is only provided for
     backward-compatibility.  It's been replaced by the "sub :
     attributes" syntax.  See "Subroutine Attributes" in perlsub
     and attributes.

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

     "use filetest" to control the behaviour of filetests ("-r"
     "-w" ...).  Currently only one subpragma implemented, "use
     filetest 'access';", that uses access(2) or equivalent to
     check permissions instead of using stat(2) as usual.  This
     matters in filesystems where there are ACLs (access control
     lists): the stat(2) might lie, but access(2) knows better.

     The "open" pragma can be used to specify default disciplines
     for handle constructors (e.g. open()) and for qx//.  The two
     pseudo-disciplines ":raw" and ":crlf" are currently sup-
     ported on DOS-derivative platforms (i.e. where binmode is
     not a no-op). See also "binmode() can be used to set :crlf
     and :raw modes".

Utility Changes

     dprofpp

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

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     find2perl

     The "find2perl" utility now uses the enhanced features of
     the File::Find module.  The -depth and -follow options are
     supported.  Pod documentation is also included in the
     script.

     h2xs

     The "h2xs" tool can now work in conjunction with "C::Scan"
     (available from CPAN) to automatically parse real-life
     header files.  The "-M", "-a", "-k", and "-o" options are
     new.

     perlcc

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

     Support for non-Unix platforms has been improved.

     perldoc

     "perldoc" has been reworked to avoid possible security
     holes. It will not by default let itself be run as the
     superuser, but you may still use the -U switch to try to
     make it drop privileges first.

     The Perl Debugger

     Many bug fixes and enhancements were added to perl5db.pl,
     the Perl debugger.  The help documentation was rearranged.
     New commands include "< ?", "> ?", and "{ ?" to list out
     current actions, "man docpage" to run your doc viewer on
     some perl docset, and support for quoted options.  The help
     information was rearranged, and should be viewable once
     again if you're using less as your pager.  A serious secu-
     rity hole was plugged--you should immediately remove all
     older versions of the Perl debugger as installed in previous
     releases, all the way back to perl3, from your system to
     avoid being bitten by this.

Improved Documentation

     Many of the platform-specific README files are now part of
     the perl installation.  See perl for the complete list.

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

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

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

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

     perldebug.pod
         All material unrelated to running the Perl debugger,
         plus all low-level guts-like details that risked crush-
         ing the casual user of the debugger, have been relocated
         from the old manpage to the next entry below.

     perldebguts.pod
         This new manpage contains excessively low-level material
         not related to the Perl debugger, but slightly related
         to debugging Perl itself. It also contains some arcane
         internal details of how the debugging process works that
         may only be of interest to developers of Perl debuggers.

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

     perlfilter.pod
         An introduction to writing Perl source filters.

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

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

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

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

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

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

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

     perltodo.pod
         Discussion of the most often wanted features that may

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         someday be supported in Perl.

     perlunicode.pod
         An introduction to Unicode support features in Perl.

Performance enhancements

     Simple sort() using { $a <=> $b } and the like are optimized

     Many common sort() operations using a simple inlined block
     are now optimized for faster performance.

     Optimized assignments to lexical variables

     Certain operations in the RHS of assignment statements have
     been optimized to directly set the lexical variable on the
     LHS, eliminating redundant copying overheads.

     Faster subroutine calls

     Minor changes in how subroutine calls are handled internally
     provide marginal improvements in performance.

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

     The hash values returned by delete(), each(), values() and
     hashes in a list context are the actual values in the hash,
     instead of copies. This results in significantly better per-
     formance, because it eliminates needless copying in most
     situations.

Installation and Configuration Improvements

     -Dusethreads means something different

     The -Dusethreads flag now enables the experimental
     interpreter-based thread support by default.  To get the
     flavor of experimental threads that was in 5.005 instead,
     you need to run Configure with "-Dusethreads
     -Duse5005threads".

     As of v5.6.0, interpreter-threads support is still lacking a
     way to create new threads from Perl (i.e., "use Thread;"
     will not work with interpreter threads).  "use Thread;" con-
     tinues 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 com-
     mand line by running Configure with "-Dflag".

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

         use64bitint                 (equal to now deprecated 'use64bits')
         use64bitall

         uselongdouble
         usemorebits
         uselargefiles
         usesocks                    (only SOCKS v5 supported)

     Threadedness and 64-bitness now more daring

     The Configure options enabling the use of threads and the
     use of 64-bitness are now more daring in the sense that they
     no more have an explicit list of operating systems of known
     threads/64-bit capabilities.  In other words: if your
     operating system has the necessary APIs and datatypes, you
     should be able just to go ahead and use them, for threads by
     Configure -Dusethreads, and for 64 bits either explicitly by
     Configure -Duse64bitint or implicitly if your system has
     64-bit wide datatypes.  See also "64-bit support".

     Long Doubles

     Some platforms have "long doubles", floating point numbers
     of even larger range than ordinary "doubles".  To enable
     using long doubles for Perl's scalars, use -Duselongdouble.

     -Dusemorebits

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

     -Duselargefiles

     Some platforms support system APIs that are capable of han-
     dling large files (typically, files larger than two giga-
     bytes).  Perl will try to use these APIs if you ask for
     -Duselargefiles.

     See "Large file support" for more information.

     installusrbinperl

     You can use "Configure -Uinstallusrbinperl" which causes
     installperl to skip installing perl also as /usr/bin/perl.
     This is useful if you prefer not to modify /usr/bin for some
     reason or another but harmful because many scripts assume to
     find Perl in /usr/bin/perl.

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     SOCKS support

     You can use "Configure -Dusesocks" which causes Perl to
     probe for the SOCKS proxy protocol library (v5, not v4).
     For more information on SOCKS, see:

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

     "-A" flag

     You can "post-edit" the Configure variables using the Con-
     figure "-A" switch.  The editing happens immediately after
     the platform specific hints files have been processed but
     before the actual configuration process starts.  Run "Con-
     figure -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 pro-
     vide locations for vendor-supplied modules, scripts, and
     manpages, and to ease maintenance of locally-added modules,
     scripts, and manpages.  See the section on Installation
     Directories in the INSTALL file for complete details. For
     most users building and installing from source, the defaults
     should be fine.

     If you previously used "Configure -Dsitelib" or "-Dsitearch"
     to set special values for library directories, you might
     wish to consider using the new "-Dsiteprefix" setting
     instead.  Also, if you wish to re-use a config.sh file from
     an earlier version of perl, you should be sure to check that
     Configure makes sensible choices for the new directories.
     See INSTALL for complete details.

Platform specific changes

     Supported platforms

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

     +   GNU/Hurd is now supported.

     +   Rhapsody/Darwin is now supported.

     +   EPOC is now supported (on Psion 5).

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

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     DOS

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

     +   Environment variable names are not converted to upper-
         case any more.

     +   Incorrect exit codes from backticks have been fixed.

     +   This port continues to use its own builtin globbing (not
         File::Glob).

     OS390 (OpenEdition MVS)

     Support for this EBCDIC platform has not been renewed in
     this release. There are difficulties in reconciling Perl's
     standardization on UTF-8 as its internal representation for
     characters with the EBCDIC character set, because the two
     are incompatible.

     It is unclear whether future versions will renew support for
     this platform, but the possibility exists.

     VMS

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

     Expand %ENV-handling code to allow runtime mapping to logi-
     cal names, CLI symbols, and CRTL environ array.

     Extension of subprocess invocation code to accept filespecs
     as command "verbs".

     Add to Perl command line processing the ability to use
     default file types and to recognize Unix-style "2>&1".

     Expansion of File::Spec::VMS routines, and integration into
     ExtUtils::MM_VMS.

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

     Barewords at start of Unix-syntax paths may be treated as
     text rather than only as logical names.

     Optional secure translation of several logical names used
     internally by Perl.

     Miscellaneous bugfixing and porting of new core code to VMS.

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     Thanks are gladly extended to the many people who have con-
     tributed VMS patches, testing, and ideas.

     Win32

     Perl can now emulate fork() internally, using multiple
     interpreters running in different concurrent threads.  This
     support must be enabled at build time.  See perlfork for
     detailed information.

     When given a pathname that consists only of a drivename,
     such as "A:", opendir() and stat() now use the current work-
     ing directory for the drive rather than the drive root.

     The builtin XSUB functions in the Win32:: namespace are
     documented.  See Win32.

     $^X now contains the full path name of the running execut-
     able.

     A Win32::GetLongPathName() function is provided to comple-
     ment Win32::GetFullPathName() and Win32::GetShortPathName().
     See Win32.

     POSIX::uname() is supported.

     system(1,...) now returns true process IDs rather than pro-
     cess handles.  kill() accepts any real process id, rather
     than strictly return values from system(1,...).

     For better compatibility with Unix, "kill(0, $pid)" can now
     be used to test whether a process exists.

     The "Shell" module is supported.

     Better support for building Perl under command.com in Win-
     dows 95 has been added.

     Scripts are read in binary mode by default to allow
     ByteLoader (and the filter mechanism in general) to work
     properly.  For compatibility, the DATA filehandle will be
     set to text mode if a carriage return is detected at the end
     of the line containing the __END__ or __DATA__ token; if
     not, the DATA filehandle will be left open in binary mode.
     Earlier versions always opened the DATA filehandle in text
     mode.

     The glob() operator is implemented via the "File::Glob"
     extension, which supports glob syntax of the C shell.  This
     increases the flexibility of the glob() operator, but there
     may be compatibility issues for programs that relied on the
     older globbing syntax.  If you want to preserve

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     compatibility with the older syntax, you might want to run
     perl with "-MFile::DosGlob".  For details and compatibility
     information, see File::Glob.

Significant bug fixes

     <HANDLE> on empty files

     With $/ set to "undef", "slurping" an empty file returns a
     string of zero length (instead of "undef", as it used to)
     the first time the HANDLE is read after $/ is set to
     "undef".  Further reads yield "undef".

     This means that the following will append "foo" to an empty
     file (it used to do nothing):

         perl -0777 -pi -e 's/^/foo/' empty_file

     The behaviour of:

         perl -pi -e 's/^/foo/' empty_file

     is unchanged (it continues to leave the file empty).

     "eval '...'" improvements

     Line numbers (as reflected by caller() and most diagnostics)
     within "eval '...'" were often incorrect where here docu-
     ments were involved. This has been corrected.

     Lexical lookups for variables appearing in "eval '...'"
     within functions that were themselves called within an "eval
     '...'" were searching the wrong place for lexicals.  The
     lexical search now correctly ends at the subroutine's block
     boundary.

     The use of "return" within "eval {...}" caused $@ not to be
     reset correctly when no exception occurred within the eval.
     This has been fixed.

     Parsing of here documents used to be flawed when they
     appeared as the replacement expression in "eval
     's/.../.../e'".  This has been fixed.

     All compilation errors are true errors

     Some "errors" encountered at compile time were by necessity
     generated as warnings followed by eventual termination of
     the program.  This enabled more such errors to be reported
     in a single run, rather than causing a hard stop at the
     first error that was encountered.

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     The mechanism for reporting such errors has been reimple-
     mented to queue compile-time errors and report them at the
     end of the compilation as true errors rather than as warn-
     ings.  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 reli-
     ably trapped using "eval "..."".

     Implicitly closed filehandles are safer

     Sometimes implicitly closed filehandles (as when they are
     localized, and Perl automatically closes them on exiting the
     scope) could inadvertently set $? or $!.  This has been
     corrected.

     Behavior of list slices is more consistent

     When taking a slice of a literal list (as opposed to a slice
     of an array or hash), Perl used to return an empty list if
     the result happened to be composed of all undef values.

     The new behavior is to produce an empty list if (and only
     if) the original list was empty.  Consider the following
     example:

         @a = (1,undef,undef,2)[2,1,2];

     The old behavior would have resulted in @a having no ele-
     ments. The new behavior ensures it has three undefined ele-
     ments.

     Note in particular that the behavior of slices of the fol-
     lowing cases remains unchanged:

         @a = ()[1,2];
         @a = (getpwent)[7,0];
         @a = (anything_returning_empty_list())[2,1,2];
         @a = @b[2,1,2];
         @a = @c{'a','b','c'};

     See perldata.

     "(\$)" prototype and $foo{a}

     A scalar reference prototype now correctly allows a hash or
     array element in that slot.

     "goto &sub" and AUTOLOAD

     The "goto &sub" construct works correctly when &sub happens
     to be autoloaded.

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     "-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 unno-
     ticed in earlier versions of Perl, unless someone happened
     to be looking in $@ just after the point the destructor hap-
     pened to run.  Such failures are now visible as warnings
     when warnings are enabled.

     Locale bugs fixed

     printf() and sprintf() previously reset the numeric locale
     back to the default "C" locale.  This has been fixed.

     Numbers formatted according to the local numeric locale
     (such as using a decimal comma instead of a decimal dot)
     caused "isn't numeric" warnings, even while the operations
     accessing those numbers produced correct results.  These
     warnings have been discontinued.

     Memory leaks

     The "eval 'return sub {...}'" construct could sometimes leak
     memory.  This has been fixed.

     Operations that aren't filehandle constructors used to leak
     memory when used on invalid filehandles.  This has been
     fixed.

     Constructs that modified @_ could fail to deallocate values
     in @_ and thus leak memory.  This has been corrected.

     Spurious subroutine stubs after failed subroutine calls

     Perl could sometimes create empty subroutine stubs when a
     subroutine was not found in the package.  Such cases stopped
     later method lookups from progressing into base packages.
     This has been corrected.

     Taint failures under "-U"

     When running in unsafe mode, taint violations could some-
     times cause silent failures.  This has been fixed.

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     END blocks and the "-c" switch

     Prior versions used to run BEGIN and END blocks when Perl
     was run in compile-only mode.  Since this is typically not
     the expected behavior, END blocks are not executed anymore
     when the "-c" switch is used, or if compilation fails.

     See "Support for CHECK blocks" for how to run things when
     the compile phase ends.

     Potential to leak DATA filehandles

     Using the "__DATA__" token creates an implicit filehandle to
     the file that contains the token.  It is the program's
     responsibility to close it when it is done reading from it.

     This caveat is now better explained in the documentation.
     See perldata.

New or Changed Diagnostics

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

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

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

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

     / cannot take a count
         (F) You had an unpack template indicating a counted-
         length string, but you have also specified an explicit
         size for the string. See "pack" in perlfunc.

     / must be followed by a, A or Z
         (F) You had an unpack template indicating a counted-
         length string, which must be followed by one of the
         letters a, A or Z to indicate what sort of string is to
         be unpacked. See "pack" in perlfunc.

     / must be followed by a*, A* or Z*

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         (F) You had a pack template indicating a counted-length
         string, Currently the only things that can have their
         length counted are a*, A* or Z*. See "pack" in perlfunc.

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

     /%s/: Unrecognized escape \\%c passed through
         (W regexp) You used a backslash-character combination
         which is not recognized by Perl.  This combination
         appears in an interpolated variable or a "'"-delimited
         regular expression.  The character was understood
         literally.

     /%s/: Unrecognized escape \\%c in character class passed through
         (W regexp) You used a backslash-character combination
         which is not recognized by Perl inside character
         classes.  The character was understood literally.

     /%s/ should probably be written as "%s"
         (W syntax) You have used a pattern where Perl expected
         to find a string, as in the first argument to "join".
         Perl will treat the true or false result of matching the
         pattern against $_ as the string, which is probably not
         what you had in mind.

     %s() called too early to check prototype
         (W prototype) You've called a function that has a proto-
         type 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 pro-
         totype 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 warn-
         ing.  See perlsub.

     %s argument is not a HASH or ARRAY element
         (F) The argument to exists() must be a hash or array
         element, such as:

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

     %s argument is not a HASH or ARRAY element or slice
         (F) The argument to delete() must be either a hash or
         array element, such as:

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

         or a hash or array slice, such as:

             @foo[$bar, $baz, $xyzzy]
             @{$ref->[12]}{"susie", "queue"}

     %s argument is not a subroutine name
         (F) The argument to exists() for "exists &sub" must be a
         subroutine name, and not a subroutine call.  "exists
         &sub()" will generate this error.

     %s package attribute may clash with future reserved word: %s
         (W reserved) A lowercase attribute name was used that
         had a package-specific handler. That name might have a
         meaning to Perl itself some day, even though it doesn't
         yet.  Perhaps you should use a mixed-case attribute
         name, instead. See attributes.

     (in cleanup) %s
         (W misc) This prefix usually indicates that a DESTROY()
         method raised the indicated exception.  Since destruc-
         tors are usually called by the system at arbitrary
         points during execution, and often a vast number of
         times, the warning is issued only once for any number of
         failures that would otherwise result in the same message
         being repeated.

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

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

     Attempt to join self
         (F) You tried to join a thread from within itself, which
         is an impossible task.  You may be joining the wrong
         thread, or you may need to move the join() to some other
         thread.

     Bad evalled substitution pattern
         (F) You've used the /e switch to evaluate the replace-
         ment 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.

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         Mandatory, but can be disabled by setting environment
         variable "PERL_BADFREE" to 1.

     Bareword found in conditional
         (W bareword) The compiler found a bareword where it
         expected a conditional, which often indicates that an ||
         or && was parsed as part of the last argument of the
         previous construct, for example:

             open FOO || die;

         It may also indicate a misspelled constant that has been
         interpreted as a bareword:

             use constant TYPO => 1;
             if (TYOP) { print "foo" }

         The "strict" pragma is useful in avoiding such errors.

     Binary number > 0b11111111111111111111111111111111 non-
         portable
         (W portable) The binary number you specified is larger
         than 2**32-1 (4294967295) and therefore non-portable
         between systems.  See perlport for more on portability
         concerns.

     Bit vector size > 32 non-portable
         (W portable) Using bit vector sizes larger than 32 is
         non-portable.

     Buffer overflow in prime_env_iter: %s
         (W internal) A warning peculiar to VMS.  While Perl was
         preparing to iterate over %ENV, it encountered a logical
         name or symbol definition which was too long, so it was
         truncated to the string shown.

     Can't check filesystem of script "%s"
         (P) For some reason you can't check the filesystem of
         the script for nosuid.

     Can't declare class for non-scalar %s in "%s"
         (S) Currently, only scalar variables can declared with a
         specific class qualifier in a "my" or "our" declaration.
         The semantics may be extended for other types of vari-
         ables 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

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         (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 situa-
         tion typically indicates that the parent program under
         which Perl may be running (e.g., cron) is being very
         careless.

     Can't modify non-lvalue subroutine call
         (F) Subroutines meant to be used in lvalue context
         should be declared as such, see "Lvalue subroutines" in
         perlsub.

     Can't read CRTL environ
         (S) A warning peculiar to VMS.  Perl tried to read an
         element of %ENV from the CRTL's internal environment
         array and discovered the array was missing.  You need to
         figure out where your CRTL misplaced its environ or
         define PERL_ENV_TABLES (see perlvms) so that environ is
         not searched.

     Can't remove %s: %s, skipping file
         (S) You requested an inplace edit without creating a
         backup file.  Perl was unable to remove the original
         file to replace it with the modified file.  The file was
         left unmodified.

     Can't return %s from lvalue subroutine
         (F) Perl detected an attempt to return illegal lvalues
         (such as temporary or readonly values) from a subroutine
         used as an lvalue. This is not allowed.

     Can't weaken a nonreference
         (F) You attempted to weaken something that was not a
         reference.  Only references can be weakened.

     Character class [:%s:] unknown
         (F) The class in the character class [: :] syntax is
         unknown. See perlre.

     Character class syntax [%s] belongs inside character classes
         (W unsafe) The character class constructs [: :], [= =],
         and [. .]  go inside character classes, the [] are part
         of the construct, for example: /[012[:alpha:]345]/.
         Note that [= =] and [. .] are not currently implemented;
         they are simply placeholders for future extensions.

     Constant is not %s reference
         (F) A constant value (perhaps declared using the "use
         constant" pragma) is being dereferenced, but it amounts
         to the wrong type of reference.  The message indicates

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         the type of reference that was expected. This usually
         indicates a syntax error in dereferencing the constant
         value. See "Constant Functions" in perlsub and constant.

     constant(%s): %s
         (F) The parser found inconsistencies either while
         attempting to define an overloaded constant, or when
         trying to find the character name specified in the
         "\N{...}" escape.  Perhaps you forgot to load the
         corresponding "overload" or "charnames" pragma?  See
         charnames and overload.

     CORE::%s is not a keyword
         (F) The CORE:: namespace is reserved for Perl keywords.

     defined(@array) is deprecated
         (D) defined() is not usually useful on arrays because it
         checks for an undefined scalar value.  If you want to
         see if the array is empty, just use "if (@array) { # not
         empty }" for example.

     defined(%hash) is deprecated
         (D) defined() is not usually useful on hashes because it
         checks for an undefined scalar value.  If you want to
         see if the hash is empty, just use "if (%hash) { # not
         empty }" for example.

     Did not produce a valid header
         See Server error.

     (Did you mean "local" instead of "our"?)
         (W misc) Remember that "our" does not localize the
         declared global variable. You have declared it again in
         the same lexical scope, which seems superfluous.

     Document contains no data
         See Server error.

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

     false [] range "%s" in regexp
         (W regexp) A character class range must start and end at
         a literal character, not another character class like
         "\d" or "[:alpha:]".  The "-" in your false range is
         interpreted as a literal "-".  Consider quoting the "-",
         "\-". See perlre.

     Filehandle %s opened only for output
         (W io) You tried to read from a filehandle opened only
         for writing.  If you intended it to be a read/write

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         filehandle, you needed to open it with "+<" or "+>" or
         "+>>" instead of with "<" or nothing.  If you intended
         only to read from the file, use "<".  See "open" in
         perlfunc.

     flock() on closed filehandle %s
         (W closed) The filehandle you're attempting to flock()
         got itself closed some time before now.  Check your
         logic flow.  flock() operates on filehandles. Are you
         attempting to call flock() on a dirhandle by the same
         name?

     Global symbol "%s" requires explicit package name
         (F) You've said "use strict vars", which indicates that
         all variables must either be lexically scoped (using
         "my"), declared beforehand using "our", or explicitly
         qualified to say which package the global variable is in
         (using "::").

     Hexadecimal number > 0xffffffff non-portable
         (W portable) The hexadecimal number you specified is
         larger than 2**32-1 (4294967295) and therefore non-
         portable between systems.  See perlport for more on por-
         tability concerns.

     Ill-formed CRTL environ value "%s"
         (W internal) A warning peculiar to VMS.  Perl tried to
         read the CRTL's internal environ array, and encountered
         an element without the "=" delimiter used to separate
         keys from values.  The element is ignored.

     Ill-formed message in prime_env_iter: |%s|
         (W internal) A warning peculiar to VMS.  Perl tried to
         read a logical name or CLI symbol definition when
         preparing to iterate over %ENV, and didn't see the
         expected delimiter between key and value, so the line
         was ignored.

     Illegal binary digit %s
         (F) You used a digit other than 0 or 1 in a binary
         number.

     Illegal binary digit %s ignored
         (W digit) You may have tried to use a digit other than 0
         or 1 in a binary number. Interpretation of the binary
         number stopped before the offending digit.

     Illegal number of bits in vec
         (F) The number of bits in vec() (the third argument)
         must be a power of two from 1 to 32 (or 64, if your
         platform supports that).

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     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 opera-
         tions.

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

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

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

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

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

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

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

     Method %s not permitted
         See Server error.

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

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

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

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

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

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

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

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

         See also perlport for writing portable code.

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

     panic: kid popen errno read
         (F) forked child returned an incomprehensible message
         about its errno.

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     panic: magic_killbackrefs
         (P) Failed an internal consistency check while trying to
         reset all weak references to an object.

     Parentheses missing around "%s" list
         (W parenthesis) You said something like

             my $foo, $bar = @_;

         when you meant

             my ($foo, $bar) = @_;

         Remember that "my", "our", and "local" bind tighter than
         comma.

     Possible unintended interpolation of %s in string
         (W ambiguous) It used to be that Perl would try to guess
         whether you wanted an array interpolated or a literal @.
         It no longer does this; arrays are now always interpo-
         lated into strings.  This means that if you try some-
         thing like:

                 print "fred@example.com";

         and the array @example doesn't exist, Perl is going to
         print "fred.com", which is probably not what you wanted.
         To get a literal "@" sign in a string, put a backslash
         before it, just as you would to get a literal "$" sign.

     Possible Y2K bug: %s
         (W y2k) You are concatenating the number 19 with another
         number, which could be a potential Year 2000 problem.

     pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead
         (W deprecated) You have written something like this:

             sub doit
             {
                 use attrs qw(locked);
             }

         You should use the new declaration syntax instead.

             sub doit : locked
             {
                 ...

         The "use attrs" pragma is now obsolete, and is only pro-
         vided for backward-compatibility. See "Subroutine Attri-
         butes" in perlsub.

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     Premature end of script headers
         See Server error.

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

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

     realloc() of freed memory ignored
         (S) An internal routine called realloc() on something
         that had already been freed.

     Reference is already weak
         (W misc) You have attempted to weaken a reference that
         is already weak. Doing so has no effect.

     setpgrp can't take arguments
         (F) Your system has the setpgrp() from BSD 4.2, which
         takes no arguments, unlike POSIX setpgid(), which takes
         a process ID and process group ID.

     Strange *+?{} on zero-length expression
         (W regexp) You applied a regular expression quantifier
         in a place where it makes no sense, such as on a zero-
         width assertion. Try putting the quantifier inside the
         assertion instead.  For example, the way to match "abc"
         provided that it is followed by three repetitions of
         "xyz" is "/abc(?=(?:xyz){3})/", not "/abc(?=xyz){3}/".

     switching effective %s is not implemented
         (F) While under the "use filetest" pragma, we cannot
         switch the real and effective uids or gids.

     This Perl can't reset CRTL environ elements (%s)
     This Perl can't set CRTL environ elements (%s=%s)
         (W internal) Warnings peculiar to VMS.  You tried to
         change or delete an element of the CRTL's internal
         environ array, but your copy of Perl wasn't built with a
         CRTL that contained the setenv() function.  You'll need
         to rebuild Perl with a CRTL that does, or redefine
         PERL_ENV_TABLES (see perlvms) so that the environ array
         isn't the target of the change to %ENV which produced
         the warning.

     Too late to run %s block
         (W void) A CHECK or INIT block is being defined during
         run time proper, when the opportunity to run them has
         already passed.  Perhaps you are loading a file with

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         "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 charac-
         ter while parsing an attribute list, but the matching
         closing (right) parenthesis character was not found.
         You may need to add (or remove) a backslash character to
         get your parentheses to balance.  See attributes.

     Unterminated attribute list
         (F) The lexer found something other than a simple iden-
         tifier at the start of an attribute, and it wasn't a
         semicolon or the start of a block.  Perhaps you ter-
         minated the parameter list of the previous attribute too
         soon.  See attributes.

     Unterminated attribute parameter in subroutine attribute list
         (F) The lexer saw an opening (left) parenthesis charac-
         ter 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 iden-
         tifier 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,

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         and found a resultant string longer than 1024 charac-
         ters.  The return value has been truncated to 1024 char-
         acters.

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

New tests

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

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

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

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

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

     lib/io_multihomed
         INET sockets with multi-homed hosts.

     lib/io_poll
         IO poll().

     lib/io_unix
         UNIX sockets.

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

     op/filetest
         File test operators.

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

     op/exists_sub
         Verify "exists &sub" operations.

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Incompatible Changes

     Perl Source Incompatibilities

     Beware that any new warnings that have been added or old
     ones that have been enhanced are not considered incompatible
     changes.

     Since all new warnings must be explicitly requested via the
     "-w" switch or the "warnings" pragma, it is ultimately the
     programmer's responsibility to ensure that warnings are
     enabled judiciously.

     CHECK is a new keyword
         All subroutine definitions named CHECK are now special.
         See "/"Support for CHECK blocks"" for more information.

     Treatment of list slices of undef has changed
         There is a potential incompatibility in the behavior of
         list slices that are comprised entirely of undefined
         values. See "Behavior of list slices is more con-
         sistent".

     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 perl-
         bug if you are affected by this.

         See "Improved Perl version numbering system" for the
         reasons for this change.

     Literals of the form 1.2.3 parse differently
         Previously, numeric literals with more than one dot in
         them were interpreted as a floating point number con-
         catenated with one or more numbers.  Such "numbers" are
         now parsed as strings composed of the specified ordi-
         nals.

         For example, "print 97.98.99" used to output 97.9899 in
         earlier versions, but now prints "abc".

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

     Possibly changed pseudo-random number generator
         Perl programs that depend on reproducing a specific set
         of pseudo-random numbers may now produce different out-
         put due to improvements made to the rand() builtin.  You
         can use "sh Configure -Drandfunc=rand" to obtain the old
         behavior.

         See "Better pseudo-random number generator".

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     Hashing function for hash keys has changed
         Even though Perl hashes are not order preserving, the
         apparently random order encountered when iterating on
         the contents of a hash is actually determined by the
         hashing algorithm used.  Improvements in the algorithm
         may yield a random order that is different from that of
         previous versions, especially when iterating on hashes.

         See "Better worst-case behavior of hashes" for addi-
         tional 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 vari-
         able $^F.

         See "More consistent close-on-exec behavior".

     Writing "$$1" to mean "${$}1" is unsupported
         Perl 5.004 deprecated the interpretation of $$1 and
         similar within interpolated strings to mean "$$ . "1"",
         but still allowed it.

         In Perl 5.6.0 and later, "$$1" always means "${$1}".

     delete(), each(), values() and "\(%h)"
         operate on aliases to values, not copies

         delete(), each(), values() and hashes (e.g. "\(%h)") in
         a list context return the actual values in the hash,
         instead of copies (as they used to in earlier versions).
         Typical idioms for using these constructs copy the
         returned values, but this can make a significant differ-
         ence when creating references to the returned values.
         Keys in the hash are still returned as copies when
         iterating on a hash.

         See also "delete(), each(), values() and hash iteration
         are faster".

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

     Text of some diagnostic output has changed
         Most references to internal Perl operations in diagnos-
         tics have been changed to be more descriptive.  This may

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         be an issue for programs that may incorrectly rely on
         the exact text of diagnostics for proper functioning.

     "%@" has been removed
         The undocumented special variable "%@" that used to
         accumulate "background" errors (such as those that hap-
         pen 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 con-
         struct:

             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 fol-
         lowed by parentheses.

     Semantics of bareword prototype "(*)" have changed
         The semantics of the bareword prototype "*" have
         changed.  Perl 5.005 always coerced simple scalar argu-
         ments to a typeglob, which wasn't useful in situations
         where the subroutine must distinguish between a simple
         scalar and a typeglob.  The new behavior is to not
         coerce bareword arguments to a typeglob.  The value will
         always be visible as either a simple scalar or as a
         reference to a typeglob.

         See "More functional bareword prototype (*)".

     Semantics of bit operators may have changed on 64-bit platforms
         If your platform is either natively 64-bit or if Perl
         has been configured to used 64-bit integers, i.e.,
         $Config{ivsize} is 8, there may be a potential incompa-
         tibility 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.

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         In particular, note that unary "~" will produce dif-
         ferent results on platforms that have different
         $Config{ivsize}.  For portability, be sure to mask off
         the excess bits in the result of unary "~", e.g., "~$x &
         0xffffffff".

         See "Bit operators support full native integer width".

     More builtins taint their results
         As described in "Improved security features", there may
         be more sources of taint in a Perl program.

         To avoid these new tainting behaviors, you can build
         Perl with the Configure option
         "-Accflags=-DINCOMPLETE_TAINTS".  Beware that the ensu-
         ing perl binary may be insecure.

     C Source Incompatibilities

     "PERL_POLLUTE"
         Release 5.005 grandfathered old global symbol names by
         providing preprocessor macros for extension source com-
         patibility.  As of release 5.6.0, these preprocessor
         definitions are not available by default.  You need to
         explicitly compile perl with "-DPERL_POLLUTE" to get
         these definitions.  For extensions still using the old
         symbols, this option can be specified via MakeMaker:

             perl Makefile.PL POLLUTE=1

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

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

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

         See "The Perl API" in perlguts for detailed information

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         on the ramifications of building Perl with this option.

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

     "PERL_POLLUTE_MALLOC"
         Enabling Perl's malloc in release 5.005 and earlier
         caused the namespace of the system's malloc family of
         functions to be usurped by the Perl versions, since by
         default they used the same names.  Besides causing prob-
         lems on platforms that do not allow these functions to
         be cleanly replaced, this also meant that the system
         versions could not be called in programs that used
         Perl's malloc.  Previous versions of Perl have allowed
         this behaviour to be suppressed with the HIDEMYMALLOC
         and EMBEDMYMALLOC preprocessor definitions.

         As of release 5.6.0, Perl's malloc family of functions
         have default names distinct from the system versions.
         You need to explicitly compile perl with
         "-DPERL_POLLUTE_MALLOC" to get the older behaviour.
         HIDEMYMALLOC and EMBEDMYMALLOC have no effect, since the
         behaviour they enabled is now the default.

         Note that these functions do not constitute Perl's
         memory allocation API. See "Memory Allocation" in perl-
         guts for further information about that.

     Compatible C Source API Changes

     "PATCHLEVEL" is now "PERL_VERSION"
         The cpp macros "PERL_REVISION", "PERL_VERSION", and
         "PERL_SUBVERSION" are now available by default from
         perl.h, and reflect the base revision, patchlevel, and
         subversion respectively.  "PERL_REVISION" had no prior
         equivalent, while "PERL_VERSION" and "PERL_SUBVERSION"
         were previously available as "PATCHLEVEL" and "SUBVER-
         SION".

         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 incompati-
         bility 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

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     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 com-
     patible 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 func-
     tions irrespective of whether they were considered part of
     the public API or not.

     For the full list of public API functions, see perlapi.

Known Problems

     Thread test failures

     The subtests 19 and 20 of lib/thr5005.t test are known to
     fail due to fundamental problems in the 5.005 threading
     implementation.  These are not new failures--Perl 5.005_0x
     has the same bugs, but didn't have these tests.

     EBCDIC platforms not supported

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

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

     The lib/io_multihomed test may hang in HP-UX if Perl has
     been configured to be 64-bit.  Because other 64-bit plat-
     forms 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.

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     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 Con-
     figure run:

             Guessing which symbols your C compiler and preprocessor define...
             CC-20 cc: ERROR File = try.c, Line = 3
             ...
               bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K
             ...
             4 errors detected in the compilation of "try.c".

     The culprit is the broken awk of UNICOS/mk.  The effect is
     fortunately rather mild: Perl itself is not adversely
     affected by the error, only the h2ph utility coming with
     Perl, and that is rather rarely needed these days.

     Arrow operator and arrays

     When the left argument to the arrow operator "->" is an
     array, or the "scalar" operator operating on an array, the
     result of the operation must be considered erroneous. For
     example:

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

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

     Experimental features

     As discussed above, many features are still experimental.
     Interfaces and implementation of these features are subject
     to change, and in extreme cases, even subject to removal in
     some future release of Perl.  These features include the
     following:

     Threads
     Unicode
     64-bit support
     Lvalue subroutines
     Weak references
     The pseudo-hash data type
     The Compiler suite

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     Internal implementation of file globbing
     The DB module
     The regular expression code constructs:
         "(?{ code })" and "(??{ code })"

Obsolete Diagnostics

     Character class syntax [: :] is reserved for future extensions
         (W) Within regular expression character classes ([]) the
         syntax beginning with "[:" and ending with ":]" is
         reserved for future extensions. If you need to represent
         those character sequences inside a regular expression
         character class, just quote the square brackets with the
         backslash: "\[:" and ":\]".

     Ill-formed logical name |%s| in prime_env_iter
         (W) A warning peculiar to VMS.  A logical name was
         encountered when preparing to iterate over %ENV which
         violates the syntactic rules governing logical names.
         Because it cannot be translated normally, it is skipped,
         and will not appear in %ENV.  This may be a benign
         occurrence, as some software packages might directly
         modify logical name tables and introduce nonstandard
         names, or it may indicate that a logical name table has
         been corrupted.

     In string, @%s now must be written as \@%s
         The description of this error used to say:

                 (Someday it will simply assume that an unbackslashed @
                  interpolates an array.)

         That day has come, and this fatal error has been
         removed.  It has been replaced by a non-fatal warning
         instead. See "Arrays now always interpolate into
         double-quoted strings" for details.

     Probable precedence problem on %s
         (W) The compiler found a bareword where it expected a
         conditional, which often indicates that an || or && was
         parsed as part of the last argument of the previous con-
         struct, for example:

             open FOO || die;

     regexp too big
         (F) The current implementation of regular expressions
         uses shorts as address offsets within a string.  Unfor-
         tunately this means that if the regular expression com-
         piles to longer than 32767, it'll blow up. Usually when
         you want a regular expression this big, there is a
         better way to do it with multiple statements.  See
         perlre.

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     Use of "$$<digit>" to mean "${$}<digit>" is deprecated
         (D) Perl versions before 5.004 misinterpreted any type
         marker followed by "$" and a digit.  For example, "$$0"
         was incorrectly taken to mean "${$}0" instead of
         "${$0}".  This bug is (mostly) fixed in Perl 5.004.

         However, the developers of Perl 5.004 could not fix this
         bug completely, because at least two widely-used modules
         depend on the old meaning of "$$0" in a string.  So Perl
         5.004 still interprets "$$<digit>" in the old (broken)
         way inside strings; but it generates this message as a
         warning.  And in Perl 5.005, this special treatment will
         cease.

Reporting Bugs

     If you find what you think is a bug, you might check the
     articles recently posted to the comp.lang.perl.misc news-
     group. There may also be information at
     http://www.perl.com/perl/ , the Perl Home Page.

     If you believe you have an unreported bug, please run the
     perlbug program included with your release.  Be sure to trim
     your bug down to a tiny but sufficient test case.  Your bug
     report, along with the output of "perl -V", will be sent off
     to perlbug@perl.org to be analysed by the Perl porting team.

SEE ALSO

     The Changes file for exhaustive details on what changed.

     The INSTALL file for how to build Perl.

     The README file for general stuff.

     The Artistic and Copying files for copyright information.

HISTORY

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

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

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