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

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

       This feature is still in evolution.  It is eventually
       meant to be used to selectively clone a subroutine and
       data reachable from that subroutine in a separate inter­
       preter and run the cloned subroutine in a separate thread.
       Since there is no shared data between the interpreters,
       little or no locking will be needed (unless parts of the
       symbol table are explicitly shared).  This is obviously
       intended to be an easy-to-use replacement for the existing
       threads support.

       Support for cloning interpreters and interpreter concur­
       rency can be enabled using the -Dusethreads Configure
       option (see win32/Makefile for how to enable it on Win­
       dows.)  The resulting perl executable will be functionally
       identical to one that was built with -Dmultiplicity, but
       the perl_clone() API call will only be available in the

       -Dusethreads enables the cpp macro USE_ITHREADS by
       default, which in turn enables Perl source code changes
       that provide a clear separation between the op tree and
       the data it operates with.  The former is immutable, and
       can therefore be shared between an interpreter and all of
       its clones, while the latter is considered local to each
       interpreter, and is therefore copied for each clone.

       Note that building Perl with the -Dusemultiplicity Config­
       ure option is adequate if you wish to run multiple inde­
       pendent interpreters concurrently in different threads.
       -Dusethreads only provides the additional functionality of
       the perl_clone() API call and other support for running
       cloned interpreters concurrently.

       Unicode and UTF-8 support

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

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

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

       Support for interpolating named characters

       The new "\N" escape interpolates named characters within
       strings.  For example, "Hi! \N{WHITE SMILING FACE}" evalu­
       ates 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 alter­
       native to the "vars" pragma, but also provides the oppor­
       tunity 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 (possi­
       bly unicode) strings instead of interpolating characters,
       as in "\x{1}\x{2}\x{3}\x{4}".  The leading "v" may be
       omitted if there are more than two ordinals, so 1.2.3 is
       parsed the same as "v1.2.3".

       Strings written in this form are also useful to represent
       version "numbers".  It is easy to compare such version
       "numbers" (which are really just plain strings) using any
       of the usual string comparison operators "eq", "ne", "lt",
       "gt", etc., or perform bitwise string operations on them
       using "|", "&", etc.

       In conjunction with the new $^V magic variable (which con­
       tains the perl version as a string), such literals can be

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

       Also, "sprintf" and "printf" support the Perl-specific
       format flag %v to print ordinals of characters in arbi­
       trary 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

       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

       The English module now sets $PERL_VERSION to $^V (a string
       value) rather than $] (a numeric value).  (This is a
       potential incompatibility.  Send us a report via perlbug
       if you are affected by this.)

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

       To cope with the new versioning system's use of at least
       three significant digits for each version component, the
       method used for incrementing the subversion number has
       also changed slightly.  We assume that versions older than
       v5.6.0 have been incrementing the subversion component in
       multiples of 10.  Versions after v5.6.0 will increment
       them by 1.  Thus, using the new notation, 5.005_03 is the
       "same" as v5.5.30, and the first maintenance version fol­
       lowing 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
           sub othermethod :locked :method {

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

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

       File and directory handles can be autovivified

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

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

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

       open() with more than two arguments

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

       64-bit support

       Any platform that has 64-bit integers either

               (1) natively as longs or ints

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

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

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

       ·   vec()

       Note that unless you have the case (a) you will have to
       configure and compile Perl using the -Duse64bitint Config­
       ure 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,
       signed), they are silently promoted to floating point num­
           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-pro­
       cess (or your per-system, or per-process-group, or
       per-user-group) maximum filesize limits before running
       Perl scripts that try to handle large files, especially if
       you intend to write such files.

       Finally, in addition to your process/process group maximum
       filesize limits, you may have quota limits on your
       filesystems that stop you (your user id or your user group
       id) from using large files.

       Adjusting your process/user/group/file system/operating
       system limits is outside the scope of Perl core language.
       For process limits, you may try increasing the limits
       using your shell's limits/limit/ulimit command before run­
       ning Perl.  The BSD::Resource extension (not included with
       the standard Perl distribution) may also be of use, it
       offers the getrlimit/setrlimit interface that can be used
       to adjust process resource usage limits, including the
       maximum filesize limit.

       Long doubles

       In some systems you may be able to use long doubles to
       enhance the range and precision of your double precision
       floating point numbers (that is, Perl's numbers).  Use
       Configure -Duselongdouble to enable this support (if it is

       "more bits"

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

       Enhanced support for sort() subroutines

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

       File globbing implemented internally

       Perl now uses the File::Glob implementation of the glob()
       operator automatically.  This avoids using an external csh
       process and the problems associated with it.

           NOTE: This is currently an experimental feature.  Interfaces and
           implementation are subject to change.

       Support for CHECK blocks

       In addition to "BEGIN", "INIT", "END", "DESTROY" and
       "AUTOLOAD", subroutines named "CHECK" are now special.
       These are queued up during compilation and behave similar
       to END blocks, except they are called at the end of compi­
       lation 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

       Improved "qw//" operator

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


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

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

       Better worst-case behavior of hashes

       Small changes in the hashing algorithm have been imple­
       mented in order to improve the distribution of lower order
       bits in the hashed value.  This is expected to yield bet­
       pack() and unpack() support counted strings

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

       Comments in pack() templates

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

       Weak references

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

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

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

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

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

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

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

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

       See "exists" in perlfunc and "delete" in perlfunc for

       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
       handles I/O.

       This is not supported on some platforms like Solaris where
       a suitably correct implementation of fflush(NULL) isn't

       Better diagnostics on meaningless filehandle operations

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

       Where possible, buffered data discarded from duped input

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

       eof() has the same old magic as <>

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

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

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

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

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

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

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

       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 addi­
       tion to the eval sequence number and the line number
       within the evaluated text itself.  For example:

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

       Diagnostics follow STDERR

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

       More consistent close-on-exec behavior

       On systems that support a close-on-exec flag on filehan­
       dles, the flag is now set for any handles created by
       pipe(), socketpair(), socket(), and accept(), if that is
       warranted by the value of $^F that may be in effect.  Ear­
       lier versions neglected to set the flag for handles cre­
       ated with these operators.  See "pipe" in perlfunc, "sock­
       etpair" in perlfunc, "socket" in perlfunc, "accept" in
       perlfunc, and "$^F" in perlvar.

       syswrite() ease-of-use

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

       Better syntax checks on parenthesized unary operators

       Expressions such as:

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

       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 avail­
       able in $Config{ivsize}).  For example, if your platform
       is either natively 64-bit or if Perl has been configured
       to use 64-bit integers, these operations apply to 8 bytes
       (as opposed to 4 bytes on 32-bit platforms).  For porta­
       bility, be sure to mask off the excess bits in the result
       of unary "~", e.g., "~$x & 0xffffffff".

       Improved security features

       More potentially unsafe operations taint their results for
       improved security.

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

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

       More functional bareword prototype (*)

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

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

       "require" and "do" may be overridden

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

       "$^XYZ" continues to be synonymous with "$^X . "YZ"" as

       As before, lexical variables may not have names beginning
       with control characters.  As before, variables whose names
       begin with a control character are always forced to be in
       package `main'.  All such variables are reserved for
       future extensions, except those that begin with "^_",
       which may be used by user programs and are guaranteed not
       to acquire special meaning in any future version of Perl.

       New variable $^C reflects "-c" switch

       $^C has a boolean value that reflects whether perl is
       being run in compile-only mode (i.e. via the "-c" switch).
       Since BEGIN blocks are executed under such conditions,
       this variable enables perl code to determine whether
       actions that make sense only during normal running are
       warranted.  See perlvar.

       New variable $^V contains Perl version as a string

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

       See "Support for strings represented as a vector of 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
       Configure.  See INSTALL and README.Y2K.

       Arrays now always interpolate into double-quoted strings

       In double-quoted strings, arrays now interpolate, no mat­
       ter 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

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

Modules and Pragmata


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

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

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

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

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

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

           will now output something like this:

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

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

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

           timethis() now returns the iterations field in the
           For other details, see Benchmark.

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

           References can now be used.

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

           See constant.

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

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

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

           Dumping "qr//" objects works correctly.

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

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

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

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

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

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

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

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

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

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

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

           See File::Find.

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

           New methods have been added to the File::Spec module:
           devnull() returns the name of the null device
           (/dev/null on Unix) and tmpdir() the name of the temp
           directory (normally /tmp on Unix).  There are now also

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

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

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

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


               =head1 NAME

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

               =head1 SYNOPSIS

               sample [options] [file ...]

                  -help            brief help message
                  -man             full documentation

               =head1 OPTIONS

               =over 8

               =item B<-help>

               Print a brief help message and exits.

               =item B<-man>

               Prints the manual page and exits.


               =head1 DESCRIPTION

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


           You can now create a TCP-based IO::Socket::INET with­
           out 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() acces­
           sor from ever returning the correct value has been

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

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

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

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

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

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

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

           The class method "display_format" and the correspond­
           ing 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 parame­
           ter case, and two new parameters: "format", which is a
           printf()-style format string (defaults usually to
           "%.15g", you can revert to the default by setting the
           format string to "undef") used for both parts of a
           complex number, and "polar_pretty_print" (defaults to
           true), which controls whether an attempt is made to
           try to recognize small multiples and rationals of pi
           (2pi, pi/2) at the argument (angle) of a polar complex

           The potentially disruptive change is that in list con­
           text both methods now return the parameter hash,

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

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

           For further information, please see Pod::Parser and

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

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

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

       Pod::Usage, pod2usage
           Pod::Usage provides the function "pod2usage()" to
           print usage messages for a Perl script based on its
           embedded pod documentation.  The pod2usage() function
           is generally useful to all script authors since it
           lets them write and maintain a single source (the
           patibility, the module now has a new preferred inter­
           face.  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::Term­
           cap 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

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

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

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

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

           Term::ANSIColor is a very simple module to provide
           easy and readable access to the ANSI color and high­
           lighting escape sequences, supported by most ANSI ter­
           minal emulators.  It is now included standard.

           The timelocal() and timegm() functions used to
           silently return bogus results when the date fell out­
           side the machine's integer range.  They now consis­
           tently croak() if the date falls in an unsupported

           The error return value in list context has been
           changed for all functions that return a list of val­
           ues.  Previously these functions returned a list with
           a single element "undef" if an error occurred.  Now
           In list context it returns a two-element list contain­
           ing the fully qualified directory name and the file­
           name.  See Win32.

           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:


           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.


       "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 perl­
       sub 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 con­
       trol lists): the stat(2) might lie, but access(2) knows

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

Utility Changes


       header files.  The "-M", "-a", "-k", and "-o" options are


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

       Support for non-Unix platforms has been improved.


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

       The Perl Debugger

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

Improved Documentation

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

           The official list of public Perl API functions.

           A tutorial for beginners on object-oriented Perl.

           An introduction to using the Perl Compiler suite.

           A howto document on using the DBM filter facility.

           All material unrelated to running the Perl debugger,
           plus all low-level guts-like details that risked
           crushing the casual user of the debugger, have been

           An introduction to writing Perl source filters.

           Some guidelines for hacking the Perl source code.

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

           Introduction and reference information about lexically
           scoped warning categories.

           Detailed information about numbers as they are repre­
           sented in Perl.

           A tutorial on using open() effectively.

           A tutorial that introduces the essentials of refer­

           A tutorial on managing class data for object modules.

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

           An introduction to Unicode support features in Perl.

Performance enhancements

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

       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 inter­
       preter-based thread support by default.  To get the flavor
       of experimental threads that was in 5.005 instead, you
       need to run Configure with "-Dusethreads

       As of v5.6.0, interpreter-threads support is still lacking
       a way to create new threads from Perl (i.e., "use Thread;"
       will not work with interpreter threads).  "use Thread;"
       continues to be available when you specify the
       -Duse5005threads option to Configure, bugs and all.

           NOTE: Support for threads continues to be an experimental feature.
           Interfaces and implementation are subject to sudden and drastic changes.

       New Configure flags

       The following new flags may be enabled on the Configure
       command line by running Configure with "-Dflag".

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

           use64bitint                 (equal to now deprecated 'use64bits')

           usesocks                    (only SOCKS v5 supported)

       Threadedness and 64-bitness now more daring

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


       See "Large file support" for more information.


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

       SOCKS support

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


       "-A" flag

       You can "post-edit" the Configure variables using the 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
       provide locations for vendor-supplied modules, scripts,
       and manpages, and to ease maintenance of locally-added
       modules, scripts, and manpages.  See the section on
       Installation Directories in the INSTALL file for complete
       details.  For most users building and installing from
       source, the defaults should be fine.

       If you previously used "Configure -Dsitelib" or
       "-Dsitearch" to set special values for library directo­
       ries, you might wish to consider using the new "-Dsitepre­
       fix" setting instead.  Also, if you wish to re-use a con­
       fig.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 sup­
           ported by the Thread extension.

       ·   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 represen­
       tation for characters with the EBCDIC character set,
       because the two are incompatible.

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


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

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

       Extension of subprocess invocation code to accept file­
       specs 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

       Thanks are gladly extended to the many people who have
       contributed VMS patches, testing, and ideas.
       documented.  See Win32.

       $^X now contains the full path name of the running exe­

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

       POSIX::uname() is supported.

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

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

       The "Shell" module is supported.

       Better support for building Perl under command.com in 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
       compatibility with the older syntax, you might want to run
       perl with "-MFile::DosGlob".  For details and compatibil­
       ity 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):

       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 neces­
       sity generated as warnings followed by eventual termina­
       tion of the program.  This enabled more such errors to be
       reported in a single run, rather than causing a hard stop
       at the first error that was encountered.

       The mechanism for reporting such errors has been 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 reliably trapped using "eval "..."".

       Implicitly closed filehandles are safer

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

       Behavior of list slices is more consistent

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

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

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

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

       "(\$)" 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 hap­
       pens to be autoloaded.

       "-bareword" allowed under "use integer"

       The autoquoting of barewords preceded by "-" did not work
       in prior versions when the "integer" pragma was enabled.
       This has been fixed.

       Failures in DESTROY()

       When code in a destructor threw an exception, it went
       unnoticed in earlier versions of Perl, unless someone hap­
       pened to be looking in $@ just after the point the
       destructor happened to run.  Such failures are now visible
       as warnings when warnings are enabled.

       Locale bugs fixed

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

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

       Memory leaks

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

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

       Constructs that modified @_ could fail to deallocate val­
       ues 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

       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

       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 elimi­
           nating 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

       "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
           global once before in the current lexical scope.

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

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

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

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

           (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 proba­
           bly not what you had in mind.

       %s() called too early to check prototype
           (W prototype) You've called a function that has a pro­
           totype before the parser saw a definition or declara­
           tion for it, and Perl could not check that the call
           conforms to the prototype.  You need to either add an
           early prototype declaration for the subroutine in
           question, or move the subroutine definition ahead of
           the call to get proper prototype checking.  Alterna­
           tively, if you are certain that you're calling the
           function correctly, you may put an ampersand before
           the name to avoid the warning.  See perlsub.

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


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


           or a hash or array slice, such as:

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

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

       %s package attribute may clash with future reserved word:
           (W reserved) A lowercase attribute name was used that
           had a package-specific handler.  That name might have
           "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.
           Mandatory, but can be disabled by setting environment
           variable "PERL_BADFREE" to 1.

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

               open FOO || die;

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

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

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

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

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

           of variables in future.

       Can't declare %s in "%s"
           (F) Only scalar, array, and hash variables may be
           declared as "my" or "our" variables.  They must have
           ordinary identifiers as names.

       Can't ignore signal CHLD, forcing to default
           (W signal) Perl has detected that it is being run with
           the SIGCHLD signal (sometimes known as SIGCLD) dis­
           abled.  Since disabling this signal will interfere
           with proper determination of exit status of child pro­
           cesses, Perl has reset the signal to its default
           value.  This situation typically indicates that the
           parent program under which Perl may be running (e.g.,
           cron) is being very careless.

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

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

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

       Can't return %s from lvalue subroutine
           (F) Perl detected an attempt to return illegal lvalues
           (such as temporary or readonly values) from a subrou­
           tine 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
           (W unsafe) The character class constructs [: :], [=

       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 cor­
           responding "overload" or "charnames" pragma?  See
           charnames and overload.

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

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

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

       Did not produce a valid header
           See Server error.

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

       Document contains no data
           See Server error.

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

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

       Filehandle %s opened only for output
           (W io) You tried to read from a filehandle opened only
           for writing.  If you intended it to be a read/write
           filehandle, you needed to open it with "+<" or "+>" or
           "+>>" instead of with "<" or nothing.  If you intended
           explicitly qualified to say which package the global
           variable is in (using "::").

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

       Ill-formed CRTL environ value "%s"
           (W internal) A warning peculiar to VMS.  Perl tried to
           read the CRTL's internal environ array, and encoun­
           tered 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

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

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

       Integer overflow in %s number
           (W overflow) The hexadecimal, octal or binary number
           you have specified either as a literal or as an argu­
           ment to hex() or oct() is too big for your architec­
           ture, and has been converted to a floating point num­
           ber.  On a 32-bit architecture the largest hexadeci­
           mal, octal or binary number representable without
           overflow is 0xFFFFFFFF, 037777777777, or
           0b11111111111111111111111111111111 respectively.  Note
           that Perl transparently promotes all numbers to a
           floating point representation internally--subject to
           loss of precision errors in subsequent operations.

       Invalid %s attribute: %s
           The indicated attribute for a subroutine or variable
           was not recognized by Perl or by a user-supplied han­
           list, perhaps that list was terminated too soon.  See

       Invalid separator character %s in subroutine attribute
           (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

       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 subrou­
           tines used in lvalue context.  See "Lvalue subrou­
           tines" in perlsub.

       Method %s not permitted
           See Server error.

       Missing %sbrace%s on \N{}
           (F) Wrong syntax of character name literal "\N{char­
           name}" 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 subrou­
           tines 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 manda­
           tory argument, but you haven't specified one.

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

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

           See also perlport for writing portable code.

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

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

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

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

               my $foo, $bar = @_;

           when you meant

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

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

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

                   print "fred@example.com";

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

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

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

               sub doit

       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 perl­

       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

       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 repeti­
           tions of "xyz" is "/abc(?=(?:xyz){3})/", not

       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 rede­
           fine 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
           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 char­
           acter while parsing an attribute list, but the match­
           ing closing (right) parenthesis character was not
           found.  You may need to add (or remove) a backslash
           character to get your parentheses to balance.  See

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

       Unterminated attribute parameter in subroutine attribute
           (F) The lexer saw an opening (left) parenthesis char­
           acter while parsing a subroutine attribute list, but
           the matching closing (right) parenthesis character was
           not found.  You may need to add (or remove) a back­
           slash character to get your parentheses to balance.

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

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

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

           IO constants (SEEK_*, _IO*).

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

           INET sockets with multi-homed hosts.

           IO poll().

           UNIX sockets.

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

           File test operators.

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

           Verify "exists &sub" operations.

Incompatible Changes

       Perl Source Incompatibilities

       Beware that any new warnings that have been added or old
       ones that have been enhanced are not considered incompati­
       ble 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 spe­
           cial.  See "/"Support for CHECK blocks"" for more

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


           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

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

           See "Better pseudo-random number generator".

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

           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)")

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

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

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

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

               grep not($_), @things;

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

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

           needs to be written with additional parentheses now:

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

           The behavior remains unaffected when "not" is not 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
           arguments to a typeglob, which wasn't useful in situa­
           tions 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
           If your platform is either natively 64-bit or if Perl

       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=-DINCOM­
           PLETE_TAINTS".  Beware that the ensuing perl binary
           may be insecure.

       C Source Incompatibilities

           Release 5.005 grandfathered old global symbol names by
           providing preprocessor macros for extension source
           compatibility.  As of release 5.6.0, these preproces­
           sor 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

               perl Makefile.PL POLLUTE=1

           This new build option provides a set of macros for all
           API functions such that an implicit interpreter/thread
           context argument is passed to every API function.  As
           a result of this, something like "sv_setsv(foo,bar)"
           amounts to a macro invocation that actually translates
           to something like "Perl_sv_setsv(my_perl,foo,bar)".
           While this is generally expected to not have any sig­
           nificant 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 informa­
           tion on the ramifications of building Perl with this

               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.

           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_POL­
           LUTE_MALLOC" to get the older behaviour.  HIDEMYMALLOC
           and EMBEDMYMALLOC have no effect, since the behaviour
           they enabled is now the default.

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

       Compatible C Source API Changes

           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

           The new names cause less pollution of the cpp names­
           pace 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 explic­
           itly included (as required before), so there is no
           source incompatibility from the change.

       Binary Incompatibilities

       In general, the default build of this release is expected
       to be binary compatible for extensions built with the
       5.005 release or its maintenance versions.  However, spe­
       cific platforms may have broken binary compatibility due
       to changes in the defaults used in hints files.  There­
       fore, please be sure to always check the platform-specific
       README files for any notes to the contrary.

       The usethreads or usemultiplicity builds are not binary
       compatible with the corresponding builds in 5.005.

       On platforms that require an explicit list of exports
       (AIX, OS/2 and Windows, among others), purely internal
       symbols such as parser functions and the run time opcodes
       are not exported by default.  Perl 5.005 used to export
       all functions irrespective of whether they were considered
       part of the public API or not.

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


       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 sub­
       tests 19 to 27 of the lib/posix test may fail.

       Tru64 (aka Digital UNIX, aka DEC OSF/1) lib/sdbm test
       failure with gcc

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

       UNICOS/mk CC failures during Configure run

       In UNICOS/mk the following errors may appear during the
       Configure run:

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

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

       Arrow operator and arrays

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


       include the following:

       64-bit support
       Lvalue subroutines
       Weak references
       The pseudo-hash data type
       The Compiler suite
       Internal implementation of file globbing
       The DB module
       The regular expression code constructs:
           "(?{ code })" and "(??{ code })"

Obsolete Diagnostics

       Character class syntax [: :] is reserved for future exten­
           (W) Within regular expression character classes ([])
           the syntax beginning with "[:" and ending with ":]" is
           reserved for future extensions.  If you need to repre­
           sent 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 non­
           standard 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 dou­
           ble-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 previ­
           ous construct, 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.


       The Changes file for exhaustive details on what changed.

       The INSTALL file for how to build Perl.

       The README file for general stuff.

       The Artistic and Copying files for copyright information.


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

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

perl v5.8.1                 2003-09-02             PERL56DELTA(1)

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