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NAME    [Toc]    [Back]

       perl5004delta - what's new for perl5.004

DESCRIPTION    [Toc]    [Back]

       This document describes differences between the 5.003
       release (as documented in Programming Perl, second edition--the
 Camel Book) and this one.

Supported Environments    [Toc]    [Back]

       Perl5.004 builds out of the box on Unix, Plan 9, LynxOS,
       VMS, OS/2, QNX, AmigaOS, and Windows NT.  Perl runs on
       Windows 95 as well, but it cannot be built there, for lack
       of a reasonable command interpreter.

Core Changes    [Toc]    [Back]

       Most importantly, many bugs were fixed, including several
       security problems.  See the Changes file in the distribution
 for details.

       List assignment to %ENV works

       "%ENV = ()" and "%ENV = @list" now work as expected
       (except on VMS where it generates a fatal error).

       Change to "Can't locate Foo.pm in @INC" error

       The error "Can't locate Foo.pm in @INC" now lists the contents
 of @INC for easier debugging.

       Compilation option: Binary compatibility with 5.003

       There is a new Configure question that asks if you want to
       maintain binary compatibility with Perl 5.003.  If you
       choose binary compatibility, you do not have to recompile
       your extensions, but you might have symbol conflicts if
       you embed Perl in another application, just as in the
       5.003 release.  By default, binary compatibility is preserved
 at the expense of symbol table pollution.

       $PERL5OPT environment variable

       You may now put Perl options in the $PERL5OPT environment
       variable.  Unless Perl is running with taint checks, it
       will interpret this variable as if its contents had
       appeared on a "#!perl" line at the beginning of your
       script, except that hyphens are optional.  PERL5OPT may
       only be used to set the following switches: -[DIMUdmw].

       Limitations on -M, -m, and -T options

       The "-M" and "-m" options are no longer allowed on the
       "#!" line of a script.  If a script needs a module, it
       should invoke it with the "use" pragma.
       The -T option is also forbidden on the "#!" line of a
       script, unless it was present on the Perl command line.
       Due to the way "#!"  works, this usually means that -T
       must be in the first argument.  Thus:

           #!/usr/bin/perl -T -w

       will probably work for an executable script invoked as
       "scriptname", while:

           #!/usr/bin/perl -w -T

       will probably fail under the same conditions.  (Non-Unix
       systems will probably not follow this rule.)  But "perl
       scriptname" is guaranteed to fail, since then there is no
       chance of -T being found on the command line before it is
       found on the "#!" line.

       More precise warnings    [Toc]    [Back]

       If you removed the -w option from your Perl 5.003 scripts
       because it made Perl too verbose, we recommend that you
       try putting it back when you upgrade to Perl 5.004.  Each
       new perl version tends to remove some undesirable warnings,
 while adding new warnings that may catch bugs in
       your scripts.

       Deprecated: Inherited "AUTOLOAD" for non-methods

       Before Perl 5.004, "AUTOLOAD" functions were looked up as
       methods (using the @ISA hierarchy), even when the function
       to be autoloaded was called as a plain function (e.g.
       "Foo::bar()"), not a method (e.g. "Foo->bar()" or

       Perl 5.005 will use method lookup only for methods'
       "AUTOLOAD"s.  However, there is a significant base of
       existing code that may be using the old behavior.  So, as
       an interim step, Perl 5.004 issues an optional warning
       when a non-method uses an inherited "AUTOLOAD".

       The simple rule is:  Inheritance will not work when
       autoloading non-methods.  The simple fix for old code is:
       In any module that used to depend on inheriting "AUTOLOAD"
       for non-methods from a base class named "BaseClass", execute
 "*AUTOLOAD = BaseClass::AUTOLOAD" during startup.

       Previously deprecated %OVERLOAD is no longer usable

       Using %OVERLOAD to define overloading was deprecated in
       5.003.  Overloading is now defined using the overload
       pragma. %OVERLOAD is still used internally but should not
       be used by Perl scripts. See overload for more details.
       Subroutine arguments created only when they're modified

       In Perl 5.004, nonexistent array and hash elements used as
       subroutine parameters are brought into existence only if
       they are actually assigned to (via @_).

       Earlier versions of Perl vary in their handling of such
       arguments.  Perl versions 5.002 and 5.003 always brought
       them into existence.  Perl versions 5.000 and 5.001
       brought them into existence only if they were not the
       first argument (which was almost certainly a bug).  Earlier
 versions of Perl never brought them into existence.

       For example, given this code:

            undef @a; undef %a;
            sub show { print $_[0] };
            sub change { $_[0]++ };

       After this code executes in Perl 5.004, $a{b} exists but
       $a[2] does not.  In Perl 5.002 and 5.003, both $a{b} and
       $a[2] would have existed (but $a[2]'s value would have
       been undefined).

       Group vector changeable with $)

       The $) special variable has always (well, in Perl 5, at
       least) reflected not only the current effective group, but
       also the group list as returned by the "getgroups()" C
       function (if there is one).  However, until this release,
       there has not been a way to call the "setgroups()" C function
 from Perl.

       In Perl 5.004, assigning to $) is exactly symmetrical with
       examining it: The first number in its string value is used
       as the effective gid; if there are any numbers after the
       first one, they are passed to the "setgroups()" C function
       (if there is one).

       Fixed parsing of $$<digit>, &$<digit>, etc.

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

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

       Fixed localization of $<digit>, $&, etc.

       Perl versions before 5.004 did not always properly localize
 the regex-related special variables.  Perl 5.004 does
       localize them, as the documentation has always said it
       should.  This may result in $1, $2, etc. no longer being
       set where existing programs use them.

       No resetting of $. on implicit close

       The documentation for Perl 5.0 has always stated that $.
       is not reset when an already-open file handle is reopened
       with no intervening call to "close".  Due to a bug, perl
       versions 5.000 through 5.003 did reset $. under that circumstance;
 Perl 5.004 does not.

       "wantarray" may return undef

       The "wantarray" operator returns true if a subroutine is
       expected to return a list, and false otherwise.  In Perl
       5.004, "wantarray" can also return the undefined value if
       a subroutine's return value will not be used at all, which
       allows subroutines to avoid a time-consuming calculation
       of a return value if it isn't going to be used.

       "eval EXPR" determines value of EXPR in scalar context

       Perl (version 5) used to determine the value of EXPR
       inconsistently, sometimes incorrectly using the surrounding
 context for the determination.  Now, the value of EXPR
       (before being parsed by eval) is always determined in a
       scalar context.  Once parsed, it is executed as before, by
       providing the context that the scope surrounding the eval
       provided.  This change makes the behavior Perl4 compatible,
 besides fixing bugs resulting from the inconsistent
       behavior.  This program:

           @a = qw(time now is time);
           print eval @a;
           print '|', scalar eval @a;

       used to print something like "timenowis881399109|4", but
       now (and in perl4) prints "4|4".

       Changes to tainting checks    [Toc]    [Back]

       A bug in previous versions may have failed to detect some
       insecure conditions when taint checks are turned on.
       (Taint checks are used in setuid or setgid scripts, or
       when explicitly turned on with the "-T" invocation
       option.)  Although it's unlikely, this may cause a previously-working
 script to now fail -- which should be
       construed as a blessing, since that indicates a potentially-serious
 security hole was just plugged.

       The new restrictions when tainting include:

       No glob() or <*>
           These operators may spawn the C shell (csh), which
           cannot be made safe.  This restriction will be lifted
           in a future version of Perl when globbing is implemented
 without the use of an external program.

       No spawning if tainted $CDPATH, $ENV, $BASH_ENV
           These environment variables may alter the behavior of
           spawned programs (especially shells) in ways that subvert
 security.  So now they are treated as dangerous,
           in the manner of $IFS and $PATH.

       No spawning if tainted $TERM doesn't look like a terminal
           Some termcap libraries do unsafe things with $TERM.
           However, it would be unnecessarily harsh to treat all
           $TERM values as unsafe, since only shell metacharacters
 can cause trouble in $TERM.  So a tainted $TERM
           is considered to be safe if it contains only alphanumerics,
 underscores, dashes, and colons, and unsafe if
           it contains other characters (including whitespace).

       New Opcode module and revised Safe module    [Toc]    [Back]

       A new Opcode module supports the creation, manipulation
       and application of opcode masks.  The revised Safe module
       has a new API and is implemented using the new Opcode module.
  Please read the new Opcode and Safe documentation.

       Embedding improvements    [Toc]    [Back]

       In older versions of Perl it was not possible to create
       more than one Perl interpreter instance inside a single
       process without leaking like a sieve and/or crashing.  The
       bugs that caused this behavior have all been fixed.  However,
 you still must take care when embedding Perl in a C
       program.  See the updated perlembed manpage for tips on
       how to manage your interpreters.

       Internal change: FileHandle class based on IO::* classes

       File handles are now stored internally as type IO::Handle.
       The FileHandle module is still supported for backwards
       compatibility, but it is now merely a front end to the
       IO::* modules -- specifically, IO::Handle, IO::Seekable,
       and IO::File.  We suggest, but do not require, that you
       use the IO::* modules in new code.

       In harmony with this change, *GLOB{FILEHANDLE} is now just
       a backward-compatible synonym for *GLOB{IO}.

       Internal change: PerlIO abstraction interface

       It is now possible to build Perl with AT&T's sfio IO package
 instead of stdio.  See perlapio for more details, and
       the INSTALL file for how to use it.

       New and changed syntax    [Toc]    [Back]

           A subroutine reference may now be suffixed with an
           arrow and a (possibly empty) parameter list.  This
           syntax denotes a call of the referenced subroutine,
           with the given parameters (if any).

           This new syntax follows the pattern of
           "$hashref->{FOO}" and "$aryref->[$foo]": You may now
           write "&$subref($foo)" as "$subref->($foo)".  All
           these arrow terms may be chained; thus,
           "&{$table->{FOO}}($bar)" may now be written

       New and changed builtin constants    [Toc]    [Back]

           The current package name at compile time, or the undefined
 value if there is no current package (due to a
           "package;" directive).  Like "__FILE__" and
           "__LINE__", "__PACKAGE__" does not interpolate into

       New and changed builtin variables    [Toc]    [Back]

       $^E Extended error message on some platforms.  (Also known
           as $EXTENDED_OS_ERROR if you "use English").

       $^H The current set of syntax checks enabled by "use
           strict".  See the documentation of "strict" for more
           details.  Not actually new, but newly documented.
           Because it is intended for internal use by Perl core
           components, there is no "use English" long name for
           this variable.

       $^M By default, running out of memory it is not trappable.
           However, if compiled for this, Perl may use the contents
 of $^M as an emergency pool after die()ing with
           this message.  Suppose that your Perl were compiled
           with -DPERL_EMERGENCY_SBRK and used Perl's malloc.
               $^M = 'a' x (1<<16);

           would allocate a 64K buffer for use when in emergency.
           See the INSTALL file for information on how to enable
           this option.  As a disincentive to casual use of this
           advanced feature, there is no "use English" long name
           for this variable.

       New and changed builtin functions    [Toc]    [Back]

       delete on slices
           This now works.  (e.g. "delete @ENV{'PATH', 'MANPATH'}")

           is now supported on more platforms, prefers fcntl to
           lockf when emulating, and always flushes before

       printf and sprintf
           Perl now implements these functions itself; it doesn't
           use the C library function sprintf() any more, except
           for floating-point numbers, and even then only known
           flags are allowed.  As a result, it is now possible to
           know which conversions and flags will work, and what
           they will do.

           The new conversions in Perl's sprintf() are:

              %i   a synonym for %d
              %p   a pointer (the address of the Perl  value,  in
              %n    special:  *stores*  the  number of characters
output so far
                   into the next variable in the parameter list

           The new flags that go between the "%" and the conversion

              #    prefix octal with "0", hex with "0x"
              h    interpret integer as C type  "short"  or  "unsigned short"
              V     interpret  integer as Perl's standard integer

           Also, where a number would appear in the flags, an
           asterisk ("*") may be used instead, in which case Perl
           uses the next item in the parameter list as the given
           number (that is, as the field width or precision).  If
           a field width obtained through "*" is negative, it has
           the same effect as the '-' flag: left-justification.

           See "sprintf" in perlfunc for a complete list of conversion
 and flags.

       keys as an lvalue
           As an lvalue, "keys" allows you to increase the number
           of hash buckets allocated for the given hash.  This
           can gain you a measure of efficiency if you know the
           hash is going to get big.  (This is similar to preextending
 an array by assigning a larger number to
           $#array.)  If you say

               keys %hash = 200;

           then %hash will have at least 200 buckets allocated
           for it.  These buckets will be retained even if you do
           "%hash = ()"; use "undef %hash" if you want to free
           the storage while %hash is still in scope.  You can't
           shrink the number of buckets allocated for the hash
           using "keys" in this way (but you needn't worry about
           doing this by accident, as trying has no effect).

       my() in Control Structures
           You can now use my() (with or without the parentheses)
           in the control expressions of control structures such

               while (defined(my $line = <>)) {
                   $line = lc $line;
               } continue {
                   print $line;

               if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
               } elsif ($answer =~ /^n(o)?$/i) {
               } else {
                   chomp $answer;
                   die "`$answer' is neither `yes' nor `no'";

           Also, you can declare a foreach loop control variable
           as lexical by preceding it with the word "my".  For
           example, in:

               foreach my $i (1, 2, 3) {

           $i is a lexical variable, and the scope of $i extends
           to the end of the loop, but not beyond it.

           Note that you still cannot use my() on global punctuation
 variables such as $_ and the like.

       pack() and unpack()
           A new format 'w' represents a BER compressed integer
           (as defined in ASN.1).  Its format is a sequence of
           one or more bytes, each of which provides seven bits
           of the total value, with the most significant first.
           Bit eight of each byte is set, except for the last
           byte, in which bit eight is clear.

           If 'p' or 'P' are given undef as values, they now generate
 a NULL pointer.

           Both pack() and unpack() now fail when their templates
           contain invalid types.  (Invalid types used to be

           The new sysseek() operator is a variant of seek() that
           sets and gets the file's system read/write position,
           using the lseek(2) system call.  It is the only reliable
 way to seek before using sysread() or syswrite().
           Its return value is the new position, or the undefined
           value on failure.

       use VERSION
           If the first argument to "use" is a number, it is
           treated as a version number instead of a module  name.
           If the version of the Perl interpreter is less than
           VERSION, then an error message is printed and Perl
           exits immediately.  Because "use" occurs at compile
           time, this check happens immediately during the compilation
 process, unlike "require VERSION", which waits
           until runtime for the check.  This is often useful if
           you need to check the current Perl version before
           "use"ing library modules which have changed in incompatible
 ways from older versions of Perl.  (We try not
           to do this more than we have to.)

       use Module VERSION LIST
           If the VERSION argument is present between Module and
           LIST, then the "use" will call the VERSION method in
           class Module with the given version as an argument.
           The default VERSION method, inherited from the UNIVERSAL
 class, croaks if the given version is larger than
           the value of the variable $Module::VERSION.  (Note
           that there is not a comma after VERSION!)

           This version-checking mechanism is similar to the one
           currently used in the Exporter module, but it is
           faster and can be used with modules that don't use the
           Exporter.   It is the recommended method for new code.

           Returns the prototype of a function as a string (or
           "undef" if the function has no prototype).  FUNCTION
           is a reference to or the name of the function whose
           prototype you want to retrieve.  (Not actually new;
           just never documented before.)
           The default seed for "srand", which used to be "time",
           has been changed.  Now it's a heady mix of difficultto-predict
 system-dependent values, which should be
           sufficient for most everyday purposes.

           Previous to version 5.004, calling "rand" without
           first calling "srand" would yield the same sequence of
           random numbers on most or all machines.  Now, when
           perl sees that you're calling "rand" and haven't yet
           called "srand", it calls "srand" with the default
           seed. You should still call "srand" manually if your
           code might ever be run on a pre-5.004 system, of
           course, or if you want a seed other than the  default.

       $_ as Default
           Functions documented in the Camel to default to $_ now
           in fact do, and all those that do are so documented in

       "m//gc" does not reset search position on failure
           The "m//g" match iteration construct has always reset
           its target string's search position (which is visible
           through the "pos" operator) when a match fails; as a
           result, the next "m//g" match after a failure starts
           again at the beginning of the string.  With Perl
           5.004, this reset may be disabled by adding the "c"
           (for "continue") modifier, i.e. "m//gc".  This feature,
 in conjunction with the "G" zero-width assertion,
 makes it possible to chain matches together.
           See perlop and perlre.

       "m//x" ignores whitespace before ?*+{}
           The "m//x" construct has always been intended to
           ignore all unescaped whitespace.  However, before Perl
           5.004, whitespace had the effect of escaping repeat
           modifiers like "*" or "?"; for example, "/a *b/x" was
           (mis)interpreted as "/a/x".  This bug has been
           fixed in 5.004.

       nested "sub{}" closures work now
           Prior to the 5.004 release, nested anonymous functions
           didn't work right.  They do now.

       formats work right on changing lexicals
           Just like anonymous functions that contain lexical
           variables that change (like a lexical index variable
           for a "foreach" loop), formats now work properly.  For
           example, this silently failed before (printed only
           zeros), but is fine now:
               my $i;
               foreach $i ( 1 .. 10 ) {
               format =
                   my i is @#

           However, it still fails (without a warning) if the
           foreach is within a subroutine:

               my $i;
               sub foo {
                 foreach $i ( 1 .. 10 ) {
               format =
                   my i is @#

       New builtin methods    [Toc]    [Back]

       The "UNIVERSAL" package automatically contains the following
 methods that are inherited by all other classes:

           "isa" returns true if its object is blessed into a
           subclass of "CLASS"

           "isa" is also exportable and can be called as a sub
           with two arguments. This allows the ability to check
           what a reference points to. Example:

               use UNIVERSAL qw(isa);

               if(isa($ref, 'ARRAY')) {

           "can" checks to see if its object has a method called
           "METHOD", if it does then a reference to the sub is
           returned; if it does not then undef is returned.

       VERSION( [NEED] )
           "VERSION" returns the version number of the class
           (package).  If the NEED argument is given then it will
           check that the current version (as defined by the
           $VERSION variable in the given package) not less than
           NEED; it will die if this is not the case.  This
           method is normally called as a class method.  This
           method is called automatically by the "VERSION" form
           of "use".

               use A 1.2 qw(some imported subs);
               # implies:

       NOTE: "can" directly uses Perl's internal code for method
       lookup, and "isa" uses a very similar method and caching
       strategy. This may cause strange effects if the Perl code
       dynamically changes @ISA in any package.

       You may add other methods to the UNIVERSAL class via Perl
       or XS code.  You do not need to "use UNIVERSAL" in order
       to make these methods available to your program.  This is
       necessary only if you wish to have "isa" available as a
       plain subroutine in the current package.

       TIEHANDLE now supported    [Toc]    [Back]

       See perltie for other kinds of tie()s.

       TIEHANDLE classname, LIST
           This is the constructor for the class.  That means it
           is expected to return an object of some sort. The reference
  can be used to hold some internal information.

               sub TIEHANDLE {
                   print "<shout>0;
                   my $i;
                   return bless , shift;

       PRINT this, LIST
           This method will be triggered every time the tied handle
 is printed to.  Beyond its self reference it also
           expects the list that was passed to the print function.

               sub PRINT {
                   $r = shift;
                   return print join( $, => map {uc} @_), $;

       PRINTF this, LIST
           This method will be triggered every time the tied handle
 is printed to with the "printf()" function.
           Beyond its self reference it also expects the format
           and list that was passed to the printf function.
               sub PRINTF {
                     my $fmt = shift;
                   print sprintf($fmt, @_)."0;

       READ this LIST
           This method will be called when the handle is read
           from via the "read" or "sysread" functions.

               sub READ {
                   $r = shift;
                   my($buf,$len,$offset) = @_;
                   print  "READ  called,  uf=$buf,  en=$len,  ffset=$offset";

       READLINE this
           This method will be called when the handle is read
           from. The method should return undef when there is no
           more data.

               sub READLINE {
                   $r = shift;
                   return "PRINT called $$r times0

       GETC this
           This method will be called when the "getc" function is

               sub GETC { print "Don't GETC,  Get  Perl";  return
"a"; }

       DESTROY this
           As with the other types of ties, this method will be
           called  when the tied handle is about to be destroyed.
           This is useful for debugging and possibly for cleaning

               sub DESTROY {
                   print "</shout>0;

       Malloc enhancements    [Toc]    [Back]

       If perl is compiled with the malloc included with the perl
       distribution (that is, if "perl -V:d_mymalloc" is
       'define') then you can print memory statistics at runtime
       by running Perl thusly:

         env PERL_DEBUG_MSTATS=2 perl your_script_here

       The value of 2 means to print statistics after compilation
       and on exit; with a value of 1, the statistics are printed
       only on exit.  (If you want the statistics at an arbitrary
       time, you'll need to install the optional module

       Three new compilation flags are recognized by malloc.c.
       (They have no effect if perl is compiled with system mal-

           If this macro is defined, running out of memory need
           not be a fatal error: a memory pool can allocated by
           assigning to the special variable $^M.  See "$^M".

           Perl memory allocation is by bucket with sizes close
           to powers of two.  Because of these malloc overhead
           may be big, especially for data of size exactly a
           power of two.  If "PACK_MALLOC" is defined, perl uses
           a slightly different algorithm for small allocations
           (up to 64 bytes long), which makes it possible to have
           overhead down to 1 byte for allocations which are powers
 of two (and appear quite often).

           Expected memory savings (with 8-byte alignment in
           "alignbytes") is about 20% for typical Perl usage.
           Expected slowdown due to additional malloc overhead is
           in fractions of a percent (hard to measure, because of
           the effect of saved memory on speed).

           Similarly to "PACK_MALLOC", this macro improves allocations
 of data with size close to a power of two; but
           this works for big allocations (starting with 16K by
           default).  Such allocations are typical for big hashes
           and special-purpose scripts, especially image processing.

           On recent systems, the fact that perl requires 2M from
           system for 1M allocation will not affect speed of execution,
 since the tail of such a chunk is not going to
           be touched (and thus will not require real memory).
           However, it may result in a premature out-of-memory
           error.  So if you will be manipulating very large
           blocks with sizes close to powers of two, it would be
           wise to define this macro.

           Expected saving of memory is 0-100% (100% in applications
 which require most memory in such 2**n chunks);
           expected slowdown is negligible.

       Miscellaneous efficiency enhancements    [Toc]    [Back]

       Functions that have an empty prototype and that do nothing
       but return a fixed value are now inlined (e.g. "sub PI ()
       { 3.14159 }").
       Each unique hash key is only allocated once, no matter how
       many hashes have an entry with that key.  So even if you
       have 100 copies of the same hash, the hash keys never have
       to be reallocated.

Support for More Operating Systems    [Toc]    [Back]

       Support for the following operating systems is new in Perl

       Win32    [Toc]    [Back]

       Perl 5.004 now includes support for building a "native"
       perl under Windows NT, using the Microsoft Visual C++ compiler
 (versions 2.0 and above) or the Borland C++ compiler
       (versions 5.02 and above).  The resulting perl can be used
       under Windows 95 (if it is installed in the same directory
       locations as it got installed in Windows NT).  This port
       includes support for perl extension building tools like
       MakeMaker and h2xs, so that many extensions available on
       the Comprehensive Perl Archive Network (CPAN) can now be
       readily built under Windows NT.  See http://www.perl.com/
       for more information on CPAN and README.win32 in the perl
       distribution for more details on how to get started with
       building this port.

       There is also support for building perl under the Cygwin32
       environment.  Cygwin32 is a set of GNU tools that make it
       possible to compile and run many Unix programs under Windows
 NT by providing a mostly Unix-like interface for compilation
 and execution.  See README.cygwin32 in the perl
       distribution for more details on this port and how to
       obtain the Cygwin32 toolkit.

       Plan 9    [Toc]    [Back]

       See README.plan9 in the perl distribution.

       QNX    [Toc]    [Back]

       See README.qnx in the perl distribution.

       AmigaOS    [Toc]    [Back]

       See README.amigaos in the perl distribution.

Pragmata    [Toc]    [Back]

       Six new pragmatic modules exist:

       use autouse MODULE => qw(sub1 sub2 sub3)
           Defers "require MODULE" until someone calls one of the
           specified subroutines (which must be exported by MODULE).
  This pragma should be used with caution, and
           only when necessary.
       use blib
       use blib 'dir'
           Looks for MakeMaker-like 'blib' directory structure
           starting in dir (or current directory) and working
           back up to five levels of parent directories.

           Intended for use on command line with -M option as a
           way of testing arbitrary scripts against an uninstalled
 version of a package.

       use constant NAME => VALUE
           Provides a convenient interface for creating compiletime
 constants, See "Constant Functions" in perlsub.

       use locale
           Tells the compiler to enable (or disable) the use of
           POSIX locales for builtin operations.

           When "use locale" is in effect, the current LC_CTYPE
           locale is used for regular expressions and case mapping;
 LC_COLLATE for string ordering; and LC_NUMERIC
           for numeric formatting in printf and sprintf (but not
           in print).  LC_NUMERIC is always used in write, since
           lexical scoping of formats is problematic at best.

           Each "use locale" or "no locale" affects statements to
           the end of the enclosing BLOCK or, if not inside a
           BLOCK, to the end of the current file.  Locales can be
           switched and queried with POSIX::setlocale().

           See perllocale for more information.

       use ops
           Disable unsafe opcodes, or any named opcodes, when
           compiling Perl code.

       use vmsish
           Enable VMS-specific language features.  Currently,
           there are three VMS-specific features available: 'status',
 which makes $? and "system" return genuine VMS
           status values instead of emulating POSIX; 'exit',
           which makes "exit" take a genuine VMS status value
           instead of assuming that "exit 1" is an error; and
           'time', which makes all times relative to the local
           time zone, in the VMS tradition.

Modules    [Toc]    [Back]

       Required Updates

       Though Perl 5.004 is compatible with almost all modules
       that work with Perl 5.003, there are a few exceptions:
           Module   Required Version for Perl 5.004
           ------   -------------------------------
           Filter   Filter-1.12
           LWP      libwww-perl-5.08
           Tk       Tk400.202 (-w makes noise)

       Also, the majordomo mailing list program, version 1.94.1,
       doesn't work with Perl 5.004 (nor with perl 4), because it
       executes an invalid regular expression.  This bug is fixed
       in majordomo version 1.94.2.

       Installation directories    [Toc]    [Back]

       The installperl script now places the Perl source files
       for extensions in the architecture-specific library directory,
 which is where the shared libraries for extensions
       have always been.  This change is intended to allow administrators
 to keep the Perl 5.004 library directory
       unchanged from a previous version, without running the
       risk of binary incompatibility between extensions' Perl
       source and shared libraries.

       Module information summary    [Toc]    [Back]

       Brand new modules, arranged by topic rather than strictly

           CGI.pm                Web  server  interface  ("Common
Gateway Interface")
           CGI/Apache.pm        Support for Apache's Perl module
           CGI/Carp.pm          Log server  errors  with  helpful
           CGI/Fast.pm           Support  for FastCGI (persistent
server process)
           CGI/Push.pm          Support for server push
           CGI/Switch.pm         Simple  interface  for  multiple
server types

           CPAN                  Interface  to Comprehensive Perl
Archive Network
           CPAN::FirstTime      Utility for creating CPAN configuration file
           CPAN::Nox            Runs CPAN while avoiding compiled

           IO.pm                 Top-level  interface  to   IO::*
           IO/File.pm           IO::File extension Perl module
           IO/Handle.pm         IO::Handle extension Perl module
           IO/Pipe.pm           IO::Pipe extension Perl module
           IO/Seekable.pm        IO::Seekable extension Perl module
           IO/Select.pm         IO::Select extension Perl module
           IO/Socket.pm         IO::Socket extension Perl module

           Opcode.pm            Disable named opcodes  when  compiling Perl code

           ExtUtils/Embed.pm    Utilities for embedding Perl in C
           ExtUtils/testlib.pm  Fixes up @INC to  use  just-built

           FindBin.pm            Find path of currently executing
           Class/Struct.pm      Declare struct-like datatypes  as
Perl classes
           File/stat.pm           By-name   interface  to  Perl's
builtin stat
           Net/hostent.pm        By-name  interface   to   Perl's
builtin gethost*
           Net/netent.pm          By-name   interface  to  Perl's
builtin getnet*
           Net/protoent.pm       By-name  interface   to   Perl's
builtin getproto*
           Net/servent.pm         By-name   interface  to  Perl's
builtin getserv*
           Time/gmtime.pm        By-name  interface   to   Perl's
builtin gmtime
           Time/localtime.pm      By-name   interface  to  Perl's
builtin localtime
           Time/tm.pm           Internal object for Time::{gm,local}time
           User/grent.pm          By-name   interface  to  Perl's
builtin getgr*
           User/pwent.pm         By-name  interface   to   Perl's
builtin getpw*

           Tie/RefHash.pm        Base  class for tied hashes with
references as keys

           UNIVERSAL.pm         Base class for *ALL* classes

       Fcntl    [Toc]    [Back]

       New constants in the existing Fcntl modules are now supported,
 provided that your operating system happens to
       support them:

           F_GETOWN F_SETOWN
           O_EXLOCK O_SHLOCK

       These constants are intended for use with the Perl operators
 sysopen() and fcntl() and the basic database modules
       like SDBM_File.  For the exact meaning of these and other
       Fcntl constants please refer to your operating system's
       documentation for fcntl() and open().

       In addition, the Fcntl module now provides these constants
       for use with the Perl operator flock():


       These constants are defined in all environments (because
       where  there is no flock() system call, Perl emulates it).
       However, for historical reasons, these constants are not
       exported unless they are explicitly requested with the
       ":flock" tag (e.g. "use Fcntl ':flock'").

       IO    [Toc]    [Back]

       The IO module provides a simple mechanism to load all the
       IO modules at one go.  Currently this includes:

       For more information on any of these modules, please see
       its respective documentation.


       The Math::Complex module has been totally rewritten, and
       now supports more operations.  These are overloaded:

            + - * / ** <=> neg ~ abs sqrt exp log sin  cos  atan2
"" (stringify)

       And these functions are now exported:

           pi i Re Im arg
           log10 logn ln cbrt root
           csc sec cot
           asin acos atan
           acsc asec acot
           sinh cosh tanh
           csch sech coth
           asinh acosh atanh
           acsch asech acoth
           cplx cplxe


       This new module provides a simpler interface to parts of
       Math::Complex for those who need trigonometric functions
       only for real numbers.

       DB_File    [Toc]    [Back]

       There have been quite a few changes made to DB_File. Here
       are a few of the highlights:

       o   Fixed a handful of bugs.

       o   By public demand, added support for the standard hash
           function exists().

       o   Made it compatible with Berkeley DB 1.86.

       o   Made negative subscripts work with RECNO interface.

       o   Changed the default flags from O_RDWR to
           O_CREAT|O_RDWR and the default mode from 0640 to 0666.

       o   Made DB_File automatically import the open() constants
           (O_RDWR, O_CREAT etc.) from Fcntl, if available.

       o   Updated documentation.

       Refer to the HISTORY section in DB_File.pm for a complete
       list of changes. Everything after DB_File 1.01 has been
       added since 5.003.


       Major rewrite - support added for both udp echo and real
       icmp pings.

       Object-oriented overrides for builtin operators    [Toc]    [Back]

       Many of the Perl builtins returning lists now have objectoriented
 overrides.  These are:


       For example, you can now say

           use File::stat;
           use User::pwent;
           $his  =  (stat($filename)->st_uid   ==   pwent($whoever)->pw_uid);

Utility Changes    [Toc]    [Back]


       Sends converted HTML to standard output
           The pod2html utility included with Perl 5.004 is
           entirely new.  By default, it sends the converted HTML
           to its standard output, instead of writing it to a
           file like Perl 5.003's pod2html did.  Use the --out-
           file=FILENAME option to write to a file.


       "void" XSUBs now default to returning nothing
           Due to a documentation/implementation bug in previous
           versions of Perl, XSUBs with a return type of "void"
           have actually been returning one value.  Usually that
           value was the GV for the XSUB, but sometimes it was
           some already freed or reused value, which would sometimes
 lead to program failure.

           In Perl 5.004, if an XSUB is declared as returning
           "void", it actually returns no value, i.e. an empty
           list (though there is a backward-compatibility exception;
 see below).  If your XSUB really does return an
           SV, you should give it a return type of "SV *".

           For backward compatibility, xsubpp tries to guess
           whether a "void" XSUB is really "void" or if it wants
           to return an "SV *".  It does so by examining the text
           of the XSUB: if xsubpp finds what looks like an
           assignment to ST(0), it assumes that the XSUB's return
           type is really "SV *".

C Language API Changes    [Toc]    [Back]

       "gv_fetchmethod" and "perl_call_sv"
           The "gv_fetchmethod" function finds a method for an
           object, just like in Perl 5.003.  The GV it returns
           may be a method cache entry.  However, in Perl 5.004,
           method cache entries are not visible to users; therefore,
 they can no longer be passed directly to
           "perl_call_sv".  Instead, you should use the "GvCV"
           macro on the GV to extract its CV, and pass the CV to

           The most likely symptom of passing the result of
           "gv_fetchmethod" to "perl_call_sv" is Perl's producing
           an "Undefined subroutine called" error on the second
           call to a given method (since there is no cache on the
           first call).

           A new function handy for eval'ing strings of Perl code
           inside C code.  This function returns the value from
           the eval statement, which can be used instead of
           fetching globals from the symbol table.  See perlguts,
           perlembed and perlcall for details and examples.

       Extended API for manipulating hashes
           Internal handling of hash keys has changed.  The old
           hashtable API is still fully supported, and will
           likely remain so.  The additions to the API allow
           passing keys as "SV*"s, so that "tied" hashes can be
           given real scalars as keys rather than plain strings
           (nontied hashes still can only use strings as keys).
           New extensions must use the new hash access functions
           and macros if they wish to use "SV*" keys.  These
           additions also make it feasible to manipulate "HE*"s
           (hash entries), which can be more efficient.  See
           perlguts for details.

Documentation Changes    [Toc]    [Back]

       Many of the base and library pods were updated.  These new
       pods are included in section 1:

           This document.
           Frequently asked questions.

           Locale support (internationalization and localization).

           Tutorial on Perl OO programming.

           Perl internal IO abstraction interface.

           Perl module library and recommended practice for module
 creation.  Extracted from perlmod (which is much
           smaller as a result).

           Although not new, this has been massively updated.

           Although not new, this has been massively updated.

New Diagnostics    [Toc]    [Back]

       Several new conditions will trigger warnings that were
       silent before.  Some only affect certain platforms.  The
       following new warnings and errors outline these.  These
       messages are classified as follows (listed in increasing
       order of desperation):

          (W) A warning (optional).
          (D) A deprecation (optional).
          (S) A severe warning (mandatory).
          (F) A fatal error (trappable).
          (P) An internal error you should never see (trappable).
          (X) A very fatal error (nontrappable).
          (A) An alien error message (not generated by Perl).

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

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

           or a hash slice, such as

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

       Allocation too large: %lx
           (X) You can't allocate more than 64K on an MS-DOS

       Allocation too large
           (F) You can't allocate more than 2^31+"small amount"

       Applying %s to %s will act on scalar(%s)
           (W) The pattern match (//), substitution (s///), and
           transliteration (tr///) operators work on scalar values.
  If you apply one of them to an array or a hash,
           it will convert the array or hash to a scalar value --
           the length of an array, or the population info of a
           hash -- and then work on that scalar value.  This is
           probably not what you meant to do.  See "grep" in
           perlfunc and "map" in perlfunc for alternatives.

       Attempt to free nonexistent shared string
           (P) Perl maintains a reference counted internal table
           of strings to optimize the storage and access of hash
           keys and other strings.  This indicates someone tried
           to decrement the reference count of a string that can
           no longer be found in the table.

       Attempt to use reference as lvalue in substr
           (W) You supplied a reference as the first argument to
           substr() used as an lvalue, which is pretty strange.
           Perhaps you forgot to dereference it first.  See "substr"
 in perlfunc.

       Bareword "%s" refers to nonexistent package
           (W) You used a qualified bareword of the form "Foo::",
           but the compiler saw no other uses of that namespace
           before that point.  Perhaps you need to predeclare a

       Can't redefine active sort subroutine %s
           (F) Perl optimizes the internal handling of sort subroutines
 and keeps pointers into them.  You tried to
           redefine one such sort subroutine when it was currently
 active, which is not allowed.  If you really
           want to do this, you should write "sort { &func } @x"
           instead of "sort func @x".

       Can't use bareword ("%s") as %s ref while "strict refs" in
           (F) Only hard references are allowed by "strict refs".
           Symbolic references are disallowed.  See perlref.
       Cannot resolve method `%s' overloading `%s' in package
           (P) Internal error trying to resolve overloading specified
 by a method name (as opposed to a subroutine

       Constant subroutine %s redefined
           (S) You redefined a subroutine which had previously
           been eligible for inlining.  See "Constant Functions"
           in perlsub for commentary and workarounds.

       Constant subroutine %s undefined
           (S) You undefined a subroutine which had previously
           been eligible for inlining.  See "Constant Functions"
           in perlsub for commentary and workarounds.

       Copy method did not return a reference
           (F) The method which overloads "=" is buggy. See "Copy
           Constructor" in overload.

           (F) You passed die() an empty string (the equivalent
           of "die """) or you called it with no args and both $@
           and $_ were empty.

       Exiting pseudo-block via %s
           (W) You are exiting a rather special block construct
           (like a sort block or subroutine) by unconventional
           means, such as a goto, or a loop control statement.
           See "sort" in perlfunc.

       Identifier too long
           (F) Perl limits identifiers (names for variables,
           functions, etc.) to 252 characters for simple names,
           somewhat more for compound names (like $A::B).  You've
           exceeded Perl's limits.  Future versions of Perl are
           likely to eliminate these arbitrary limitations.

       Illegal character %s (carriage return)
           (F) A carriage return character was found in the
           input.  This is an error, and not a warning, because
           carriage return characters can break multi-line
           strings, including here documents (e.g., "print

       Illegal switch in PERL5OPT: %s
           (X) The PERL5OPT environment variable may only be used
           to set the following switches: -[DIMUdmw].

       Integer overflow in hex number
           (S) The literal hex number you have specified is too
           big for your architecture. On a 32-bit architecture
           the largest hex literal is 0xFFFFFFFF.
       Integer overflow in octal number
           (S) The literal octal number you have specified is too
           big for your architecture. On a 32-bit architecture
           the largest octal literal is 037777777777.

       internal error: glob failed
           (P) Something went wrong with the external program(s)
           used for "glob" and "<*.c>".  This may mean that your
           csh (C shell) is broken.  If so, you should change all
           of the csh-related variables in config.sh:  If you
           have tcsh, make the variables refer to it as if it
           were csh (e.g. "full_csh='/usr/bin/tcsh'"); otherwise,
           make them all empty (except that "d_csh" should be
           'undef') so that Perl will think csh is missing.  In
           either case, after editing config.sh, run "./Configure
           -S" and rebuild Perl.

       Invalid conversion in %s: "%s"
           (W) Perl does not understand the given format conversion.
  See "sprintf" in perlfunc.

       Invalid type in pack: '%s'
           (F) The given character is not a valid pack type.  See
           "pack" in perlfunc.

       Invalid type in unpack: '%s'
           (F) The given character is not a valid unpack type.
           See "unpack" in perlfunc.

       Name "%s::%s" used only once: possible typo
           (W) Typographical errors often show up as unique variable
 names.  If you had a good reason for having a
           unique name, then just mention it again somehow to
           suppress the message (the "use vars" pragma is provided
 for just this purpose).

       Null picture in formline
           (F) The first argument to formline must be a valid
           format picture specification.  It was found to be
           empty, which probably means you supplied it an uninitialized
 value.  See perlform.

       Offset outside string
           (F) You tried to do a read/write/send/recv operation
           with an offset pointing outside the buffer.  This is
           difficult to imagine.  The sole exception to this is
           that "sysread()"ing past the buffer will extend the
           buffer and zero pad the new area.

       Out of memory!
           (X|F) The malloc() function returned 0, indicating
           there was insufficient remaining memory (or virtual
           memory) to satisfy the request.
           The request was judged to be small, so the possibility
           to trap it depends on the way Perl was compiled.  By
           default it is not trappable.  However, if compiled for
           this, Perl may use the contents of $^M as an emergency
           pool after die()ing with this message.  In this case
           the error is trappable once.


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