perl5004delta - what's new for perl5.004


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

Supported Environments

   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

   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 in @INC" error
   The error "Can't locate 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"

   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",

       #!/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
   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 "$obj->bar()").

   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

   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 cease.

   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
   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

   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 name
       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
   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
   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
       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
       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
   $^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

   $^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.  Then

           $^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
   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 (un)locking.

   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 hexadecimal)
          %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 are:

          #    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 type

       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

   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 pre-extending 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 as:

           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

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

       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 difficult-to-predict system-
       dependent values, which should be sufficient for most everyday

       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 perlfunc.

   "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\*b/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
   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

       "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" 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

   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
   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>\n";
               my $i;
               return bless \$i, 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, @_)."\n";

   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, \$buf=$buf, \$len=$len, \$offset=$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 times\n"

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

           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 up.

           sub DESTROY {
               print "</shout>\n";

   Malloc enhancements
   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 Devel::Peek.)

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

       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

       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

   Miscellaneous efficiency enhancements
   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

   Support for the following operating systems is new in Perl 5.004.

   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
   ExtUtils::MakeMaker and h2xs, so that many extensions available on the
   Comprehensive Perl Archive Network (CPAN) can now be readily built
   under Windows NT.  See 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
   See README.plan9 in the perl distribution.

   See README.qnx in the perl distribution.

   See README.amigaos in the perl distribution.


   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

       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 compile-time
       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

       See perllocale for more information.

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

   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


   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
   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

   Module information summary
   Brand new modules, arranged by topic rather than strictly
   alphabetically:               Web server interface ("Common Gateway Interface")
       CGI/        Support for Apache's Perl module
       CGI/          Log server errors with helpful context
       CGI/          Support for FastCGI (persistent server process)
       CGI/          Support for server push
       CGI/        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 extensions                Top-level interface to IO::* classes
       IO/           IO::File extension Perl module
       IO/         IO::Handle extension Perl module
       IO/           IO::Pipe extension Perl module
       IO/       IO::Seekable extension Perl module
       IO/         IO::Select extension Perl module
       IO/         IO::Socket extension Perl module            Disable named opcodes when compiling Perl code

       ExtUtils/    Utilities for embedding Perl in C programs
       ExtUtils/  Fixes up @INC to use just-built extension           Find path of currently executing program

       Class/      Declare struct-like datatypes as Perl classes
       File/         By-name interface to Perl's builtin stat
       Net/       By-name interface to Perl's builtin gethost*
       Net/        By-name interface to Perl's builtin getnet*
       Net/      By-name interface to Perl's builtin getproto*
       Net/       By-name interface to Perl's builtin getserv*
       Time/       By-name interface to Perl's builtin gmtime
       Time/    By-name interface to Perl's builtin localtime
       Time/           Internal object for Time::{gm,local}time
       User/        By-name interface to Perl's builtin getgr*
       User/        By-name interface to Perl's builtin getpw*

       Tie/       Base class for tied hashes with references as keys         Base class for *ALL* classes

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


   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'").

   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

   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.

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

   *   Fixed a handful of bugs.

   *   By public demand, added support for the standard hash function

   *   Made it compatible with Berkeley DB 1.86.

   *   Made negative subscripts work with RECNO interface.

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

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

   *   Updated documentation.

   Refer to the HISTORY section in 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
   Many of the Perl builtins returning lists now have object-oriented
   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

   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 --outfile=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

   "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 "perl_call_sv".

       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

   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

   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

   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 machine.

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

   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 package?

   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 use
       (F) Only hard references are allowed by "strict refs".  Symbolic
       references are disallowed.  See perlref.

   Cannot resolve method `%s' overloading `%s' in package `%s'
       (P) Internal error trying to resolve overloading specified by a
       method name (as opposed to a subroutine reference).

   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

   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

   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

   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  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, 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

   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

       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.

   Out of memory during request for %s
       (F) The malloc() function returned 0, indicating there was
       insufficient remaining memory (or virtual memory) to satisfy the
       request. However, the request was judged large enough (compile-time
       default is 64K), so a possibility to shut down by trapping this
       error is granted.

   panic: frexp
       (P) The library function frexp() failed, making printf("%f")

   Possible attempt to put comments in qw() list
       (W) qw() lists contain items separated by whitespace; as with
       literal strings, comment characters are not ignored, but are
       instead treated as literal data.  (You may have used different
       delimiters than the parentheses shown here; braces are also
       frequently used.)

       You probably wrote something like this:

           @list = qw(
               a # a comment
               b # another comment

       when you should have written this:

           @list = qw(

       If you really want comments, build your list the old-fashioned way,
       with quotes and commas:

           @list = (
               'a',    # a comment
               'b',    # another comment

   Possible attempt to separate words with commas
       (W) qw() lists contain items separated by whitespace; therefore
       commas aren't needed to separate the items. (You may have used
       different delimiters than the parentheses shown here; braces are
       also frequently used.)

       You probably wrote something like this:

           qw! a, b, c !;

       which puts literal commas into some of the list items.  Write it
       without commas if you don't want them to appear in your data:

           qw! a b c !;

   Scalar value @%s{%s} better written as $%s{%s}
       (W) You've used a hash slice (indicated by @) to select a single
       element of a hash.  Generally it's better to ask for a scalar value
       (indicated by $).  The difference is that $foo{&bar} always behaves
       like a scalar, both when assigning to it and when evaluating its
       argument, while @foo{&bar} behaves like a list when you assign to
       it, and provides a list context to its subscript, which can do
       weird things if you're expecting only one subscript.

   Stub found while resolving method `%s' overloading `%s' in %s
       (P) Overloading resolution over @ISA tree may be broken by
       importing stubs.  Stubs should never be implicitly created, but
       explicit calls to "can" may break this.

   Too late for "-T" option
       (X) The #! line (or local equivalent) in a Perl script contains the
       -T option, but Perl was not invoked with -T in its argument list.
       This is an error because, by the time Perl discovers a -T in a
       script, it's too late to properly taint everything from the
       environment.  So Perl gives up.

   untie attempted while %d inner references still exist
       (W) A copy of the object returned from "tie" (or "tied") was still
       valid when "untie" was called.

   Unrecognized character %s
       (F) The Perl parser has no idea what to do with the specified
       character in your Perl script (or eval).  Perhaps you tried to run
       a compressed script, a binary program, or a directory as a Perl

   Unsupported function fork
       (F) Your version of executable does not support forking.

       Note that under some systems, like OS/2, there may be different
       flavors of Perl executables, some of which may support fork, some
       not. Try changing the name you call Perl by to "perl_", "perl__",
       and so on.

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

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

   Value of %s can be "0"; test with defined()
       (W) In a conditional expression, you used <HANDLE>, <*> (glob),
       "each()", or "readdir()" as a boolean value.  Each of these
       constructs can return a value of "0"; that would make the
       conditional expression false, which is probably not what you
       intended.  When using these constructs in conditional expressions,
       test their values with the "defined" operator.

   Variable "%s" may be unavailable
       (W) An inner (nested) anonymous subroutine is inside a named
       subroutine, and outside that is another subroutine; and the
       anonymous (innermost) subroutine is referencing a lexical variable
       defined in the outermost subroutine.  For example:

          sub outermost { my $a; sub middle { sub { $a } } }

       If the anonymous subroutine is called or referenced (directly or
       indirectly) from the outermost subroutine, it will share the
       variable as you would expect.  But if the anonymous subroutine is
       called or referenced when the outermost subroutine is not active,
       it will see the value of the shared variable as it was before and
       during the *first* call to the outermost subroutine, which is
       probably not what you want.

       In these circumstances, it is usually best to make the middle
       subroutine anonymous, using the "sub {}" syntax.  Perl has specific
       support for shared variables in nested anonymous subroutines; a
       named subroutine in between interferes with this feature.

   Variable "%s" will not stay shared
       (W) An inner (nested) named subroutine is referencing a lexical
       variable defined in an outer subroutine.

       When the inner subroutine is called, it will probably see the value
       of the outer subroutine's variable as it was before and during the
       *first* call to the outer subroutine; in this case, after the first
       call to the outer subroutine is complete, the inner and outer
       subroutines will no longer share a common value for the variable.
       In other words, the variable will no longer be shared.

       Furthermore, if the outer subroutine is anonymous and references a
       lexical variable outside itself, then the outer and inner
       subroutines will never share the given variable.

       This problem can usually be solved by making the inner subroutine
       anonymous, using the "sub {}" syntax.  When inner anonymous subs
       that reference variables in outer subroutines are called or
       referenced, they are automatically rebound to the current values of
       such variables.

   Warning: something's wrong
       (W) You passed warn() an empty string (the equivalent of "warn """)
       or you called it with no args and $_ was empty.

   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.  Since it cannot be translated normally,
       it is skipped, and will not appear in %ENV.  This may be a benign
       occurrence, as some software packages might directly modify logical
       name tables and introduce nonstandard names, or it may indicate
       that a logical name table has been corrupted.

   Got an error from DosAllocMem
       (P) An error peculiar to OS/2.  Most probably you're using an
       obsolete version of Perl, and this should not happen anyway.

       (F) An error peculiar to OS/2.  PERLLIB_PREFIX should be of the



           prefix1 prefix2

       with nonempty prefix1 and prefix2.  If "prefix1" is indeed a prefix
       of a builtin library search path, prefix2 is substituted.  The
       error may appear if components are not found, or are too long.  See
       "PERLLIB_PREFIX" in README.os2.

   PERL_SH_DIR too long
       (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find
       the "sh"-shell in.  See "PERL_SH_DIR" in README.os2.

   Process terminated by SIG%s
       (W) This is a standard message issued by OS/2 applications, while
       *nix applications die in silence.  It is considered a feature of
       the OS/2 port.  One can easily disable this by appropriate
       sighandlers, see "Signals" in perlipc.  See also "Process
       terminated by SIGTERM/SIGINT" in README.os2.


   If you find what you think is a bug, you might check the headers of
   recently posted articles in the comp.lang.perl.misc newsgroup.  There
   may also be information at , the Perl Home

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


   The Changes file for exhaustive details on what changed.

   The INSTALL file for how to build Perl.  This file has been
   significantly updated for 5.004, so even veteran users should look
   through it.

   The README file for general stuff.

   The Copying file for copyright information.


   Constructed by Tom Christiansen, grabbing material with permission from
   innumerable contributors, with kibitzing by more than a few Perl

   Last update: Wed May 14 11:14:09 EDT 1997

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