manpagez: man pages & more
man perl5004delta(1)
Home | html | info | man
PERL5004DELTA(1pm)     Perl Programmers Reference Guide     PERL5004DELTA(1pm)


       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( [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

       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

                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:

           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'").

       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:

       o   Fixed a handful of bugs.

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

       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 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.

       Malformed PERLLIB_PREFIX
           (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

perl v5.24.0                      2015-10-14                PERL5004DELTA(1pm)

perl 5.24 - Generated Sun Nov 27 07:04:34 CST 2016
© 2000-2024
Individual documents may contain additional copyright information.