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PERL5004DELTA(1)
NAME
perldelta - what's new for perl5.004
DESCRIPTION
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 Foo.pm in @INC" error
The error "Can't locate Foo.pm in @INC" now lists the contents of @INC for
easier debugging.
Compilation option: Binary compatibility with 5.003
There is a new Configure question that asks if you want to maintain binary
compatibility with Perl 5.003. If you choose binary compatibility, you do
not have to recompile your extensions, but you might have symbol conflicts
if you embed Perl in another application, just as in the 5.003 release. By
default, binary compatibility is preserved at the expense of symbol table
pollution.
$PERL5OPT environment variable
You may now put Perl options in the $PERL5OPT environment variable. Unless
Perl is running with taint checks, it will interpret this variable as if
its contents had appeared on a "#!perl" line at the beginning of your
script, except that hyphens are optional. PERL5OPT may only be used to set
the following switches: -[DIMUdmw].
Limitations on -M, -m, and -T options
The "-M" and "-m" options are no longer allowed on the "#!" line of a
script. If a script needs a module, it should invoke it with the "use"
pragma.
The -T option is also forbidden on the "#!" line of a script, unless it was
present on the Perl command line. Due to the way "#!" works, this usually
means that -T must be in the first argument. Thus:
#!/usr/bin/perl -T -w
will probably work for an executable script invoked as "scriptname", while:
#!/usr/bin/perl -w -T
will probably fail under the same conditions. (Non-Unix systems will
probably not follow this rule.) But "perl scriptname" is guaranteed to
fail, since then there is no chance of -T being found on the command line
before it is found on the "#!" line.
More precise warnings
If you removed the -w option from your Perl 5.003 scripts because it made
Perl too verbose, we recommend that you try putting it back when you
upgrade to Perl 5.004. Each new perl version tends to remove some
undesirable warnings, while adding new warnings that may catch bugs in your
scripts.
Deprecated: Inherited "AUTOLOAD" for non-methods
Before Perl 5.004, "AUTOLOAD" functions were looked up as methods (using
the "@ISA" hierarchy), even when the function to be autoloaded was called
as a plain function (e.g. "Foo::bar()"), not a method (e.g. "Foo->bar()" or
"$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 startup.
Previously deprecated %OVERLOAD is no longer usable
Using %OVERLOAD to define overloading was deprecated in 5.003. Overloading
is now defined using the overload pragma. %OVERLOAD is still used
internally but should not be used by Perl scripts. See the overload manpage
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 { $_[0]++ };
show($a[2]);
change($a{b});
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 program.
No spawning if tainted $CDPATH, $ENV, $BASH_ENV
These environment variables may alter the behavior of spawned programs
(especially shells) in ways that subvert security. So now they are
treated as dangerous, in the manner of $IFS and $PATH.
No spawning if tainted $TERM doesn't look like a terminal 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 the perlapio manpage for more details, and the INSTALL file for
how to use it.
New and changed syntax
$coderef->(PARAMS)
A subroutine reference may now be suffixed with an arrow and a
(possibly empty) parameter list. This syntax denotes a call of the
referenced subroutine, with the given parameters (if any).
This new syntax follows the pattern of "$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 "$table->{FOO}->($bar)".
New and changed builtin constants
__PACKAGE__
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
strings.
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 variable.
$^M By default, running out of memory it is not trappable. However, if
compiled for this, Perl may use the contents of "$^M" as an emergency
pool after die()ing with this message. Suppose that your Perl were
compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc. 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'}")
flock
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 the sprintf entry in the perlfunc manpage for a complete list of
conversion and flags.
keys as an lvalue
As an lvalue, "keys" allows you to increase the number of hash buckets
allocated for the given hash. This can gain you a measure of
efficiency if you know the hash is going to get big. (This is similar
to 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) {
user_agrees();
} elsif ($answer =~ /^n(o)?$/i) {
user_disagrees();
} 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) {
some_function();
}
$i is a lexical variable, and the scope of $i extends to the end of the
loop, but not beyond it.
Note that you still cannot use my() on global punctuation variables
such as $_ and the like.
pack() and unpack()
A new format 'w' represents a BER compressed integer (as defined in
ASN.1). Its format is a sequence of one or more bytes, each of which
provides seven bits of the total value, with the most significant
first. Bit eight of each byte is set, except for the last byte, in
which bit eight is clear.
If 'p' or 'P' are given undef as values, they now generate a NULL
pointer.
Both pack() and unpack() now fail when their templates contain invalid
types. (Invalid types used to be ignored.)
sysseek()
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.
prototype(FUNCTION)
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.)
srand
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 purposes.
Previous to version 5.004, calling "rand" without first calling "srand"
would yield the same sequence of random numbers on most or all
machines. Now, when perl sees that you're calling "rand" and haven't
yet called "srand", it calls "srand" with the default seed. You should
still call "srand" manually if your code might ever be run on a pre-
5.004 system, of course, or if you want a seed other than the default.
$_ as Default
Functions documented in the Camel to default to $_ now in fact do, and
all those that do are so documented in the perlfunc manpage.
"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 the perlop
manpage and the perlre manpage.
"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 ) {
write;
}
format =
my i is @#
$i
.
However, it still fails (without a warning) if the foreach is within a
subroutine:
my $i;
sub foo {
foreach $i ( 1 .. 10 ) {
write;
}
}
foo;
format =
my i is @#
$i
.
New builtin methods
The "UNIVERSAL" package automatically contains the following methods that
are inherited by all other classes:
isa(CLASS)
"isa" returns true if its object is blessed into a subclass of "CLASS"
"isa" is also exportable and can be called as a sub with two arguments.
This allows the ability to check what a reference points to. Example:
use UNIVERSAL qw(isa);
if(isa($ref, 'ARRAY')) {
...
}
can(METHOD)
"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:
A->VERSION(1.2);
NOTE: "can" directly uses Perl's internal code for method lookup, and "isa"
uses a very similar method and caching strategy. This may cause strange
effects if the Perl code dynamically changes @ISA in any package.
You may add other methods to the UNIVERSAL class via Perl or XS code. You
do not need to "use UNIVERSAL" in order to make these methods available to
your program. This is necessary only if you wish to have "isa" available
as a plain subroutine in the current package.
TIEHANDLE now supported
See the perltie manpage 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;
$$r++;
return print join( $, => map {uc} @_), $\;
}
PRINTF this, LIST
This method will be triggered every time the tied handle is printed to
with the "printf()" function. Beyond its self reference it also
expects the format and list that was passed to the printf function.
sub PRINTF {
shift;
my $fmt = shift;
print sprintf($fmt, @_)."\n";
}
READ this LIST
This method will be called when the handle is read from via the "read"
or "sysread" functions.
sub READ {
$r = shift;
my($buf,$len,$offset) = @_;
print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
}
READLINE this
This method will be called when the handle is read from. The method
should return undef when there is no more data.
sub READLINE {
$r = shift;
return "PRINT called $$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().)
-DPERL_EMERGENCY_SBRK
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
"$^M". See the section on "$^M".
-DPACK_MALLOC
Perl memory allocation is by bucket with sizes close to powers of two.
Because of these malloc overhead may be big, especially for data of
size exactly a power of two. If "PACK_MALLOC" is defined, perl uses a
slightly different algorithm for small allocations (up to 64 bytes
long), which makes it possible to have overhead down to 1 byte for
allocations which are powers of two (and appear quite often).
Expected memory savings (with 8-byte alignment in "alignbytes") is
about 20% for typical Perl usage. Expected slowdown due to additional
malloc overhead is in fractions of a percent (hard to measure, because
of the effect of saved memory on speed).
-DTWO_POT_OPTIMIZE
Similarly to "PACK_MALLOC", this macro improves allocations of data
with size close to a power of two; but this works for big allocations
(starting with 16K by default). Such allocations are typical for big
hashes and special-purpose scripts, especially image processing.
On recent systems, the fact that perl requires 2M from system for 1M
allocation will not affect speed of execution, since the tail of such a
chunk is not going to be touched (and thus will not require real
memory). However, it may result in a premature out-of-memory error.
So if you will be manipulating very large blocks with sizes close to
powers of two, it would be wise to define this macro.
Expected saving of memory is 0-100% (100% in applications which require
most memory in such 2**n chunks); expected slowdown is negligible.
Miscellaneous efficiency enhancements
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.
Win32
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 the MakeMaker manpage and the h2xs manpage,
so that many extensions available on the Comprehensive Perl Archive Network
(CPAN) can now be readily built under Windows NT. See http://www.perl.com/
for more information on CPAN and README.win32 in the perl distribution for
more details on how to get started with building this port.
There is also support for building perl under the Cygwin32 environment.
Cygwin32 is a set of GNU tools that make it possible to compile and run
many Unix programs under Windows NT by providing a mostly Unix-like
interface for compilation and execution. See README.cygwin32 in the perl
distribution for more details on this port and how to obtain the Cygwin32
toolkit.
Plan 9
See README.plan9 in the perl distribution.
QNX
See README.qnx in the perl distribution.
AmigaOS
See README.amigaos in the perl distribution.
Pragmata
Six new pragmatic modules exist:
use autouse MODULE => qw(sub1 sub2 sub3)
Defers "require MODULE" until someone calls one of the specified
subroutines (which must be exported by MODULE). This pragma should be
used with caution, and only when necessary.
use blib
use blib 'dir'
Looks for MakeMaker-like 'blib' directory structure starting in dir (or
current directory) and working back up to five levels of parent
directories.
Intended for use on command line with -M option as a way of testing
arbitrary scripts against an uninstalled version of a package.
use constant NAME => VALUE
Provides a convenient interface for creating compile-time constants,
See the Constant Functions entry in the perlsub manpage.
use locale
Tells the compiler to enable (or disable) the use of POSIX locales for
builtin operations.
When "use locale" is in effect, the current LC_CTYPE locale is used for
regular expressions and case mapping; LC_COLLATE for string ordering;
and LC_NUMERIC for numeric formatting in printf and sprintf (but not in
print). LC_NUMERIC is always used in write, since lexical scoping of
formats is problematic at best.
Each "use locale" or "no locale" affects statements to the end of the
enclosing BLOCK or, if not inside a BLOCK, to the end of the current
file. Locales can be switched and queried with
POSIX:\fIs0:setlocale().
See the perllocale manpage for more information.
use ops
Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
use vmsish
Enable VMS-specific language features. Currently, there are three
VMS-specific features available: 'status', which makes "$?" and
"system" return genuine VMS status values instead of emulating POSIX;
'exit', which makes "exit" take a genuine VMS status value instead of
assuming that "exit 1" is an error; and 'time', which makes all times
relative to the local time zone, in the VMS tradition.
Modules
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 libraries.
Module information summary
Brand new modules, arranged by topic rather than strictly alphabetically:
CGI.pm Web server interface ("Common Gateway Interface")
CGI/Apache.pm Support for Apache's Perl module
CGI/Carp.pm Log server errors with helpful context
CGI/Fast.pm Support for FastCGI (persistent server process)
CGI/Push.pm Support for server push
CGI/Switch.pm Simple interface for multiple server types
CPAN Interface to Comprehensive Perl Archive Network
CPAN::FirstTime Utility for creating CPAN configuration file
CPAN::Nox Runs CPAN while avoiding compiled extensions
IO.pm Top-level interface to IO::* classes
IO/File.pm IO::File extension Perl module
IO/Handle.pm IO::Handle extension Perl module
IO/Pipe.pm IO::Pipe extension Perl module
IO/Seekable.pm IO::Seekable extension Perl module
IO/Select.pm IO::Select extension Perl module
IO/Socket.pm IO::Socket extension Perl module
Opcode.pm Disable named opcodes when compiling Perl code
ExtUtils/Embed.pm Utilities for embedding Perl in C programs
ExtUtils/testlib.pm Fixes up @INC to use just-built extension
FindBin.pm Find path of currently executing program
Class/Struct.pm Declare struct-like datatypes as Perl classes
File/stat.pm By-name interface to Perl's builtin stat
Net/hostent.pm By-name interface to Perl's builtin gethost*
Net/netent.pm By-name interface to Perl's builtin getnet*
Net/protoent.pm By-name interface to Perl's builtin getproto*
Net/servent.pm By-name interface to Perl's builtin getserv*
Time/gmtime.pm By-name interface to Perl's builtin gmtime
Time/localtime.pm By-name interface to Perl's builtin localtime
Time/tm.pm Internal object for Time::{gm,local}time
User/grent.pm By-name interface to Perl's builtin getgr*
User/pwent.pm By-name interface to Perl's builtin getpw*
Tie/RefHash.pm Base class for tied hashes with references as keys
UNIVERSAL.pm Base class for *ALL* classes
Fcntl
New constants in the existing Fcntl modules are now supported, provided
that your operating system happens to support them:
F_GETOWN F_SETOWN
O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
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():
LOCK_SH LOCK_EX LOCK_NB LOCK_UN
These constants are defined in all environments (because where there is no
flock() system call, Perl emulates it). However, for historical reasons,
these constants are not exported unless they are explicitly requested with
the ":flock" tag (e.g. "use Fcntl ':flock'").
IO
The IO module provides a simple mechanism to load all the IO modules at one
go. Currently this includes:
IO::Handle
IO::Seekable
IO::File
IO::Pipe
IO::Socket
For more information on any of these modules, please see its respective
documentation.
Math::Complex
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
tan
csc sec cot
asin acos atan
acsc asec acot
sinh cosh tanh
csch sech coth
asinh acosh atanh
acsch asech acoth
cplx cplxe
Math::Trig
This new module provides a simpler interface to parts of Math::Complex for
those who need trigonometric functions only for real numbers.
DB_File
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
exists().
· 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 DB_File.pm for a complete list of changes.
Everything after DB_File 1.01 has been added since 5.003.
Net::Ping
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:
File::stat
Net::hostent
Net::netent
Net::protoent
Net::servent
Time::gmtime
Time::localtime
User::grent
User::pwent
For example, you can now say
use File::stat;
use User::pwent;
$his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
Utility Changes
pod2html
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.
xsubpp
"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).
"perl_eval_pv"
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 the
perlguts manpage, the perlembed manpage and the perlcall manpage for
details and examples.
Extended API for manipulating hashes
Internal handling of hash keys has changed. The old hashtable API is
still fully supported, and will likely remain so. The additions to the
API allow passing keys as "SV*"s, so that "tied" hashes can be given
real scalars as keys rather than plain strings (nontied hashes still
can only use strings as keys). New extensions must use the new hash
access functions and macros if they wish to use "SV*" keys. These
additions also make it feasible to manipulate "HE*"s (hash entries),
which can be more efficient. See the perlguts manpage for details.
Documentation Changes
Many of the base and library pods were updated. These new pods are
included in section 1:
the perldelta manpage
This document.
the perlfaq manpage
Frequently asked questions.
the perllocale manpage
Locale support (internationalization and localization).
the perltoot manpage
Tutorial on Perl OO programming.
the perlapio manpage
Perl internal IO abstraction interface.
the perlmodlib manpage
Perl module library and recommended practice for module creation.
Extracted from the perlmod manpage (which is much smaller as a result).
the perldebug manpage
Although not new, this has been massively updated.
the perlsec manpage
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
$foo{$bar}
$ref->[12]->{"susie"}
or a hash slice, such as
@foo{$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 the grep entry in the perlfunc manpage and the map entry in the
perlfunc manpage 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 the substr entry in the perlfunc manpage.
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 the perlref manpage.
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 the Constant Functions entry in the perlsub manpage for
commentary and workarounds.
Constant subroutine %s undefined
(S) You undefined a subroutine which had previously been eligible for
inlining. See the Constant Functions entry in the perlsub manpage for
commentary and workarounds.
Copy method did not return a reference
(F) The method which overloads "=" is buggy. See the Copy Constructor
entry in the overload manpage.
Died
(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 the sort entry in the perlfunc manpage.
Identifier too long
(F) Perl limits identifiers (names for variables, functions, etc.) to
252 characters for simple names, somewhat more for compound names (like
"$A::B"). You've exceeded Perl's limits. Future versions of Perl are
likely to eliminate these arbitrary limitations.
Illegal character %s (carriage return)
(F) A carriage return character was found in the input. This is an
error, and not a warning, because carriage return characters can break
multi-line strings, including here documents (e.g., "print <<EOF;").
Illegal switch in PERL5OPT: %s
(X) The PERL5OPT environment variable may only be used to set the
following switches: -[DIMUdmw].
Integer overflow in hex number
(S) The literal hex number you have specified is too big for your
architecture. On a 32-bit architecture the largest hex literal is
0xFFFFFFFF.
Integer overflow in octal number
(S) The literal octal number you have specified is too big for your
architecture. On a 32-bit architecture the largest octal literal is
037777777777.
internal error: glob failed
(P) Something went wrong with the external program(s) used for "glob"
and "<*.c>". This may mean that your csh (C shell) is broken. If so,
you should change all of the csh-related variables in config.sh: If
you have tcsh, make the variables refer to it as if it were csh (e.g.
"full_csh='/usr/bin/tcsh'"); otherwise, make them all empty (except
that "d_csh" should be "'undef'") so that Perl will think csh is
missing. In either case, after editing config.sh, run "./Configure -S"
and rebuild Perl.
Invalid conversion in %s: "%s"
(W) Perl does not understand the given format conversion. See the
sprintf entry in the perlfunc manpage.
Invalid type in pack: '%s'
(F) The given character is not a valid pack type. See the pack entry
in the perlfunc manpage.
Invalid type in unpack: '%s'
(F) The given character is not a valid unpack type. See the unpack
entry in the perlfunc manpage.
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 the perlform manpage.
Offset outside string
(F) You tried to do a read/write/send/recv operation with an offset
pointing outside the buffer. This is difficult to imagine. The sole
exception to this is that "sysread()"ing past the buffer will extend
the buffer and zero pad the new area.
Out of memory!
(X|F) The malloc() function returned 0, indicating there was
insufficient remaining memory (or virtual memory) to satisfy the
request.
The request was judged to be small, so the possibility to trap it
depends on the way Perl was compiled. By default it is not trappable.
However, if compiled for this, Perl may use the contents of "$^M" as an
emergency pool after die()ing with this message. In this case the
error is trappable once.
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")
impossible.
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(
a
b
);
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 program.
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 form
prefix1;prefix2
or
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 the
Signals entry in the perlipc manpage. See also "Process terminated by
SIGTERM/SIGINT" in README.os2.
BUGS
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 http://www.perl.com/perl/, the Perl Home Page.
If you believe you have an unreported bug, please run the perlbug program
included with your release. 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 <perlbug@perl.com> to be analysed by the Perl porting
team.
SEE ALSO
The Changes file for exhaustive details on what changed.
The INSTALL file for how to build Perl. 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.
HISTORY
Constructed by Tom Christiansen, grabbing material with permission from
innumerable contributors, with kibitzing by more than a few Perl porters.
Last update: Wed May 14 11:14:09 EDT 1997
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