perl5004delta
PERL5004DELTA(1) Perl Programmers Reference Guide PERL5004DELTA(1)
NAME
perl5004delta - 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
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 { $_[0]++ };
show($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 perlapio 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 "sprintf" in perlfunc for a complete list of conversion and
flags.
keys as an lvalue
As an lvalue, "keys" allows you to increase the number of hash
buckets allocated for the given hash. This can gain you a measure
of efficiency if you know the hash is going to get big. (This is
similar to 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 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 ) {
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 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;
$$r++;
return print join( $, => map {uc} @_), $\;
}
PRINTF this, LIST
This method will be triggered every time the tied handle is printed
to with the "printf()" function. Beyond its self reference it also
expects the format and list that was passed to the printf function.
sub PRINTF {
shift;
my $fmt = shift;
print sprintf($fmt, @_)."\n";
}
READ this LIST
This method will be called when the handle is read from via the
"read" or "sysread" functions.
sub READ {
$r = shift;
my($buf,$len,$offset) = @_;
print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
}
READLINE this
This method will be called when the handle is read from. The method
should return undef when there is no more data.
sub READLINE {
$r = shift;
return "PRINT called $$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 $^M. See "$^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
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 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 "Constant Functions" in perlsub.
use locale
Tells the compiler to enable (or disable) the use of POSIX locales
for builtin operations.
When "use locale" is in effect, the current LC_CTYPE locale is used
for regular expressions and case mapping; LC_COLLATE for string
ordering; and LC_NUMERIC for numeric formatting in printf and
sprintf (but not in print). LC_NUMERIC is always used in write,
since lexical scoping of formats is problematic at best.
Each "use locale" or "no locale" affects statements to the end of
the enclosing BLOCK or, if not inside a BLOCK, to the end of the
current file. Locales can be switched and queried with
POSIX::setlocale().
See perllocale for more information.
use ops
Disable unsafe opcodes, or any named opcodes, when compiling Perl
code.
use vmsish
Enable VMS-specific language features. Currently, there are three
VMS-specific features available: 'status', which makes $? and
"system" return genuine VMS status values instead of emulating
POSIX; 'exit', which makes "exit" take a genuine VMS status value
instead of assuming that "exit 1" is an error; and 'time', which
makes all times relative to the local time zone, in the VMS
tradition.
Modules
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:
o Fixed a handful of bugs.
o By public demand, added support for the standard hash function
exists().
o Made it compatible with Berkeley DB 1.86.
o Made negative subscripts work with RECNO interface.
o Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the
default mode from 0640 to 0666.
o Made DB_File automatically import the open() constants (O_RDWR,
O_CREAT etc.) from Fcntl, if available.
o Updated documentation.
Refer to the HISTORY section in DB_File.pm for a complete list of
changes. Everything after DB_File 1.01 has been added since 5.003.
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 perlguts, perlembed and perlcall for details and
examples.
Extended API for manipulating hashes
Internal handling of hash keys has changed. The old hashtable API
is still fully supported, and will likely remain so. The additions
to the API allow passing keys as "SV*"s, so that "tied" hashes can
be given real scalars as keys rather than plain strings (nontied
hashes still can only use strings as keys). New extensions must
use the new hash access functions and macros if they wish to use
"SV*" keys. These additions also make it feasible to manipulate
"HE*"s (hash entries), which can be more efficient. See perlguts
for details.
Documentation Changes
Many of the base and library pods were updated. These new pods are
included in section 1:
perldelta
This document.
perlfaq
Frequently asked questions.
perllocale
Locale support (internationalization and localization).
perltoot
Tutorial on Perl OO programming.
perlapio
Perl internal IO abstraction interface.
perlmodlib
Perl module library and recommended practice for module creation.
Extracted from perlmod (which is much smaller as a result).
perldebug
Although not new, this has been massively updated.
perlsec
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 "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.
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 "sort" in perlfunc.
Identifier too long
(F) Perl limits identifiers (names for variables, functions, etc.)
to 252 characters for simple names, somewhat more for compound
names (like $A::B). You've exceeded Perl's limits. Future
versions of Perl are likely to eliminate these arbitrary
limitations.
Illegal character %s (carriage return)
(F) A carriage return character was found in the input. This is an
error, and not a warning, because carriage return characters can
break multi-line strings, including here documents (e.g., "print
<<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
"sprintf" in perlfunc.
Invalid type in pack: '%s'
(F) The given character is not a valid pack type. See "pack" in
perlfunc.
Invalid type in unpack: '%s'
(F) The given character is not a valid unpack type. See "unpack"
in perlfunc.
Name "%s::%s" used only once: possible typo
(W) Typographical errors often show up as unique variable names.
If you had a good reason for having a unique name, then just
mention it again somehow to suppress the message (the "use vars"
pragma is provided for just this purpose).
Null picture in formline
(F) The first argument to formline must be a valid format picture
specification. It was found to be empty, which probably means you
supplied it an uninitialized value. See perlform.
Offset outside string
(F) You tried to do a read/write/send/recv operation with an offset
pointing outside the buffer. This is difficult to imagine. The
sole exception to this is that "sysread()"ing past the buffer will
extend the buffer and zero pad the new area.
Out of memory!
(X|F) The malloc() function returned 0, indicating there was
insufficient remaining memory (or virtual memory) to satisfy the
request.
The request was judged to be small, so the possibility to trap it
depends on the way Perl was compiled. By default it is not
trappable. However, if compiled for this, Perl may use the
contents of $^M as an emergency pool after die()ing with this
message. In this case the error is trappable once.
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 "Signals" in perlipc. 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
perl v5.30.0 2023-11-23 PERL5004DELTA(1)
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