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PERL5004DELTA(1)
Contents
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perl5004delta - what's new for perl5.004
This document describes differences between the 5.003
release (as documented in Programming Perl, second edition--the
Camel Book) and this one.
Supported Environments [Toc] [Back] Perl5.004 builds out of the box on Unix, Plan 9, LynxOS,
VMS, OS/2, QNX, AmigaOS, and Windows NT. Perl runs on
Windows 95 as well, but it cannot be built there, for lack
of a reasonable command interpreter.
Most importantly, many bugs were fixed, including several
security problems. See the Changes file in the distribution
for details.
List assignment to %ENV works
"%ENV = ()" and "%ENV = @list" now work as expected
(except on VMS where it generates a fatal error).
Change to "Can't locate Foo.pm in @INC" error
The error "Can't locate Foo.pm in @INC" now lists the contents
of @INC for easier debugging.
Compilation option: Binary compatibility with 5.003
There is a new Configure question that asks if you want to
maintain binary compatibility with Perl 5.003. If you
choose binary compatibility, you do not have to recompile
your extensions, but you might have symbol conflicts if
you embed Perl in another application, just as in the
5.003 release. By default, binary compatibility is preserved
at the expense of symbol table pollution.
$PERL5OPT environment variable
You may now put Perl options in the $PERL5OPT environment
variable. Unless Perl is running with taint checks, it
will interpret this variable as if its contents had
appeared on a "#!perl" line at the beginning of your
script, except that hyphens are optional. PERL5OPT may
only be used to set the following switches: -[DIMUdmw].
Limitations on -M, -m, and -T options
The "-M" and "-m" options are no longer allowed on the
"#!" line of a script. If a script needs a module, it
should invoke it with the "use" pragma.
The -T option is also forbidden on the "#!" line of a
script, unless it was present on the Perl command line.
Due to the way "#!" works, this usually means that -T
must be in the first argument. Thus:
#!/usr/bin/perl -T -w
will probably work for an executable script invoked as
"scriptname", while:
#!/usr/bin/perl -w -T
will probably fail under the same conditions. (Non-Unix
systems will probably not follow this rule.) But "perl
scriptname" is guaranteed to fail, since then there is no
chance of -T being found on the command line before it is
found on the "#!" line.
More precise warnings [Toc] [Back]
If you removed the -w option from your Perl 5.003 scripts
because it made Perl too verbose, we recommend that you
try putting it back when you upgrade to Perl 5.004. Each
new perl version tends to remove some undesirable warnings,
while adding new warnings that may catch bugs in
your scripts.
Deprecated: Inherited "AUTOLOAD" for non-methods
Before Perl 5.004, "AUTOLOAD" functions were looked up as
methods (using the @ISA hierarchy), even when the function
to be autoloaded was called as a plain function (e.g.
"Foo::bar()"), not a method (e.g. "Foo->bar()" or
"$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 [Toc] [Back]
A bug in previous versions may have failed to detect some
insecure conditions when taint checks are turned on.
(Taint checks are used in setuid or setgid scripts, or
when explicitly turned on with the "-T" invocation
option.) Although it's unlikely, this may cause a previously-working
script to now fail -- which should be
construed as a blessing, since that indicates a potentially-serious
security hole was just plugged.
The new restrictions when tainting include:
No glob() or <*>
These operators may spawn the C shell (csh), which
cannot be made safe. This restriction will be lifted
in a future version of Perl when globbing is implemented
without the use of an external program.
No spawning if tainted $CDPATH, $ENV, $BASH_ENV
These environment variables may alter the behavior of
spawned programs (especially shells) in ways that subvert
security. So now they are treated as dangerous,
in the manner of $IFS and $PATH.
No spawning if tainted $TERM doesn't look like a terminal
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 [Toc] [Back]
A new Opcode module supports the creation, manipulation
and application of opcode masks. The revised Safe module
has a new API and is implemented using the new Opcode module.
Please read the new Opcode and Safe documentation.
Embedding improvements [Toc] [Back]
In older versions of Perl it was not possible to create
more than one Perl interpreter instance inside a single
process without leaking like a sieve and/or crashing. The
bugs that caused this behavior have all been fixed. However,
you still must take care when embedding Perl in a C
program. See the updated perlembed manpage for tips on
how to manage your interpreters.
Internal change: FileHandle class based on IO::* classes
File handles are now stored internally as type IO::Handle.
The FileHandle module is still supported for backwards
compatibility, but it is now merely a front end to the
IO::* modules -- specifically, IO::Handle, IO::Seekable,
and IO::File. We suggest, but do not require, that you
use the IO::* modules in new code.
In harmony with this change, *GLOB{FILEHANDLE} is now just
a backward-compatible synonym for *GLOB{IO}.
Internal change: PerlIO abstraction interface
It is now possible to build Perl with AT&T's sfio IO package
instead of stdio. See perlapio for more details, and
the INSTALL file for how to use it.
New and changed syntax [Toc] [Back]
$coderef->(PARAMS)
A subroutine reference may now be suffixed with an
arrow and a (possibly empty) parameter list. This
syntax denotes a call of the referenced subroutine,
with the given parameters (if any).
This new syntax follows the pattern of
"$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 [Toc] [Back]
__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 [Toc] [Back]
$^E Extended error message on some platforms. (Also known
as $EXTENDED_OS_ERROR if you "use English").
$^H The current set of syntax checks enabled by "use
strict". See the documentation of "strict" for more
details. Not actually new, but newly documented.
Because it is intended for internal use by Perl core
components, there is no "use English" long name for
this variable.
$^M By default, running out of memory it is not trappable.
However, if compiled for this, Perl may use the contents
of $^M as an emergency pool after die()ing with
this message. Suppose that your Perl were compiled
with -DPERL_EMERGENCY_SBRK and used Perl's malloc.
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 [Toc] [Back]
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 preextending
an array by assigning a larger number to
$#array.) If you say
keys %hash = 200;
then %hash will have at least 200 buckets allocated
for it. These buckets will be retained even if you do
"%hash = ()"; use "undef %hash" if you want to free
the storage while %hash is still in scope. You can't
shrink the number of buckets allocated for the hash
using "keys" in this way (but you needn't worry about
doing this by accident, as trying has no effect).
my() in Control Structures
You can now use my() (with or without the parentheses)
in the control expressions of control structures such
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 difficultto-predict
system-dependent values, which should be
sufficient for most everyday purposes.
Previous to version 5.004, calling "rand" without
first calling "srand" would yield the same sequence of
random numbers on most or all machines. Now, when
perl sees that you're calling "rand" and haven't yet
called "srand", it calls "srand" with the default
seed. You should still call "srand" manually if your
code might ever be run on a pre-5.004 system, of
course, or if you want a seed other than the default.
$_ as Default
Functions documented in the Camel to default to $_ now
in fact do, and all those that do are so documented in
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/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 @#
$i
.
New builtin methods [Toc] [Back]
The "UNIVERSAL" package automatically contains the following
methods that are inherited by all other classes:
isa(CLASS)
"isa" returns true if its object is blessed into a
subclass of "CLASS"
"isa" is also exportable and can be called as a sub
with two arguments. This allows the ability to check
what a reference points to. Example:
use UNIVERSAL qw(isa);
if(isa($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 [Toc] [Back]
See perltie for other kinds of tie()s.
TIEHANDLE classname, LIST
This is the constructor for the class. That means it
is expected to return an object of some sort. The reference
can be used to hold some internal information.
sub TIEHANDLE {
print "<shout>0;
my $i;
return bless , shift;
}
PRINT this, LIST
This method will be triggered every time the tied handle
is printed to. Beyond its self reference it also
expects the list that was passed to the print function.
sub PRINT {
$r = shift;
$$r++;
return print join( $, => map {uc} @_), $;
}
PRINTF this, LIST
This method will be triggered every time the tied handle
is printed to with the "printf()" function.
Beyond its self reference it also expects the format
and list that was passed to the printf function.
sub PRINTF {
shift;
my $fmt = shift;
print sprintf($fmt, @_)."0;
}
READ this LIST
This method will be called when the handle is read
from via the "read" or "sysread" functions.
sub READ {
$r = shift;
my($buf,$len,$offset) = @_;
print "READ called, uf=$buf, en=$len, ffset=$offset";
}
READLINE this
This method will be called when the handle is read
from. The method should return undef when there is no
more data.
sub READLINE {
$r = shift;
return "PRINT called $$r times0
}
GETC this
This method will be called when the "getc" function is
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>0;
}
Malloc enhancements [Toc] [Back]
If perl is compiled with the malloc included with the perl
distribution (that is, if "perl -V:d_mymalloc" is
'define') then you can print memory statistics at runtime
by running Perl thusly:
env PERL_DEBUG_MSTATS=2 perl your_script_here
The value of 2 means to print statistics after compilation
and on exit; with a value of 1, the statistics are printed
only on exit. (If you want the statistics at an arbitrary
time, you'll need to install the optional module
Devel::Peek.)
Three new compilation flags are recognized by malloc.c.
(They have no effect if perl is compiled with system mal-
loc().)
-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 [Toc] [Back]
Functions that have an empty prototype and that do nothing
but return a fixed value are now inlined (e.g. "sub PI ()
{ 3.14159 }").
Each unique hash key is only allocated once, no matter how
many hashes have an entry with that key. So even if you
have 100 copies of the same hash, the hash keys never have
to be reallocated.
Support for More Operating Systems [Toc] [Back] Support for the following operating systems is new in Perl
5.004.
Win32 [Toc] [Back]
Perl 5.004 now includes support for building a "native"
perl under Windows NT, using the Microsoft Visual C++ compiler
(versions 2.0 and above) or the Borland C++ compiler
(versions 5.02 and above). The resulting perl can be used
under Windows 95 (if it is installed in the same directory
locations as it got installed in Windows NT). This port
includes support for perl extension building tools like
MakeMaker and h2xs, so that many extensions available on
the Comprehensive Perl Archive Network (CPAN) can now be
readily built under Windows NT. See http://www.perl.com/
for more information on CPAN and README.win32 in the perl
distribution for more details on how to get started with
building this port.
There is also support for building perl under the Cygwin32
environment. Cygwin32 is a set of GNU tools that make it
possible to compile and run many Unix programs under Windows
NT by providing a mostly Unix-like interface for compilation
and execution. See README.cygwin32 in the perl
distribution for more details on this port and how to
obtain the Cygwin32 toolkit.
Plan 9 [Toc] [Back]
See README.plan9 in the perl distribution.
QNX [Toc] [Back]
See README.qnx in the perl distribution.
AmigaOS [Toc] [Back]
See README.amigaos in the perl distribution.
Six new pragmatic modules exist:
use autouse MODULE => qw(sub1 sub2 sub3)
Defers "require MODULE" until someone calls one of the
specified subroutines (which must be exported by MODULE).
This pragma should be used with caution, and
only when necessary.
use blib
use blib 'dir'
Looks for MakeMaker-like 'blib' directory structure
starting in dir (or current directory) and working
back up to five levels of parent directories.
Intended for use on command line with -M option as a
way of testing arbitrary scripts against an uninstalled
version of a package.
use constant NAME => VALUE
Provides a convenient interface for creating compiletime
constants, See "Constant Functions" in perlsub.
use locale
Tells the compiler to enable (or disable) the use of
POSIX locales for builtin operations.
When "use locale" is in effect, the current LC_CTYPE
locale is used for regular expressions and case mapping;
LC_COLLATE for string ordering; and LC_NUMERIC
for numeric formatting in printf and sprintf (but not
in print). LC_NUMERIC is always used in write, since
lexical scoping of formats is problematic at best.
Each "use locale" or "no locale" affects statements to
the end of the enclosing BLOCK or, if not inside a
BLOCK, to the end of the current file. Locales can be
switched and queried with POSIX::setlocale().
See perllocale for more information.
use ops
Disable unsafe opcodes, or any named opcodes, when
compiling Perl code.
use vmsish
Enable VMS-specific language features. Currently,
there are three VMS-specific features available: 'status',
which makes $? and "system" return genuine VMS
status values instead of emulating POSIX; 'exit',
which makes "exit" take a genuine VMS status value
instead of assuming that "exit 1" is an error; and
'time', which makes all times relative to the local
time zone, in the VMS tradition.
Required Updates
Though Perl 5.004 is compatible with almost all modules
that work with Perl 5.003, there are a few exceptions:
Module Required Version for Perl 5.004
------ -------------------------------
Filter Filter-1.12
LWP libwww-perl-5.08
Tk Tk400.202 (-w makes noise)
Also, the majordomo mailing list program, version 1.94.1,
doesn't work with Perl 5.004 (nor with perl 4), because it
executes an invalid regular expression. This bug is fixed
in majordomo version 1.94.2.
Installation directories [Toc] [Back]
The installperl script now places the Perl source files
for extensions in the architecture-specific library directory,
which is where the shared libraries for extensions
have always been. This change is intended to allow administrators
to keep the Perl 5.004 library directory
unchanged from a previous version, without running the
risk of binary incompatibility between extensions' Perl
source and shared libraries.
Module information summary [Toc] [Back]
Brand new modules, arranged by topic rather than strictly
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 [Toc] [Back]
New constants in the existing Fcntl modules are now supported,
provided that your operating system happens to
support them:
F_GETOWN F_SETOWN
O_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 [Toc] [Back]
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 [Toc] [Back]
There have been quite a few changes made to DB_File. Here
are a few of the highlights:
o Fixed a handful of bugs.
o By public demand, added support for the standard hash
function exists().
o Made it compatible with Berkeley DB 1.86.
o Made negative subscripts work with RECNO interface.
o Changed the default flags from O_RDWR to
O_CREAT|O_RDWR and the default mode from 0640 to 0666.
o Made DB_File automatically import the open() constants
(O_RDWR, O_CREAT etc.) from Fcntl, if available.
o Updated documentation.
Refer to the HISTORY section in DB_File.pm for a complete
list of changes. Everything after DB_File 1.01 has been
added since 5.003.
Net::Ping
Major rewrite - support added for both udp echo and real
icmp pings.
Object-oriented overrides for builtin operators [Toc] [Back]
Many of the Perl builtins returning lists now have objectoriented
overrides. These are:
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);
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 --out-
file=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 [Toc] [Back] "gv_fetchmethod" and "perl_call_sv"
The "gv_fetchmethod" function finds a method for an
object, just like in Perl 5.003. The GV it returns
may be a method cache entry. However, in Perl 5.004,
method cache entries are not visible to users; therefore,
they can no longer be passed directly to
"perl_call_sv". Instead, you should use the "GvCV"
macro on the GV to extract its CV, and pass the CV to
"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 [Toc] [Back] 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.
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.
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