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NAME
perldelta - what's new for perl5.004
DESCRIPTION
This document describes differences between the 5.003 release
(as documented in *Programming Perl*, second edition--the Camel
Book) and this one.
Supported Environments
Perl5.004 builds out of the box on Unix, Plan 9, LynxOS, VMS,
OS/2, QNX, AmigaOS, and Windows NT. Perl runs on Windows 95 as
well, but it cannot be built there, for lack of a reasonable
command interpreter.
Core Changes
Most importantly, many bugs were fixed, including several
security problems. See the Changes file in the distribution for
details.
List assignment to %ENV works
`%ENV = ()' and `%ENV = @list' now work as expected (except on
VMS where it generates a fatal error).
"Can't locate Foo.pm in @INC" error now lists @INC
Compilation option: Binary compatibility with 5.003
There is a new Configure question that asks if you want to
maintain binary compatibility with Perl 5.003. If you choose
binary compatibility, you do not have to recompile your
extensions, but you might have symbol conflicts if you embed
Perl in another application, just as in the 5.003 release. By
default, binary compatibility is preserved at the expense of
symbol table pollution.
$PERL5OPT environment variable
You may now put Perl options in the $PERL5OPT environment
variable. Unless Perl is running with taint checks, it will
interpret this variable as if its contents had appeared on a
"#!perl" line at the beginning of your script, except that
hyphens are optional. PERL5OPT may only be used to set the
following switches: -[DIMUdmw].
Limitations on -M, -m, and -T options
The `-M' and `-m' options are no longer allowed on the `#!' line
of a script. If a script needs a module, it should invoke it
with the `use' pragma.
The -T option is also forbidden on the `#!' line of a script,
unless it was present on the Perl command line. Due to the way
`#!' works, this usually means that -T must be in the first
argument. Thus:
#!/usr/bin/perl -T -w
will probably work for an executable script invoked as
`scriptname', while:
#!/usr/bin/perl -w -T
will probably fail under the same conditions. (Non-Unix systems
will probably not follow this rule.) But `perl scriptname' is
guaranteed to fail, since then there is no chance of -T being
found on the command line before it is found on the `#!' line.
More precise warnings
If you removed the -w option from your Perl 5.003 scripts
because it made Perl too verbose, we recommend that you try
putting it back when you upgrade to Perl 5.004. Each new perl
version tends to remove some undesirable warnings, while adding
new warnings that may catch bugs in your scripts.
Deprecated: Inherited `AUTOLOAD' for non-methods
Before Perl 5.004, `AUTOLOAD' functions were looked up as
methods (using the `@ISA' hierarchy), even when the function to
be autoloaded was called as a plain function (e.g.
`Foo::bar()'), not a method (e.g. `Foo->bar()' or `$obj-
>bar()').
Perl 5.005 will use method lookup only for methods' `AUTOLOAD's.
However, there is a significant base of existing code that may
be using the old behavior. So, as an interim step, Perl 5.004
issues an optional warning when a non-method uses an inherited
`AUTOLOAD'.
The simple rule is: Inheritance will not work when autoloading
non-methods. The simple fix for old code is: In any module that
used to depend on inheriting `AUTOLOAD' for non-methods from a
base class named `BaseClass', execute `*AUTOLOAD =
\&BaseClass::AUTOLOAD' during startup.
Previously deprecated %OVERLOAD is no longer usable
Using %OVERLOAD to define overloading was deprecated in 5.003.
Overloading is now defined using the overload pragma. %OVERLOAD
is still used internally but should not be used by Perl scripts.
See the overload manpage for more details.
Subroutine arguments created only when they're modified
In Perl 5.004, nonexistent array and hash elements used as
subroutine parameters are brought into existence only if they
are actually assigned to (via `@_').
Earlier versions of Perl vary in their handling of such
arguments. Perl versions 5.002 and 5.003 always brought them
into existence. Perl versions 5.000 and 5.001 brought them into
existence only if they were not the first argument (which was
almost certainly a bug). Earlier versions of Perl never brought
them into existence.
For example, given this code:
undef @a; undef %a;
sub show { print $_[0] };
sub change { $_[0]++ };
show($a[2]);
change($a{b});
After this code executes in Perl 5.004, $a{b} exists but $a[2]
does not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would
have existed (but $a[2]'s value would have been undefined).
Group vector changeable with `$)'
The `$)' special variable has always (well, in Perl 5, at least)
reflected not only the current effective group, but also the
group list as returned by the `getgroups()' C function (if there
is one). However, until this release, there has not been a way
to call the `setgroups()' C function from Perl.
In Perl 5.004, assigning to `$)' is exactly symmetrical with
examining it: The first number in its string value is used as
the effective gid; if there are any numbers after the first one,
they are passed to the `setgroups()' C function (if there is
one).
Fixed parsing of $$<digit>, &$<digit>, etc.
Perl versions before 5.004 misinterpreted any type marker
followed by "$" and a digit. For example, "$$0" was incorrectly
taken to mean "${$}0" instead of "${$0}". This bug is (mostly)
fixed in Perl 5.004.
However, the developers of Perl 5.004 could not fix this bug
completely, because at least two widely-used modules depend on
the old meaning of "$$0" in a string. So Perl 5.004 still
interprets "$$<digit>" in the old (broken) way inside strings;
but it generates this message as a warning. And in Perl 5.005,
this special treatment will cease.
Fixed localization of $<digit>, $&, etc.
Perl versions before 5.004 did not always properly localize the
regex-related special variables. Perl 5.004 does localize them,
as the documentation has always said it should. This may result
in $1, $2, etc. no longer being set where existing programs use
them.
No resetting of $. on implicit close
The documentation for Perl 5.0 has always stated that `$.' is
*not* reset when an already-open file handle is reopened with no
intervening call to `close'. Due to a bug, perl versions 5.000
through 5.003 *did* reset `$.' under that circumstance; Perl
5.004 does not.
`wantarray' may return undef
The `wantarray' operator returns true if a subroutine is
expected to return a list, and false otherwise. In Perl 5.004,
`wantarray' can also return the undefined value if a
subroutine's return value will not be used at all, which allows
subroutines to avoid a time-consuming calculation of a return
value if it isn't going to be used.
Changes to tainting checks
A bug in previous versions may have failed to detect some
insecure conditions when taint checks are turned on. (Taint
checks are used in setuid or setgid scripts, or when explicitly
turned on with the `-T' invocation option.) Although it's
unlikely, this may cause a previously-working script to now fail
-- which should be construed as a blessing, since that indicates
a potentially-serious security hole was just plugged.
The new restrictions when tainting include:
No glob() or <*>
These operators may spawn the C shell (csh), which cannot be
made safe. This restriction will be lifted in a future
version of Perl when globbing is implemented without the use
of an external program.
No spawning if tainted $CDPATH, $ENV, $BASH_ENV
These environment variables may alter the behavior of
spawned programs (especially shells) in ways that subvert
security. So now they are treated as dangerous, in the
manner of $IFS and $PATH.
No spawning if tainted $TERM doesn't look like a terminal name
Some termcap libraries do unsafe things with $TERM. However,
it would be unnecessarily harsh to treat all $TERM values as
unsafe, since only shell metacharacters can cause trouble in
$TERM. So a tainted $TERM is considered to be safe if it
contains only alphanumerics, underscores, dashes, and
colons, and unsafe if it contains other characters
(including whitespace).
New Opcode module and revised Safe module
A new Opcode module supports the creation, manipulation and
application of opcode masks. The revised Safe module has a new
API and is implemented using the new Opcode module. Please read
the new Opcode and Safe documentation.
Embedding improvements
In older versions of Perl it was not possible to create more
than one Perl interpreter instance inside a single process
without leaking like a sieve and/or crashing. The bugs that
caused this behavior have all been fixed. However, you still
must take care when embedding Perl in a C program. See the
updated perlembed manpage for tips on how to manage your
interpreters.
Internal change: FileHandle class based on IO::* classes
File handles are now stored internally as type IO::Handle. The
FileHandle module is still supported for backwards
compatibility, but it is now merely a front end to the IO::*
modules -- specifically, IO::Handle, IO::Seekable, and IO::File.
We suggest, but do not require, that you use the IO::* modules
in new code.
In harmony with this change, `*GLOB{FILEHANDLE}' is now just a
backward-compatible synonym for `*GLOB{IO}'.
Internal change: PerlIO abstraction interface
It is now possible to build Perl with AT&T's sfio IO package
instead of stdio. See the perlapio manpage for more details, and
the INSTALL file for how to use it.
New and changed syntax
$coderef->(PARAMS)
A subroutine reference may now be suffixed with an arrow and
a (possibly empty) parameter list. This syntax denotes a
call of the referenced subroutine, with the given parameters
(if any).
This new syntax follows the pattern of `$hashref->{FOO}' and
`$aryref->[$foo]': You may now write `&$subref($foo)' as
`$subref->($foo)'. All of these arrow terms may be chained;
thus, `&{$table->{FOO}}($bar)' may now be written `$table-
>{FOO}->($bar)'.
New and changed builtin constants
__PACKAGE__
The current package name at compile time, or the undefined
value if there is no current package (due to a `package;'
directive). Like `__FILE__' and `__LINE__', `__PACKAGE__'
does *not* interpolate into strings.
New and changed builtin variables
$^E Extended error message on some platforms. (Also known as
$EXTENDED_OS_ERROR if you `use English').
$^H The current set of syntax checks enabled by `use strict'. See
the documentation of `strict' for more details. Not actually
new, but newly documented. Because it is intended for
internal use by Perl core components, there is no `use
English' long name for this variable.
$^M By default, running out of memory it is not trappable. However,
if compiled for this, Perl may use the contents of `$^M' as
an emergency pool after die()ing with this message. Suppose
that your Perl were compiled with -DPERL_EMERGENCY_SBRK and
used Perl's malloc. Then
$^M = 'a' x (1<<16);
would allocate a 64K buffer for use when in emergency. See
the INSTALL file for information on how to enable this
option. As a disincentive to casual use of this advanced
feature, there is no `use English' long name for this
variable.
New and changed builtin functions
delete on slices
This now works. (e.g. `delete @ENV{'PATH', 'MANPATH'}')
flock
is now supported on more platforms, prefers fcntl to lockf
when emulating, and always flushes before (un)locking.
printf and sprintf
Perl now implements these functions itself; it doesn't use
the C library function sprintf() any more, except for
floating-point numbers, and even then only known flags are
allowed. As a result, it is now possible to know which
conversions and flags will work, and what they will do.
The new conversions in Perl's sprintf() are:
%i a synonym for %d
%p a pointer (the address of the Perl value, in hexadecimal)
%n special: *stores* the number of characters output so far
into the next variable in the parameter list
The new flags that go between the `%' and the conversion
are:
# prefix octal with "0", hex with "0x"
h interpret integer as C type "short" or "unsigned short"
V interpret integer as Perl's standard integer type
Also, where a number would appear in the flags, an asterisk
("*") may be used instead, in which case Perl uses the next
item in the parameter list as the given number (that is, as
the field width or precision). If a field width obtained
through "*" is negative, it has the same effect as the '-'
flag: left-justification.
See the "sprintf" entry in the perlfunc manpage for a
complete list of conversion and flags.
keys as an lvalue
As an lvalue, `keys' allows you to increase the number of
hash buckets allocated for the given hash. This can gain you
a measure of efficiency if you know the hash is going to get
big. (This is similar to pre-extending an array by assigning
a larger number to $#array.) If you say
keys %hash = 200;
then `%hash' will have at least 200 buckets allocated for
it. These buckets will be retained even if you do `%hash =
()'; use `undef %hash' if you want to free the storage while
`%hash' is still in scope. You can't shrink the number of
buckets allocated for the hash using `keys' in this way (but
you needn't worry about doing this by accident, as trying
has no effect).
my() in Control Structures
You can now use my() (with or without the parentheses) in
the control expressions of control structures such as:
while (defined(my $line = <>)) {
$line = lc $line;
} continue {
print $line;
}
if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
user_agrees();
} elsif ($answer =~ /^n(o)?$/i) {
user_disagrees();
} else {
chomp $answer;
die "`$answer' is neither `yes' nor `no'";
}
Also, you can declare a foreach loop control variable as
lexical by preceding it with the word "my". For example, in:
foreach my $i (1, 2, 3) {
some_function();
}
$i is a lexical variable, and the scope of $i extends to the
end of the loop, but not beyond it.
Note that you still cannot use my() on global punctuation
variables such as $_ and the like.
pack() and unpack()
A new format 'w' represents a BER compressed integer (as
defined in ASN.1). Its format is a sequence of one or more
bytes, each of which provides seven bits of the total value,
with the most significant first. Bit eight of each byte is
set, except for the last byte, in which bit eight is clear.
If 'p' or 'P' are given undef as values, they now generate a
NULL pointer.
Both pack() and unpack() now fail when their templates
contain invalid types. (Invalid types used to be ignored.)
sysseek()
The new sysseek() operator is a variant of seek() that sets
and gets the file's system read/write position, using the
lseek(2) system call. It is the only reliable way to seek
before using sysread() or syswrite(). Its return value is
the new position, or the undefined value on failure.
use VERSION
If the first argument to `use' is a number, it is treated as
a version number instead of a module name. If the version of
the Perl interpreter is less than VERSION, then an error
message is printed and Perl exits immediately. Because `use'
occurs at compile time, this check happens immediately
during the compilation process, unlike `require VERSION',
which waits until runtime for the check. This is often
useful if you need to check the current Perl version before
`use'ing library modules which have changed in incompatible
ways from older versions of Perl. (We try not to do this
more than we have to.)
use Module VERSION LIST
If the VERSION argument is present between Module and LIST,
then the `use' will call the VERSION method in class Module
with the given version as an argument. The default VERSION
method, inherited from the UNIVERSAL class, croaks if the
given version is larger than the value of the variable
$Module::VERSION. (Note that there is not a comma after
VERSION!)
This version-checking mechanism is similar to the one
currently used in the Exporter module, but it is faster and
can be used with modules that don't use the Exporter. It is
the recommended method for new code.
prototype(FUNCTION)
Returns the prototype of a function as a string (or `undef'
if the function has no prototype). FUNCTION is a reference
to or the name of the function whose prototype you want to
retrieve. (Not actually new; just never documented before.)
srand
The default seed for `srand', which used to be `time', has
been changed. Now it's a heady mix of difficult-to-predict
system-dependent values, which should be sufficient for most
everyday purposes.
Previous to version 5.004, calling `rand' without first
calling `srand' would yield the same sequence of random
numbers on most or all machines. Now, when perl sees that
you're calling `rand' and haven't yet called `srand', it
calls `srand' with the default seed. You should still call
`srand' manually if your code might ever be run on a pre-
5.004 system, of course, or if you want a seed other than
the default.
$_ as Default
Functions documented in the Camel to default to $_ now in
fact do, and all those that do are so documented in the
perlfunc manpage.
`m//gc' does not reset search position on failure
The `m//g' match iteration construct has always reset its
target string's search position (which is visible through
the `pos' operator) when a match fails; as a result, the
next `m//g' match after a failure starts again at the
beginning of the string. With Perl 5.004, this reset may be
disabled by adding the "c" (for "continue") modifier, i.e.
`m//gc'. This feature, in conjunction with the `\G' zero-
width assertion, makes it possible to chain matches
together. See the perlop manpage and the perlre manpage.
`m//x' ignores whitespace before ?*+{}
The `m//x' construct has always been intended to ignore all
unescaped whitespace. However, before Perl 5.004, whitespace
had the effect of escaping repeat modifiers like "*" or "?";
for example, `/a *b/x' was (mis)interpreted as `/a\*b/x'.
This bug has been fixed in 5.004.
nested `sub{}' closures work now
Prior to the 5.004 release, nested anonymous functions
didn't work right. They do now.
formats work right on changing lexicals
Just like anonymous functions that contain lexical variables
that change (like a lexical index variable for a `foreach'
loop), formats now work properly. For example, this silently
failed before (printed only zeros), but is fine now:
my $i;
foreach $i ( 1 .. 10 ) {
write;
}
format =
my i is @#
$i
.
However, it still fails (without a warning) if the foreach
is within a subroutine:
my $i;
sub foo {
foreach $i ( 1 .. 10 ) {
write;
}
}
foo;
format =
my i is @#
$i
.
New builtin methods
The `UNIVERSAL' package automatically contains the following
methods that are inherited by all other classes:
isa(CLASS)
`isa' returns *true* if its object is blessed into a
subclass of `CLASS'
`isa' is also exportable and can be called as a sub with two
arguments. This allows the ability to check what a reference
points to. Example:
use UNIVERSAL qw(isa);
if(isa($ref, 'ARRAY')) {
...
}
can(METHOD)
`can' checks to see if its object has a method called
`METHOD', if it does then a reference to the sub is
returned; if it does not then *undef* is returned.
VERSION( [NEED] )
`VERSION' returns the version number of the class (package).
If the NEED argument is given then it will check that the
current version (as defined by the $VERSION variable in the
given package) not less than NEED; it will die if this is
not the case. This method is normally called as a class
method. This method is called automatically by the `VERSION'
form of `use'.
use A 1.2 qw(some imported subs);
# implies:
A->VERSION(1.2);
NOTE: `can' directly uses Perl's internal code for method
lookup, and `isa' uses a very similar method and caching
strategy. This may cause strange effects if the Perl code
dynamically changes @ISA in any package.
You may add other methods to the UNIVERSAL class via Perl or XS
code. You do not need to `use UNIVERSAL' in order to make these
methods available to your program. This is necessary only if you
wish to have `isa' available as a plain subroutine in the
current package.
TIEHANDLE now supported
See the perltie manpage for other kinds of tie()s.
TIEHANDLE classname, LIST
This is the constructor for the class. That means it is
expected to return an object of some sort. The reference can
be used to hold some internal information.
sub TIEHANDLE {
print "<shout>\n";
my $i;
return bless \$i, shift;
}
PRINT this, LIST
This method will be triggered every time the tied handle is
printed to. Beyond its self reference it also expects the
list that was passed to the print function.
sub PRINT {
$r = shift;
$$r++;
return print join( $, => map {uc} @_), $\;
}
PRINTF this, LIST
This method will be triggered every time the tied handle is
printed to with the `printf()' function. Beyond its self
reference it also expects the format and list that was
passed to the printf function.
sub PRINTF {
shift;
my $fmt = shift;
print sprintf($fmt, @_)."\n";
}
READ this LIST
This method will be called when the handle is read from via
the `read' or `sysread' functions.
sub READ {
$r = shift;
my($buf,$len,$offset) = @_;
print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
}
READLINE this
This method will be called when the handle is read from. The
method should return undef when there is no more data.
sub READLINE {
$r = shift;
return "PRINT called $$r times\n"
}
GETC this
This method will be called when the `getc' function is
called.
sub GETC { print "Don't GETC, Get Perl"; return "a"; }
DESTROY this
As with the other types of ties, this method will be called
when the tied handle is about to be destroyed. This is
useful for debugging and possibly for cleaning up.
sub DESTROY {
print "</shout>\n";
}
Malloc enhancements
If perl is compiled with the malloc included with the perl
distribution (that is, if `perl -V:d_mymalloc' is 'define') then
you can print memory statistics at runtime by running Perl
thusly:
env PERL_DEBUG_MSTATS=2 perl your_script_here
The value of 2 means to print statistics after compilation and
on exit; with a value of 1, the statistics are printed only on
exit. (If you want the statistics at an arbitrary time, you'll
need to install the optional module Devel::Peek.)
Three new compilation flags are recognized by malloc.c. (They
have no effect if perl is compiled with system malloc().)
-DPERL_EMERGENCY_SBRK
If this macro is defined, running out of memory need not be
a fatal error: a memory pool can allocated by assigning to
the special variable `$^M'. See the section on "$^M".
-DPACK_MALLOC
Perl memory allocation is by bucket with sizes close to
powers of two. Because of these malloc overhead may be big,
especially for data of size exactly a power of two. If
`PACK_MALLOC' is defined, perl uses a slightly different
algorithm for small allocations (up to 64 bytes long), which
makes it possible to have overhead down to 1 byte for
allocations which are powers of two (and appear quite
often).
Expected memory savings (with 8-byte alignment in
`alignbytes') is about 20% for typical Perl usage. Expected
slowdown due to additional malloc overhead is in fractions
of a percent (hard to measure, because of the effect of
saved memory on speed).
-DTWO_POT_OPTIMIZE
Similarly to `PACK_MALLOC', this macro improves allocations
of data with size close to a power of two; but this works
for big allocations (starting with 16K by default). Such
allocations are typical for big hashes and special-purpose
scripts, especially image processing.
On recent systems, the fact that perl requires 2M from
system for 1M allocation will not affect speed of execution,
since the tail of such a chunk is not going to be touched
(and thus will not require real memory). However, it may
result in a premature out-of-memory error. So if you will be
manipulating very large blocks with sizes close to powers of
two, it would be wise to define this macro.
Expected saving of memory is 0-100% (100% in applications
which require most memory in such 2**n chunks); expected
slowdown is negligible.
Miscellaneous efficiency enhancements
Functions that have an empty prototype and that do nothing but
return a fixed value are now inlined (e.g. `sub PI () { 3.14159
}').
Each unique hash key is only allocated once, no matter how many
hashes have an entry with that key. So even if you have 100
copies of the same hash, the hash keys never have to be
reallocated.
Support for More Operating Systems
Support for the following operating systems is new in Perl
5.004.
Win32
Perl 5.004 now includes support for building a "native" perl
under Windows NT, using the Microsoft Visual C++ compiler
(versions 2.0 and above) or the Borland C++ compiler (versions
5.02 and above). The resulting perl can be used under Windows 95
(if it is installed in the same directory locations as it got
installed in Windows NT). This port includes support for perl
extension building tools like the MakeMaker manpage and the h2xs
manpage, so that many extensions available on the Comprehensive
Perl Archive Network (CPAN) can now be readily built under
Windows NT. See http://www.perl.com/ for more information on
CPAN, and the README.win32 manpage 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 the README.cygwin32 manpage for more details on
this port, and how to obtain the Cygwin32 toolkit.
Plan 9
See the README.plan9 manpage.
QNX
See the README.qnx manpage.
AmigaOS
See the README.amigaos manpage.
Pragmata
Six new pragmatic modules exist:
use autouse MODULE => qw(sub1 sub2 sub3)
Defers `require MODULE' until someone calls one of the
specified subroutines (which must be exported by MODULE).
This pragma should be used with caution, and only when
necessary.
use blib
use blib 'dir'
Looks for MakeMaker-like *'blib'* directory structure
starting in *dir* (or current directory) and working back up
to five levels of parent directories.
Intended for use on command line with -M option as a way of
testing arbitrary scripts against an uninstalled version of
a package.
use constant NAME => VALUE
Provides a convenient interface for creating compile-time
constants, See the section on "Constant Functions" in the
perlsub manpage.
use locale
Tells the compiler to enable (or disable) the use of POSIX
locales for builtin operations.
When `use locale' is in effect, the current LC_CTYPE locale
is used for regular expressions and case mapping; LC_COLLATE
for string ordering; and LC_NUMERIC for numeric formating 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 the perllocale manpage for more information.
use ops
Disable unsafe opcodes, or any named opcodes, when compiling
Perl code.
use vmsish
Enable VMS-specific language features. Currently, there are
three VMS-specific features available: 'status', which makes
`$?' and `system' return genuine VMS status values instead
of emulating POSIX; 'exit', which makes `exit' take a
genuine VMS status value instead of assuming that `exit 1'
is an error; and 'time', which makes all times relative to
the local time zone, in the VMS tradition.
Modules
Required Updates
Though Perl 5.004 is compatible with almost all modules that
work with Perl 5.003, there are a few exceptions:
Module Required Version for Perl 5.004
------ -------------------------------
Filter Filter-1.12
LWP libwww-perl-5.08
Tk Tk400.202 (-w makes noise)
Also, the majordomo mailing list program, version 1.94.1,
doesn't work with Perl 5.004 (nor with perl 4), because it
executes an invalid regular expression. This bug is fixed in
majordomo version 1.94.2.
Installation directories
The *installperl* script now places the Perl source files for
extensions in the architecture-specific library directory, which
is where the shared libraries for extensions have always been.
This change is intended to allow administrators to keep the Perl
5.004 library directory unchanged from a previous version,
without running the risk of binary incompatibility between
extensions' Perl source and shared libraries.
Module information summary
Brand new modules, arranged by topic rather than strictly
alphabetically:
CGI.pm Web server interface ("Common Gateway Interface")
CGI/Apache.pm Support for Apache's Perl module
CGI/Carp.pm Log server errors with helpful context
CGI/Fast.pm Support for FastCGI (persistent server process)
CGI/Push.pm Support for server push
CGI/Switch.pm Simple interface for multiple server types
CPAN Interface to Comprehensive Perl Archive Network
CPAN::FirstTime Utility for creating CPAN configuration file
CPAN::Nox Runs CPAN while avoiding compiled extensions
IO.pm Top-level interface to IO::* classes
IO/File.pm IO::File extension Perl module
IO/Handle.pm IO::Handle extension Perl module
IO/Pipe.pm IO::Pipe extension Perl module
IO/Seekable.pm IO::Seekable extension Perl module
IO/Select.pm IO::Select extension Perl module
IO/Socket.pm IO::Socket extension Perl module
Opcode.pm Disable named opcodes when compiling Perl code
ExtUtils/Embed.pm Utilities for embedding Perl in C programs
ExtUtils/testlib.pm Fixes up @INC to use just-built extension
FindBin.pm Find path of currently executing program
Class/Struct.pm Declare struct-like datatypes as Perl classes
File/stat.pm By-name interface to Perl's builtin stat
Net/hostent.pm By-name interface to Perl's builtin gethost*
Net/netent.pm By-name interface to Perl's builtin getnet*
Net/protoent.pm By-name interface to Perl's builtin getproto*
Net/servent.pm By-name interface to Perl's builtin getserv*
Time/gmtime.pm By-name interface to Perl's builtin gmtime
Time/localtime.pm By-name interface to Perl's builtin localtime
Time/tm.pm Internal object for Time::{gm,local}time
User/grent.pm By-name interface to Perl's builtin getgr*
User/pwent.pm By-name interface to Perl's builtin getpw*
Tie/RefHash.pm Base class for tied hashes with references as keys
UNIVERSAL.pm Base class for *ALL* classes
Fcntl
New constants in the existing Fcntl modules are now supported,
provided that your operating system happens to support them:
F_GETOWN F_SETOWN
O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
O_EXLOCK O_SHLOCK
These constants are intended for use with the Perl operators
sysopen() and fcntl() and the basic database modules like
SDBM_File. For the exact meaning of these and other Fcntl
constants please refer to your operating system's documentation
for fcntl() and open().
In addition, the Fcntl module now provides these constants for
use with the Perl operator flock():
LOCK_SH LOCK_EX LOCK_NB LOCK_UN
These constants are defined in all environments (because where
there is no flock() system call, Perl emulates it). However, for
historical reasons, these constants are not exported unless they
are explicitly requested with the ":flock" tag (e.g. `use Fcntl
':flock'').
IO
The IO module provides a simple mechanism to load all of the IO
modules at one go. Currently this includes:
IO::Handle
IO::Seekable
IO::File
IO::Pipe
IO::Socket
For more information on any of these modules, please see its
respective documentation.
Math::Complex
The Math::Complex module has been totally rewritten, and now
supports more operations. These are overloaded:
+ - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
And these functions are now exported:
pi i Re Im arg
log10 logn ln cbrt root
tan
csc sec cot
asin acos atan
acsc asec acot
sinh cosh tanh
csch sech coth
asinh acosh atanh
acsch asech acoth
cplx cplxe
Math::Trig
This new module provides a simpler interface to parts of
Math::Complex for those who need trigonometric functions only
for real numbers.
DB_File
There have been quite a few changes made to DB_File. Here are a
few of the highlights:
* Fixed a handful of bugs.
* By public demand, added support for the standard hash function
exists().
* Made it compatible with Berkeley DB 1.86.
* Made negative subscripts work with RECNO interface.
* Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the
default mode from 0640 to 0666.
* Made DB_File automatically import the open() constants (O_RDWR,
O_CREAT etc.) from Fcntl, if available.
* Updated documentation.
Refer to the HISTORY section in DB_File.pm for a complete list
of changes. Everything after DB_File 1.01 has been added since
5.003.
Net::Ping
Major rewrite - support added for both udp echo and real icmp
pings.
Object-oriented overrides for builtin operators
Many of the Perl builtins returning lists now have object-
oriented overrides. These are:
File::stat
Net::hostent
Net::netent
Net::protoent
Net::servent
Time::gmtime
Time::localtime
User::grent
User::pwent
For example, you can now say
use File::stat;
use User::pwent;
$his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
Utility Changes
pod2html
Sends converted HTML to standard output
The *pod2html* utility included with Perl 5.004 is entirely
new. By default, it sends the converted HTML to its standard
output, instead of writing it to a file like Perl 5.003's
*pod2html* did. Use the --outfile=FILENAME option to write
to a file.
xsubpp
`void' XSUBs now default to returning nothing
Due to a documentation/implementation bug in previous
versions of Perl, XSUBs with a return type of `void' have
actually been returning one value. Usually that value was
the GV for the XSUB, but sometimes it was some already freed
or reused value, which would sometimes lead to program
failure.
In Perl 5.004, if an XSUB is declared as returning `void',
it actually returns no value, i.e. an empty list (though
there is a backward-compatibility exception; see below). If
your XSUB really does return an SV, you should give it a
return type of `SV *'.
For backward compatibility, *xsubpp* tries to guess whether
a `void' XSUB is really `void' or if it wants to return an
`SV *'. It does so by examining the text of the XSUB: if
*xsubpp* finds what looks like an assignment to `ST(0)', it
assumes that the XSUB's return type is really `SV *'.
C Language API Changes
`gv_fetchmethod' and `perl_call_sv'
The `gv_fetchmethod' function finds a method for an object,
just like in Perl 5.003. The GV it returns may be a method
cache entry. However, in Perl 5.004, method cache entries
are not visible to users; therefore, they can no longer be
passed directly to `perl_call_sv'. Instead, you should use
the `GvCV' macro on the GV to extract its CV, and pass the
CV to `perl_call_sv'.
The most likely symptom of passing the result of
`gv_fetchmethod' to `perl_call_sv' is Perl's producing an
"Undefined subroutine called" error on the *second* call to
a given method (since there is no cache on the first call).
`perl_eval_pv'
A new function handy for eval'ing strings of Perl code
inside C code. This function returns the value from the eval
statement, which can be used instead of fetching globals
from the symbol table. See the perlguts manpage, the
perlembed manpage and the perlcall manpage for details and
examples.
Extended API for manipulating hashes
Internal handling of hash keys has changed. The old
hashtable API is still fully supported, and will likely
remain so. The additions to the API allow passing keys as
`SV*'s, so that `tied' hashes can be given real scalars as
keys rather than plain strings (nontied hashes still can
only use strings as keys). New extensions must use the new
hash access functions and macros if they wish to use `SV*'
keys. These additions also make it feasible to manipulate
`HE*'s (hash entries), which can be more efficient. See the
perlguts manpage for details.
Documentation Changes
Many of the base and library pods were updated. These new pods
are included in section 1:
the perldelta manpage
This document.
the perlfaq manpage
Frequently asked questions.
the perllocale manpage
Locale support (internationalization and localization).
the perltoot manpage
Tutorial on Perl OO programming.
the perlapio manpage
Perl internal IO abstraction interface.
the perlmodlib manpage
Perl module library and recommended practice for module
creation. Extracted from the perlmod manpage (which is much
smaller as a result).
the perldebug manpage
Although not new, this has been massively updated.
the perlsec manpage
Although not new, this has been massively updated.
New Diagnostics
Several new conditions will trigger warnings that were silent
before. Some only affect certain platforms. The following new
warnings and errors outline these. These messages are classified
as follows (listed in increasing order of desperation):
(W) A warning (optional).
(D) A deprecation (optional).
(S) A severe warning (mandatory).
(F) A fatal error (trappable).
(P) An internal error you should never see (trappable).
(X) A very fatal error (nontrappable).
(A) An alien error message (not generated by Perl).
"my" variable %s masks earlier declaration in same scope
(W) A lexical variable has been redeclared in the same
scope, effectively eliminating all access to the previous
instance. This is almost always a typographical error. Note
that the earlier variable will still exist until the end of
the scope or until all closure referents to it are
destroyed.
%s argument is not a HASH element or slice
(F) The argument to delete() must be either a hash element,
such as
$foo{$bar}
$ref->[12]->{"susie"}
or a hash slice, such as
@foo{$bar, $baz, $xyzzy}
@{$ref->[12]}{"susie", "queue"}
Allocation too large: %lx
(X) You can't allocate more than 64K on an MS-DOS machine.
Allocation too large
(F) You can't allocate more than 2^31+"small amount" bytes.
Applying %s to %s will act on scalar(%s)
(W) The pattern match (//), substitution (s///), and
translation (tr///) operators work on scalar values. If you
apply one of them to an array or a hash, it will convert the
array or hash to a scalar value -- the length of an array,
or the population info of a hash -- and then work on that
scalar value. This is probably not what you meant to do. See
the "grep" entry in the perlfunc manpage and the "map" entry
in the perlfunc manpage for alternatives.
Attempt to free nonexistent shared string
(P) Perl maintains a reference counted internal table of
strings to optimize the storage and access of hash keys and
other strings. This indicates someone tried to decrement the
reference count of a string that can no longer be found in
the table.
Attempt to use reference as lvalue in substr
(W) You supplied a reference as the first argument to
substr() used as an lvalue, which is pretty strange. Perhaps
you forgot to dereference it first. See the "substr" entry
in the perlfunc manpage.
Can't redefine active sort subroutine %s
(F) Perl optimizes the internal handling of sort subroutines
and keeps pointers into them. You tried to redefine one such
sort subroutine when it was currently active, which is not
allowed. If you really want to do this, you should write
`sort { &func } @x' instead of `sort func @x'.
Can't use bareword ("%s") as %s ref while "strict refs" in use
(F) Only hard references are allowed by "strict refs".
Symbolic references are disallowed. See the perlref manpage.
Cannot resolve method `%s' overloading `%s' in package `%s'
(P) Internal error trying to resolve overloading specified
by a method name (as opposed to a subroutine reference).
Constant subroutine %s redefined
(S) You redefined a subroutine which had previously been
eligible for inlining. See the section on "Constant
Functions" in the perlsub manpage for commentary and
workarounds.
Constant subroutine %s undefined
(S) You undefined a subroutine which had previously been
eligible for inlining. See the section on "Constant
Functions" in the perlsub manpage for commentary and
workarounds.
Copy method did not return a reference
(F) The method which overloads "=" is buggy. See the section
on "Copy Constructor" in the overload manpage.
Died
(F) You passed die() an empty string (the equivalent of `die
""') or you called it with no args and both `$@' and `$_'
were empty.
Exiting pseudo-block via %s
(W) You are exiting a rather special block construct (like a
sort block or subroutine) by unconventional means, such as a
goto, or a loop control statement. See the "sort" entry in
the perlfunc manpage.
Identifier too long
(F) Perl limits identifiers (names for variables, functions,
etc.) to 252 characters for simple names, somewhat more for
compound names (like `$A::B'). You've exceeded Perl's
limits. Future versions of Perl are likely to eliminate
these arbitrary limitations.
Illegal character %s (carriage return)
(F) A carriage return character was found in the input. This
is an error, and not a warning, because carriage return
characters can break multi-line strings, including here
documents (e.g., `print <<EOF;').
Illegal switch in PERL5OPT: %s
(X) The PERL5OPT environment variable may only be used to
set the following switches: -[DIMUdmw].
Integer overflow in hex number
(S) The literal hex number you have specified is too big for
your architecture. On a 32-bit architecture the largest hex
literal is 0xFFFFFFFF.
Integer overflow in octal number
(S) The literal octal number you have specified is too big
for your architecture. On a 32-bit architecture the largest
octal literal is 037777777777.
internal error: glob failed
(P) Something went wrong with the external program(s) used
for `glob' and `<*.c>'. This may mean that your csh (C
shell) is broken. If so, you should change all of the csh-
related variables in config.sh: If you have tcsh, make the
variables refer to it as if it were csh (e.g.
`full_csh='/usr/bin/tcsh''); otherwise, make them all empty
(except that `d_csh' should be `'undef'') so that Perl will
think csh is missing. In either case, after editing
config.sh, run `./Configure -S' and rebuild Perl.
Invalid conversion in %s: "%s"
(W) Perl does not understand the given format conversion.
See the "sprintf" entry in the perlfunc manpage.
Invalid type in pack: '%s'
(F) The given character is not a valid pack type. See the
"pack" entry in the perlfunc manpage.
Invalid type in unpack: '%s'
(F) The given character is not a valid unpack type. See the
"unpack" entry in the perlfunc manpage.
Name "%s::%s" used only once: possible typo
(W) Typographical errors often show up as unique variable
names. If you had a good reason for having a unique name,
then just mention it again somehow to suppress the message
(the `use vars' pragma is provided for just this purpose).
Null picture in formline
(F) The first argument to formline must be a valid format
picture specification. It was found to be empty, which
probably means you supplied it an uninitialized value. See
the perlform manpage.
Offset outside string
(F) You tried to do a read/write/send/recv operation with an
offset pointing outside the buffer. This is difficult to
imagine. The sole exception to this is that `sysread()'ing
past the buffer will extend the buffer and zero pad the new
area.
Out of memory!
(X|F) The malloc() function returned 0, indicating there was
insufficient remaining memory (or virtual memory) to satisfy
the request.
The request was judged to be small, so the possibility to
trap it depends on the way Perl was compiled. By default it
is not trappable. However, if compiled for this, Perl may
use the contents of `$^M' as an emergency pool after
die()ing with this message. In this case the error is
trappable *once*.
Out of memory during request for %s
(F) The malloc() function returned 0, indicating there was
insufficient remaining memory (or virtual memory) to satisfy
the request. However, the request was judged large enough
(compile-time default is 64K), so a possibility to shut down
by trapping this error is granted.
panic: frexp
(P) The library function frexp() failed, making printf("%f")
impossible.
Possible attempt to put comments in qw() list
(W) qw() lists contain items separated by whitespace; as
with literal strings, comment characters are not ignored,
but are instead treated as literal data. (You may have used
different delimiters than the exclamation marks 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 package `%s'
(P) Overloading resolution over @ISA tree may be broken by
importing stubs. Stubs should never be implicitely created,
but explicit calls to `can' may break this.
Too late for "-T" option
(X) The #! line (or local equivalent) in a Perl script
contains the -T option, but Perl was not invoked with -T in
its argument list. This is an error because, by the time
Perl discovers a -T in a script, it's too late to properly
taint everything from the environment. So Perl gives up.
untie attempted while %d inner references still exist
(W) A copy of the object returned from `tie' (or `tied') was
still valid when `untie' was called.
Unrecognized character %s
(F) The Perl parser has no idea what to do with the
specified character in your Perl script (or eval). Perhaps
you tried to run a compressed script, a binary program, or a
directory as a Perl program.
Unsupported function fork
(F) Your version of executable does not support forking.
Note that under some systems, like OS/2, there may be
different flavors of Perl executables, some of which may
support fork, some not. Try changing the name you call Perl
by to `perl_', `perl__', and so on.
Use of "$$<digit>" to mean "${$}<digit>" is deprecated
(D) Perl versions before 5.004 misinterpreted any type
marker followed by "$" and a digit. For example, "$$0" was
incorrectly taken to mean "${$}0" instead of "${$0}". This
bug is (mostly) fixed in Perl 5.004.
However, the developers of Perl 5.004 could not fix this bug
completely, because at least two widely-used modules depend
on the old meaning of "$$0" in a string. So Perl 5.004 still
interprets "$$<digit>" in the old (broken) way inside
strings; but it generates this message as a warning. And in
Perl 5.005, this special treatment will cease.
Value of %s can be "0"; test with defined()
(W) In a conditional expression, you used <HANDLE>, <*>
(glob), `each()', or `readdir()' as a boolean value. Each of
these constructs can return a value of "0"; that would make
the conditional expression false, which is probably not what
you intended. When using these constructs in conditional
expressions, test their values with the `defined' operator.
Variable "%s" may be unavailable
(W) An inner (nested) *anonymous* subroutine is inside a
*named* subroutine, and outside that is another subroutine;
and the anonymous (innermost) subroutine is referencing a
lexical variable defined in the outermost subroutine. For
example:
sub outermost { my $a; sub middle { sub { $a } } }
If the anonymous subroutine is called or referenced
(directly or indirectly) from the outermost subroutine, it
will share the variable as you would expect. But if the
anonymous subroutine is called or referenced when the
outermost subroutine is not active, it will see the value of
the shared variable as it was before and during the *first*
call to the outermost subroutine, which is probably not what
you want.
In these circumstances, it is usually best to make the
middle subroutine anonymous, using the `sub {}' syntax. Perl
has specific support for shared variables in nested
anonymous subroutines; a named subroutine in between
interferes with this feature.
Variable "%s" will not stay shared
(W) An inner (nested) *named* subroutine is referencing a
lexical variable defined in an outer subroutine.
When the inner subroutine is called, it will probably see
the value of the outer subroutine's variable as it was
before and during the *first* call to the outer subroutine;
in this case, after the first call to the outer subroutine
is complete, the inner and outer subroutines will no longer
share a common value for the variable. In other words, the
variable will no longer be shared.
Furthermore, if the outer subroutine is anonymous and
references a lexical variable outside itself, then the outer
and inner subroutines will *never* share the given variable.
This problem can usually be solved by making the inner
subroutine anonymous, using the `sub {}' syntax. When inner
anonymous subs that reference variables in outer subroutines
are called or referenced, they are automatically rebound to
the current values of such variables.
Warning: something's wrong
(W) You passed warn() an empty string (the equivalent of
`warn ""') or you called it with no args and `$_' was empty.
Ill-formed logical name |%s| in prime_env_iter
(W) A warning peculiar to VMS. A logical name was
encountered when preparing to iterate over %ENV which
violates the syntactic rules governing logical names. Since
it cannot be translated normally, it is skipped, and will
not appear in %ENV. This may be a benign occurrence, as some
software packages might directly modify logical name tables
and introduce nonstandard names, or it may indicate that a
logical name table has been corrupted.
Got an error from DosAllocMem
(P) An error peculiar to OS/2. Most probably you're using an
obsolete version of Perl, and this should not happen anyway.
Malformed PERLLIB_PREFIX
(F) An error peculiar to OS/2. PERLLIB_PREFIX should be of
the form
prefix1;prefix2
or
prefix1 prefix2
with nonempty prefix1 and prefix2. If `prefix1' is indeed a
prefix of a builtin library search path, prefix2 is
substituted. The error may appear if components are not
found, or are too long. See "PERLLIB_PREFIX" in README.os2.
PERL_SH_DIR too long
(F) An error peculiar to OS/2. PERL_SH_DIR is the directory
to find the `sh'-shell in. See "PERL_SH_DIR" in README.os2.
Process terminated by SIG%s
(W) This is a standard message issued by OS/2 applications,
while *nix applications die in silence. It is considered a
feature of the OS/2 port. One can easily disable this by
appropriate sighandlers, see the section on "Signals" in the
perlipc manpage. See also "Process terminated by
SIGTERM/SIGINT" in README.os2.
BUGS
If you find what you think is a bug, you might check the headers
of recently posted articles in the comp.lang.perl.misc
newsgroup. There may also be information at
http://www.perl.com/perl/, the Perl Home Page.
If you believe you have an unreported bug, please run the
perlbug program included with your release. Make sure you trim
your bug down to a tiny but sufficient test case. Your bug
report, along with the output of `perl -V', will be sent off to
<perlbug@perl.com> to be analysed by the Perl porting team.
SEE ALSO
The Changes file for exhaustive details on what changed.
The INSTALL file for how to build Perl. This file has been
significantly updated for 5.004, so even veteran users should
look through it.
The README file for general stuff.
The Copying file for copyright information.
HISTORY
Constructed by Tom Christiansen, grabbing material with
permission from innumerable contributors, with kibitzing by more
than a few Perl porters.
Last update: Wed May 14 11:14:09 EDT 1997
