perl5004delta
Current Perl documentation can be found at perldoc.perl.org.
Here is our local, out-dated (pre-5.6) version:
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 perlman:perlrun 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 perlman:perlop options are no longer allowed on the #!
line of a script. If a script needs a module, it should invoke it with the
use pragma.
The -T option is also forbidden on the #!
line of a script, unless it was present on the Perl command line. Due to
the way #!
works, this usually means that -T must be in the first argument. Thus:
#!/usr/bin/perl -T -w
will probably work for an executable script invoked as scriptname
, while:
#!/usr/bin/perl -w -T
will probably fail under the same conditions. (Non-Unix systems will
probably not follow this rule.) But perl scriptname
is guaranteed to fail, since then there is no chance of -T being found on the command line before it is found on the #!
line.
More precise warnings
If you removed the -w option from your Perl 5.003 scripts because it made Perl too verbose, we recommend that you try putting it back when you upgrade to Perl 5.004. Each new perl version tends to remove some undesirable warnings, while adding new warnings that may catch bugs in your scripts.
Deprecated: Inherited AUTOLOAD
for non-methods
Before Perl 5.004, AUTOLOAD
functions were looked up as methods (using the @ISA
hierarchy), even when the function to be autoloaded was called as a plain
function (e.g. Foo::bar()
), not a method (e.g. Foo->bar()
or $obj->bar()
).
Perl 5.005 will use method lookup only for methods' AUTOLOAD
s. However, there is a significant base of existing code that may be using
the old behavior. So, as an interim step, Perl 5.004 issues an optional
warning when a non-method uses an inherited AUTOLOAD
.
The simple rule is: Inheritance will not work when autoloading non-methods.
The simple fix for old code is: In any module that used to depend on
inheriting AUTOLOAD
for non-methods from a base class named
BaseClass
, execute *AUTOLOAD = \&BaseClass::AUTOLOAD
during startup.
Previously deprecated %OVERLOAD is no longer usable
Using %OVERLOAD
to define overloading was deprecated in 5.003.
Overloading is now defined using the overload pragma.
%OVERLOAD
is still used internally but should not be used by
Perl scripts. See
the overload manpage for more details.
Subroutine arguments created only when they're modified
In Perl 5.004, nonexistent array and hash elements used as subroutine
parameters are brought into existence only if they are actually assigned to
(via @_
).
Earlier versions of Perl vary in their handling of such arguments. Perl versions 5.002 and 5.003 always brought them into existence. Perl versions 5.000 and 5.001 brought them into existence only if they were not the first argument (which was almost certainly a bug). Earlier versions of Perl never brought them into existence.
For example, given this code:
undef @a; undef %a; sub show { print $_[0] }; sub change { $_[0]++ }; show($a[2]); change($a{b});
After this code executes in Perl 5.004, $a{b} exists but $a[2] does not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed (but $a[2]'s value would have been undefined).
Group vector changeable with $)
The $)
special variable has always (well, in Perl 5, at least) reflected not only
the current effective group, but also the group list as returned by the getgroups()
C function (if there is one). However, until this
release, there has not been a way to call the
setgroups()
C function from Perl.
In Perl 5.004, assigning to $)
is exactly symmetrical with examining it: The first number in its string
value is used as the effective gid; if there are any numbers after the
first one, they are passed to the
setgroups()
C function (if there is one).
Fixed parsing of $$<digit>, &$<digit>, etc.
Perl versions before 5.004 misinterpreted any type marker followed by ``$'' and a digit. For example, ``$$0'' was incorrectly taken to mean ``${$}0'' instead of ``${$0}''. This bug is (mostly) fixed in Perl 5.004.
However, the developers of Perl 5.004 could not fix this bug completely, because at least two widely-used modules depend on the old meaning of ``$$0'' in a string. So Perl 5.004 still interprets ``$$<digit>'' in the old (broken) way inside strings; but it generates this message as a warning. And in Perl 5.005, this special treatment will cease.
Fixed localization of $<digit>, $&, etc.
Perl versions before 5.004 did not always properly localize the regex-related special variables. Perl 5.004 does localize them, as the documentation has always said it should. This may result in $1, $2, etc. no longer being set where existing programs use them.
No resetting of $. on implicit close
The documentation for Perl 5.0 has always stated that $.
is not
reset when an already-open file handle is reopened with no intervening call
to close. Due to a bug, perl versions 5.000 through 5.003
did reset $.
under that circumstance; Perl 5.004 does not.
wantarray may return undef
The wantarray operator returns true if a subroutine is expected to return a list, and false otherwise. In Perl 5.004, wantarray can also return the undefined value if a subroutine's return value will not be used at all, which allows subroutines to avoid a time-consuming calculation of a return value if it isn't going to be used.
eval EXPR
determines value of EXPR in scalar context
Perl (version 5) used to determine the value of EXPR inconsistently, sometimes incorrectly using the surrounding context for the determination. Now, the value of EXPR (before being parsed by eval) is always determined in a scalar context. Once parsed, it is executed as before, by providing the context that the scope surrounding the eval provided. This change makes the behavior Perl4 compatible, besides fixing bugs resulting from the inconsistent behavior. This program:
@a = qw(time now is time); print eval @a; print '|', scalar eval @a;
used to print something like ``timenowis881399109|4'', but now (and in perl4) prints ``4|4''.
Changes to tainting checks
A bug in previous versions may have failed to detect
some insecure conditions when taint checks are turned on. (Taint checks are
used in setuid or setgid scripts, or when explicitly turned on with the
-T
invocation option.) Although it's unlikely, this may cause a
previously-working script to now fail -- which should be construed as a
blessing, since that indicates a potentially-serious security hole was just
plugged.
The new restrictions when tainting include:
- No glob() or <*>
- These operators may spawn the C shell (csh), which cannot be made safe. This restriction will be lifted in a future version of Perl when globbing is implemented without the use of an external program.
- No spawning if tainted $CDPATH, $ENV, $BASH_ENV
-
These environment variables may alter the behavior of spawned programs (especially shells) in ways that subvert security. So now they are treated as dangerous, in the manner of
$IFS
and $PATH. - No spawning if tainted $TERM doesn't look like a terminal name
-
Some termcap libraries do unsafe things with
$TERM. However, it would be unnecessarily harsh to treat all
$TERM
values as unsafe, since only shell metacharacters can cause trouble in $TERM. So a tainted$TERM
is considered to be safe if it contains only alphanumerics, underscores, dashes, and colons, and unsafe if it contains other characters (including whitespace).
New Opcode module and revised Safe module
A new Opcode module supports the creation, manipulation and application of opcode masks. The revised Safe module has a new API and is implemented using the new Opcode module. Please read the new Opcode and Safe documentation.
Embedding improvements
In older versions of Perl it was not possible to create more than one Perl interpreter instance inside a single process without leaking like a sieve and/or crashing. The bugs that caused this behavior have all been fixed. However, you still must take care when embedding Perl in a C program. See the updated perlembed manpage for tips on how to manage your interpreters.
Internal change: FileHandle class based on IO::* classes
File handles are now stored internally as type IO::Handle. The FileHandle module is still supported for backwards compatibility, but it is now merely a front end to the IO::* modules -- specifically, IO::Handle, IO::Seekable, and IO::File. We suggest, but do not require, that you use the IO::* modules in new code.
In harmony with this change, *GLOB{FILEHANDLE}
is now just a backward-compatible synonym for *GLOB{IO}
.
Internal change: PerlIO abstraction interface
It is now possible to build Perl with AT&T's sfio IO package instead of stdio. See the perlapio manpage for more details, and the INSTALL file for how to use it.
New and changed syntax
- $coderef->(PARAMS)
-
A subroutine reference may now be suffixed with an
arrow and a (possibly empty) parameter list. This syntax denotes a call of
the referenced subroutine, with the given parameters (if any).
This new syntax follows the pattern of
$hashref->{FOO}
and$aryref->[$foo]
: You may now write&$subref($foo)
as$subref->($foo)
. All of these arrow terms may be chained; thus,&{$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 perlfunc: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 youuse English
). - $^H
-
The current set of syntax checks enabled by
use strict
. See the documentation ofstrict
for more details. Not actually new, but newly documented. Because it is intended for internal use by Perl core components, there is nouse 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
$^M
as an emergency pool afterdie()ing
with this message. Suppose that your Perl were compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc. Then$^M = 'a' x (1<<16);
would allocate a 64K buffer for use when in emergency. See the INSTALL file for information on how to enable this option. As a disincentive to casual use of this advanced feature, there is no
use English
long name for this variable.
New and changed builtin functions
- delete on slices
-
This now works. (e.g.
delete @ENV{'PATH', 'MANPATH'}
) - flock
- is now supported on more platforms, prefers fcntl to lockf when emulating, and always flushes before (un)locking.
- printf and sprintf
-
Perl now implements these functions itself; it doesn't use the
C library function
sprintf()
any more, except for floating-point numbers, and even then only known flags are allowed. As a result, it is now possible to know which conversions and flags will work, and what they will do.The new conversions in Perl's
sprintf()
are:%i a synonym for %d %p a pointer (the address of the Perl value, in hexadecimal) %n special: *stores* the number of characters output so far into the next variable in the parameter list
The new flags that go between the
%
and the conversion are:# prefix octal with "0", hex with "0x" h interpret integer as C type "short" or "unsigned short" V interpret integer as Perl's standard integer type
Also, where a number would appear in the flags, an asterisk (``*'') may be used instead, in which case Perl uses the next item in the parameter list as the given number (that is, as the field width or precision). If a field width obtained through ``*'' is negative, it has the same effect as the '-' flag: left-justification.
See sprintf 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 = ()
; useundef %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()
andunpack()
now fail when their templates contain invalid types. (Invalid types used to be ignored.) - sysseek()
-
The new
sysseek()
operator is a variant ofseek()
that sets and gets the file's system read/write position, using thelseek(2)
system call. It is the only reliable way to seek before usingsysread()
orsyswrite().
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 useing 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 nextm//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 @# $i .
New builtin methods
The UNIVERSAL
package automatically contains the following methods that are inherited by
all other classes:
- isa(CLASS)
-
isa
returns true if its object is blessed into a subclass of perlman:perlgutsisa
is also exportable and can be called as a sub with two arguments. This allows the ability to check what a reference points to. Example:use UNIVERSAL qw(isa);
if(isa($ref, 'ARRAY')) { ... }
- can(METHOD)
-
can
checks to see if its object has a method calledMETHOD
, 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 theVERSION
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 $^M. - -DPACK_MALLOC
-
Perl memory allocation is by bucket with sizes close to powers of two.
Because of these malloc overhead may be big, especially for data of size
exactly a power of two. If
PACK_MALLOC
is defined, perl uses a slightly different algorithm for small allocations (up to 64 bytes long), which makes it possible to have overhead down to 1 byte for allocations which are powers of two (and appear quite often).Expected memory savings (with 8-byte alignment in
alignbytes
) is about 20% for typical Perl usage. Expected slowdown due to additional malloc overhead is in fractions of a percent (hard to measure, because of the effect of saved memory on speed). - -DTWO_POT_OPTIMIZE
-
Similarly to
PACK_MALLOC
, this macro improves allocations of data with size close to a power of two; but this works for big allocations (starting with 16K by default). Such allocations are typical for big hashes and special-purpose scripts, especially image processing.On recent systems, the fact that perl requires 2M from system for 1M allocation will not affect speed of execution, since the tail of such a chunk is not going to be touched (and thus will not require real memory). However, it may result in a premature out-of-memory error. So if you will be manipulating very large blocks with sizes close to powers of two, it would be wise to define this macro.
Expected saving of memory is 0-100% (100% in applications which require most memory in such 2**n chunks); expected slowdown is negligible.
Miscellaneous efficiency enhancements
Functions that have an empty prototype and that do nothing but return a
fixed value are now inlined (e.g. sub PI () { 3.14159 }
).
Each unique hash key is only allocated once, no matter how many hashes have an entry with that key. So even if you have 100 copies of the same hash, the hash keys never have to be reallocated.
Support for More Operating Systems
Support for the following operating systems is new in Perl 5.004.
Win32
Perl 5.004 now includes support for building a ``native'' perl under Windows NT, using the Microsoft Visual C++ compiler (versions 2.0 and above) or the Borland C++ compiler (versions 5.02 and above). The resulting perl can be used under Windows 95 (if it is installed in the same directory locations as it got installed in Windows NT). This port includes support for perl extension building tools like the MakeMaker manpage and the h2xs manpage, so that many extensions available on the Comprehensive Perl Archive Network (CPAN) can now be readily built under Windows NT. See http://www.perl.com/ for more information on CPAN and README.win32 in the perl distribution for more details on how to get started with building this port.
There is also support for building perl under the Cygwin32 environment. Cygwin32 is a set of GNU tools that make it possible to compile and run many UNIX programs under Windows NT by providing a mostly UNIX-like interface for compilation and execution. See README.cygwin32 in the perl distribution for more details on this port and how to obtain the Cygwin32 toolkit.
Plan 9
See README.plan9 in the perl distribution.
QNX
See README.qnx in the perl distribution.
AmigaOS
See README.amigaos in the perl distribution.
Pragmata
Six new pragmatic modules exist:
- use autouse MODULE => qw(sub1 sub2 sub3)
-
Defers
require MODULE
until someone calls one of the specified subroutines (which must be exported by MODULE). This pragma should be used with caution, and only when necessary. - use blib
- use blib 'dir'
-
Looks for MakeMaker-like 'blib' directory structure starting in
dir (or current directory) and working back up to five levels of parent
directories.
Intended for use on command line with -M option as a way of testing arbitrary scripts against an uninstalled version of a package.
- use constant NAME => VALUE
- Provides a convenient interface for creating compile-time constants, See perlman: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 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
orno 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 thatexit 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 perlman:perlguts 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 perlman:perlguts, 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 perlman:perlguts.
For backward compatibility, xsubpp tries to guess whether a perlman:perlguts XSUB is really perlman:perlguts or if it wants to return an perlman:perlguts. It does so by examining the text of the XSUB: if xsubpp finds what looks like an assignment to perlman:perlguts, it assumes that the XSUB's return type is really perlman:perlguts.
C Language API Changes
- gv_fetchmethod and perl_call_sv
-
The perlman:perlguts 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 perlman:perlguts. Instead, you should use the
GvCV
macro on the GV to extract its CV, and pass the CV to perlman:perlguts.The most likely symptom of passing the result of perlman:perlguts to perlman:perlguts 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
perlman:perlgutss, 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 perlman:perlguts keys. These additions also make it feasible to manipulateHE*
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:
- 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 the perlmod manpage (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.