| PERL5004DELTA(1) | Perl Programmers Reference Guide | PERL5004DELTA(1) |
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.
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.
"%ENV = ()" and "%ENV = @list" now work as expected (except on VMS where it generates a fatal error).
The error "Can't locate Foo.pm in @INC" now lists the contents of @INC for easier debugging.
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.
You may now put Perl options in the $PERL5OPT environment variable. Unless Perl is running with taint checks, it will interpret this variable as if its contents had appeared on a "#!perl" line at the beginning of your script, except that hyphens are optional. PERL5OPT may only be used to set the following switches: -[DIMUdmw].
The "-M" and "-m" options are no longer allowed on the "#!" line of a script. If a script needs a module, it should invoke it with the "use" pragma.
The -T option is also forbidden on the "#!" line of a script, unless it was present on the Perl command line. Due to the way "#!" works, this usually means that -T must be in the first argument. Thus:
#!/usr/bin/perl -T -w
will probably work for an executable script invoked as "scriptname", while:
#!/usr/bin/perl -w -T
will probably fail under the same conditions. (Non-Unix systems will probably not follow this rule.) But "perl scriptname" is guaranteed to fail, since then there is no chance of -T being found on the command line before it is found on the "#!" line.
If you removed the -w option from your Perl 5.003 scripts because it made Perl too verbose, we recommend that you try putting it back when you upgrade to Perl 5.004. Each new perl version tends to remove some undesirable warnings, while adding new warnings that may catch bugs in your scripts.
Before Perl 5.004, "AUTOLOAD" functions were looked up as methods (using the @ISA hierarchy), even when the function to be autoloaded was called as a plain function (e.g. "Foo::bar()"), not a method (e.g. "Foo->bar()" or "$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.
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.
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).
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 $) is exactly symmetrical with examining it: The first number in its string value is used as the effective gid; if there are any numbers after the first one, they are passed to the "setgroups()" C function (if there is one).
Perl versions before 5.004 misinterpreted any type marker followed by "$" 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.
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.
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.
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.
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".
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:
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.
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.
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}.
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.
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)".
$^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.
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 %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).
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.
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.)
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.
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.
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
.
The "UNIVERSAL" package automatically contains the following methods that are inherited by all other classes:
"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')) {
...
}
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.
See perltie for other kinds of tie()s.
sub TIEHANDLE {
print "<shout>\n";
my $i;
return bless \$i, shift;
}
sub PRINT {
$r = shift;
$$r++;
return print join( $, => map {uc} @_), $\;
}
sub PRINTF {
shift;
my $fmt = shift;
print sprintf($fmt, @_)."\n";
}
sub READ {
$r = shift;
my($buf,$len,$offset) = @_;
print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
}
sub READLINE {
$r = shift;
return "PRINT called $$r times\n"
}
sub GETC { print "Don't GETC, Get Perl"; return "a"; }
sub DESTROY {
print "</shout>\n";
}
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().)
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).
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.
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 the following operating systems is new in Perl 5.004.
Perl 5.004 now includes support for building a "native" perl under Windows NT, using the Microsoft Visual C++ compiler (versions 2.0 and above) or the Borland C++ compiler (versions 5.02 and above). The resulting perl can be used under Windows 95 (if it is installed in the same directory locations as it got installed in Windows NT). This port includes support for perl extension building tools like ExtUtils::MakeMaker and h2xs, so that many extensions available on the Comprehensive Perl Archive Network (CPAN) can now be readily built under Windows NT. See http://www.perl.com/ for more information on CPAN and README.win32 in the perl distribution for more details on how to get started with building this port.
There is also support for building perl under the Cygwin32 environment. Cygwin32 is a set of GNU tools that make it possible to compile and run many Unix programs under Windows NT by providing a mostly Unix-like interface for compilation and execution. See README.cygwin32 in the perl distribution for more details on this port and how to obtain the Cygwin32 toolkit.
See README.plan9 in the perl distribution.
See README.qnx in the perl distribution.
See README.amigaos in the perl distribution.
Six new pragmatic modules exist:
Intended for use on command line with -M option as a way of testing arbitrary scripts against an uninstalled version of a package.
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.
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.
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.
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
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'").
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.
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
This new module provides a simpler interface to parts of Math::Complex for those who need trigonometric functions only for real numbers.
There have been quite a few changes made to DB_File. Here are a few of the highlights:
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.
Major rewrite - support added for both udp echo and real icmp pings.
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);
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 *".
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).
Many of the base and library pods were updated. These new pods are included in section 1:
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).
$foo{$bar}
$ref->[12]->{"susie"}
or a hash slice, such as
@foo{$bar, $baz, $xyzzy}
@{$ref->[12]}{"susie", "queue"}
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.
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
);
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 !;
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.
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.
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.
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.
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.
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.
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.
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
| 2022-02-19 | perl v5.34.1 |