PERL5005DELTA(1) Perl Programmers Reference Guide PERL5005DELTA(1)
NAME
perl5005delta - what's new for perl5.005
DESCRIPTION
This document describes differences between the 5.004 release and this one.
About the new versioning system
Perl is now developed on two tracks: a maintenance track that makes small, safe updates to released production
versions with emphasis on compatibility; and a development track that pursues more aggressive evolution.
Maintenance releases (which should be considered production quality) have subversion numbers that run from 1
to 49, and development releases (which should be considered "alpha" quality) run from 50 to 99.
Perl 5.005 is the combined product of the new dual-track development scheme.
Incompatible Changes
WARNING: This version is not binary compatible with Perl 5.004.
Starting with Perl 5.004_50 there were many deep and far-reaching changes to the language internals. If you
have dynamically loaded extensions that you built under perl 5.003 or 5.004, you can continue to use them with
5.004, but you will need to rebuild and reinstall those extensions to use them 5.005. See INSTALL for
detailed instructions on how to upgrade.
Default installation structure has changed
The new Configure defaults are designed to allow a smooth upgrade from 5.004 to 5.005, but you should read
INSTALL for a detailed discussion of the changes in order to adapt them to your system.
Perl Source Compatibility
When none of the experimental features are enabled, there should be very few user-visible Perl source
compatibility issues.
If threads are enabled, then some caveats apply. @_ and $_ become lexical variables. The effect of this
should be largely transparent to the user, but there are some boundary conditions under which user will need
to be aware of the issues. For example, "local(@_)" results in a "Can't localize lexical variable @_ ..."
message. This may be enabled in a future version.
Some new keywords have been introduced. These are generally expected to have very little impact on
compatibility. See "New "INIT" keyword", "New "lock" keyword", and "New "qr//" operator".
Certain barewords are now reserved. Use of these will provoke a warning if you have asked for them with the
"-w" switch. See ""our" is now a reserved word".
C Source Compatibility
There have been a large number of changes in the internals to support the new features in this release.
· Core sources now require ANSI C compiler
An ANSI C compiler is now required to build perl. See INSTALL.
· All Perl global variables must now be referenced with an explicit prefix
All Perl global variables that are visible for use by extensions now have a "PL_" prefix. New extensions
should "not" refer to perl globals by their unqualified names. To preserve sanity, we provide limited
backward compatibility for globals that are being widely used like "sv_undef" and "na" (which should now
be written as "PL_sv_undef", "PL_na" etc.)
If you find that your XS extension does not compile anymore because a perl global is not visible, try
adding a "PL_" prefix to the global and rebuild.
that elicited the error.
The API function "perl_get_sv("@",GV_ADD)" should be used instead of directly accessing perl globals as
"GvSV(errgv)". The API call is backward compatible with existing perls and provides source compatibility
with threading is enabled.
See "C Source Compatibility" for more information.
Binary Compatibility
This version is NOT binary compatible with older versions. All extensions will need to be recompiled.
Further binaries built with threads enabled are incompatible with binaries built without. This should largely
be transparent to the user, as all binary incompatible configurations have their own unique architecture name,
and extension binaries get installed at unique locations. This allows coexistence of several configurations
in the same directory hierarchy. See INSTALL.
Security fixes may affect compatibility
A few taint leaks and taint omissions have been corrected. This may lead to "failure" of scripts that used to
work with older versions. Compiling with -DINCOMPLETE_TAINTS provides a perl with minimal amounts of changes
to the tainting behavior. But note that the resulting perl will have known insecurities.
Oneliners with the "-e" switch do not create temporary files anymore.
Relaxed new mandatory warnings introduced in 5.004
Many new warnings that were introduced in 5.004 have been made optional. Some of these warnings are still
present, but perl's new features make them less often a problem. See "New Diagnostics".
Licensing
Perl has a new Social Contract for contributors. See Porting/Contract.
The license included in much of the Perl documentation has changed. Most of the Perl documentation was
previously under the implicit GNU General Public License or the Artistic License (at the user's choice). Now
much of the documentation unambiguously states the terms under which it may be distributed. Those terms are
in general much less restrictive than the GNU GPL. See perl and the individual perl manpages listed therein.
Core Changes
Threads
WARNING: Threading is considered an experimental feature. Details of the implementation may change without
notice. There are known limitations and some bugs. These are expected to be fixed in future versions.
See README.threads.
Compiler
WARNING: The Compiler and related tools are considered experimental. Features may change without notice, and
there are known limitations and bugs. Since the compiler is fully external to perl, the default configuration
will build and install it.
The Compiler produces three different types of transformations of a perl program. The C backend generates C
code that captures perl's state just before execution begins. It eliminates the compile-time overheads of the
regular perl interpreter, but the run-time performance remains comparatively the same. The CC backend
generates optimized C code equivalent to the code path at run-time. The CC backend has greater potential for
big optimizations, but only a few optimizations are implemented currently. The Bytecode backend generates a
platform independent bytecode representation of the interpreter's state just before execution. Thus, the
Bytecode back end also eliminates much of the compilation overhead of the interpreter.
"perlcc" is a simple frontend for compiling perl.
See "ext/B/README", B, and the respective compiler modules.
Regular Expressions
Perl's regular expression engine has been seriously overhauled, and many new constructs are supported.
Several bugs have been fixed.
Here is an itemized summary:
Many new and improved optimizations
Changes in the RE engine:
Unneeded nodes removed;
Substrings merged together;
New types of nodes to process (SUBEXPR)* and similar expressions
quickly, used if the SUBEXPR has no side effects and matches
strings of the same length;
Better optimizations by lookup for constant substrings;
Better search for constants substrings anchored by $ ;
Changes in Perl code using RE engine:
More optimizations to s/longer/short/;
study() was not working;
/blah/ may be optimized to an analogue of index() if $& $` $' not seen;
Unneeded copying of matched-against string removed;
Only matched part of the string is copying if $` $' were not seen;
Many bug fixes
Note that only the major bug fixes are listed here. See Changes for others.
Backtracking might not restore start of $3.
No feedback if max count for * or + on "complex" subexpression
was reached, similarly (but at compile time) for {3,34567}
Primitive restrictions on max count introduced to decrease a
possibility of a segfault;
(ZERO-LENGTH)* could segfault;
(ZERO-LENGTH)* was prohibited;
Long REs were not allowed;
/RE/g could skip matches at the same position after a
zero-length match;
New regular expression constructs
The following new syntax elements are supported:
(?<=RE)
(?<!RE)
(?{ CODE })
(?i-x)
(?i:RE)
(?(COND)YES_RE|NO_RE)
(?>RE)
\z
Incompatible changes
(?i) localized inside enclosing group;
$( is not interpolated into RE any more;
/RE/g may match at the same position (with non-zero length)
after a zero-length match (bug fix).
See perlre and perlop.
Improved malloc()
See banner at the beginning of "malloc.c" for details.
Quicksort is internally implemented
Perl now contains its own highly optimized qsort() routine. The new qsort() is resistant to inconsistent
comparison functions, so Perl's "sort()" will not provoke coredumps any more when given poorly written sort
subroutines. (Some C library "qsort()"s that were being used before used to have this problem.) In our
testing, the new "qsort()" required the minimal number of pair-wise compares on average, among all known
"qsort()" implementations.
See "perlfunc/sort".
Reliable signals
Perl's signal handling is susceptible to random crashes, because signals arrive asynchronously, and the Perl
runtime is not reentrant at arbitrary times.
However, one experimental implementation of reliable signals is available when threads are enabled. See
"Thread::Signal". Also see INSTALL for how to build a Perl capable of threads.
Reliable stack pointers
The internals now reallocate the perl stack only at predictable times. In particular, magic calls never
trigger reallocations of the stack, because all reentrancy of the runtime is handled using a "stack of
stacks". This should improve reliability of cached stack pointers in the internals and in XSUBs.
More generous treatment of carriage returns
Perl used to complain if it encountered literal carriage returns in scripts. Now they are mostly treated like
whitespace within program text. Inside string literals and here documents, literal carriage returns are
ignored if they occur paired with linefeeds, or get interpreted as whitespace if they stand alone. This
behavior means that literal carriage returns in files should be avoided. You can get the older, more
compatible (but less generous) behavior by defining the preprocessor symbol "PERL_STRICT_CR" when building
perl. Of course, all this has nothing whatever to do with how escapes like "\r" are handled within strings.
Note that this doesn't somehow magically allow you to keep all text files in DOS format. The generous
treatment only applies to files that perl itself parses. If your C compiler doesn't allow carriage returns in
files, you may still be unable to build modules that need a C compiler.
Memory leaks
"substr", "pos" and "vec" don't leak memory anymore when used in lvalue context. Many small leaks that
impacted applications that embed multiple interpreters have been fixed.
Better support for multiple interpreters
The build-time option "-DMULTIPLICITY" has had many of the details reworked. Some previously global variables
that should have been per-interpreter now are. With care, this allows interpreters to call each other. See
the "PerlInterp" extension on CPAN.
Keywords can be globally overridden
See perlsub.
$^E is meaningful on Win32
See perlvar.
"foreach (1..1000000)" optimized
"foreach (1..1000000)" is now optimized into a counting loop. It does not try to allocate a 1000000-size list
anymore.
"Foo::" can be used as implicitly quoted package name
Barewords caused unintuitive behavior when a subroutine with the same name as a package happened to be
defined. Thus, "new Foo @args", use the result of the call to "Foo()" instead of "Foo" being treated as a
literal. The recommended way to write barewords in the indirect object slot is "new Foo:: @args". Note that
the method "new()" is called with a first argument of "Foo", not "Foo::" when you do that.
"exists $Foo::{Bar::}" tests existence of a package
It was impossible to test for the existence of a package without actually creating it before. Now "exists
$Foo::{Bar::}" can be used to test if the "Foo::Bar" namespace has been created.
Better locale support
See perllocale.
Experimental support for 64-bit platforms
Perl5 has always had 64-bit support on systems with 64-bit longs. Starting with 5.005, the beginnings of
experimental support for systems with 32-bit long and 64-bit 'long long' integers has been added. If you add
-DUSE_LONG_LONG to your ccflags in config.sh (or manually define it in perl.h) then perl will be built with
'long long' support. There will be many compiler warnings, and the resultant perl may not work on all
systems. There are many other issues related to third-party extensions and libraries. This option exists to
allow people to work on those issues.
prototype() returns useful results on builtins
See "prototype" in perlfunc.
Extended support for exception handling
"die()" now accepts a reference value, and $@ gets set to that value in exception traps. This makes it
possible to propagate exception objects. This is an undocumented experimental feature.
Re-blessing in DESTROY() supported for chaining DESTROY() methods
See "Destructors" in perlobj.
All "printf" format conversions are handled internally
See "printf" in perlfunc.
New "INIT" keyword
"INIT" subs are like "BEGIN" and "END", but they get run just before the perl runtime begins execution. e.g.,
the Perl Compiler makes use of "INIT" blocks to initialize and resolve pointers to XSUBs.
New "lock" keyword
The "lock" keyword is the fundamental synchronization primitive in threaded perl. When threads are not
enabled, it is currently a noop.
To minimize impact on source compatibility this keyword is "weak", i.e., any user-defined subroutine of the
same name overrides it, unless a "use Thread" has been seen.
Tied handles support is better
Several missing hooks have been added. There is also a new base class for TIEARRAY implementations. See
Tie::Array.
4th argument to substr
substr() can now both return and replace in one operation. The optional 4th argument is the replacement
string. See "substr" in perlfunc.
Negative LENGTH argument to splice
splice() with a negative LENGTH argument now work similar to what the LENGTH did for substr(). Previously a
negative LENGTH was treated as 0. See "splice" in perlfunc.
Magic lvalues are now more magical
When you say something like "substr($x, 5) = "hi"", the scalar returned by substr() is special, in that any
modifications to it affect $x. (This is called a 'magic lvalue' because an 'lvalue' is something on the left
side of an assignment.) Normally, this is exactly what you would expect to happen, but Perl uses the same
magic if you use substr(), pos(), or vec() in a context where they might be modified, like taking a reference
with "\" or as an argument to a sub that modifies @_. In previous versions, this 'magic' only went one way,
but now changes to the scalar the magic refers to ($x in the above example) affect the magic lvalue too. For
instance, this code now acts differently:
$x = "hello";
sub printit {
$x = "g'bye";
print $_[0], "\n";
}
printit(substr($x, 0, 5));
In previous versions, this would print "hello", but it now prints "g'bye".
<> now reads in records
If $/ is a reference to an integer, or a scalar that holds an integer, <> will read in records instead of
lines. For more info, see "$/" in perlvar.
Supported Platforms
Configure has many incremental improvements. Site-wide policy for building perl can now be made persistent,
via Policy.sh. Configure also records the command-line arguments used in config.sh.
New Platforms
BeOS is now supported. See README.beos.
DOS is now supported under the DJGPP tools. See README.dos (installed as perldos on some systems).
MiNT is now supported. See README.mint.
MPE/iX is now supported. See README.mpeix.
MVS (aka OS390, aka Open Edition) is now supported. See README.os390 (installed as perlos390 on some
systems).
Stratus VOS is now supported. See README.vos.
Changes in existing support
Win32 support has been vastly enhanced. Support for Perl Object, a C++ encapsulation of Perl. GCC and EGCS
Dumpvalue
A module to dump perl values to the screen. See Dumpvalue.
Errno
A module to look up errors more conveniently. See Errno.
File::Spec
A portable API for file operations.
ExtUtils::Installed
Query and manage installed modules.
ExtUtils::Packlist
Manipulate .packlist files.
Fatal
Make functions/builtins succeed or die.
IPC::SysV
Constants and other support infrastructure for System V IPC operations in perl.
Test
A framework for writing test suites.
Tie::Array
Base class for tied arrays.
Tie::Handle
Base class for tied handles.
Thread
Perl thread creation, manipulation, and support.
attrs
Set subroutine attributes.
fields
Compile-time class fields.
re Various pragmata to control behavior of regular expressions.
Changes in existing modules
Benchmark
You can now run tests for x seconds instead of guessing the right number of tests to run.
Keeps better time.
Carp
Carp has a new function cluck(). cluck() warns, like carp(), but also adds a stack backtrace to the error
message, like confess().
CGI CGI has been updated to version 2.42.
distance.
POSIX
POSIX now has its own platform-specific hints files.
DB_File
DB_File supports version 2.x of Berkeley DB. See "ext/DB_File/Changes".
MakeMaker
MakeMaker now supports writing empty makefiles, provides a way to specify that site umask() policy should
be honored. There is also better support for manipulation of .packlist files, and getting information
about installed modules.
Extensions that have both architecture-dependent and architecture-independent files are now always
installed completely in the architecture-dependent locations. Previously, the shareable parts were shared
both across architectures and across perl versions and were therefore liable to be overwritten with newer
versions that might have subtle incompatibilities.
CPAN
See perlmodinstall and CPAN.
Cwd Cwd::cwd is faster on most platforms.
Utility Changes
"h2ph" and related utilities have been vastly overhauled.
"perlcc", a new experimental front end for the compiler is available.
The crude GNU "configure" emulator is now called "configure.gnu" to avoid trampling on "Configure" under case-
insensitive filesystems.
"perldoc" used to be rather slow. The slower features are now optional. In particular, case-insensitive
searches need the "-i" switch, and recursive searches need "-r". You can set these switches in the "PERLDOC"
environment variable to get the old behavior.
Documentation Changes
Config.pm now has a glossary of variables.
Porting/patching.pod has detailed instructions on how to create and submit patches for perl.
perlport specifies guidelines on how to write portably.
perlmodinstall describes how to fetch and install modules from "CPAN" sites.
Some more Perl traps are documented now. See perltrap.
perlopentut gives a tutorial on using open().
perlreftut gives a tutorial on references.
perlthrtut gives a tutorial on threads.
New Diagnostics
Ambiguous call resolved as CORE::%s(), qualify as such or use &
(F) The index looked up in the hash found as the 0'th element of a pseudo-hash is not legal. Index values
must be at 1 or greater. See perlref.
Bareword "%s" refers to nonexistent package
(W) You used a qualified bareword of the form "Foo::", but the compiler saw no other uses of that
namespace before that point. Perhaps you need to predeclare a package?
Can't call method "%s" on an undefined value
(F) You used the syntax of a method call, but the slot filled by the object reference or package name
contains an undefined value. Something like this will reproduce the error:
$BADREF = 42;
process $BADREF 1,2,3;
$BADREF->process(1,2,3);
Can't check filesystem of script "%s" for nosuid
(P) For some reason you can't check the filesystem of the script for nosuid.
Can't coerce array into hash
(F) You used an array where a hash was expected, but the array has no information on how to map from keys
to array indices. You can do that only with arrays that have a hash reference at index 0.
Can't goto subroutine from an eval-string
(F) The "goto subroutine" call can't be used to jump out of an eval "string". (You can use it to jump out
of an eval {BLOCK}, but you probably don't want to.)
Can't localize pseudo-hash element
(F) You said something like "local $ar->{'key'}", where $ar is a reference to a pseudo-hash. That hasn't
been implemented yet, but you can get a similar effect by localizing the corresponding array element
directly: "local $ar->[$ar->[0]{'key'}]".
Can't use %%! because Errno.pm is not available
(F) The first time the %! hash is used, perl automatically loads the Errno.pm module. The Errno module is
expected to tie the %! hash to provide symbolic names for $! errno values.
Cannot find an opnumber for "%s"
(F) A string of a form "CORE::word" was given to prototype(), but there is no builtin with the name
"word".
Character class syntax [. .] is reserved for future extensions
(W) Within regular expression character classes ([]) the syntax beginning with "[." and ending with ".]"
is reserved for future extensions. If you need to represent those character sequences inside a regular
expression character class, just quote the square brackets with the backslash: "\[." and ".\]".
Character class syntax [: :] is reserved for future extensions
(W) Within regular expression character classes ([]) the syntax beginning with "[:" and ending with ":]"
is reserved for future extensions. If you need to represent those character sequences inside a regular
expression character class, just quote the square brackets with the backslash: "\[:" and ":\]".
Character class syntax [= =] is reserved for future extensions
(W) Within regular expression character classes ([]) the syntax beginning with "[=" and ending with "=]"
is reserved for future extensions. If you need to represent those character sequences inside a regular
expression character class, just quote the square brackets with the backslash: "\[=" and "=\]".
string at run time and using that in an eval(). See "(?{ code })" in perlre.
Explicit blessing to '' (assuming package main)
(W) You are blessing a reference to a zero length string. This has the effect of blessing the reference
into the package main. This is usually not what you want. Consider providing a default target package,
e.g. bless($ref, $p || 'MyPackage');
Illegal hex digit ignored
(W) You may have tried to use a character other than 0 - 9 or A - F in a hexadecimal number.
Interpretation of the hexadecimal number stopped before the illegal character.
No such array field
(F) You tried to access an array as a hash, but the field name used is not defined. The hash at index 0
should map all valid field names to array indices for that to work.
No such field "%s" in variable %s of type %s
(F) You tried to access a field of a typed variable where the type does not know about the field name.
The field names are looked up in the %FIELDS hash in the type package at compile time. The %FIELDS hash
is usually set up with the 'fields' pragma.
Out of memory during ridiculously large request
(F) You can't allocate more than 2^31+"small amount" bytes. This error is most likely to be caused by a
typo in the Perl program. e.g., $arr[time] instead of $arr[$time].
Range iterator outside integer range
(F) One (or both) of the numeric arguments to the range operator ".." are outside the range which can be
represented by integers internally. One possible workaround is to force Perl to use magical string
increment by prepending "0" to your numbers.
Recursive inheritance detected while looking for method '%s' %s
(F) More than 100 levels of inheritance were encountered while invoking a method. Probably indicates an
unintended loop in your inheritance hierarchy.
Reference found where even-sized list expected
(W) You gave a single reference where Perl was expecting a list with an even number of elements (for
assignment to a hash). This usually means that you used the anon hash constructor when you meant to use
parens. In any case, a hash requires key/value pairs.
%hash = { one => 1, two => 2, }; # WRONG
%hash = [ qw/ an anon array / ]; # WRONG
%hash = ( one => 1, two => 2, ); # right
%hash = qw( one 1 two 2 ); # also fine
Undefined value assigned to typeglob
(W) An undefined value was assigned to a typeglob, a la "*foo = undef". This does nothing. It's possible
that you really mean "undef *foo".
Use of reserved word "%s" is deprecated
(D) The indicated bareword is a reserved word. Future versions of perl may use it as a keyword, so you're
better off either explicitly quoting the word in a manner appropriate for its context of use, or using a
different name altogether. The warning can be suppressed for subroutine names by either adding a "&"
prefix, or using a package qualifier, e.g. "&our()", or "Foo::our()".
perl: warning: Setting locale failed.
not dead serious, fortunately: there is a "default locale" called "C" that Perl can and will use, the
script will be run. Before you really fix the problem, however, you will get the same error message each
time you run Perl. How to really fix the problem can be found in "LOCALE PROBLEMS" in perllocale.
Obsolete Diagnostics
Can't mktemp()
(F) The mktemp() routine failed for some reason while trying to process a -e switch. Maybe your /tmp
partition is full, or clobbered.
Removed because -e doesn't use temporary files any more.
Can't write to temp file for -e: %s
(F) The write routine failed for some reason while trying to process a -e switch. Maybe your /tmp
partition is full, or clobbered.
Removed because -e doesn't use temporary files any more.
Cannot open temporary file
(F) The create routine failed for some reason while trying to process a -e switch. Maybe your /tmp
partition is full, or clobbered.
Removed because -e doesn't use temporary files any more.
regexp too big
(F) The current implementation of regular expressions uses shorts as address offsets within a string.
Unfortunately this means that if the regular expression compiles to longer than 32767, it'll blow up.
Usually when you want a regular expression this big, there is a better way to do it with multiple
statements. See perlre.
Configuration Changes
You can use "Configure -Uinstallusrbinperl" which causes installperl to skip installing perl also as
/usr/bin/perl. This is useful if you prefer not to modify /usr/bin for some reason or another but harmful
because many scripts assume to find Perl in /usr/bin/perl.
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 <[email protected]> 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.
The README file for general stuff.
The Artistic and Copying files for copyright information.
HISTORY
Written by Gurusamy Sarathy <[email protected]>, with many contributions from The Perl Porters.
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