perl5100delta - what is new for perl 5.10.0
This document describes the differences between the 5.8.8 release and the 5.10.0 release.
Many of the bug fixes in 5.10.0 were already seen in the 5.8.X maintenance releases; they are not duplicated here and are documented in the set of man pages named perl58[1-8]?delta.
feature
pragmaThe feature
pragma is used to enable new syntax that would break Perl's
backwards-compatibility with older releases of the language. It's a lexical
pragma, like strict
or warnings
.
Currently the following new features are available: switch
(adds a
switch statement), say (adds a say built-in function), and state
(adds a state keyword for declaring "static" variables). Those
features are described in their own sections of this document.
The feature
pragma is also implicitly loaded when you require a minimal
perl version (with the use VERSION
construct) greater than, or equal
to, 5.9.5. See feature for details.
-E is equivalent to -e, but it implicitly enables all
optional features (like use feature ":5.10"
).
A new operator //
(defined-or) has been implemented.
The following expression:
- $a // $b
is merely equivalent to
- defined $a ? $a : $b
and the statement
- $c //= $d;
can now be used instead of
- $c = $d unless defined $c;
The //
operator has the same precedence and associativity as ||.
Special care has been taken to ensure that this operator Do What You Mean
while not breaking old code, but some edge cases involving the empty
regular expression may now parse differently. See perlop for
details.
Perl 5 now has a switch statement. It's available when use feature
'switch'
is in effect. This feature introduces three new keywords,
given
, when
, and default
:
- given ($foo) {
- when (/^abc/) { $abc = 1; }
- when (/^def/) { $def = 1; }
- when (/^xyz/) { $xyz = 1; }
- default { $nothing = 1; }
- }
A more complete description of how Perl matches the switch variable
against the when
conditions is given in Switch statements in perlsyn.
This kind of match is called smart match, and it's also possible to use
it outside of switch statements, via the new ~~
operator. See
Smart matching in detail in perlsyn.
This feature was contributed by Robin Houston.
It is now possible to write recursive patterns without using the (??{})
construct. This new way is more efficient, and in many cases easier to
read.
Each capturing parenthesis can now be treated as an independent pattern
that can be entered by using the (?PARNO) syntax (PARNO
standing for
"parenthesis number"). For example, the following pattern will match
nested balanced angle brackets:
- /
- ^ # start of line
- ( # start capture buffer 1
- < # match an opening angle bracket
- (?: # match one of:
- (?> # don't backtrack over the inside of this group
- [^<>]+ # one or more non angle brackets
- ) # end non backtracking group
- | # ... or ...
- (?1) # recurse to bracket 1 and try it again
- )* # 0 or more times.
- > # match a closing angle bracket
- ) # end capture buffer one
- $ # end of line
- /x
PCRE users should note that Perl's recursive regex feature allows backtracking into a recursed pattern, whereas in PCRE the recursion is atomic or "possessive" in nature. As in the example above, you can add (?>) to control this selectively. (Yves Orton)
It is now possible to name capturing parenthesis in a pattern and refer to
the captured contents by name. The naming syntax is (?<NAME>....).
It's possible to backreference to a named buffer with the \k<NAME>
syntax. In code, the new magical hashes %+
and %-
can be used to
access the contents of the capture buffers.
Thus, to replace all doubled chars with a single copy, one could write
- s/(?<letter>.)\k<letter>/$+{letter}/g
Only buffers with defined contents will be "visible" in the %+
hash, so
it's possible to do something like
The %-
hash is a bit more complete, since it will contain array refs
holding values from all capture buffers similarly named, if there should
be many of them.
%+
and %-
are implemented as tied hashes through the new module
Tie::Hash::NamedCapture
.
Users exposed to the .NET regex engine will find that the perl implementation differs in that the numerical ordering of the buffers is sequential, and not "unnamed first, then named". Thus in the pattern
- /(A)(?<B>B)(C)(?<D>D)/
$1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer would expect. This is considered a feature. :-) (Yves Orton)
Perl now supports the "possessive quantifier" syntax of the "atomic match"
pattern. Basically a possessive quantifier matches as much as it can and never
gives any back. Thus it can be used to control backtracking. The syntax is
similar to non-greedy matching, except instead of using a '?' as the modifier
the '+' is used. Thus ?+, *+
, ++
, {min,max}+
are now legal
quantifiers. (Yves Orton)
The regex engine now supports a number of special-purpose backtrack control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL) and (*ACCEPT). See perlre for their descriptions. (Yves Orton)
A new syntax \g{N}
or \gN
where "N" is a decimal integer allows a
safer form of back-reference notation as well as allowing relative
backreferences. This should make it easier to generate and embed patterns
that contain backreferences. See Capture buffers in perlre. (Yves Orton)
\K
escape
The functionality of Jeff Pinyan's module Regexp::Keep has been added to
the core. In regular expressions you can now use the special escape \K
as a way to do something like floating length positive lookbehind. It is
also useful in substitutions like:
- s/(foo)bar/$1/g
that can now be converted to
- s/foo\Kbar//g
which is much more efficient. (Yves Orton)
Regular expressions now recognize the \v
and \h
escapes that match
vertical and horizontal whitespace, respectively. \V
and \H
logically match their complements.
\R
matches a generic linebreak, that is, vertical whitespace, plus
the multi-character sequence "\x0D\x0A"
.
say()say() is a new built-in, only available when use feature 'say'
is in
effect, that is similar to print(), but that implicitly appends a newline
to the printed string. See say. (Robin Houston)
$_
The default variable $_
can now be lexicalized, by declaring it like
any other lexical variable, with a simple
- my $_;
The operations that default on $_
will use the lexically-scoped
version of $_
when it exists, instead of the global $_
.
In a map or a grep block, if $_
was previously my'ed, then the
$_
inside the block is lexical as well (and scoped to the block).
In a scope where $_
has been lexicalized, you can still have access to
the global version of $_
by using $::_
, or, more simply, by
overriding the lexical declaration with our $_
. (Rafael Garcia-Suarez)
_
prototypeA new prototype character has been added. _
is equivalent to $
but
defaults to $_
if the corresponding argument isn't supplied (both $
and _
denote a scalar). Due to the optional nature of the argument,
you can only use it at the end of a prototype, or before a semicolon.
This has a small incompatible consequence: the prototype() function has
been adjusted to return _
for some built-ins in appropriate cases (for
example, prototype('CORE::rmdir')). (Rafael Garcia-Suarez)
UNITCHECK
, a new special code block has been introduced, in addition to
BEGIN
, CHECK
, INIT
and END
.
CHECK
and INIT
blocks, while useful for some specialized purposes,
are always executed at the transition between the compilation and the
execution of the main program, and thus are useless whenever code is
loaded at runtime. On the other hand, UNITCHECK
blocks are executed
just after the unit which defined them has been compiled. See perlmod
for more information. (Alex Gough)
mro
A new pragma, mro
(for Method Resolution Order) has been added. It
permits to switch, on a per-class basis, the algorithm that perl uses to
find inherited methods in case of a multiple inheritance hierarchy. The
default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
available: the C3 algorithm. See mro for more information.
(Brandon Black)
Note that, due to changes in the implementation of class hierarchy search,
code that used to undef the *ISA
glob will most probably break. Anyway,
undef'ing *ISA
had the side-effect of removing the magic on the @ISA
array and should not have been done in the first place. Also, the
cache *::ISA::CACHE::
no longer exists; to force reset the @ISA cache,
you now need to use the mro
API, or more simply to assign to @ISA
(e.g. with @ISA = @ISA
).
The readdir() function may return a "short filename" when the long filename contains characters outside the ANSI codepage. Similarly Cwd::cwd() may return a short directory name, and glob() may return short names as well. On the NTFS file system these short names can always be represented in the ANSI codepage. This will not be true for all other file system drivers; e.g. the FAT filesystem stores short filenames in the OEM codepage, so some files on FAT volumes remain unaccessible through the ANSI APIs.
Similarly, $^X, @INC, and $ENV{PATH} are preprocessed at startup to make sure all paths are valid in the ANSI codepage (if possible).
The Win32::GetLongPathName() function now returns the UTF-8 encoded correct long file name instead of using replacement characters to force the name into the ANSI codepage. The new Win32::GetANSIPathName() function can be used to turn a long pathname into a short one only if the long one cannot be represented in the ANSI codepage.
Many other functions in the Win32
module have been improved to accept
UTF-8 encoded arguments. Please see Win32 for details.
The built-in function readpipe() is now overridable. Overriding it permits
also to override its operator counterpart, qx// (a.k.a. ``
).
Moreover, it now defaults to $_
if no argument is provided. (Rafael
Garcia-Suarez)
readline() now defaults to *ARGV
if no argument is provided. (Rafael
Garcia-Suarez)
A new class of variables has been introduced. State variables are similar
to my variables, but are declared with the state keyword in place of
my. They're visible only in their lexical scope, but their value is
persistent: unlike my variables, they're not undefined at scope entry,
but retain their previous value. (Rafael Garcia-Suarez, Nicholas Clark)
To use state variables, one needs to enable them by using
- use feature 'state';
or by using the -E
command-line switch in one-liners.
See Persistent Private Variables in perlsub.
As a new form of syntactic sugar, it's now possible to stack up filetest
operators. You can now write -f -w -x $file
in a row to mean
-x $file && -w _ && -f _
. See -X.
The UNIVERSAL
class has a new method, DOES()
. It has been added to
solve semantic problems with the isa()
method. isa()
checks for
inheritance, while DOES()
has been designed to be overridden when
module authors use other types of relations between classes (in addition
to inheritance). (chromatic)
See $obj->DOES( ROLE ) in UNIVERSAL.
Formats were improved in several ways. A new field, ^*, can be used for
variable-width, one-line-at-a-time text. Null characters are now handled
correctly in picture lines. Using @#
and ~~
together will now
produce a compile-time error, as those format fields are incompatible.
perlform has been improved, and miscellaneous bugs fixed.
There are two new byte-order modifiers, > (big-endian) and <
(little-endian), that can be appended to most pack() and unpack() template
characters and groups to force a certain byte-order for that type or group.
See pack and perlpacktut for details.
no VERSION
You can now use no followed by a version number to specify that you
want to use a version of perl older than the specified one.
chdir, chmod and chown on filehandleschdir, chmod and chown can now work on filehandles as well as
filenames, if the system supports respectively fchdir
, fchmod
and
fchown
, thanks to a patch provided by Gisle Aas.
$(
and $)
now return groups in the order where the OS returns them,
thanks to Gisle Aas. This wasn't previously the case.
You can now use recursive subroutines with sort(), thanks to Robin Houston.
The constant folding routine is now wrapped in an exception handler, and if folding throws an exception (such as attempting to evaluate 0/0), perl now retains the current optree, rather than aborting the whole program. Without this change, programs would not compile if they had expressions that happened to generate exceptions, even though those expressions were in code that could never be reached at runtime. (Nicholas Clark, Dave Mitchell)
It's possible to enhance the mechanism of subroutine hooks in @INC by adding a source filter on top of the filehandle opened and returned by the hook. This feature was planned a long time ago, but wasn't quite working until now. See require for details. (Nicholas Clark)
${^RE_DEBUG_FLAGS}
This variable controls what debug flags are in effect for the regular
expression engine when running under use re "debug"
. See re for
details.
${^CHILD_ERROR_NATIVE}
This variable gives the native status returned by the last pipe close, backtick command, successful call to wait() or waitpid(), or from the system() operator. See perlvar for details. (Contributed by Gisle Aas.)
${^RE_TRIE_MAXBUF}
${^WIN32_SLOPPY_STAT}
unpack() now defaults to unpacking the $_
variable.
mkdir() without arguments now defaults to $_
.
The internal dump output has been improved, so that non-printable characters
such as newline and backspace are output in \x
notation, rather than
octal.
The -C option can no longer be used on the #!
line. It wasn't
working there anyway, since the standard streams are already set up
at this point in the execution of the perl interpreter. You can use
binmode() instead to get the desired behaviour.
The copy of the Unicode Character Database included in Perl 5 has been updated to version 5.0.0.
MAD, which stands for Miscellaneous Attribute Decoration, is a
still-in-development work leading to a Perl 5 to Perl 6 converter. To
enable it, it's necessary to pass the argument -Dmad
to Configure. The
obtained perl isn't binary compatible with a regular perl 5.10, and has
space and speed penalties; moreover not all regression tests still pass
with it. (Larry Wall, Nicholas Clark)
On Windows platforms, kill(-9, $pid)
now kills a process tree.
(On UNIX, this delivers the signal to all processes in the same process
group.)
The semantics of pack() and unpack() regarding UTF-8-encoded data has been
changed. Processing is now by default character per character instead of
byte per byte on the underlying encoding. Notably, code that used things
like pack("a*", $string)
to see through the encoding of string will now
simply get back the original $string. Packed strings can also get upgraded
during processing when you store upgraded characters. You can get the old
behaviour by using use bytes
.
To be consistent with pack(), the C0
in unpack() templates indicates
that the data is to be processed in character mode, i.e. character by
character; on the contrary, U0
in unpack() indicates UTF-8 mode, where
the packed string is processed in its UTF-8-encoded Unicode form on a byte
by byte basis. This is reversed with regard to perl 5.8.X, but now consistent
between pack() and unpack().
Moreover, C0
and U0
can also be used in pack() templates to specify
respectively character and byte modes.
C0
and U0
in the middle of a pack or unpack format now switch to the
specified encoding mode, honoring parens grouping. Previously, parens were
ignored.
Also, there is a new pack() character format, W
, which is intended to
replace the old C
. C
is kept for unsigned chars coded as bytes in
the strings internal representation. W
represents unsigned (logical)
character values, which can be greater than 255. It is therefore more
robust when dealing with potentially UTF-8-encoded data (as C
will wrap
values outside the range 0..255, and not respect the string encoding).
In practice, that means that pack formats are now encoding-neutral, except
C
.
For consistency, A
in unpack() format now trims all Unicode whitespace
from the end of the string. Before perl 5.9.2, it used to strip only the
classical ASCII space characters.
A new unpack() template character, "."
, returns the number of bytes or
characters (depending on the selected encoding mode, see above) read so far.
$*
and $#
variables have been removed$*
, which was deprecated in favor of the /s and /m regexp
modifiers, has been removed.
The deprecated $#
variable (output format for numbers) has been
removed.
Two new severe warnings, $#/$* is no longer supported, have been added.
The lvalues returned by the three argument form of substr() used to be a "fixed length window" on the original string. In some cases this could cause surprising action at distance or other undefined behaviour. Now the length of the window adjusts itself to the length of the string assigned to it.
-f _
The identifier _
is now forced to be a bareword after a filetest
operator. This solves a number of misparsing issues when a global _
subroutine is defined.
:unique
The :unique
attribute has been made a no-op, since its current
implementation was fundamentally flawed and not threadsafe.
The compile-time value of the %^H
hint variable can now propagate into
eval("")uated code. This makes it more useful to implement lexical
pragmas.
As a side-effect of this, the overloaded-ness of constants now propagates into eval("").
A bareword argument to chdir() is now recognized as a file handle. Earlier releases interpreted the bareword as a directory name. (Gisle Aas)
An old feature of perl was that before require or use look for a
file with a .pm extension, they will first look for a similar filename
with a .pmc extension. If this file is found, it will be loaded in
place of any potentially existing file ending in a .pm extension.
Previously, .pmc files were loaded only if more recent than the matching .pm file. Starting with 5.9.4, they'll be always loaded if they exist.
version
object instead of a v-string$^V can still be used with the %vd
format in printf, but any
character-level operations will now access the string representation
of the version
object and not the ordinals of a v-string.
Expressions like substr($^V, 0, 2)
or split //, $^V
no longer work and must be rewritten.
The special arrays @-
and @+
are no longer interpolated in regular
expressions. (Sadahiro Tomoyuki)
If you call a subroutine by a tainted name, and if it defers to an AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted. (Rick Delaney)
When perl is run under taint mode, printf() and sprintf() will now
reject any tainted format argument. (Rafael Garcia-Suarez)
Undefining or deleting a signal handler via undef $SIG{FOO}
is now
equivalent to setting it to 'DEFAULT'
. (Rafael Garcia-Suarez)
use strict 'refs'
was ignoring taking a hard reference in an argument
to defined(), as in :
This now correctly produces the run-time error Can't use string as a
SCALAR ref while "strict refs" in use.
defined @$foo
and defined %$bar
are now also subject to strict
'refs'
(that is, $foo
and $bar
shall be proper references there.)
(defined(@foo) and defined(%bar) are discouraged constructs anyway.)
(Nicholas Clark)
(?p{}) has been removedThe regular expression construct (?p{}), which was deprecated in perl
5.8, has been removed. Use (??{})
instead. (Rafael Garcia-Suarez)
Support for pseudo-hashes has been removed from Perl 5.9. (The fields
pragma remains here, but uses an alternate implementation.)
perlcc
, the byteloader and the supporting modules (B::C, B::CC,
B::Bytecode, etc.) are no longer distributed with the perl sources. Those
experimental tools have never worked reliably, and, due to the lack of
volunteers to keep them in line with the perl interpreter developments, it
was decided to remove them instead of shipping a broken version of those.
The last version of those modules can be found with perl 5.9.4.
However the B compiler framework stays supported in the perl core, as with the more useful modules it has permitted (among others, B::Deparse and B::Concise).
The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.
Perl will now immediately throw an exception if you modify any package's
@ISA
in such a way that it would cause recursive inheritance.
Previously, the exception would not occur until Perl attempted to make
use of the recursive inheritance while resolving a method or doing a
$foo->isa($bar)
lookup.
Even more core modules are now also available separately through the
CPAN. If you wish to update one of these modules, you don't need to
wait for a new perl release. From within the cpan shell, running the
'r' command will report on modules with upgrades available. See
perldoc CPAN
for more information.
feature
The new pragma feature
is used to enable new features that might break
old code. See The feature pragma above.
mro
This new pragma enables to change the algorithm used to resolve inherited methods. See New Pragma, mro above.
sort pragma
The sort pragma is now lexically scoped. Its effect used to be global.
bignum
, bigint
, bigrat
The three numeric pragmas bignum
, bigint
and bigrat
are now
lexically scoped. (Tels)
base
The base
pragma now warns if a class tries to inherit from itself.
(Curtis "Ovid" Poe)
strict
and warnings
strict
and warnings
will now complain loudly if they are loaded via
incorrect casing (as in use Strict;
). (Johan Vromans)
version
The version
module provides support for version objects.
warnings
The warnings
pragma doesn't load Carp
anymore. That means that code
that used Carp
routines without having loaded it at compile time might
need to be adjusted; typically, the following (faulty) code won't work
anymore, and will require parentheses to be added after the function name:
less
less
now does something useful (or at least it tries to). In fact, it
has been turned into a lexical pragma. So, in your modules, you can now
test whether your users have requested to use less CPU, or less memory,
less magic, or maybe even less fat. See less for more. (Joshua ben
Jore)
encoding::warnings
, by Audrey Tang, is a module to emit warnings
whenever an ASCII character string containing high-bit bytes is implicitly
converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
perls, its effect is global.
Module::CoreList
, by Richard Clamp, is a small handy module that tells
you what versions of core modules ship with any versions of Perl 5. It
comes with a command-line frontend, corelist
.
Math::BigInt::FastCalc
is an XS-enabled, and thus faster, version of
Math::BigInt::Calc
.
Compress::Zlib
is an interface to the zlib compression library. It
comes with a bundled version of zlib, so having a working zlib is not a
prerequisite to install it. It's used by Archive::Tar
(see below).
IO::Zlib
is an IO::
-style interface to Compress::Zlib
.
Archive::Tar
is a module to manipulate tar
archives.
Digest::SHA
is a module used to calculate many types of SHA digests,
has been included for SHA support in the CPAN module.
ExtUtils::CBuilder
and ExtUtils::ParseXS
have been added.
Hash::Util::FieldHash
, by Anno Siegel, has been added. This module
provides support for field hashes: hashes that maintain an association
of a reference with a value, in a thread-safe garbage-collected way.
Such hashes are useful to implement inside-out objects.
Module::Build
, by Ken Williams, has been added. It's an alternative to
ExtUtils::MakeMaker
to build and install perl modules.
Module::Load
, by Jos Boumans, has been added. It provides a single
interface to load Perl modules and .pl files.
Module::Loaded
, by Jos Boumans, has been added. It's used to mark
modules as loaded or unloaded.
Package::Constants
, by Jos Boumans, has been added. It's a simple
helper to list all constants declared in a given package.
Win32API::File
, by Tye McQueen, has been added (for Windows builds).
This module provides low-level access to Win32 system API calls for
files/dirs.
Locale::Maketext::Simple
, needed by CPANPLUS, is a simple wrapper around
Locale::Maketext::Lexicon
. Note that Locale::Maketext::Lexicon
isn't
included in the perl core; the behaviour of Locale::Maketext::Simple
gracefully degrades when the later isn't present.
Params::Check
implements a generic input parsing/checking mechanism. It
is used by CPANPLUS.
Term::UI
simplifies the task to ask questions at a terminal prompt.
Object::Accessor
provides an interface to create per-object accessors.
Module::Pluggable
is a simple framework to create modules that accept
pluggable sub-modules.
Module::Load::Conditional
provides simple ways to query and possibly
load installed modules.
Time::Piece
provides an object oriented interface to time functions,
overriding the built-ins localtime() and gmtime().
IPC::Cmd
helps to find and run external commands, possibly
interactively.
File::Fetch
provide a simple generic file fetching mechanism.
Log::Message
and Log::Message::Simple
are used by the log facility
of CPANPLUS
.
Archive::Extract
is a generic archive extraction mechanism
for .tar (plain, gziped or bzipped) or .zip files.
CPANPLUS
provides an API and a command-line tool to access the CPAN
mirrors.
Pod::Escapes
provides utilities that are useful in decoding Pod
E<...> sequences.
Pod::Simple
is now the backend for several of the Pod-related modules
included with Perl.
Attribute::Handlers
Attribute::Handlers
can now report the caller's file and line number.
(David Feldman)
All interpreted attributes are now passed as array references. (Damian Conway)
B::Lint
B::Lint
is now based on Module::Pluggable
, and so can be extended
with plugins. (Joshua ben Jore)
B
It's now possible to access the lexical pragma hints (%^H
) by using the
method B::COP::hints_hash(). It returns a B::RHE
object, which in turn
can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
ben Jore)
Thread
As the old 5005thread threading model has been removed, in favor of the
ithreads scheme, the Thread
module is now a compatibility wrapper, to
be used in old code only. It has been removed from the default list of
dynamic extensions.
The Perl debugger can now save all debugger commands for sourcing later; notably, it can now emulate stepping backwards, by restarting and rerunning all bar the last command from a saved command history.
It can also display the parent inheritance tree of a given class, with the
i
command.
ptar
is a pure perl implementation of tar
that comes with
Archive::Tar
.
ptardiff
is a small utility used to generate a diff between the contents
of a tar archive and a directory tree. Like ptar
, it comes with
Archive::Tar
.
shasum
is a command-line utility, used to print or to check SHA
digests. It comes with the new Digest::SHA
module.
The corelist
utility is now installed with perl (see New modules
above).
h2ph
and h2xs
have been made more robust with regard to
"modern" C code.
h2xs
implements a new option --use-xsloader
to force use of
XSLoader
even in backwards compatible modules.
The handling of authors' names that had apostrophes has been fixed.
Any enums with negative values are now skipped.
perlivp
no longer checks for *.ph files by default. Use the new -a
option to run all tests.
find2perl
now assumes -print
as a default action. Previously, it
needed to be specified explicitly.
Several bugs have been fixed in find2perl
, regarding -exec
and
-eval
. Also the options -path
, -ipath
and -iname
have been
added.
config_data
is a new utility that comes with Module::Build
. It
provides a command-line interface to the configuration of Perl modules
that use Module::Build's framework of configurability (that is,
*::ConfigData
modules that contain local configuration information for
their parent modules.)
cpanp
, the CPANPLUS shell, has been added. (cpanp-run-perl
, a
helper for CPANPLUS operation, has been added too, but isn't intended for
direct use).
cpan2dist
is a new utility that comes with CPANPLUS. It's a tool to
create distributions (or packages) from CPAN modules.
The output of pod2html
has been enhanced to be more customizable via
CSS. Some formatting problems were also corrected. (Jari Aalto)
The perlpragma manpage documents how to write one's own lexical pragmas in pure Perl (something that is possible starting with 5.9.4).
The new perlglossary manpage is a glossary of terms used in the Perl documentation, technical and otherwise, kindly provided by O'Reilly Media, Inc.
The perlreguts manpage, courtesy of Yves Orton, describes internals of the Perl regular expression engine.
The perlreapi manpage describes the interface to the perl interpreter used to write pluggable regular expression engines (by Ævar Arnfjörð Bjarmason).
The perlunitut manpage is an tutorial for programming with Unicode and string encodings in Perl, courtesy of Juerd Waalboer.
A new manual page, perlunifaq (the Perl Unicode FAQ), has been added (Juerd Waalboer).
The perlcommunity manpage gives a description of the Perl community on the Internet and in real life. (Edgar "Trizor" Bering)
The CORE manual page documents the CORE::
namespace. (Tels)
The long-existing feature of /(?{...})/
regexps setting $_
and pos()
is now documented.
Sorting arrays in place (@a = sort @a
) is now optimized to avoid
making a temporary copy of the array.
Likewise, reverse sort ...
is now optimized to sort in reverse,
avoiding the generation of a temporary intermediate list.
Access to elements of lexical arrays via a numeric constant between 0 and 255 is now faster. (This used to be only the case for global arrays.)
Some pure-perl code that perl was using to retrieve Unicode properties and transliteration mappings has been reimplemented in XS.
The interpreter internals now support a far more memory efficient form of inlineable constants. Storing a reference to a constant value in a symbol table is equivalent to a full typeglob referencing a constant subroutine, but using about 400 bytes less memory. This proxy constant subroutine is automatically upgraded to a real typeglob with subroutine if necessary. The approach taken is analogous to the existing space optimisation for subroutine stub declarations, which are stored as plain scalars in place of the full typeglob.
Several of the core modules have been converted to use this feature for
their system dependent constants - as a result use POSIX;
now takes about
200K less memory.
PERL_DONT_CREATE_GVSV
The new compilation flag PERL_DONT_CREATE_GVSV
, introduced as an option
in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
from creating an empty scalar with every new typeglob. See perl589delta
for details.
Weak reference creation is now O(1) rather than O(n), courtesy of Nicholas Clark. Weak reference deletion remains O(n), but if deletion only happens at program exit, it may be skipped completely.
Salvador Fandiño provided improvements to reduce the memory usage of sort
and to speed up some cases.
Several internal data structures (typeglobs, GVs, CVs, formats) have been restructured to use less memory. (Nicholas Clark)
The UTF-8 caching code is now more efficient, and used more often. (Nicholas Clark)
On Windows, perl's stat() function normally opens the file to determine the link count and update attributes that may have been changed through hard links. Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up stat() by not performing this operation. (Jan Dubois)
The regular expression engine is no longer recursive, meaning that patterns that used to overflow the stack will either die with useful explanations, or run to completion, which, since they were able to blow the stack before, will likely take a very long time to happen. If you were experiencing the occasional stack overflow (or segfault) and upgrade to discover that now perl apparently hangs instead, look for a degenerate regex. (Dave Mitchell)
Classes of a single character are now treated the same as if the character had been used as a literal, meaning that code that uses char-classes as an escaping mechanism will see a speedup. (Yves Orton)
Alternations, where possible, are optimised into more efficient matching structures. String literal alternations are merged into a trie and are matched simultaneously. This means that instead of O(N) time for matching N alternations at a given point, the new code performs in O(1) time. A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune this optimization. (Yves Orton)
Note: Much code exists that works around perl's historic poor performance on alternations. Often the tricks used to do so will disable the new optimisations. Hopefully the utility modules used for this purpose will be educated about these new optimisations.
When a pattern starts with a trie-able alternation and there aren't better optimisations available, the regex engine will use Aho-Corasick matching to find the start point. (Yves Orton)
-Dusesitecustomize
Run-time customization of @INC can be enabled by passing the
-Dusesitecustomize
flag to Configure. When enabled, this will make perl
run $sitelibexp/sitecustomize.pl before anything else. This script can
then be set up to add additional entries to @INC.
There is now Configure support for creating a relocatable perl tree. If
you Configure with -Duserelocatableinc
, then the paths in @INC (and
everything else in %Config) can be optionally located via the path of the
perl executable.
That means that, if the string ".../"
is found at the start of any
path, it's substituted with the directory of $^X. So, the relocation can
be configured on a per-directory basis, although the default with
-Duserelocatableinc
is that everything is relocated. The initial
install is done to the original configured prefix.
The configuration process now detects whether strlcat() and strlcpy() are available. When they are not available, perl's own version is used (from Russ Allbery's public domain implementation). Various places in the perl interpreter now use them. (Steve Peters)
d_pseudofork
and d_printf_format_null
A new configuration variable, available as $Config{d_pseudofork}
in
the Config module, has been added, to distinguish real fork() support
from fake pseudofork used on Windows platforms.
A new configuration variable, d_printf_format_null
, has been added,
to see if printf-like formats are allowed to be NULL.
Configure -h
has been extended with the most commonly used options.
Parallel makes should work properly now, although there may still be problems
if make test
is instructed to run in parallel.
Building with Borland's compilers on Win32 should work more smoothly. In particular Steve Hay has worked to side step many warnings emitted by their compilers and at least one C compiler internal error.
Perl extensions on Windows now can be statically built into the Perl DLL.
Also, it's now possible to build a perl-static.exe
that doesn't depend
on the Perl DLL on Win32. See the Win32 makefiles for details.
(Vadim Konovalov)
All ppport.h files in the XS modules bundled with perl are now autogenerated at build time. (Marcus Holland-Moritz)
Efforts have been made to make perl and the core XS modules compilable with various C++ compilers (although the situation is not perfect with some of the compilers on some of the platforms tested.)
Support for building perl with Microsoft's 64-bit compiler has been improved. (ActiveState)
Perl can now be compiled with Microsoft Visual C++ 2005 (and 2008 Beta 2).
All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
README files and changelogs for CPAN modules bundled with perl are no longer installed.
Perl has been reported to work on Symbian OS. See perlsymbian for more information.
Many improvements have been made towards making Perl work correctly on z/OS.
Perl has been reported to work on DragonFlyBSD and MidnightBSD.
Perl has also been reported to work on NexentaOS ( http://www.gnusolaris.org/ ).
The VMS port has been improved. See perlvms.
Support for Cray XT4 Catamount/Qk has been added. See hints/catamount.sh in the source code distribution for more information.
Vendor patches have been merged for RedHat and Gentoo.
DynaLoader::dl_unload_file() now works on Windows.
strict
wasn't in effect in regexp-eval blocks (/(?{...})/
).
CORE::require() and CORE::do() were always parsed as require() and do() when they were overridden. This is now fixed.
You can now use a non-arrowed form for chained subscripts after a list slice, like in:
- ({foo => "bar"})[0]{foo}
This used to be a syntax error; a ->
was required.
no warnings 'category'
works correctly with -w
Previously when running with warnings enabled globally via -w
, selective
disabling of specific warning categories would actually turn off all warnings.
This is now fixed; now no warnings 'io';
will only turn off warnings in the
io
class. Previously it would erroneously turn off all warnings.
Several memory leaks in ithreads were closed. Also, ithreads were made less memory-intensive.
threads
is now a dual-life module, also available on CPAN. It has been
expanded in many ways. A kill() method is available for thread signalling.
One can get thread status, or the list of running or joinable threads.
A new threads->exit()
method is used to exit from the application
(this is the default for the main thread) or from the current thread only
(this is the default for all other threads). On the other hand, the exit()
built-in now always causes the whole application to terminate. (Jerry
D. Hedden)
chr() on a negative value now gives \x{FFFD}
, the Unicode replacement
character, unless when the bytes
pragma is in effect, where the low
eight bits of the value are used.
On Windows, the PERL5SHELL environment variable is now checked for taintedness. (Rafael Garcia-Suarez)
stat() and -X filetests now treat *FILE{IO} filehandles like *FILE
filehandles. (Steve Peters)
Overloading now works when references are reblessed into another class. Internally, this has been implemented by moving the flag for "overloading" from the reference to the referent, which logically is where it should always have been. (Nicholas Clark)
A few bugs related to UTF-8 handling with objects that have stringification overloaded have been fixed. (Nicholas Clark)
Traditionally, eval 'syntax error'
has leaked badly. Many (but not all)
of these leaks have now been eliminated or reduced. (Dave Mitchell)
In previous versions, perl would read the file /dev/urandom if it existed when seeding its random number generator. That file is unlikely to exist on Windows, and if it did would probably not contain appropriate data, so perl no longer tries to read it on Windows. (Alex Davies)
The PERLIO_DEBUG
environment variable no longer has any effect for
setuid scripts and for scripts run with -T.
Moreover, with a thread-enabled perl, using PERLIO_DEBUG
could lead to
an internal buffer overflow. This has been fixed.
PerlIO::scalar will now prevent writing to read-only scalars. Moreover, seek() is now supported with PerlIO::scalar-based filehandles, the underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
study() never worked for UTF-8 strings, but could lead to false results. It's now a no-op on UTF-8 data. (Yves Orton)
The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an "unsafe" manner (contrary to other signals, that are deferred until the perl interpreter reaches a reasonably stable state; see Deferred Signals (Safe Signals) in perlipc). (Rafael)
When a module or a file is loaded through an @INC-hook, and when this hook has set a filename entry in %INC, __FILE__ is now set for this module accordingly to the contents of that %INC entry. (Rafael)
-t
switch fix
The -w
and -t
switches can now be used together without messing
up which categories of warnings are activated. (Rafael)
Duping a filehandle which has the :utf8
PerlIO layer set will now
properly carry that layer on the duped filehandle. (Rafael)
Localizing a hash element whose key was given as a variable didn't work
correctly if the variable was changed while the local() was in effect (as
in local $h{$x}; ++$x
). (Bo Lindbergh)
Perl will now try to tell you the name of the variable (if any) that was undefined.
A new deprecation warning, Deprecated use of my() in false conditional, has been added, to warn against the use of the dubious and deprecated construct
- my $x if 0;
A new warning, !=~ should be !~
, is emitted to prevent this misspelling
of the non-matching operator.
The warning Newline in left-justified string has been removed.
The error Too late for "-T" option has been reformulated to be more descriptive.
This warning is now emitted in more consistent cases; in short, when one
of the declarations involved is a my variable:
On the other hand, the following:
now gives a "our" variable %s redeclared warning.
These new warnings are now emitted when a dirhandle is used but is either closed or not really a dirhandle.
Two deprecation warnings have been added: (Rafael)
- Opening dirhandle %s also as a file
- Opening filehandle %s also as a directory
Perl's command-line switch -P
is now deprecated.
Perl will warn you against potential backwards compatibility problems with
the use VERSION
syntax.
perl -V
has several improvements, making it more useable from shell
scripts to get the value of configuration variables. See perlrun for
details.
In general, the source code of perl has been refactored, tidied up, and optimized in many places. Also, memory management and allocation has been improved in several points.
When compiling the perl core with gcc, as many gcc warning flags are turned on as is possible on the platform. (This quest for cleanliness doesn't extend to XS code because we cannot guarantee the tidiness of code we didn't write.) Similar strictness flags have been added or tightened for various other C compilers.
The relative ordering of constants that define the various types of SV
have changed; in particular, SVt_PVGV
has been moved before SVt_PVLV
,
SVt_PVAV
, SVt_PVHV
and SVt_PVCV
. This is unlikely to make any
difference unless you have code that explicitly makes assumptions about that
ordering. (The inheritance hierarchy of B::*
objects has been changed
to reflect this.)
Related to this, the internal type SVt_PVBM
has been been removed. This
dedicated type of SV
was used by the index operator and parts of the
regexp engine to facilitate fast Boyer-Moore matches. Its use internally has
been replaced by SV
s of type SVt_PVGV
.
A new type SVt_BIND
has been added, in readiness for the project to
implement Perl 6 on 5. There deliberately is no implementation yet, and
they cannot yet be created or destroyed.
The C preprocessor symbols PERL_PM_APIVERSION
and
PERL_XS_APIVERSION
, which were supposed to give the version number of
the oldest perl binary-compatible (resp. source-compatible) with the
present one, were not used, and sometimes had misleading values. They have
been removed.
The BASEOP
structure now uses less space. The op_seq
field has been
removed and replaced by a single bit bit-field op_opt
. op_type
is now 9
bits long. (Consequently, the B::OP
class doesn't provide an seq
method anymore.)
perl's parser is now generated by bison (it used to be generated by byacc.) As a result, it seems to be a bit more robust.
Also, Dave Mitchell improved the lexer debugging output under -DT
.
const
Andy Lester supplied many improvements to determine which function
parameters and local variables could actually be declared const
to the C
compiler. Steve Peters provided new *_set
macros and reworked the core to
use these rather than assigning to macros in LVALUE context.
A new file, mathoms.c, has been added. It contains functions that are
no longer used in the perl core, but that remain available for binary or
source compatibility reasons. However, those functions will not be
compiled in if you add -DNO_MATHOMS
in the compiler flags.
AvFLAGS
has been removedThe AvFLAGS
macro has been removed.
av_*
changesThe av_*()
functions, used to manipulate arrays, no longer accept null
AV*
parameters.
The implementation of the special variables $^H and %^H has changed, to allow implementing lexical pragmas in pure Perl.
The inheritance hierarchy of B::
modules has changed; B::NV
now
inherits from B::SV
(it used to inherit from B::IV
).
The anonymous hash and array constructors now take 1 op in the optree instead of 3, now that pp_anonhash and pp_anonlist return a reference to an hash/array when the op is flagged with OPf_SPECIAL. (Nicholas Clark)
There's still a remaining problem in the implementation of the lexical
$_
: it doesn't work inside /(?{...})/
blocks. (See the TODO test in
t/op/mydef.t.)
Stacked filetest operators won't work when the filetest
pragma is in
effect, because they rely on the stat() buffer _
being populated, and
filetest bypasses stat().
The handling of Unicode still is unclean in several places, where it's dependent on whether a string is internally flagged as UTF-8. This will be made more consistent in perl 5.12, but that won't be possible without a certain amount of backwards incompatibility.
When compiled with g++ and thread support on Linux, it's reported that the
$!
stops working correctly. This is related to the fact that the glibc
provides two strerror_r(3) implementation, and perl selects the wrong
one.
If you find what you think is a bug, you might check the articles recently posted to the comp.lang.perl.misc newsgroup and the perl bug database at http://rt.perl.org/rt3/ . There may also be information at http://www.perl.org/ , the Perl Home Page.
If you believe you have an unreported bug, please run the perlbug
program included with your release. Be sure to 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.org to be
analysed by the Perl porting team.
The Changes file and the perl590delta to perl595delta man pages 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.