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perl5100delta
perl5100delta - what is new for perl 5.10.0
DESCRIPTION
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
they are not duplicated here and are documented in the set of
man pages named perl58[1-8]?delta.
Core Enhancements
The feature
The 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
switch statement),
built-in function), and
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
construct) greater than, or equal
to, 5.9.5. See
for details.
New -E command-line switch
-E is equivalent to -e, but it implicitly enables all
optional features (like
feature &:5.10&
Defined-or operator
A new operator //
(defined-or) has been implemented.
The following expression:
$a // $bis merely equivalent to
$a ? $a : $band the statement
$c //= $d;can now be used instead of
$c = $d unless
operator has the same precedence and associativity as ||.
Special care has been taken to ensure that this operator Do What You Mean
while not breaking old code, but some edge cases involving the empty
regular expression may now parse differently.
Switch and Smart Match operator
Perl 5 now has a switch statement. It's available when
is in effect. This feature introduces three new keywords,
, and default
given ($foo) { when (/^abc/) { $abc = 1; } when (/^def/) { $def = 1; } when (/^xyz/) { $xyz = 1; } default { $nothing = 1; }
}A more complete description of how Perl matches the switch variable
against the when
conditions is given in .
This kind of match is called smart match, and it's also possible to use
it outside of switch statements, via the new ~~
operator. See
This feature was contributed by Robin Houston.
Regular expressions
Recursive Patterns
It is now possible to write recursive patterns without using the (??{})
construct. This new way is more efficient, and in many cases easier to
Each capturing parenthesis can now be treated as an independent pattern
that can be entered by using the (?PARNO) syntax (PARNO
standing for
"parenthesis number"). For example, the following pattern will match
nested balanced angle brackets:
# start of line
# start capture buffer 1
match an opening angle bracket
match one of:
don't backtrack over the inside of this group
one or more non angle brackets
end non backtracking group
... or ...
recurse to bracket 1 and try it again
0 or more times.
match a closing angle bracket
# end capture buffer one
# end of line
/xPCRE users should note that Perl's recursive regex feature allows
backtracking into a recursed pattern, whereas in PCRE the recursion is
atomic or "possessive" in nature.
As in the example above, you can
add (?&) to control this selectively.
(Yves Orton)
Named Capture Buffers
It is now possible to name capturing parenthesis in a pattern and refer to
the captured contents by name. The naming syntax is (?&NAME&....).
It's possible to backreference to a named buffer with the \k&NAME&
syntax. In code, the new magical hashes %+
can be used to
access the contents of the capture buffers.
Thus, to replace all doubled chars with a single copy, one could write
s/(?&letter&.)\k&letter&/$+{letter}/gOnly buffers with defined contents will be "visible" in the %+
it's possible to do something like
$name ( %+) {
&content of buffer '$name' is $+{$name}\n&;
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.
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)
Possessive Quantifiers
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)
Backtracking control verbs
The regex engine now supports a number of special-purpose backtrack
control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
and (*ACCEPT). See
for their descriptions. (Yves Orton)
Relative backreferences
A new syntax \g{N}
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 . (Yves Orton)
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/gthat can now be converted to
s/foo\Kbar//gwhich is much more efficient. (Yves Orton)
Vertical and horizontal whitespace, and linebreak
Regular expressions now recognize the \v
escapes that match
vertical and horizontal whitespace, respectively. \V
logically match their complements.
matches a generic linebreak, that is, vertical whitespace, plus
the multi-character sequence &\x0D\x0A&
Optional pre-match and post-match captures with the /p flag
There is a new flag /p for regular expressions.
Using this
makes the engine preserve a copy of the part of the matched string before
the matching substring to the new special variable ${^PREMATCH}
part after the matching substring to ${^POSTMATCH}
, and the matched
substring itself to ${^MATCH}
Perl is still able to store these substrings to the special variables
, but using these variables anywhere in the program
adds a penalty to all regular expression matches, whereas if you use
the /p flag and the new special variables instead, you pay only for
the regular expressions where the flag is used.
For more detail on the new variables, for the use of
the regular expression flag, see
say() is a new built-in, only available when
feature 'say'
effect, that is similar to print(), but that implicitly appends a newline
to the printed string. See . (Robin Houston)
Lexical $_
The default variable $_
can now be lexicalized, by declaring it like
any other lexical variable, with a simple
$_;The operations that default on $_
will use the lexically-scoped
version of $_
when it exists, instead of the global $_
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
. (Rafael Garcia-Suarez)
A new prototype character has been added. _
is equivalent to $
defaults to $_
if the corresponding argument isn't supplied (both $
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, ). (Rafael Garcia-Suarez)
UNITCHECK blocks
, a new special code block has been introduced, in addition to
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
for more information. (Alex Gough)
New Pragma, 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
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::
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
readdir() may return a "short filename" on Windows
The readdir() function may return a "short filename" when the long
filename contains characters outside the ANSI codepage.
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
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
for details.
readpipe() is now overridable
The built-in function readpipe() is now overridable. Overriding it permits
also to override its operator counterpart,
(a.k.a. ``
Moreover, it now defaults to $_
if no argument is provided. (Rafael
Garcia-Suarez)
Default argument for readline()
readline() now defaults to *ARGV
if no argument is provided. (Rafael
Garcia-Suarez)
state() variables
A new class of variables has been introduced. State variables are similar
variables, but are declared with the
keyword in place of
. They're visible only in their lexical scope, but their value is
persistent: unlike
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
feature 'state';or by using the -E
command-line switch in one-liners.
Stacked filetest operators
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 _
UNIVERSAL::DOES()
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)
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 @#
together will now
produce a compile-time error, as those format fields are incompatible.
has been improved, and miscellaneous bugs fixed.
Byte-order modifiers for pack() and unpack()
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.
for details.
You can now use
followed by a version number to specify that you
want to use a version of perl older than the specified one.
on filehandles
can now work on filehandles as well as
filenames, if the system supports respectively fchdir
, thanks to a patch provided by Gisle Aas.
now return groups in the order where the OS returns them,
thanks to Gisle Aas. This wasn't previously the case.
Recursive sort subs
You can now use recursive subroutines with sort(), thanks to Robin Houston.
Exceptions in constant folding
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)
Source filters in @INC
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
for details. (Nicholas Clark)
New internal variables
${^RE_DEBUG_FLAGS}
This variable controls what debug flags are in effect for the regular
expression engine when running under
re &debug&
${^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
for details. (Contributed by Gisle Aas.)
${^RE_TRIE_MAXBUF}
${^WIN32_SLOPPY_STAT}
Miscellaneous
now defaults to unpacking the $_
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
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 moreover not all regression tests still pass
with it. (Larry Wall, Nicholas Clark)
kill() on Windows
On Windows platforms, (-9, $pid)
now kills a process tree.
(On Unix, this delivers the signal to all processes in the same process
Incompatible Changes
Packing and UTF-8 strings
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 (&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
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
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
can also be used in pack() templates to specify
respectively character and byte modes.
in the middle of a pack or unpack format now switch to the
specified encoding mode, honoring parens grouping. Previously, parens were
Also, there is a new pack() character format, W
, which is intended to
replace the old 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
values outside the range 0..255, and not respect the string encoding).
In practice, that means that pack formats are now encoding-neutral, except
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.
Byte/character count feature in unpack()
A new unpack() template character, &.&
, returns the number of bytes or
characters (depending on the selected encoding mode, see above) read so far.
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
Two new severe warnings, $#/$* is no longer supported, have been added.
substr() lvalues are no longer fixed-length
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
Parsing of -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.
The :unique
attribute has been made a no-op, since its current
implementation was fundamentally flawed and not threadsafe.
Effect of pragmas in eval
The compile-time value of the %^H
hint variable can now propagate into
eval("")uated code. This makes it more useful to implement lexical
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)
Handling of .pmc files
An old feature of perl was that before
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.
$^V is now a version
object instead of a v-string
$^V can still be used with the %vd
format in printf, but any
character-level operations will now access the string representation
of the version
object and not the ordinals of a v-string.
Expressions like ($^V, 0, 2)
no longer work and must be rewritten.
@- and @+ in patterns
The special arrays @-
are no longer interpolated in regular
expressions. (Sadahiro Tomoyuki)
$AUTOLOAD can now be tainted
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)
Tainting and printf
When perl is run under taint mode,
reject any tainted format argument. (Rafael Garcia-Suarez)
undef and signal handlers
Undefining or deleting a signal handler via
equivalent to setting it to 'DEFAULT'
. (Rafael Garcia-Suarez)
strictures and dereferencing in defined()
strict 'refs'
was ignoring taking a hard reference in an argument
to defined(), as in :
strict 'refs';
$x = 'foo';
if ( $$x) {...}This now correctly produces the run-time error Can't use string as a
SCALAR ref while "strict refs" in use.
are now also subject to strict
(that is, $foo
shall be proper references there.)
are discouraged constructs anyway.)
(Nicholas Clark)
(?p{}) has been removed
The regular expression construct (?p{}), which was deprecated in perl
5.8, has been removed. Use (??{})
instead. (Rafael Garcia-Suarez)
Pseudo-hashes have been removed
Support for pseudo-hashes has been removed from Perl 5.9. (The fields
pragma remains here, but uses an alternate implementation.)
Removal of the bytecode compiler and of 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).
Removal of the JPL
The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.
Recursive inheritance detected earlier
Perl will now immediately throw an exception if you modify any package's
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)
warnings::enabled and warnings::warnif changed to favor users of modules
The behaviour in 5.10.x favors the per
The behaviour in 5.8.x favo
Assume the following code:
main calls Foo::Bar::baz()
Foo::Bar inherits from Foo::Base
Foo::Bar::baz() calls Foo::Base::_bazbaz()
Foo::Base::_bazbaz() calls: warnings::warnif('substr', 'some warning message');On 5.8.x, the code warns when Foo::Bar contains
It does not matter if Foo::Base or main have warnings enabled
to disable the warning one has to modify Foo::Bar.
On 5.10.0 and newer, the code warns when main contains
It does not matter if Foo::Base or Foo::Bar have warnings enabled
to disable the warning one has to modify main.
Modules and Pragmata
Upgrading individual core modules
Even more core modules are now also available separately through the
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.
perldoc CPAN
for more information.
Pragmata Changes
The new pragma feature
is used to enable new features that might break
old code. See
This new pragma enables to change the algorithm used to resolve inherited
methods. See
Scoping of the
pragma is now lexically scoped. Its effect used to be global.
Scoping of bignum
The three numeric pragmas bignum
and bigrat
lexically scoped. (Tels)
pragma now warns if a class tries to inherit from itself.
(Curtis "Ovid" Poe)
and warnings
and warnings
will now complain loudly if they are loaded via
incorrect casing (as in
). (Johan Vromans)
The version
module provides support for version objects.
The warnings
pragma doesn't load Carp
anymore. That means that code
that used Carp
routines without having loaded it at compile time might
typically, the following (faulty) code won't work
anymore, and will require parentheses to be added after the function name:
Carp::confess 'argh';
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
for more. (Joshua ben
New modules
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).
is an IO::
-style interface to Compress::Zlib
Archive::Tar
is a module to manipulate tar
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
inclu 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.
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().
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, gzipped or bzipped) or .zip files.
provides an API and a command-line tool to access the CPAN
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.
Selected Changes to Core Modules
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
is now based on Module::Pluggable
, and so can be extended
with plugins. (Joshua ben Jore)
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
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.
Utility Changes
The Perl debugger can now save all debugger command
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
is a pure perl implementation of tar
that comes with
Archive::Tar
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
is a command-line utility, used to print or to check SHA
digests. It comes with the new Digest::SHA
The corelist
utility is now installed with perl (see
h2ph and h2xs
have been made more robust with regard to
"modern" C code.
implements a new option ---xsloader
to force use of
even in backwards compatible modules.
The handling of authors' names that had apostrophes has been fixed.
Any enums with negative values are now skipped.
no longer checks for *.ph files by default.
Use the new -a
option to run all tests.
now assumes -
as a default action. Previously, it
needed to be specified explicitly.
Several bugs have been fixed in find2perl
, regarding -
. Also the options -path
and -iname
config_data
config_data
is a new utility that comes with Module::Build
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.)
, the CPANPLUS shell, has been added. (cpanp-run-perl
helper for CPANPLUS operation, has been added too, but isn't intended for
direct use).
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)
New Documentation
manpage documents how to write one's own lexical
pragmas in pure Perl (something that is possible starting with 5.9.4).
manpage is a glossary of terms used in the Perl
documentation, technical and otherwise, kindly provided by O'Reilly Media,
manpage, courtesy of Yves Orton, describes internals of the
Perl regular expression engine.
manpage describes the interface to the perl interpreter
used to write pluggable regular expression engines (by Ævar Arnfjörð
Bjarmason).
manpage is an tutorial for programming with Unicode and
string encodings in Perl, courtesy of Juerd Waalboer.
A new manual page,
(the Perl Unicode FAQ), has been added
(Juerd Waalboer).
manpage gives a description of the Perl community
on the Internet and in real life. (Edgar "Trizor" Bering)
manual page documents the CORE::
namespace. (Tels)
The long-existing feature of /(?{...})/
regexps setting $_
is now documented.
Performance Enhancements
In-place sorting
Sorting arrays in place (@a =
) is now optimized to avoid
making a temporary copy of the array.
is now optimized to sort in reverse,
avoiding the generation of a temporary intermediate list.
Lexical array access
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.)
XS-assisted SWASHGET
Some pure-perl code that perl was using to retrieve Unicode properties and
transliteration mappings has been reimplemented in XS.
Constant subroutines
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
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
for details.
Weak references are cheaper
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.
sort() enhancements
Salvador Fandiño provided improvements to reduce the memory usage of
and to speed up some cases.
Memory optimisations
Several internal data structures (typeglobs, GVs, CVs, formats) have been
restructured to use less memory. (Nicholas Clark)
UTF-8 cache optimisation
The UTF-8 caching code is now more efficient, and used more often.
(Nicholas Clark)
Sloppy stat on Windows
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)
Regular expressions optimisations
Engine de-recursivised
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)
Single char char-classes treated as literals
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)
Trie optimisation of literal string alternations
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.
Aho-Corasick start-point optimisation
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)
Installation and Configuration Improvements
Configuration improvements
-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.
Relocatable installations
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.
strlcat() and strlcpy()
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}
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 help
Configure -h
has been extended with the most commonly used options.
Compilation improvements
Parallel build
Parallel makes should work properly now, although there may still be problems
if make test
is instructed to run in parallel.
Borland's compilers support
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.
Static build on Windows
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)
ppport.h files
All ppport.h files in the XS modules bundled with perl are now
autogenerated at build time. (Marcus Holland-Moritz)
C++ compatibility
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 Microsoft 64-bit compiler
Support for building perl with Microsoft's 64-bit compiler has been
improved. (ActiveState)
Visual C++
Perl can now be compiled with Microsoft Visual C++ 2005 (and 2008 Beta 2).
Win32 builds
All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
Installation improvements
Module auxiliary files
README files and changelogs for CPAN modules bundled with perl are no
longer installed.
New Or Improved Platforms
Perl has been reported to work on Symbian OS. See
information.
Many improvements have been made towards making Perl work correctly on
Perl has been reported to work on DragonFlyBSD and MidnightBSD.
Perl has also been reported to work on NexentaOS
The VMS port has been improved. See .
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.
Selected Bug Fixes
strictures in regexp-eval blocks
wasn't in effect in regexp-eval blocks (/(?{...})/
Calling CORE::require()
CORE::require() and CORE::do() were always parsed as require() and do()
when they were overridden. This is now fixed.
Subscripts of slices
You can now use a non-arrowed form for chained subscripts after a list
slice, like in:
({foo =& &bar&})[0]{foo}This used
was required.
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.
warnings 'io';
will only turn off warnings in the
class. Previously it would erroneously turn off all warnings.
threads improvements
Several memory leaks in ithreads were closed. Also, ithreads were made
less memory-intensive.
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() and negative values
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.
PERL5SHELL and tainting
On Windows, the PERL5SHELL environment variable is now checked for
taintedness. (Rafael Garcia-Suarez)
Using *FILE{IO}
filetests now treat *FILE{IO} filehandles like *FILE
filehandles. (Steve Peters)
Overloading and reblessing
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)
Overloading and UTF-8
A few bugs related to UTF-8 handling with objects that have
stringification overloaded have been fixed. (Nicholas Clark)
eval memory leaks fixed
Traditionally,
'syntax error'
has leaked badly. Many (but not all)
of these leaks have now been eliminated or reduced. (Dave Mitchell)
Random device on Windows
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)
PERLIO_DEBUG
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 and read-only scalars
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() and UTF-8
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)
Critical signals
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 rea see
). (Rafael)
@INC-hook fix
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)
switch fix
switches can now be used together without messing
up which categories of warnings are activated. (Rafael)
Duping UTF-8 filehandles
Duping a filehandle which has the :utf8
PerlIO layer set will now
properly carry that layer on the duped filehandle. (Rafael)
Localisation of hash elements
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
$h{$x}; ++$x
). (Bo Lindbergh)
New or Changed Diagnostics
Use of uninitialized value
Perl will now try to tell you the name of the variable (if any) that was
undefined.
Deprecated use of my() in false conditional
A new deprecation warning, Deprecated use of my() in false conditional,
has been added, to warn against the use of the dubious and deprecated
$x if 0;See . Use
variables instead.
!=~ should be !~
A new warning, !=~ should be !~
, is emitted to prevent this misspelling
of the non-matching operator.
Newline in left-justified string
The warning Newline in left-justified string has been removed.
Too late for "-T" option
The error Too late for "-T" option has been reformulated to be more
descriptive.
"%s" variable %s masks earlier declaration
This warning is now emitted in m in short, when one
of the declarations involved is a
$x; # warns
$x; # warns
$x; # warnsOn the other hand, the following:
$x;now gives a "our" variable %s redeclared warning.
readdir()/closedir()/etc. attempted on invalid dirhandle
These new warnings are now emitted when a dirhandle is used but is
either closed or not really a dirhandle.
Opening dirhandle/filehandle %s also as a file/directory
Two deprecation warnings have been added: (Rafael)
Opening dirhandle %s also as a file
Opening filehandle %s also as a directory
Use of -P is deprecated
Perl's command-line switch -P
is now deprecated.
v-string in use/require is non-portable
Perl will warn you against potential backwards compatibility problems with
has several improvements, making it more useable from shell
scripts to get the value of configuration variables. See
Changed Internals
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.
Reordering of SVt_* constants
The relative ordering of constants that define the various types of SV
in particular, SVt_PVGV
has been moved before SVt_PVLV
, 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.)
Elimination of SVt_PVBM
Related to this, the internal type SVt_PVBM
has been removed. This
dedicated type of SV
was used by the
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
New type SVt_BIND
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.
Removal of CPP symbols
The C preprocessor symbols PERL_PM_APIVERSION
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.
Less space is used by ops
The BASEOP
structure now uses less space. The op_seq
field has been
removed and replaced by a single bit bit-field op_opt
bits long. (Consequently, the B::OP
class doesn't provide an seq
method anymore.)
New parser
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
Use of const
Andy Lester supplied many improvements to determine which function
parameters and local variables could actually be declared const
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.
has been removed
The AvFLAGS
macro has been removed.
The av_*()
functions, used to manipulate arrays, no longer accept null
parameters.
$^H and %^H
The implementation of the special variables $^H and %^H has changed, to
allow implementing lexical pragmas in pure Perl.
B:: modules inheritance changed
The inheritance hierarchy of B::
inherits from B::SV
(it used to inherit from B::IV
Anonymous hash and array constructors
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)
Known Problems
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().
UTF-8 problems
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.
Platform Specific Problems
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
Reporting Bugs
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
There may also be
information at
, 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.
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