PERL5100DELTA(1) Perl Programmers Reference Guide PERL5100DELTA(1)
NAME
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 releases; they are not duplicated here and are documented
in the set of man pages named perl58[1-8]?delta.
Core Enhancements
The "feature" pragma
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" (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.
New -E command-line switch
-E is equivalent to -e, but it implicitly enables all optional features
(like "use feature ":5.10"").
Defined-or operator
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 $c;
The "//" operator has the same precedence and associativity as "||".
Special care has been taken to ensure that this operator Do What You
Mean while not breaking old code, but some edge cases involving the
empty regular expression may now parse differently. See perlop for
details.
Switch and Smart Match operator
Perl 5 now has a switch statement. It's available when "use feature
'switch'" is in effect. This feature introduces three new keywords,
"given", "when", and "default":
given ($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.
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 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)
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 "%+"
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
foreach my $name (keys %+) {
print "content of buffer '$name' is $+{$name}\n";
}
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)
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 perlre for their descriptions. (Yves
Orton)
Relative backreferences
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)
Vertical and horizontal whitespace, and linebreak
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" in perlfunc. (Robin Houston)
Lexical $_
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 $_". (Rafael Garcia-Suarez)
The "_" prototype
A new prototype character has been added. "_" is equivalent to "$" 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 blocks
"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)
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 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").
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. 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.
readpipe() is now overridable
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)
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 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.
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 $file && -w _ && -f _". See "-X" in perlfunc.
UNIVERSAL::DOES()
The "UNIVERSAL" class has a new method, "DOES()". It has been added to
solve semantic problems with the "isa()" method. "isa()" checks for
inheritance, while "DOES()" has been designed to be overridden when
module authors use other types of relations between classes (in
addition to inheritance). (chromatic)
See "$obj->DOES( ROLE )" in UNIVERSAL.
Formats
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.
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. See "pack" in perlfunc 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 filehandles
"chdir", "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.
OS groups
$( and $) now return groups in the order where the OS returns them,
thanks to Gisle Aas. This wasn't previously the case.
Recursive sort subs
You can now use recursive subroutines with sort(), thanks to Robin
Houston.
Exceptions in constant folding
The constant folding routine is now wrapped in an exception handler,
and if folding throws an exception (such as attempting to evaluate
0/0), perl now retains the current optree, rather than aborting the
whole program. Without this change, programs would not compile if they
had expressions that happened to generate exceptions, even though those
expressions were in code that could never be reached at runtime.
(Nicholas Clark, Dave Mitchell)
Source filters in @INC
It's possible to enhance the mechanism of subroutine hooks in @INC by
adding a source filter on top of the filehandle opened and returned by
the hook. This feature was planned a long time ago, but wasn't quite
working until now. See "require" in perlfunc for details. (Nicholas
Clark)
New internal variables
"${^RE_DEBUG_FLAGS}"
This variable controls what debug flags are in effect for the
regular expression engine when running under "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}"
See "Trie optimisation of literal string alternations".
"${^WIN32_SLOPPY_STAT}"
See "Sloppy stat on Windows".
Miscellaneous
"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.
UCD 5.0.0
The copy of the Unicode Character Database included in Perl 5 has been
updated to version 5.0.0.
MAD
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)
kill() on Windows
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.)
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 "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.
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.
The $* 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.
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 it.
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.
":unique"
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
pragmas.
As a side-effect of this, the overloaded-ness of constants now
propagates into eval("").
chdir FOO
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 "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.
$^V is now a "version" object instead of a v-string
$^V can still be used with the %vd format in printf, but any character-
level operations will now access the string representation of the
"version" object and not the ordinals of a v-string. Expressions like
"substr($^V, 0, 2)" or "split //, $^V" no longer work and must be
rewritten.
@- and @+ in patterns
The special arrays "@-" and "@+" 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, "printf()" and "sprintf()" will now
reject any tainted format argument. (Rafael Garcia-Suarez)
undef and signal handlers
Undefining or deleting a signal handler via "undef $SIG{FOO}" is now
equivalent to setting it to 'DEFAULT'. (Rafael Garcia-Suarez)
strictures and dereferencing in defined()
"use strict 'refs'" was ignoring taking a hard reference in an argument
to defined(), as in :
use strict 'refs';
my $x = 'foo';
if (defined $$x) {...}
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 $bar shall be proper references there.)
("defined(@foo)" and "defined(%bar)" are discouraged constructs
anyway.) (Nicholas Clark)
"(?p{})" has been removed
The regular expression construct "(?p{})", which was deprecated in perl
5.8, has been removed. Use "(??{})" instead. (Rafael Garcia-Suarez)
Pseudo-hashes have been removed
Support for pseudo-hashes has been removed from Perl 5.9. (The "fields"
pragma remains here, but uses an alternate implementation.)
Removal of the bytecode compiler and of perlcc
"perlcc", the byteloader and the supporting modules (B::C, B::CC,
B::Bytecode, etc.) are no longer distributed with the perl sources.
Those experimental tools have never worked reliably, and, due to the
lack of volunteers to keep them in line with the perl interpreter
developments, it was decided to remove them instead of shipping a
broken version of those. The last version of those modules can be
found with perl 5.9.4.
However the B compiler framework stays supported in the perl core, as
with the more useful modules it has permitted (among others, B::Deparse
and B::Concise).
Removal of the JPL
The JPL (Java-Perl Lingo) has been removed from the perl sources
tarball.
Recursive inheritance detected earlier
Perl will now immediately throw an exception if you modify any
package's @ISA in such a way that it would cause recursive inheritance.
Previously, the exception would not occur until Perl attempted to make
use of the recursive inheritance while resolving a method or doing a
"$foo->isa($bar)" lookup.
warnings::enabled and warnings::warnif changed to favor users of modules
The behaviour in 5.10.x favors the person using the module; The
behaviour in 5.8.x favors the module writer;
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 "use warnings;" 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 "use warnings;"
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
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.
Pragmata Changes
"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.
Scoping of the "sort" pragma
The "sort" pragma is now lexically scoped. Its effect used to be
global.
Scoping of "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:
use warnings;
require Carp;
Carp::confess 'argh';
"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)
New modules
o "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.
o "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".
o "Math::BigInt::FastCalc" is an XS-enabled, and thus faster, version
of "Math::BigInt::Calc".
o "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).
o "IO::Zlib" is an "IO::"-style interface to "Compress::Zlib".
o "Archive::Tar" is a module to manipulate "tar" archives.
o "Digest::SHA" is a module used to calculate many types of SHA
digests, has been included for SHA support in the CPAN module.
o "ExtUtils::CBuilder" and "ExtUtils::ParseXS" have been added.
o "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.
o "Module::Build", by Ken Williams, has been added. It's an
alternative to "ExtUtils::MakeMaker" to build and install perl
modules.
o "Module::Load", by Jos Boumans, has been added. It provides a
single interface to load Perl modules and .pl files.
o "Module::Loaded", by Jos Boumans, has been added. It's used to mark
modules as loaded or unloaded.
o "Package::Constants", by Jos Boumans, has been added. It's a simple
helper to list all constants declared in a given package.
o "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.
o "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.
o "Params::Check" implements a generic input parsing/checking
mechanism. It is used by CPANPLUS.
o "Term::UI" simplifies the task to ask questions at a terminal
prompt.
o "Object::Accessor" provides an interface to create per-object
accessors.
o "Module::Pluggable" is a simple framework to create modules that
accept pluggable sub-modules.
o "Module::Load::Conditional" provides simple ways to query and
possibly load installed modules.
o "Time::Piece" provides an object oriented interface to time
functions, overriding the built-ins localtime() and gmtime().
o "IPC::Cmd" helps to find and run external commands, possibly
interactively.
o "File::Fetch" provide a simple generic file fetching mechanism.
o "Log::Message" and "Log::Message::Simple" are used by the log
facility of "CPANPLUS".
o "Archive::Extract" is a generic archive extraction mechanism for
.tar (plain, gzipped or bzipped) or .zip files.
o "CPANPLUS" provides an API and a command-line tool to access the
CPAN mirrors.
o "Pod::Escapes" provides utilities that are useful in decoding Pod
E<...> sequences.
o "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 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.
Utility Changes
perl -d
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
"ptar" is a pure perl implementation of "tar" that comes with
"Archive::Tar".
ptardiff
"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
"shasum" is a command-line utility, used to print or to check SHA
digests. It comes with the new "Digest::SHA" module.
corelist
The "corelist" utility is now installed with perl (see "New
modules" above).
h2ph and h2xs
"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
"perlivp" no longer checks for *.ph files by default. Use the new
"-a" option to run all tests.
find2perl
"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
"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
"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
"cpan2dist" is a new utility that comes with CPANPLUS. It's a tool
to create distributions (or packages) from CPAN modules.
pod2html
The output of "pod2html" has been enhanced to be more customizable
via CSS. Some formatting problems were also corrected. (Jari Aalto)
New Documentation
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 var Arnfjoer`
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.
Performance Enhancements
In-place sorting
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.
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 "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 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 Fandin~o provided improvements to reduce the memory usage of
"sort" 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} 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 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 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.
Selected Bug Fixes
strictures in regexp-eval blocks
"strict" 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 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.
threads improvements
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() 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}
"stat()" and "-X" 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, "eval '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 reasonably stable state; see
"Deferred Signals (Safe Signals)" in perlipc). (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)
"-t" switch fix
The "-w" and "-t" 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 in "local $h{$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 construct
my $x if 0;
See perldiag. Use "state" 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 more consistent cases; in short,
when one of the declarations involved is a "my" variable:
my $x; my $x; # warns
my $x; our $x; # warns
our $x; my $x; # warns
On the other hand, the following:
our $x; our $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 the "use VERSION" syntax.
perl -V
"perl -V" has several improvements, making it more useable from
shell scripts to get the value of configuration variables. See
perlrun for details.
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" 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.)
Elimination of SVt_PVBM
Related to this, the internal type "SVt_PVBM" has 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".
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" 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.
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". "op_type" is
now 9 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" 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.
Mathoms
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 removed
The "AvFLAGS" macro has been removed.
"av_*" changes
The "av_*()" functions, used to manipulate arrays, no longer accept
null "AV*" 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::" modules has changed; "B::NV" now
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 one.
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 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 AT perl.org to be analysed by
the Perl porting team.
SEE ALSO
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.
perl v5.16.3 2013-03-04 PERL5100DELTA(1)
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