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perl5120delta - what is new for perl v5.12.0


This document describes differences between the 5.10.0 release and the 5.12.0 release.

Many of the bug fixes in 5.12.0 are already included in the 5.10.1 maintenance release.

You can see the list of those changes in the 5.10.1 release notes (perl5101delta).

Core Enhancements

New package NAME VERSION syntax

This new syntax allows a module author to set the $VERSION of a namespace when the namespace is declared with 'package'. It eliminates the need for our $VERSION = ... and similar constructs. E.g.

package Foo::Bar 1.23;
# $Foo::Bar::VERSION == 1.23

There are several advantages to this:

It does not break old code with only package NAME, but code that uses package NAME VERSION will need to be restricted to perl 5.12.0 or newer. This is analogous to the change to open from two-args to three-args. Users requiring the latest Perl will benefit, and perhaps after several years, it will become a standard practice.

However, package NAME VERSION requires a new, 'strict' version number format. See "Version number formats" for details.

The ... operator

A new operator, ..., nicknamed the Yada Yada operator, has been added. It is intended to mark placeholder code that is not yet implemented. See "Yada Yada Operator" in perlop.

Implicit strictures

Using the use VERSION syntax with a version number greater or equal to 5.11.0 will lexically enable strictures just like use strict would do (in addition to enabling features.) The following:

use 5.12.0;


use strict;
use feature ':5.12';

Unicode improvements

Perl 5.12 comes with Unicode 5.2, the latest version available to us at the time of release. This version of Unicode was released in October 2009. See for further details about what's changed in this version of the standard. See perlunicode for instructions on installing and using other versions of Unicode.

Additionally, Perl's developers have significantly improved Perl's Unicode implementation. For full details, see "Unicode overhaul" below.

Y2038 compliance

Perl's core time-related functions are now Y2038 compliant. (It may not mean much to you, but your kids will love it!)

qr overloading

It is now possible to overload the qr// operator, that is, conversion to regexp, like it was already possible to overload conversion to boolean, string or number of objects. It is invoked when an object appears on the right hand side of the =~ operator or when it is interpolated into a regexp. See overload.

Pluggable keywords

Extension modules can now cleanly hook into the Perl parser to define new kinds of keyword-headed expression and compound statement. The syntax following the keyword is defined entirely by the extension. This allows a completely non-Perl sublanguage to be parsed inline, with the correct ops cleanly generated.

See "PL_keyword_plugin" in perlapi for the mechanism. The Perl core source distribution also includes a new module XS::APItest::KeywordRPN, which implements reverse Polish notation arithmetic via pluggable keywords. This module is mainly used for test purposes, and is not normally installed, but also serves as an example of how to use the new mechanism.

Perl's developers consider this feature to be experimental. We may remove it or change it in a backwards-incompatible way in Perl 5.14.

APIs for more internals

The lowest layers of the lexer and parts of the pad system now have C APIs available to XS extensions. These are necessary to support proper use of pluggable keywords, but have other uses too. The new APIs are experimental, and only cover a small proportion of what would be necessary to take full advantage of the core's facilities in these areas. It is intended that the Perl 5.13 development cycle will see the addition of a full range of clean, supported interfaces.

Perl's developers consider this feature to be experimental. We may remove it or change it in a backwards-incompatible way in Perl 5.14.

Overridable function lookup

Where an extension module hooks the creation of rv2cv ops to modify the subroutine lookup process, this now works correctly for bareword subroutine calls. This means that prototypes on subroutines referenced this way will be processed correctly. (Previously bareword subroutine names were initially looked up, for parsing purposes, by an unhookable mechanism, so extensions could only properly influence subroutine names that appeared with an & sigil.)

A proper interface for pluggable Method Resolution Orders

As of Perl 5.12.0 there is a new interface for plugging and using method resolution orders other than the default linear depth first search. The C3 method resolution order added in 5.10.0 has been re-implemented as a plugin, without changing its Perl-space interface. See perlmroapi for more information.

\N experimental regex escape

Perl now supports \N, a new regex escape which you can think of as the inverse of \n. It will match any character that is not a newline, independently from the presence or absence of the single line match modifier /s. It is not usable within a character class. \N{3} means to match 3 non-newlines; \N{5,} means to match at least 5. \N{NAME} still means the character or sequence named NAME, but NAME no longer can be things like 3, or 5,.

This will break a custom charnames translator which allows numbers for character names, as \N{3} will now mean to match 3 non-newline characters, and not the character whose name is 3. (No name defined by the Unicode standard is a number, so only custom translators might be affected.)

Perl's developers are somewhat concerned about possible user confusion with the existing \N{...} construct which matches characters by their Unicode name. Consequently, this feature is experimental. We may remove it or change it in a backwards-incompatible way in Perl 5.14.

DTrace support

Perl now has some support for DTrace. See "DTrace support" in INSTALL.

Support for configure_requires in CPAN module metadata

Both CPAN and CPANPLUS now support the configure_requires keyword in the META.yml metadata file included in most recent CPAN distributions. This allows distribution authors to specify configuration prerequisites that must be installed before running Makefile.PL or Build.PL.

See the documentation for ExtUtils::MakeMaker or Module::Build for more on how to specify configure_requires when creating a distribution for CPAN.

each, keys, values are now more flexible

The each, keys, values function can now operate on arrays.

when as a statement modifier

when is now allowed to be used as a statement modifier.

$, flexibility

The variable $, may now be tied.

// in when clauses

// now behaves like || in when clauses

Enabling warnings from your shell environment

You can now set -W from the PERL5OPT environment variable

delete local

delete local now allows you to locally delete a hash entry.

New support for Abstract namespace sockets

Abstract namespace sockets are Linux-specific socket type that live in AF_UNIX family, slightly abusing it to be able to use arbitrary character arrays as addresses: They start with nul byte and are not terminated by nul byte, but with the length passed to the socket() system call.

32-bit limit on substr arguments removed

The 32-bit limit on substr arguments has now been removed. The full range of the system's signed and unsigned integers is now available for the pos and len arguments.

Potentially Incompatible Changes

Deprecations warn by default

Over the years, Perl's developers have deprecated a number of language features for a variety of reasons. Perl now defaults to issuing a warning if a deprecated language feature is used. Many of the deprecations Perl now warns you about have been deprecated for many years. You can find a list of what was deprecated in a given release of Perl in the perl5xxdelta.pod file for that release.

To disable this feature in a given lexical scope, you should use no warnings 'deprecated'; For information about which language features are deprecated and explanations of various deprecation warnings, please see perldiag. See "Deprecations" below for the list of features and modules Perl's developers have deprecated as part of this release.

Version number formats

Acceptable version number formats have been formalized into "strict" and "lax" rules. package NAME VERSION takes a strict version number. UNIVERSAL::VERSION and the version object constructors take lax version numbers. Providing an invalid version will result in a fatal error. The version argument in use NAME VERSION is first parsed as a numeric literal or v-string and then passed to UNIVERSAL::VERSION (and must then pass the "lax" format test).

These formats are documented fully in the version module. To a first approximation, a "strict" version number is a positive decimal number (integer or decimal-fraction) without exponentiation or else a dotted-decimal v-string with a leading 'v' character and at least three components. A "lax" version number allows v-strings with fewer than three components or without a leading 'v'. Under "lax" rules, both decimal and dotted-decimal versions may have a trailing "alpha" component separated by an underscore character after a fractional or dotted-decimal component.

The version module adds version::is_strict and version::is_lax functions to check a scalar against these rules.

@INC reorganization

In @INC, ARCHLIB and PRIVLIB now occur after the current version's site_perl and vendor_perl. Modules installed into site_perl and vendor_perl will now be loaded in preference to those installed in ARCHLIB and PRIVLIB.

REGEXPs are now first class

Internally, Perl now treats compiled regular expressions (such as those created with qr//) as first class entities. Perl modules which serialize, deserialize or otherwise have deep interaction with Perl's internal data structures need to be updated for this change. Most affected CPAN modules have already been updated as of this writing.

Switch statement changes

The given/when switch statement handles complex statements better than Perl 5.10.0 did (These enhancements are also available in 5.10.1 and subsequent 5.10 releases.) There are two new cases where when now interprets its argument as a boolean, instead of an expression to be used in a smart match:

flip-flop operators

The .. and ... flip-flop operators are now evaluated in boolean context, following their usual semantics; see "Range Operators" in perlop.

Note that, as in perl 5.10.0, when (1..10) will not work to test whether a given value is an integer between 1 and 10; you should use when ([1..10]) instead (note the array reference).

However, contrary to 5.10.0, evaluating the flip-flop operators in boolean context ensures it can now be useful in a when(), notably for implementing bistable conditions, like in:

when (/^=begin/ .. /^=end/) {
  # do something
defined-or operator

A compound expression involving the defined-or operator, as in when (expr1 // expr2), will be treated as boolean if the first expression is boolean. (This just extends the existing rule that applies to the regular or operator, as in when (expr1 || expr2).)

Smart match changes

Since Perl 5.10.0, Perl's developers have made a number of changes to the smart match operator. These, of course, also alter the behaviour of the switch statements where smart matching is implicitly used. These changes were also made for the 5.10.1 release, and will remain in subsequent 5.10 releases.

Changes to type-based dispatch

The smart match operator ~~ is no longer commutative. The behaviour of a smart match now depends primarily on the type of its right hand argument. Moreover, its semantics have been adjusted for greater consistency or usefulness in several cases. While the general backwards compatibility is maintained, several changes must be noted:

The full dispatch table for the smart match operator is given in "Smart matching in detail" in perlsyn.

Smart match and overloading

According to the rule of dispatch based on the rightmost argument type, when an object overloading ~~ appears on the right side of the operator, the overload routine will always be called (with a 3rd argument set to a true value, see overload.) However, when the object will appear on the left, the overload routine will be called only when the rightmost argument is a simple scalar. This way, distributivity of smart match across arrays is not broken, as well as the other behaviours with complex types (coderefs, hashes, regexes). Thus, writers of overloading routines for smart match mostly need to worry only with comparing against a scalar, and possibly with stringification overloading; the other common cases will be automatically handled consistently.

~~ will now refuse to work on objects that do not overload it (in order to avoid relying on the object's underlying structure). (However, if the object overloads the stringification or the numification operators, and if overload fallback is active, it will be used instead, as usual.)

Other potentially incompatible changes


From time to time, Perl's developers find it necessary to deprecate features or modules we've previously shipped as part of the core distribution. We are well aware of the pain and frustration that a backwards-incompatible change to Perl can cause for developers building or maintaining software in Perl. You can be sure that when we deprecate a functionality or syntax, it isn't a choice we make lightly. Sometimes, we choose to deprecate functionality or syntax because it was found to be poorly designed or implemented. Sometimes, this is because they're holding back other features or causing performance problems. Sometimes, the reasons are more complex. Wherever possible, we try to keep deprecated functionality available to developers in its previous form for at least one major release. So long as a deprecated feature isn't actively disrupting our ability to maintain and extend Perl, we'll try to leave it in place as long as possible.

The following items are now deprecated:


suidperl is no longer part of Perl. It used to provide a mechanism to emulate setuid permission bits on systems that don't support it properly.

Use of := to mean an empty attribute list

An accident of Perl's parser meant that these constructions were all equivalent:

my $pi := 4;
my $pi : = 4;
my $pi :  = 4;

with the : being treated as the start of an attribute list, which ends before the =. As whitespace is not significant here, all are parsed as an empty attribute list, hence all the above are equivalent to, and better written as

my $pi = 4;

because no attribute processing is done for an empty list.

As is, this meant that := cannot be used as a new token, without silently changing the meaning of existing code. Hence that particular form is now deprecated, and will become a syntax error. If it is absolutely necessary to have empty attribute lists (for example, because of a code generator) then avoid the warning by adding a space before the =.


The method UNIVERSAL->import() is now deprecated. Attempting to pass import arguments to a use UNIVERSAL statement will result in a deprecation warning.

Use of "goto" to jump into a construct

Using goto to jump from an outer scope into an inner scope is now deprecated. This rare use case was causing problems in the implementation of scopes.

Custom character names in \N{name} that don't look like names

In \N{name}, name can be just about anything. The standard Unicode names have a very limited domain, but a custom name translator could create names that are, for example, made up entirely of punctuation symbols. It is now deprecated to make names that don't begin with an alphabetic character, and aren't alphanumeric or contain other than a very few other characters, namely spaces, dashes, parentheses and colons. Because of the added meaning of \N (See "\N" experimental regex escape), names that look like curly brace -enclosed quantifiers won't work. For example, \N{3,4} now means to match 3 to 4 non-newlines; before a custom name 3,4 could have been created.

Deprecated Modules

The following modules will be removed from the core distribution in a future release, and should be installed from CPAN instead. Distributions on CPAN which require these should add them to their prerequisites. The core versions of these modules warnings will issue a deprecation warning.

If you ship a packaged version of Perl, either alone or as part of a larger system, then you should carefully consider the repercussions of core module deprecations. You may want to consider shipping your default build of Perl with packages for some or all deprecated modules which install into vendor or site perl library directories. This will inhibit the deprecation warnings.

Alternatively, you may want to consider patching lib/ to provide deprecation warnings specific to your packaging system or distribution of Perl, consistent with how your packaging system or distribution manages a staged transition from a release where the installation of a single package provides the given functionality, to a later release where the system administrator needs to know to install multiple packages to get that same functionality.

You can silence these deprecation warnings by installing the modules in question from CPAN. To install the latest version of all of them, just install Task::Deprecations::5_12.


Switch is buggy and should be avoided. You may find Perl's new given/when feature a suitable replacement. See "Switch statements" in perlsyn for more information.

Assignment to $[
Use of the attribute :locked on subroutines
Use of "locked" with the attributes pragma
Use of "unique" with the attributes pragma

Perl_pmflag is no longer part of Perl's public API. Calling it now generates a deprecation warning, and it will be removed in a future release. Although listed as part of the API, it was never documented, and only ever used in toke.c, and prior to 5.10, regcomp.c. In core, it has been replaced by a static function.

Numerous Perl 4-era libraries,,,,,,,,,,,,,,,,,,,,,,,,,,,, and are all now deprecated. Earlier, Perl's developers intended to remove these libraries from Perl's core for the 5.14.0 release.

During final testing before the release of 5.12.0, several developers discovered current production code using these ancient libraries, some inside the Perl core itself. Accordingly, the pumpking granted them a stay of execution. They will begin to warn about their deprecation in the 5.14.0 release and will be removed in the 5.16.0 release.

Unicode overhaul

Perl's developers have made a concerted effort to update Perl to be in sync with the latest Unicode standard. Changes for this include:

Perl can now handle every Unicode character property. New documentation, perluniprops, lists all available non-Unihan character properties. By default, perl does not expose Unihan, deprecated or Unicode-internal properties. See below for more details on these; there is also a section in the pod listing them, and explaining why they are not exposed.

Perl now fully supports the Unicode compound-style of using = and : in writing regular expressions: \p{property=value} and \p{property:value} (both of which mean the same thing).

Perl now fully supports the Unicode loose matching rules for text between the braces in \p{...} constructs. In addition, Perl allows underscores between digits of numbers.

Perl now accepts all the Unicode-defined synonyms for properties and property values.

qr/\X/, which matches a Unicode logical character, has been expanded to work better with various Asian languages. It now is defined as an extended grapheme cluster. (See Anything matched previously and that made sense will continue to be accepted. Additionally:

Otherwise, this change should be transparent for the non-affected languages.

\p{...} matches using the Canonical_Combining_Class property were completely broken in previous releases of Perl. They should now work correctly.

Before Perl 5.12, the Unicode Decomposition_Type=Compat property and a Perl extension had the same name, which led to neither matching all the correct values (with more than 100 mistakes in one, and several thousand in the other). The Perl extension has now been renamed to be Decomposition_Type=Noncanonical (short: dt=noncanon). It has the same meaning as was previously intended, namely the union of all the non-canonical Decomposition types, with Unicode Compat being just one of those.

\p{Decomposition_Type=Canonical} now includes the Hangul syllables.

\p{Uppercase} and \p{Lowercase} now work as the Unicode standard says they should. This means they each match a few more characters than they used to.

\p{Cntrl} now matches the same characters as \p{Control}. This means it no longer will match Private Use (gc=co), Surrogates (gc=cs), nor Format (gc=cf) code points. The Format code points represent the biggest possible problem. All but 36 of them are either officially deprecated or strongly discouraged from being used. Of those 36, likely the most widely used are the soft hyphen (U+00AD), and BOM, ZWSP, ZWNJ, WJ, and similar characters, plus bidirectional controls.

\p{Alpha} now matches the same characters as \p{Alphabetic}. Before 5.12, Perl's definition included a number of things that aren't really alpha (all marks) while omitting many that were. The definitions of \p{Alnum} and \p{Word} depend on Alpha's definition and have changed accordingly.

\p{Word} no longer incorrectly matches non-word characters such as fractions.

\p{Print} no longer matches the line control characters: Tab, LF, CR, FF, VT, and NEL. This brings it in line with standards and the documentation.

\p{XDigit} now matches the same characters as \p{Hex_Digit}. This means that in addition to the characters it currently matches, [A-Fa-f0-9], it will also match the 22 fullwidth equivalents, for example U+FF10: FULLWIDTH DIGIT ZERO.

The Numeric type property has been extended to include the Unihan characters.

There is a new Perl extension, the 'Present_In', or simply 'In', property. This is an extension of the Unicode Age property, but \p{In=5.0} matches any code point whose usage has been determined as of Unicode version 5.0. The \p{Age=5.0} only matches code points added in precisely version 5.0.

A number of properties now have the correct values for unassigned code points. The affected properties are Bidi_Class, East_Asian_Width, Joining_Type, Decomposition_Type, Hangul_Syllable_Type, Numeric_Type, and Line_Break.

The Default_Ignorable_Code_Point, ID_Continue, and ID_Start properties are now up to date with current Unicode definitions.

Earlier versions of Perl erroneously exposed certain properties that are supposed to be Unicode internal-only. Use of these in regular expressions will now generate, if enabled, a deprecation warning message. The properties are: Other_Alphabetic, Other_Default_Ignorable_Code_Point, Other_Grapheme_Extend, Other_ID_Continue, Other_ID_Start, Other_Lowercase, Other_Math, and Other_Uppercase.

It is now possible to change which Unicode properties Perl understands on a per-installation basis. As mentioned above, certain properties are turned off by default. These include all the Unihan properties (which should be accessible via the CPAN module Unicode::Unihan) and any deprecated or Unicode internal-only property that Perl has never exposed.

The generated files in the lib/unicore/To directory are now more clearly marked as being stable, directly usable by applications. New hash entries in them give the format of the normal entries, which allows for easier machine parsing. Perl can generate files in this directory for any property, though most are suppressed. You can find instructions for changing which are written in perluniprops.

Modules and Pragmata

New Modules and Pragmata


autodie is a new lexically-scoped alternative for the Fatal module. The bundled version is 2.06_01. Note that in this release, using a string eval when autodie is in effect can cause the autodie behaviour to leak into the surrounding scope. See "BUGS" in autodie for more details.

Version 2.06_01 has been added to the Perl core.


Version 2.024 has been added to the Perl core.


overloading allows you to lexically disable or enable overloading for some or all operations.

Version 0.001 has been added to the Perl core.


parent establishes an ISA relationship with base classes at compile time. It provides the key feature of base without further unwanted behaviors.

Version 0.223 has been added to the Perl core.


Version 1.40 has been added to the Perl core.


Version 1.03 has been added to the Perl core.


Version 2.4 has been added to the Perl core.


Version 0.003 has been added to the Perl core.

Updated Pragmata


Upgraded from version 2.13 to 2.15.


Upgraded from version 0.22 to 0.23.


charnames now contains the Unicode NameAliases.txt database file. This has the effect of adding some extra \N character names that formerly wouldn't have been recognised; for example, "\N{LATIN CAPITAL LETTER GHA}".

Upgraded from version 1.06 to 1.07.


Upgraded from version 1.13 to 1.20.


diagnostics now supports %.0f formatting internally.

diagnostics no longer suppresses Use of uninitialized value in range (or flip) warnings. [perl #71204]

Upgraded from version 1.17 to 1.19.


In feature, the meaning of the :5.10 and :5.10.X feature bundles has changed slightly. The last component, if any (i.e. X) is simply ignored. This is predicated on the assumption that new features will not, in general, be added to maintenance releases. So :5.10 and :5.10.X have identical effect. This is a change to the behaviour documented for 5.10.0.

feature now includes the unicode_strings feature:

use feature "unicode_strings";

This pragma turns on Unicode semantics for the case-changing operations (uc, lc, ucfirst, lcfirst) on strings that don't have the internal UTF-8 flag set, but that contain single-byte characters between 128 and 255.

Upgraded from version 1.11 to 1.16.


less now includes the stash_name method to allow subclasses of less to pick where in %^H to store their stash.

Upgraded from version 0.02 to 0.03.


Upgraded from version 0.5565 to 0.62.


mro is now implemented as an XS extension. The documented interface has not changed. Code relying on the implementation detail that some mro:: methods happened to be available at all times gets to "keep both pieces".

Upgraded from version 1.00 to 1.02.


overload now allow overloading of 'qr'.

Upgraded from version 1.06 to 1.10.


Upgraded from version 1.67 to 1.75.


Upgraded from version 1.14 to 1.32.


version now has support for "Version number formats" as described earlier in this document and in its own documentation.

Upgraded from version 0.74 to 0.82.


warnings has a new warnings::fatal_enabled() function. It also includes a new illegalproto warning category. See also "New or Changed Diagnostics" for this change.

Upgraded from version 1.06 to 1.09.

Updated Modules


Upgraded from version 0.24 to 0.38.


Upgraded from version 1.38 to 1.54.


Upgraded from version 0.79 to 0.87.


Upgraded from version 5.63 to 5.70.


Upgraded from version 0.74 to 0.78.


Upgraded from version 1.05 to 1.12.


Upgraded from version 0.83 to 0.96.


Upgraded from version 1.09 to 1.11_01.


Upgraded from version 3.29 to 3.48.


Upgraded from version 0.33 to 0.36.

NOTE: Class::ISA is deprecated and may be removed from a future version of Perl.


Upgraded from version 2.008 to 2.024.


Upgraded from version 1.9205 to 1.94_56.


Upgraded from version 0.84 to 0.90.


Upgraded from version 0.06_02 to 0.46.


Upgraded from version 2.121_14 to 2.125.


Upgraded from version 1.816_1 to 1.820.


Upgraded from version 3.13 to 3.19.


Upgraded from version 1.15 to 1.16.


Upgraded from version 2.36_01 to 2.39.


Upgraded from version 5.45 to 5.47.


Upgraded from version 2.23 to 2.39.


Upgraded from version 5.62 to 5.64_01.


Upgraded from version 0.21 to 0.27.


Upgraded from version 1.13 to 1.16.


Upgraded from version 0.2 to 0.22.


Upgraded from version 1.44 to 1.55.


Upgraded from version 6.42 to 6.56.


Upgraded from version 1.51_01 to 1.57.


Upgraded from version 2.18_02 to 2.21.


Upgraded from version 0.14 to 0.24.


Upgraded from version 2.04 to 2.08_01.


Upgraded from version 0.18 to 0.22.


Upgraded from version 0.82 to 0.84.


Upgraded from version 1.07 to 1.08.


Upgraded from version 2.37 to 2.38.


Upgraded from version 1.23_01 to 1.25_02.


Upgraded from version 1.07 to 1.10.


Upgraded from version 0.40_1 to 0.54.


Upgraded from version 1.05 to 2.01.


Upgraded from version 1.12 to 1.14.


Upgraded from version 0.18 to 0.21.


Upgraded from version 0.01 to 0.02.


Upgraded from version 0.04 to 0.06.


Upgraded from version 1.88 to 1.89_01.


Upgraded from version 0.16 to 0.19.


Upgraded from version 0.21 to 0.24.


Upgraded from version 1.37 to 1.56.


Upgraded from version 1.01_02 to 1.01_03.


Upgraded from version 3.07_01 to 3.08.


Upgraded from version 0.2808_01 to 0.3603.


Upgraded from version 2.12 to 2.29.


Upgraded from version 0.12 to 0.16.


Upgraded from version 0.22 to 0.34.


Upgraded from version 0.01 to 0.06.


Upgraded from version 3.6 to 3.9.


Upgraded from version 2.33 to 2.36.


Upgraded from version 0.60_01 to 0.64.


Upgraded from version 0.32 to 0.36.


Upgraded from version 0.01 to 0.02.


Upgraded from version 1.04 to 1.06.


Upgraded from version 1.35 to 1.37.


Upgraded from version 3.14_02 to 3.15_02.


Upgraded from version 0.01 to 1.02.

NOTE: Pod::Plainer is deprecated and may be removed from a future version of Perl.


Upgraded from version 3.05 to 3.13.


Upgraded from version 2.12 to 2.22.


Upgraded from version 1.11 to 1.17.


Upgraded from version 2.18 to 2.22.


Upgraded from version 2.13 to 2.16.

NOTE: Switch is deprecated and may be removed from a future version of Perl.


Upgraded from version 0.22 to 0.27.


Upgraded from version 1.12 to 2.02.


Upgraded from version 0.18 to 0.20.


Upgraded from version 1.25 to 1.25_02.


Upgraded from version 2.64 to 3.17.


Upgraded from version 0.72 to 0.94.


Upgraded from version 2.0.0 to 2.02.


Upgraded from version 3.26 to 3.27.


Upgraded from version 3.03 to 3.03_01.


Upgraded from version 2.00 to 2.11.


Upgraded from version 2.01 to 2.09.


Upgraded from version 1.37 to 1.38.


Upgraded from version 1.9711 to 1.9719.


Upgraded from version 1.18 to 1.1901_01.


Upgraded from version 1.12 to 1.15.


Upgraded from version 0.52 to 0.52_01.


Upgraded from version 1.02 to 1.03.


Upgraded from version 0.34 to 0.39.


Upgraded from version 0.1001_01 to 0.1101.


Upgraded from version 0.08 to 0.10.

Removed Modules and Pragmata


Removed from the Perl core. Prior version was 1.02.


Removed from the Perl core. Prior version was 'undef'.


Removed from the Perl core. Prior version was 5.50.


Removed from the Perl core. Prior version was 'undef'.


Removed from the Perl core. Prior version was 1.03.


Removed from the Perl core. Prior version was 6.42.


Removed from the Perl core. Prior version was 6.42.


Removed from the Perl core. Prior version was 2.3.


Removed from the Perl core. Prior version was 0.02.


Removed from the Perl core. Prior version was 0.02.


Removed from the Perl core. Prior version was 0.01.


Removed from the Perl core. Prior version was 0.01.


Removed from the Perl core. Prior version was 0.26_01.


Removed from the Perl core. Prior version was 0.01.


Removed from the Perl core. Prior version was 1.1.

Deprecated Modules and Pragmata

See "Deprecated Modules" above.


New Documentation

Changes to Existing Documentation

Selected Performance Enhancements

Installation and Configuration Improvements

Internal Changes

Each release of Perl sees numerous internal changes which shouldn't affect day to day usage but may still be notable for developers working with Perl's source code.


Testing improvements

Parallel tests

The core distribution can now run its regression tests in parallel on Unix-like platforms. Instead of running make test, set TEST_JOBS in your environment to the number of tests to run in parallel, and run make test_harness. On a Bourne-like shell, this can be done as

TEST_JOBS=3 make test_harness  # Run 3 tests in parallel

An environment variable is used, rather than parallel make itself, because TAP::Harness needs to be able to schedule individual non-conflicting test scripts itself, and there is no standard interface to make utilities to interact with their job schedulers.

Note that currently some test scripts may fail when run in parallel (most notably ext/IO/t/io_dir.t). If necessary run just the failing scripts again sequentially and see if the failures go away.

Test harness flexibility

It's now possible to override PERL5OPT and friends in t/TEST

Test watchdog

Several tests that have the potential to hang forever if they fail now incorporate a "watchdog" functionality that will kill them after a timeout, which helps ensure that make test and make test_harness run to completion automatically.

New Tests

Perl's developers have added a number of new tests to the core. In addition to the items listed below, many modules updated from CPAN incorporate new tests.

New or Changed Diagnostics

New Diagnostics

Changed Diagnostics

A number of existing diagnostic messages have been improved or corrected:

The following diagnostic messages have been removed:

Utility Changes

Selected Bug Fixes

Platform Specific Changes

Perl is incredibly portable. In general, if a platform has a C compiler, someone has ported Perl to it (or will soon). We're happy to announce that Perl 5.12 includes support for several new platforms. At the same time, it's time to bid farewell to some (very) old friends.

New Platforms


Perl's developers have merged patches from Haiku's maintainers. Perl should now build on Haiku.


Perl should now build on MirOS BSD.

Discontinued Platforms

Tenon MachTen

Updated Platforms

  • Removed libbsd for AIX 5L and 6.1. Only flock() was used from libbsd.

  • Removed libgdbm for AIX 5L and 6.1 if libgdbm < 1.8.3-5 is installed. The libgdbm is delivered as an optional package with the AIX Toolbox. Unfortunately the versions below 1.8.3-5 are broken.

  • Hints changes mean that AIX 4.2 should work again.

  • Perl now supports IPv6 on Cygwin 1.7 and newer.

  • On Cygwin we now strip the last number from the DLL. This has been the behaviour in the build for years. The hints files have been updated.

Darwin (Mac OS X)
  • Skip testing the be_BY.CP1131 locale on Darwin 10 (Mac OS X 10.6), as it's still buggy.

  • Correct infelicities in the regexp used to identify buggy locales on Darwin 8 and 9 (Mac OS X 10.4 and 10.5, respectively).

DragonFly BSD
  • Fix thread library selection [perl #69686]

  • The hints files now identify the correct threading libraries on FreeBSD 7 and later.

  • We now work around a bizarre preprocessor bug in the Irix 6.5 compiler: cc -E - unfortunately goes into K&R mode, but cc -E file.c doesn't.

  • Hints now supports versions 5.*.

  • -UDEBUGGING is now the default on VMS.

    Like it has been everywhere else for ages and ages. Also make command-line selection of -UDEBUGGING and -DDEBUGGING work in; before the only way to turn it off was by saying no in answer to the interactive question.

  • The default pipe buffer size on VMS has been updated to 8192 on 64-bit systems.

  • Reads from the in-memory temporary files of PerlIO::scalar used to fail if $/ was set to a numeric reference (to indicate record-style reads). This is now fixed.

  • VMS now supports getgrgid.

  • Many improvements and cleanups have been made to the VMS file name handling and conversion code.

  • Enabling the PERL_VMS_POSIX_EXIT logical name now encodes a POSIX exit status in a VMS condition value for better interaction with GNV's bash shell and other utilities that depend on POSIX exit values. See "$?" in perlvms for details.

  • File::Copy now detects Unix compatibility mode on VMS.

Stratus VOS
  • Various changes from Stratus have been merged in.

  • There is now support for Symbian S60 3.2 SDK and S60 5.0 SDK.

  • Perl 5.12 supports Windows 2000 and later. The supporting code for legacy versions of Windows is still included, but will be removed during the next development cycle.

  • Initial support for building Perl with MinGW-w64 is now available.

  • perl.exe now includes a manifest resource to specify the trustInfo settings for Windows Vista and later. Without this setting Windows would treat perl.exe as a legacy application and apply various heuristics like redirecting access to protected file system areas (like the "Program Files" folder) to the users "VirtualStore" instead of generating a proper "permission denied" error.

    The manifest resource also requests the Microsoft Common-Controls version 6.0 (themed controls introduced in Windows XP). Check out the Win32::VisualStyles module on CPAN to switch back to old style unthemed controls for legacy applications.

  • The -t filetest operator now only returns true if the filehandle is connected to a console window. In previous versions of Perl it would return true for all character mode devices, including NUL and LPT1.

  • The -p filetest operator now works correctly, and the Fcntl::S_IFIFO constant is defined when Perl is compiled with Microsoft Visual C. In previous Perl versions -p always returned a false value, and the Fcntl::S_IFIFO constant was not defined.

    This bug is specific to Microsoft Visual C and never affected Perl binaries built with MinGW.

  • The socket error codes are now more widely supported: The POSIX module will define the symbolic names, like POSIX::EWOULDBLOCK, and stringification of socket error codes in $! works as well now;

    C:\>perl -MPOSIX -E "$!=POSIX::EWOULDBLOCK; say $!"
    A non-blocking socket operation could not be completed immediately.
  • flock() will now set sensible error codes in $!. Previous Perl versions copied the value of $^E into $!, which caused much confusion.

  • select() now supports all empty fd_sets more correctly.

  • '.\foo' and '..\foo' were treated differently than './foo' and '../foo' by do and require [RT #63492].

  • Improved message window handling means that alarm and kill messages will no longer be dropped under race conditions.

  • Various bits of Perl's build infrastructure are no longer converted to win32 line endings at release time. If this hurts you, please report the problem with the perlbug program included with perl.

Known Problems

This is a list of some significant unfixed bugs, which are regressions from either 5.10.x or 5.8.x.



Perl 5.12.0 represents approximately two years of development since Perl 5.10.0 and contains over 750,000 lines of changes across over 3,000 files from over 200 authors and committers.

Perl continues to flourish into its third decade thanks to a vibrant community of users and developers. The following people are known to have contributed the improvements that became Perl 5.12.0:

Aaron Crane, Abe Timmerman, Abhijit Menon-Sen, Abigail, Adam Russell, Adriano Ferreira, Ævar Arnfjörð Bjarmason, Alan Grover, Alexandr Ciornii, Alex Davies, Alex Vandiver, Andreas Koenig, Andrew Rodland,, Andy Armstrong, Andy Dougherty, Jose AUGUSTE-ETIENNE, Benjamin Smith, Ben Morrow, bharanee rathna, Bo Borgerson, Bo Lindbergh, Brad Gilbert, Bram, Brendan O'Dea, brian d foy, Charles Bailey, Chip Salzenberg, Chris 'BinGOs' Williams, Christoph Lamprecht, Chris Williams, chromatic, Claes Jakobsson, Craig A. Berry, Dan Dascalescu, Daniel Frederick Crisman, Daniel M. Quinlan, Dan Jacobson, Dan Kogai, Dave Mitchell, Dave Rolsky, David Cantrell, David Dick, David Golden, David Mitchell, David M. Syzdek, David Nicol, David Wheeler, Dennis Kaarsemaker, Dintelmann, Peter, Dominic Dunlop, Dr.Ruud, Duke Leto, Enrico Sorcinelli, Eric Brine, Father Chrysostomos, Florian Ragwitz, Frank Wiegand, Gabor Szabo, Gene Sullivan, Geoffrey T. Dairiki, George Greer, Gerard Goossen, Gisle Aas, Goro Fuji, Graham Barr, Green, Paul, Hans Dieter Pearcey, Harmen, H. Merijn Brand, Hugo van der Sanden, Ian Goodacre, Igor Sutton, Ingo Weinhold, James Bence, James Mastros, Jan Dubois, Jari Aalto, Jarkko Hietaniemi, Jay Hannah, Jerry Hedden, Jesse Vincent, Jim Cromie, Jody Belka, John E. Malmberg, John Malmberg, John Peacock, John Peacock via RT, John P. Linderman, John Wright, Josh ben Jore, Jos I. Boumans, Karl Williamson, Kenichi Ishigaki, Ken Williams, Kevin Brintnall, Kevin Ryde, Kurt Starsinic, Leon Brocard, Lubomir Rintel, Luke Ross, Marcel Grünauer, Marcus Holland-Moritz, Mark Jason Dominus, Marko Asplund, Martin Hasch, Mashrab Kuvatov, Matt Kraai, Matt S Trout, Max Maischein, Michael Breen, Michael Cartmell, Michael G Schwern, Michael Witten, Mike Giroux, Milosz Tanski, Moritz Lenz, Nicholas Clark, Nick Cleaton, Niko Tyni, Offer Kaye, Osvaldo Villalon, Paul Fenwick, Paul Gaborit, Paul Green, Paul Johnson, Paul Marquess, Philip Hazel, Philippe Bruhat, Rafael Garcia-Suarez, Rainer Tammer, Rajesh Mandalemula, Reini Urban, Renée Bäcker, Ricardo Signes, Ricardo SIGNES, Richard Foley, Rich Rauenzahn, Rick Delaney, Risto Kankkunen, Robert May, Roberto C. Sanchez, Robin Barker, SADAHIRO Tomoyuki, Salvador Ortiz Garcia, Sam Vilain, Scott Lanning, Sébastien Aperghis-Tramoni, Sérgio Durigan Júnior, Shlomi Fish, Simon 'corecode' Schubert, Sisyphus, Slaven Rezic, Smylers, Steffen Müller, Steffen Ullrich, Stepan Kasal, Steve Hay, Steven Schubiger, Steve Peters, Tels, The Doctor, Tim Bunce, Tim Jenness, Todd Rinaldo, Tom Christiansen, Tom Hukins, Tom Wyant, Tony Cook, Torsten Schoenfeld, Tye McQueen, Vadim Konovalov, Vincent Pit, Hio YAMASHINA, Yasuhiro Matsumoto, Yitzchak Scott-Thoennes, Yuval Kogman, Yves Orton, Zefram, Zsban Ambrus

This is woefully incomplete as it's automatically generated from version control history. In particular, it doesn't include the names of the (very much appreciated) contributors who reported issues in previous versions of Perl that helped make Perl 5.12.0 better. For a more complete list of all of Perl's historical contributors, please see the AUTHORS file in the Perl 5.12.0 distribution.

Our "retired" pumpkings Nicholas Clark and Rafael Garcia-Suarez deserve special thanks for their brilliant and substantive ongoing contributions. Nicholas personally authored over 30% of the patches since 5.10.0. Rafael comes in second in patch authorship with 11%, but is first by a long shot in committing patches authored by others, pushing 44% of the commits since 5.10.0 in this category, often after providing considerable coaching to the patch authors. These statistics in no way comprise all of their contributions, but express in shorthand that we couldn't have done it without them.

Many of the changes included in this version originated in the CPAN modules included in Perl's core. We're grateful to the entire CPAN community for helping Perl to flourish.

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 to be analyzed by the Perl porting team.

If the bug you are reporting has security implications, which make it inappropriate to send to a publicly archived mailing list, then please send it to This points to a closed subscription unarchived mailing list, which includes all the core committers, who will be able to help assess the impact of issues, figure out a resolution, and help co-ordinate the release of patches to mitigate or fix the problem across all platforms on which Perl is supported. Please only use this address for security issues in the Perl core, not for modules independently distributed on CPAN.


The Changes file for an explanation of how to view 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. for a list of issues found after this release, as well as a list of CPAN modules known to be incompatible with this release.