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Dave Rolsky


perl5151delta - what is new for perl v5.15.1


This document describes differences between the 5.15.0 release and the 5.15.1 release.

If you are upgrading from an earlier release such as 5.14.0, first read perl5150delta, which describes differences between 5.14.0 and 5.15.0.

Core Enhancements

splice() doesn't warn when truncating

You can now limit the size of an array using splice(@a,MAX_LEN) without worrying about warnings.

The \$ prototype accepts any scalar lvalue

The \$ and \[$] subroutine prototypes now accept any scalar lvalue argument. Previously they only accepted scalars beginning with $ and hash and array elements. This change makes them consistent with the way the built-in read and recv functions (among others) parse their arguments. This means that one can override the built-in functions with custom subroutines that parse their arguments the same way.

You can now study more than one string

The restriction that you can only have one study active at a time has been removed. You can now usefully study as many strings as you want (until you exhaust memory).

The Unicode Script_Extensions property is now supported.

New in Unicode 6.0, this is an improved Script property. Details are in "Scripts" in perlunicode.

DTrace probes for interpreter phase change

The phase-change probes will fire when the interpreter's phase changes, which tracks the ${^GLOBAL_PHASE} variable. arg0 is the new phase name; arg1 is the old one. This is useful mostly for limiting your instrumentation to one or more of: compile time, run time, destruct time.

New Pad API

Many new functions have been added to the API for manipulating lexical pads. See "Pad Data Structures" in perlapi for more information.

Performance Enhancements

  • The short-circuiting operators &&, ||, and //, when chained (such as $a || $b || $c), are now considerably faster to short-circuit, due to reduced optree traversal.

  • The implementation of s///r makes one fewer copy of the scalar's value.

  • If a studied scalar is split with a regex, the engine will now take advantage of the study data.

  • study now uses considerably less memory for shorter strings. Strings shorter than 65535 characters use roughly half the memory than previously, strings shorter than 255 characters use roughly one quarter of the memory.

  • Recursive calls to lvalue subroutines in lvalue scalar context use less memory.

Modules and Pragmata

New Modules and Pragmata

  • The logic for parsing, merging, and dumping XS typemaps has been extracted from ExtUtils::ParseXS into a module of its own, ExtUtils::Typemaps. ExtUtils::Typemaps offers an interface to typemap handling outside of the scope of the XS compiler itself.

    As a first use case of the improved API and extensibility, typemaps can now be included inline in XS code with a HEREDOC-like syntax:

      MyType        T_IV

Updated Modules and Pragmata

  • B::Deparse has been upgrade from version 1.05 to 1.06.

    It now correctly deparses interpolation of punctuation variables (like @*) that do not interpolate without braces [perl #93990].

  • CGI has been upgraded from version 3.54 to version 3.55.

    Things that may break your code:

    url() was fixed to return PATH_INFO when it is explicitly requested with either the path=>1 or path_info=>1 flag.

    If your code is running under mod_rewrite (or compatible) and you are calling self_url() or you are calling url() and passing path_info=>1, These methods will actually be returning PATH_INFO now, as you have explicitly requested, or has self_url() has requested on your behalf.

    The PATH_INFO has been omitted in such URLs since the issue was introduced in the 3.12 release in December, 2005.

    This bug is so old your application may have come to depend on it or workaround it. Check for application before upgrading to this release.

    Examples of affected method calls:

      $q->url(-absolute => 1, -query => 1, -path_info => 1 )
  • CPANPLUS has been upgraded from version 0.9105 to version 0.9108

  • Compress::Raw::Bzip2 has been upgraded from version 2.035 to version 2.037

  • Compress::Raw::Zlib has been upgraded from version 2.035 to version 2.037

    Added offset parameter to CRC32

  • Compress::Zlib has been upgraded from version 2.035 to version 2.037

    IO::Compress::Zip and IO::Uncompress::Unzip now have support for LZMA (method 14). There is a fix for a CRC issue in IO::Compress::Unzip and it supports Streamed Stored context now. And fixed a Zip64 issue in IO::Compress::Zip when the content size was exactly 0xFFFFFFFF.

  • Cwd has been upgraded from version 3.36 to 3.37, to address an incompatibility with the EPIC debugger.

  • ExtUtils::MakeMaker has been upgraded from version 6.57_05 to version 6.58

  • ExtUtils::ParseXS has been upgraded from version 2.2210 to 3.00_01.

    Much of ExtUtils::ParseXS, the module behind the XS compiler xsubpp, was rewritten and cleaned up. It has been made somewhat more extensible and now finally uses strictures.

    The typemap logic has been moved into a separate module, ExtUtils::Typemaps. See "New Modules and Pragmata", above.

  • HTTP::Tiny has been upgraded from version 0.012 to version 0.013.

    Added support for using $ENV{http_proxy} to set the default proxy host.

  • IPC::Cmd has been upgraded from version 0.70 to version 0.72

    Capturing of command output (both STDOUT and STDERR) is now supported using IPC::Open3 on MSWin32 without requiring IPC::Run.

  • Locale::Codes has been upgraded from version 3.16 to version 3.17

    Added Language Extension codes (langext) and Language Variation codes (langvar) as defined in the IANA language registry.

    Added language codes from ISO 639-5

    Added language/script codes from the IANA language subtag registry

    Fixed an uninitialized value warning. RT 67438

    Fixed the return value for the all_XXX_codes and all_XXX_names functions. RT 69100

    Reorganized modules to move Locale::MODULE to Locale::Codes::MODULE to allow for cleaner future additions. The original four modules (Locale::Language, Locale::Currency, Locale::Country, Locale::Script) will continue to work, but all new sets of codes will be added in the Locale::Codes namespace.

  • Math::BigInt::FastCalc has been upgraded from version 0.28 to version 0.29.

    The XS code is now compiled with PERL_NO_GET_CONTEXT, which will aid performance under ithreads.

  • Module::CoreList has been upgraded from version 2.51 to 2.54.

    Some extraneous (and erroneous) entries have been removed [rt.cpan.org #69108].

    The corelist utility now understands the -r option for displaying Perl release dates.

  • Pod::Perldoc has been upgraded from version 3.15_05 to 3.15_06.

    The -v option now fetches the right section for $0.

  • Pod::Simple has been upgraded from version 3.16 to version 3.18

  • Unicode::Collate has been upgraded from version 0.76 to version 0.77

    Applied [perl #93470] silencing compiler warnings with -Wwrite-strings

  • Win32API::File has been upgraded from version 0.1101 to version 0.1200

    Added SetStdHandle and GetStdHandle functions

  • attributes has been upgraded from version 0.14 to 0.15, as part of the lvalue attribute warnings fix. See "Selected Bug Fixes", below.

  • diagnostics has been upgraded from version 1.22 to 1.23.

    It now knows how to find descriptions for diagnostic messages ending with a dot, instead getting confused by it.

  • threads has been upgraded from version 1.83 to 1.84

    An unused variable was removed from the XS code.

Removed Modules and Pragmata

  • Perl 4-era .pl libraries

    Perl used to bundle a handful of library files that predate Perl 5. Most of these files, which have been deprecated since version 5.14.0, have now been removed. If your code still relies on these libraries, you can install them again from Perl4::CoreLibs on CPAN.


New Documentation


perldtrace describes Perl's DTrace support, listing the provided probes and gives examples of their use.


The delta file for Perl 5.14.1 has been copied to blead.

Changes to Existing Documentation

  • perlxs was extended with documentation on inline typemaps.

  • perlref has a new Circular References section explaining how circularities may not be freed and how to solve that with weak references.

  • The documentation for smart match in perlsyn has been corrected for the case of undef on the left-hand side. The list of different smart match behaviours had an item in the wrong place.

  • Parts of perlapi were clarified, and Perl equivalents of some C functions have been added as an additional mode of exposition.

  • A few parts of perlre and perlrecharclass were clarified.


The following additions or changes have been made to diagnostic output, including warnings and fatal error messages. For the complete list of diagnostic messages, see perldiag.

Changes to Existing Diagnostics

  • The Invalid version format error message now says "negative version number" within the parentheses, rather than "non-numeric data", for negative numbers.

  • The two warnings Possible attempt to put comments in qw() list and Possible attempt to separate words with commas are no longer mutually exclusive: the same qw construct may produce both.

  • Warnings that mention the names of lexical (my) variables with Unicode characters in them now respect the presence or absence of the :utf8 layer on the output handle, instead of outputting UTF8 regardless. Also, the correct names are included in the strings passed to $SIG{__WARN__} handlers, rather than the raw UTF8 bytes.


  • t/run/dtrace.t was added to test Perl's DTrace support. This test will only be run if your Perl was built with -Dusedtrace and if calling dtrace actually lets you instrument code. This generally requires being run as root, so this test file is primarily intended for use by the dtrace subcommittee of p5p.

  • t/win32/runenv.t was added to test aspects of Perl's environment variable handling on MSWin32 platforms. Previously, such tests were skipped on MSWin32 platforms.

  • Some bitrot has been fixed in the miniperl test suite, so that it now nearly passes. The minitest is normally only run when building the full perl fails, so it was liable to fall into disrepair making it a less useful debugging tool. When it is fully passing it is hoped to start including it in regular smoke tests, so that future bitrot will be quickly detected.

Platform Support

Platform-Specific Notes


  • On Windows 7, 2008 and Vista, @INC is now always properly populated based on the value of PERL5LIB set in the environment. Previously, values of PERL5LIB longer than 32766 bytes were skipped when @INC was being populated. Tests for environment handling were also added (see "Testing" section). Fixes RT #87322.

Internal Changes

  • The experimental fetch_cop_label function has been renamed to cop_fetch_label.

  • The cop_store_label function has been added to the API, but is experimental.

Selected Bug Fixes

  • Applying the :lvalue attribute to subroutine that is already defined does not work properly, as the attribute changes the way the sub is compiled. Hence, Perl 5.12 began warning when an attempt is made to apply the attribute to an already defined sub. In such cases, the attribute is discarded.

    But the change in 5.12 missed the case where custom attributes are also present: that case still silently and ineffectively applied the attribute. That omission has now been corrected. sub foo :lvalue :Whatever (when foo is already defined) now warns about the :lvalue attribute, and does not apply it.

    attributes.pm has likewise been updated to warn and not apply the attribute.

  • The remaining discrepancies between explicit and implicit return from lvalue subroutines have been resolved. They mainly involved which error message to display when a read-only value is returned in lvalue context. Also, returning a PADTMP (the result of most built-ins, like index) in lvalue context is now forbidden for explicit return, as it always has been for implicit return. This is not a regression from 5.14, as all the cases in which it could happen where previously syntax errors.

  • Explicitly returning a tied my variable from an lvalue subroutine in list lvalue context used to clear the variable before the assignment could happen. This is something that was missed when explicit return was made to work in 5.15.0.

  • A minor memory leak, introduced in 5.15.0, has been fixed. It would occur when a hash is freed that has had its current iterator deleted [perl #93454].

  • The prototype function no longer dies for the __FILE__, __LINE__ and __PACKAGE__ directives. It now returns an empty-string prototype for them, because they are syntactically very similar to nullary functions like time.

  • prototype now returns undef for all overridable infix operators, such as eq, which are not callable in any way resembling functions. It used to return incorrect prototypes for some and die for others [perl #94984].

  • A bug affecting lvalue context propagation through nested lvalue subroutine calls has been fixed. Previously, returning a value in nested rvalue context would be treated as lvalue context by the inner subroutine call, resulting in some values (such as read-only values) being rejected.

  • Some core bugs affecting Hash::Util have been fixed: locking a hash element that is a glob copy no longer causes subsequent assignment to it to corrupt the glob, and unlocking a hash element that holds a copy-on-write scalar no longer causes modifications to that scalar to modify other scalars that were sharing the same string buffer.

  • when blocks are now capable of returning variables declared inside the enclosing given block [perl #93548].

  • A problem with context propagation when a do block is an argument to return has been fixed. It used to cause undef to be returned in some cases of a return inside an if block which itself is followed by another return.

  • Calling index with a tainted constant no longer causes constants in subsequently compiled code to become tainted [perl #64804].

  • Use of lexical (my) variables in code blocks embedded in regular expressions will no longer result in memory corruption or crashes.

    Nevertheless, these code blocks are still experimental, as there are still problems with the wrong variables being closed over (in loops for instance) and with abnormal exiting (e.g., die) causing memory corruption.

  • The SvIsCOW C macro now returns false for read-only copies of typeglobs, such as those created by:

      $hash{elem} = *foo;
      Hash::Util::lock_value %hash, 'elem';

    It used to return true.

  • Assignment to $^A (the format output accumulator) now recalculates the number of lines output.

  • The regexp optimiser no longer crashes on debugging builds when merging fixed-string nodes with inconvenient contents.


Perl 5.15.1 represents approximately 5 weeks of development since Perl 5.15.0 and contains approximately 220,000 lines of changes across 650 files from 37 authors.

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 5.15.1:

Abhijit Menon-Sen, Alan Haggai Alavi, Brian Fraser, Brian Greenfield, Chris 'BinGOs' Williams, Claes Jacobsson, Craig A. Berry, Dave Rolsky, David Golden, David Mitchell, Dee Newcum, Eric Brine, Father Chrysostomos, Florian Ragwitz, Gerard Goossen, H.Merijn Brand, Hojung Yoon, James E Keenan, Jesse Luehrs, Jesse Vincent, John Peacock, Karl Williamson, Keith Thompson, Leon Brocard, Matthew Horsfall, Nicholas Clark, Niko Tyni, Phil Monsen, Reini Urban, Ricardo Signes, Robin Barker, Sam Kimbrel, Shawn M Moore, Shlomi Fish, Steffen Müller, Vincent Pit, Zefram.

The list above is almost certainly incomplete as it is automatically generated from version control history. In particular, it does not include the names of the (very much appreciated) contributors who reported issues to the Perl bug tracker.

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.

For a more complete list of all of Perl's historical contributors, please see the AUTHORS file in the Perl source distribution.

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/perlbug/ . There may also be information at http://www.perl.org/ , the Perl Home Page.

If you believe you have an unreported bug, please run the perlbug program included with your release. Be sure to trim your bug down to a tiny but sufficient test case. Your bug report, along with the output of perl -V, will be sent off to perlbug@perl.org to be analysed by the Perl porting team.

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 perl5-security-report@perl.org. 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.

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