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perldelta - what is new for perl v5.15.5


This document describes differences between the 5.15.4 release and the 5.15.5 release.

If you are upgrading from an earlier release such as 5.15.3, first read perl5154delta, which describes differences between 5.15.3 and 5.15.4.

Core Enhancements

More consistent eval

The eval operator sometimes treats a string argument as a sequence of characters and sometimes as a sequence of bytes, depending on the internal encoding. The internal encoding is not supposed to make any difference, but there is code that relies on this inconsistency.

Under use v5.15 and higher, the unicode_eval and evalbytes features resolve this. The unicode_eval feature causes eval $string to treat the string always as Unicode. The evalbytes features provides a function, itself called evalbytes, which evaluates its argument always as a string of bytes.

These features also fix oddities with source filters leaking to outer dynamic scopes.

See feature for more detail.

$[ is back

The $[ variable is back again, but is now implemented as a module, so programs that do not mention it (i.e., most of them), will not incur any run-time penalty. In a later release in the 5.15 branch it might be disabled in the scope of use v5.16.

The new implementation has some bug fixes. See arybase.


Privileges are now set correctly when assigning to $(

A hypothetical bug (probably non-exploitable in practice) due to the incorrect setting of the effective group ID while setting $( has been fixed. The bug would only have affected systems that have setresgid() but not setregid(), but no such systems are known of.

Incompatible Changes

Certain deprecated Unicode properties are no longer supported by default

Perl should never have exposed certain Unicode properties that are used by Unicode internally and not meant to be publicly available. Use of these has generated deprecated warning messages since Perl 5.12. The removed 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.

Perl may be recompiled to include any or all of them; instructions are given in "Unicode character properties that are NOT accepted by Perl" in perluniprops.

Dereferencing IO thingies as typeglobs

The *{...} operator, when passed a reference to an IO thingy (as in *{*STDIN{IO}}), creates a new typeglob containing just that IO object.

Previously, it would stringify as an empty string, but some operators would treat it as undefined, producing an "uninitialized" warning.

Having a typeglob appear as an empty string is a side effect of the implementation that has caused various bugs over the years.

The solution was to make it stringify like a normal anonymous typeglob, like those produced by open($foo->{bar}, ...) [perl #96326].


Don't read the Unicode data base files in lib/unicore

It is now deprecated to directly read the Unicode data base files. These are stored in the lib/unicore directory. Instead, you should use the new functions in Unicode::UCD. These provide a stable API, and give complete information. (This API is, however, subject to change somewhat during the 5.15 development cycle, as we gain experience and get feedback from using it.)

Perl may at some point in the future change or remove the files. The file most likely for applications to have used is lib/unicore/ToDigit.pl. "prop_invmap()" in Unicode::UCD can be used to get at its data instead.

Performance Enhancements

  • Due to changes in File::Glob, Perl's glob function and its <...> equivalent are now much faster. The splitting of the pattern into words has been rewritten in C, resulting in speed-ups of 20% in some cases.

    This does not affect VMS, as it does not use File::Glob.

Modules and Pragmata

New Modules and Pragmata

  • arybase -- this new module implements the $[ variable.

Updated Modules and Pragmata

  • Archive::Extract has been upgraded from version 0.56 to version 0.58.

  • B::Concise has been upgraded from version 0.86 to version 0.87.

  • B::Deparse has been upgraded from version 1.08 to version 1.09.

    It now correctly deparses CORE::do, CORE::glob and slices of empty lists.

  • CGI has been upgraded from version 3.55 to version 3.58.

    Use public and documented FCGI.pm API in CGI::Fast CGI::Fast was using an FCGI API that was deprecated and removed from documentation more than ten years ago. Usage of this deprecated API with FCGI >= 0.70 or FCGI <= 0.73 introduces a security issue. https://rt.cpan.org/Public/Bug/Display.html?id=68380 http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2011-2766

  • charnames has been upgraded from version 1.23 to version 1.24.

  • Compress::Raw::Bzip2 has been upgraded from version 2.037 to version 2.042.

  • Compress::Raw::Zlib has been upgraded from version 2.037 to version 2.042.

  • Compress::Zlib has been upgraded from version 2.037 to version 2.042.

  • CPANPLUS has been upgraded from version 0.9111 to version 0.9112.

  • CPANPLUS::Dist::Build has been upgraded from version 0.58 to version 0.60.

  • Digest::SHA has been upgraded from version 5.62 to version 5.63.

    Added code to allow very large data inputs all at once, which had previously been limited to several hundred megabytes at a time

  • Errno has been upgraded from version 1.14 to version 1.15.

    Choosing an archname containing a @, $ or % character no longer results in unintended interpolation in Errno's architecture check.

  • ExtUtils::MakeMaker has been upgraded from version 6.61_01 to version 6.63_02.

  • feature has been upgraded from version 1.22 to version 1.23.

  • File::DosGlob has been upgraded from version 1.05 to version 1.06.

  • File::Glob has been upgraded from version 1.13 to version 1.14.

    It has a new :bsd_glob export tag, intended to replace :glob. Like :glob it overrides glob with a function that does not split the glob pattern into words, but, unlike :glob, it iterates properly in scalar context, instead of returning the last file.

    There are other changes affecting Perl's own glob operator (which uses File::Glob internally, except on VMS). See "Performance Enhancements" and "Selected Bug Fixes".

  • HTTP::Tiny has been upgraded from version 0.013 to version 0.016.

    Adds additional shorthand methods for all common HTTP verbs, a post_form() method for POST-ing x-www-form-urlencoded data and a www_form_urlencode() utility method.

  • Module::CoreList has been upgraded from version 2.57 to version 2.58.

  • Opcode has been upgraded from version 1.20 to version 1.21.

  • perlfaq has been upgraded from version 5.0150035 to version 5.0150036.

  • Socket as been upgraded from version 1.94_01 to 1.94_02.

    It has new functions and constants for handling IPv6 sockets:

  • Storable has been upgraded from version 2.32 to 2.33.

    The ability to add a fake entry to %INC to prevent Log::Agent from loading has been restored. In version 2.27 (included with perl 5.14.0), Storable starting producing an error instead.

  • strict has been upgraded from version 1.04 to version 1.05.

  • Unicode::Collate has been upgraded from version 0.80 to version 0.85.

    Locales updated to CLDR 2.0: mk, mt, nb, nn, ro, ru, sk, sr, sv, uk, zh__pinyin, zh__stroke Newly supported locales: bn, fa, ml, mr, or, pa, sa, si, si__dictionary, sr_Latn, sv__reformed, ta, te, th, ur, wae.

  • Unicode::UCD has been upgraded from version 0.36 to version 0.37.

    This adds four new functions: prop_aliases(), and prop_value_aliases() which are used to find all the Unicode-approved synonyms for property names, or to convert from one name to another; prop_invlist which returns all the code points matching a given Unicode binary property; and prop_invmap which returns the complete specification of a given Unicode property.

  • UNIVERSAL has been upgraded from version 1.09 to version 1.10.


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.

New Diagnostics

New Errors

New Warnings

  • length() used on %s

    This new warning occurs when length is used on an array or hash, instead of scalar(@array) or scalar(keys %hash).

  • $[ used in %s (did you mean $] ?)

    This new warning exists to catch the mistaken use of $[ in version checks. $], not $[, contains the version number. $[ in a numeric comparison is almost always wrong.

  • Use of assignment to $[ is deprecated

    This previously removed warning has been restored with the re-implementation of $[ as a module.

Changes to Existing Diagnostics

  • The uninitialized warning for y///r when $_ is implicit and undefined now mentions the variable name, just like the non-/r variation of the operator.

  • The "Applying pattern match..." or similar warning produced when an array or hash is on the left-hand side of the =~ operator now mentions the name of the variable.

Configuration and Compilation

  • pod/buildtoc, used by the build process to build perltoc, has been refactored and simplified. It now only contains code to build perltoc; the code to regenerate Makefiles has been moved to Porting/pod_rules.pl. It's a bug if this change has any material effect on the build process.

Platform Support

Platform-Specific Notes


Numerous build and test failures on GNU/Hurd have been resolved with hints for building DBM modules, detection of the library search path, and enabling of large file support.


Perl is now built with dynamic linking on OpenVOS, the minimum supported version of which is now Release 17.1.0.


The CC workshop C++ compiler is now detected and used on systems that ship without cc.

Internal Changes

  • PL_curstash is now reference-counted.

Selected Bug Fixes

  • Perl now holds an extra reference count on the package that code is currently compiling in. This means that the following code no longer crashes [perl #101486]:

        package Foo;
        BEGIN {*Foo:: = *Bar::}
        sub foo;
  • dumpvar.pl, and consequently the x command in the debugger, have been fixed to handle objects blessed into classes whose names contain "=". The contents of such objects used not to be dumped [perl #101814].

  • The x repetition operator no longer crashes on 64-bit builds with large repeat counts [perl #94560].

  • A fix to glob under miniperl (used to configure modules when perl itself is built) in Perl 5.15.3 stopped <~> from returning the home directory, because it cleared %ENV before calling csh. Now $ENV{HOME} is preserved. This fix probably does not affect anything. If File::Glob fails to load for some reason, Perl reverts to using csh. So it would apply in that case.

  • On OSes other than VMS, Perl's glob operator (and the <...> form) use File::Glob underneath. File::Glob splits the pattern into words, before feeding each word to its bsd_glob function.

    There were several inconsistencies in the way the split was done. Now quotation marks (' and ") are always treated as shell-style word delimiters (that allow whitespace as part of a word) and backslashes are always preserved, unless they exist to escape quotation marks. Before, those would only sometimes be the case, depending on whether the pattern contained whitespace. Also, escaped whitespace at the end of the pattern is no longer stripped [perl #40470].

  • CORE::glob now works as a way to call the default globbing function. It used to respect overrides, despite the CORE:: prefix.

  • In 5.14, /[[:lower:]]/i and /[[:upper:]]/i no longer matched the opposite case. This has been fixed [perl #101970].

  • A regular expression match with an overloaded object on the right-hand side would in some cases stringify the object too many times.

  • The C-level pregcomp function could become confused as to whether the pattern was in UTF8 if the pattern was an overloaded, tied, or otherwise magical scalar [perl #101940].

  • A regression has been fixed that was introduced in 5.14, in /i regular expression matching, in which a match improperly fails if the pattern is in UTF-8, the target string is not, and a Latin-1 character precedes a character in the string that should match the pattern. [perl #101710]

  • @{"..."} = reverse ... started crashing in 5.15.3. This has been fixed.

  • ref in a tainted expression started producing an "sv_upgrade" error in 5.15.4. This has been fixed.

  • Weak references to lexical hashes going out of scope were not going stale (becoming undefined), but continued to point to the hash.

  • Weak references to lexical variables going out of scope are now broken before any magical methods (e.g., DESTROY on a tie object) are called. This prevents such methods from modifying the variable that will be seen the next time the scope is entered.

  • A keys optimisation in Perl 5.12.0 to make it faster on empty hashes caused each not to reset the iterator if called after the last element was deleted. This has been fixed.

  • The #line 42 foo directive used not to update the arrays of lines used by the debugger if it occurred in a string eval. This was partially fixed in 5.14, but it only worked for a single #line 42 foo in each eval. Now it works for multiple.

  • String eval used not to localise %^H when compiling its argument if it was empty at the time the eval call itself was compiled. This could lead to scary side effects, like use re "/m" enabling other flags that the surrounding code was trying to enable for its caller [perl #68750].

  • Creating a BEGIN block from XS code (via newXS or newATTRSUB) would, on completion, make the hints of the current compiling code the current hints. This could cause warnings to occur in a non-warning scope.

  • eval $string and require no longer localise hints ($^H and %^H) at run time, but only during compilation of the $string or required file. This makes BEGIN { $^H{foo}=7 } equivalent to BEGIN { eval '$^H{foo}=7' } [perl #70151].

  • When subroutine calls are intercepted by the debugger, the name of the subroutine or a reference to it is stored in $DB::sub, for the debugger to access. In some cases (such as $foo = *bar; undef *bar; &$foo) $DB::sub would be set to a name that could not be used to find the subroutine, and so the debugger's attempt to call it would fail. Now the check to see whether a reference is needed is more robust, so those problems should not happen anymore [rt.cpan.org #69862].

  • Localising a tied scalar that returns a typeglob no longer stops it from being tied till the end of the scope.

  • When open is called with three arguments, the third being a file handle (as in open $fh, ">&", $fh2), if the third argument is tied or a reference to a tied variable, FETCH is now called exactly once, instead of 0, 2, or 3 times (all of which could occur in various circumstances).

  • sort no longer ignores FETCH when passed a reference to a tied glob for the comparison routine.

  • Warnings emitted by sort when a custom comparison routine returns a non-numeric value now show the line number of the sort operator, rather than the last line of the comparison routine. The warnings also occur now only if warnings are enabled in the scope where sort occurs. Previously the warnings would occur if enabled in the comparison routine's scope.

  • Internals::SvREFCNT now behaves consistently in 'get' and 'set' scenarios [perl #103222] and also treats the reference count as unsigned.

  • Calling require on an implicit $_ when *CORE::GLOBAL::require has been overridden does not segfault anymore, and $_ is now passed to the overriding subroutine [perl #78260].


Perl 5.15.5 represents approximately 1 month of development since Perl 5.15.4 and contains approximately 28,000 lines of changes across 440 files from 29 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 5.15.5:

Brian Fraser, Chris 'BinGOs' Williams, chromatic, Craig A. Berry, David Golden, Father Chrysostomos, Florian Ragwitz, H.Merijn Brand, Jilles Tjoelker, Jim Meyering, Karl Williamson, Laurent Dami, Leon Timmermans, Mark A. Stratman, Matthew Horsfall, Michael G Schwern, Moritz Lenz, Nicholas Clark, Paul Evans, Paul Green, Paul Johnson, Perlover, Pino Toscano, Reini Urban, Steve Hay, Tom Christiansen, Tony Cook, 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.