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perl5138delta - what is new for perl v5.13.8


This document describes differences between the 5.13.7 release and the 5.13.8 release.

If you are upgrading from an earlier release such as 5.13.6, first read perl5137delta, which describes differences between 5.13.6 and 5.13.7.

Core Enhancements

-d:-foo calls Devel::foo::unimport

The syntax -d:foo was extended in 5.6.1 to make -d:foo=bar equivalent to -MDevel::foo=bar , which expands internally to use Devel::foo 'bar'; . perl now allows prefixing the module name with - , with the same semantics as -M , i.e.

  • -d:-foo

    Equivalent to -M-Devel::foo , expands to no Devel::foo; , calls Devel::foo->unimport() if the method exists.

  • -d:-foo=bar

    Equivalent to -M-Devel::foo=bar , expands to no Devel::foo 'bar'; , calls Devel::foo->unimport('bar') if the method exists.

This is particularly useful to suppresses the default actions of a Devel::* module's import method whilst still loading it for debugging.

Filehandle method calls load IO::File on demand

When a method call on a filehandle would die because the method cannot be resolved, and IO::File has not been loaded, Perl now loads IO::File via require and attempts method resolution again:

  1. open my $fh, ">", $file;
  2. $fh->binmode(":raw"); # loads IO::File and succeeds

This also works for globs like STDOUT, STDERR and STDIN:

  1. STDOUT->autoflush(1);

Because this on-demand load only happens if method resolution fails, the legacy approach of manually loading an IO::File parent class for partial method support still works as expected:

  1. use IO::Handle;
  2. open my $fh, ">", $file;
  3. $fh->autoflush(1); # IO::File not loaded

Full functionality for use feature 'unicode_strings'

This release provides full functionality for use feature 'unicode_strings' . Under its scope, all string operations executed and regular expressions compiled (even if executed outside its scope) have Unicode semantics. See feature.

This feature avoids most forms of the "Unicode Bug" (See The Unicode Bug in perlunicode for details.) If there is a possibility that your code will process Unicode strings, you are strongly encouraged to use this subpragma to avoid nasty surprises.

The availability of this should strongly affect the whole tone of various documents, such as perlunicode and perluniintro, but this work has not been done yet.

Exception Handling Backcompat Hack

When an exception is thrown in an eval BLOCK , $@ is now set before unwinding, as well as being set after unwinding as the eval block exits. This early setting supports code that has historically treated $@ during unwinding as an indicator of whether the unwinding was due to an exception. These modules had been broken by 5.13.1's change from setting $@ early to setting it late. This double setting arrangement is a stopgap until the reason for unwinding can be made properly introspectable. $@ has never been a reliable indicator of the reason for unwinding.

printf-like functions understand post-1980 size modifiers

Perl's printf and sprintf operators, and Perl's internal printf replacement function, now understand the C90 size modifiers "hh" (char ), "z" (size_t ), and "t" (ptrdiff_t ). Also, when compiled with a C99 compiler, Perl now understands the size modifier "j" (intmax_t ).

So, for example, on any modern machine, sprintf('%hhd', 257) returns '1'.

DTrace probes now include package name

The DTrace probes now include an additional argument (arg3 ) which contains the package the subroutine being entered or left was compiled in.

For example using the following DTrace script:

  1. perl$target:::sub-entry
  2. {
  3. printf("%s::%s\n", copyinstr(arg0), copyinstr(arg3));
  4. }

and then running:

  1. perl -e'sub test { }; test'

DTrace will print:

  1. main::test

Stacked labels

Multiple statement labels can now appear before a single statement.

Incompatible Changes

:= is now a syntax error

Previously my $pi := 4; was exactly equivalent to my $pi : = 4; , with the : being treated as the start of an attribute list, ending before the = . The use of := to mean : = was deprecated in 5.12.0, and is now a syntax error. This will allow the future use of := as a new token.

We find no Perl 5 code on CPAN using this construction, outside the core's tests for it, so we believe that this change will have very little impact on real-world codebases.

If it is absolutely necessary to have empty attribute lists (for example, because of a code generator) then avoid the error by adding a space before the = .

Run-time code block in regular expressions

Code blocks in regular expressions ((?{...}) and (??{...}) ) used not to inherit any pragmata (strict, warnings, etc.) if the regular expression was compiled at run time as happens in cases like these two:

  1. use re 'eval';
  2. $foo =~ $bar; # when $bar contains (?{...})
  3. $foo =~ /$bar(?{ $finished = 1 })/;

This was a bug, which has now been fixed. But it has the potential to break any code that was relying on this bug.


?PATTERN? is deprecated

?PATTERN? (without the initial m) has been deprecated and now produces a warning. This is to allow future use of ? in new operators. The match-once functionality is still available in the form of m?PATTERN?.

sv_compile_2op() is now deprecated

The sv_compile_2op() API function is now deprecated. Searches suggest that nothing on CPAN is using it, so this should have zero impact.

It attempted to provide an API to compile code down to an optree, but failed to bind correctly to lexicals in the enclosing scope. It's not possible to fix this problem within the constraints of its parameters and return value.

Tie functions on scalars holding typeglobs

Calling a tie function (tie, tied, untie) with a scalar argument acts on a file handle if the scalar happens to hold a typeglob.

This is a long-standing bug that will be removed in Perl 5.16, as there is currently no way to tie the scalar itself when it holds a typeglob, and no way to untie a scalar that has had a typeglob assigned to it.

This bug was fixed in 5.13.7 but, because of the breakage it caused, the fix has been reverted. Now there is a deprecation warning whenever a tie function is used on a handle without an explicit * .

Modules and Pragmata

Updated Modules and Pragmata

  • Archive::Tar has been upgraded from version 1.72 to 1.74.

    Skip extracting pax extended headers.

  • autodie has been upgraded from version 2.10 to 2.1001.

    Test fix in blead for VMS.

  • B has been upgraded from version 1.26 to 1.27.

    Avoid compiler warnings.

  • B::Concise has been upgraded from version 0.81 to 0.82.

    It no longer produces mangled output with the -tree option [perl #80632].

  • B::Deparse has been upgraded from version 1.01 to 1.02.

    Test improvements.

  • Cwd has been upgraded from version 3.34 to 3.35.

    Avoid compiler warnings.

  • Data::Dumper has been upgraded from version 2.130_01 to 2.130_02.

    Avoid compiler warnings.

  • Devel::Peek has been upgraded from version 1.05 to 1.06.

    Avoid compiler warnings.

    Test improvements.

  • Devel::SelfStubber has been upgraded from version 1.03 to 1.05.

    Whitespace changes.

  • Digest::SHA has been upgraded from 5.48 to 5.50.

    shasum now more closely mimics sha1sum /md5sum .

    Addfile accepts all POSIX filenames.

  • Dumpvalue has been upgraded from version 1.14 to 1.15.

    Test improvements.

  • DynaLoader has been upgraded from version 1.11 to 1.12.

    Remove obsolete RCS keywords.

  • Env has been upgraded from version 1.01 to 1.02.

    Test improvements.

  • ExtUtils::CBuilder has been upgraded from 0.2703 to 0.280201.

    Handle C and C++ compilers separately.

    Preserves exit status on VMS.

    Test improvements.

  • ExtUtils::Constant::Utils has been upgraded from 0.02 to 0.03.

    Refactoring and fixing of backcompat code, preparing for resynchronisation with CPAN.

  • ExtUtils::Embed has been upgraded from 1.29 to 1.30.

    Remove obsolete RCS keywords.

  • ExtUtils::ParseXS has been upgraded from 2.2207 to 2.2208.

    Avoid compiler warnings.

  • Fcntl has been upgraded from 1.10 to 1.11.

    Avoid compiler warnings.

    Test improvements.

  • feature has been upgraded from 1.18 to 1.19.

    Documentation and test updates for the unicode_strings feature. See Full functionality for use feature 'unicode_strings'.

  • File::CheckTree has been upgraded from 4.4 to 4.41.

    Whitespace changes.

  • File::Glob has been upgraded from 1.10 to 1.11.

    Avoid compiler warnings.

    Test improvements.

  • GDBM_File has been upgraded from 1.12 to 1.13.

    Test improvements.

    Remove obsolete RCS keywords.

  • Hash::Util::FieldHash has been upgraded from 1.06 to 1.07.

    Avoid compiler warnings.

  • I18N::Collate has been upgraded from 1.01 to 1.02.

    Whitespace changes.

    Test improvements.

  • if has been upgraded from 0.06 to 0.0601.

    Test improvements.

  • IO has been upgraded from 1.25_02 to 1.25_03.

    Avoid compiler warnings.

  • IPC::Cmd has been upgraded from 0.64 to 0.66.

    Resolves an issue with splitting Win32 command lines.

    Documentation enhancements.

  • IPC::Open3 has been upgraded from 1.07 to 1.08.

    Remove obsolete RCS keywords.

    Test improvements.

  • Locale::Codes has been upgraded from version 3.14 to 3.15.

    Adds some codes.

  • Math::BigInt has been upgraded from 1.99_01 to 1.99_02.

    Documentation and comment spelling fixes.

  • Memoize has been upgraded from version 1.01_03 to 1.02.

    Remove obsolete RCS keywords.

    Whitespace changes.

  • MIME::Base64 has been upgraded from 3.10 to 3.13.

    Now provides encode_base64url and decode_base64url functions to process the base64 scheme for "URL applications".

  • mro has been upgraded from version 1.05 to 1.06.

    next::method et al. now take into account that every class inherits from UNIVERSAL [perl #68654].

  • NDBM_File has been upgraded from 1.10 to 1.11.

    Remove obsolete RCS keywords.

    Test improvements.

  • Net::Ping has been upgraded from 2.36 to 2.37.

    Remove obsolete RCS keywords.

  • ODBM_File has been upgraded from 1.09 to 1.10.

    Remove obsolete RCS keywords.

    Test improvements.

  • Opcode has been upgraded from 1.17 to 1.18.

    Avoid compiler warnings.

    Test improvements.

  • overload has been upgraded from 1.11 to 1.12.

    Avoid a taint problem in use of sprintf.

    Test asymmetric fallback cases [perl #71286].

  • PerlIO::encoding has been upgraded from 0.13 to 0.14.

    Avoid compiler warnings.

    Remove obsolete RCS keywords.

    Test improvements.

  • PerlIO::scalar has been upgraded from 0.10 to 0.11.

    A read after a seek beyond the end of the string no longer thinks it has data to read [perl #78716].

    Avoid compiler warnings.

  • PerlIO::via has been upgraded from 0.10 to 0.11.

    Avoid compiler warnings.

  • POSIX has been upgraded from 1.22 to 1.23.

    Avoid compiler warnings.

  • re has been upgraded from 0.14 to 0.15.

    Enforce that /d, /u , and /l are mutually exclusive.

  • SDBM_File has been upgraded from 1.08 to 1.09.

    Avoid compiler warnings.

    Remove obsolete RCS keywords.

    Test improvements.

  • Socket has been upgraded from 1.91 to 1.92.

    It has several new functions for handling IPv6 addresses.

  • Storable has been upgraded from 2.24 to 2.25.

    This adds support for serialising code references that contain UTF-8 strings correctly. The Storable minor version number changed as a result, meaning that Storable users who set $Storable::accept_future_minor to a FALSE value will see errors (see FORWARD COMPATIBILITY in Storable for more details).

    Freezing no longer gets confused if the Perl stack gets reallocated during freezing [perl #80074].

    Avoid compiler warnings.

  • threads has been upgraded from 1.81_02 to 1.81_03.

    Avoid compiler warnings.

  • threads::shared has been upgraded from 1.34 to 1.35.

    Avoid compiler warnings.

  • Time::HiRes has been upgraded from 1.9721 to 1.9721_01.

    Build fix in blead for VMS.

  • Unicode::Collate has been upgraded from 0.67 to 0.6801.

    Documentation clarification.

    Test improvements.

  • Unicode::Normalize has been upgraded from 1.07 to 1.08.

    Avoid compiler warnings.

  • Unicode::UCD has been upgraded from 0.29 to 0.30.

    Add info about named sequence alternatives.

    Don't use CompositionExclusions.txt .

  • version has been upgraded from 0.82 to 0.86.

    Modify export logic for is_strict and is_lax .

    Various backcompat fixes.

  • Win32 has been upgraded from 0.39 to 0.41.

    Add several functions.

    Corrections to names returned by Win32::GetOSName and Win32::GetOSDisplayName .

  • XS::APItest has been upgraded from 0.26 to 0.27.

    Test new API functions.

    Avoid compiler warnings.

Dual-life Modules and Pragmata

These modules were formerly distributed only in the Perl core distribution, and are now dual-lifed (meaning they are now also available separately on CPAN):

  • autouse

  • Devel::SelfStubber

  • Dumpvalue

  • Env

  • File::CheckTree

  • I18N::Collate


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

Changes to Existing Diagnostics

  • The "Found = in conditional" warning that is emitted when a constant is assigned to a variable in a condition is now withheld if the constant is actually a subroutine or one generated by use constant , since the value of the constant may not be known at the time the program is written [perl #77762].

Configuration and Compilation

  • The Encode module can now (once again) be included in a static Perl build. The special-case handling for this situation got broken in Perl 5.11.0, and has now been repaired.


  • Tests for Fcntl , File::Glob , GDBM_File , IPC::Open3 , NDBM_File , ODBM_File , Opcode , PerlIO::encoding , SDBM_File , and Storable now use the Test::More framework.

Platform Support

Platform-Specific Notes

  • NetBSD

    The NetBSD hints file has been changed to make the system's malloc the default.

  • Windows

    The option to use an externally-supplied crypt(), or to build with no crypt() at all, has been removed. Perl supplies its own crypt() implementation for Windows, and the political situation that required this part of the distribution to sometimes be omitted is long gone.

Internal Changes

  • The mg_findext() and sv_unmagicext() functions have been added to the API. They allow extension authors to find and remove magic attached to scalars based on both the magic type and the magic virtual table, similar to how sv_magicext() attaches magic of a certain type and with a given virtual table to a scalar. This eliminates the need for extensions to walk the list of MAGIC pointers of an SV to find the magic that belongs to them.

  • The parse_fullexpr() , parse_listexpr() , parse_termexpr() , and parse_arithexpr() functions have been added to the API. They perform recursive-descent parsing of expressions at various precedence levels. They are expected to be used by syntax plugins.

Selected Bug Fixes

  • BEGIN {require 5.12.0} now behaves as documented, rather than behaving identically to use 5.12.0; . Previously, require in a BEGIN block was erroneously executing the use feature ':5.12.0' and use strict; use warnings; behaviour, which only use was documented to provide [perl #69050].

  • use 5.42 [perl #69050], use 6 and no 5 no longer leak memory.

  • eval "BEGIN{die}" no longer leaks memory on non-threaded builds.

  • PerlIO no longer crashes when called recursively, e.g., from a signal handler. Now it just leaks memory [perl #75556].

  • Defining a constant with the same name as one of perl's special blocks (e.g., INIT) stopped working in 5.12.0, but has now been fixed [perl #78634].

  • A reference to a literal value used as a hash key ($hash{\"foo"} ) used to be stringified, even if the hash was tied [perl #79178].

  • A closure containing an if statement followed by a constant or variable is no longer treated as a constant [perl #63540].

  • Calling a closure prototype (what is passed to an attribute handler for a closure) now results in a "Closure prototype called" error message instead of a crash [perl #68560].

  • A regular expression optimisation would sometimes cause a match with a {n,m} quantifier to fail when it should match [perl #79152].

  • What has become known as the "Unicode Bug" is mostly resolved in this release. Under use feature 'unicode_strings' , the internal storage format of a string no longer affects the external semantics. There are two known exceptions. User-defined case changing functions, which are planned to be deprecated in 5.14, require utf8-encoded strings to function; and the character LATIN SMALL LETTER SHARP S in regular expression case-insensitive matching has a somewhat different set of bugs depending on the internal storage format. Case-insensitive matching of all characters that have multi-character matches, as this one does, is problematical in Perl. [perl #58182].

  • Mentioning a read-only lexical variable from the enclosing scope in a string eval no longer causes the variable to become writable [perl #19135].

  • state can now be used with attributes. It used to mean the same thing as my if attributes were present [perl #68658].

  • Expressions like @$a > 3 no longer cause $a to be mentioned in the "Use of uninitialized value in numeric gt" warning when $a is undefined (since it is not part of the > expression, but the operand of the @ ) [perl #72090].

  • require no longer causes caller to return the wrong file name for the scope that called require and other scopes higher up that had the same file name [perl #68712].

  • The ref types in the typemap for XS bindings now support magical variables [perl #72684].

  • Match variables (e.g., $1 ) no longer persist between calls to a sort subroutine [perl #76026].

  • The B module was returning B::OP s instead of B::LOGOP s for entertry [perl #80622]. This was due to a bug in the perl core, not in B itself.

  • Some numeric operators were converting integers to floating point, resulting in loss of precision on 64-bit platforms [perl #77456].

  • The fallback behaviour of overloading on binary operators was asymmetric [perl #71286].


Perl 5.13.8 represents approximately one month of development since Perl 5.13.7 and contains 38715 lines of changes across 546 files from 38 authors and committers.

Thank you to the following for contributing to this release:

Abhijit Menon-Sen, Abigail, Andreas König, Ben Morrow, Brad Gilbert, brian d foy, Chip Salzenberg, Chris 'BinGOs' Williams, Craig A. Berry, David Golden, David Leadbeater, David Mitchell, Father Chrysostomos, Florian Ragwitz, Goro Fuji, H.Merijn Brand, Jan Dubois, Jerry D. Hedden, Jesse Vincent, John Peacock, Karl Williamson, Lukas Mai, Marvin Humphrey, Max Maischein, Michael Breen, Michael Fig, Nicholas Clark, Nick Cleaton, Paul Evans, Peter J. Holzer, Peter John Acklam, Rafael Garcia-Suarez, Reini Urban, Renee Baecker, Ricardo Signes, Tony Cook, Yves Orton, Zefram

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 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 This points to a closed subscription unarchived mailing list, which includes all the core committers, who 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.