NAME

DESCRIPTION

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

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

    use 5.12.0;

    use strict;
    use feature ':5.12';

Potentially Incompatible Changes

Deprecations

The following items are now deprecated:

suidperl

"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 "=".

"UNIVERSAL->import()"

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/deprecate.pm 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".

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

"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

termcap.pl, tainted.pl, stat.pl, shellwords.pl, pwd.pl, open3.pl, open2.pl, newgetopt.pl, look.pl, find.pl, finddepth.pl, importenv.pl, hostname.pl, getopts.pl, getopt.pl, getcwd.pl, flush.pl, fastcwd.pl, exceptions.pl, ctime.pl, complete.pl, cacheout.pl, bigrat.pl, bigint.pl, bigfloat.pl, assert.pl, abbrev.pl, dotsh.pl, and timelocal.pl 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 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 <http://www.unicode.org/reports/tr29/>). Anything matched previously and that made sense will continue to be accepted. Additionally:

• "\X" will not break apart a "CR LF" sequence.
• "\X" will now match a sequence which includes the "ZWJ" and "ZWNJ" characters.
• "\X" will now always match at least one character, including an initial mark. Marks generally come after a base character, but it is possible in Unicode to have them in isolation, and "\X" will now handle that case, for example at the beginning of a line, or after a "ZWSP". And this is the part where "\X" doesn't match the things that it used to that don't make sense. Formerly, for example, you could have the nonsensical case of an accented LF.
• "\X" will now match a (Korean) Hangul syllable sequence, and the Thai and Lao exception cases.

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

Documentation

Selected Performance Enhancements

• A new internal cache means that "isa()" will often be faster.
• The implementation of "C3" Method Resolution Order has been optimised - linearisation for classes with single inheritance is 40% faster. Performance for multiple inheritance is unchanged.
• Under "use locale", the locale-relevant information is now cached on read-only values, such as the list returned by "keys %hash". This makes operations such as "sort keys %hash" in the scope of "use locale" much faster.
• Empty "DESTROY" methods are no longer called.
• "Perl_sv_utf8_upgrade()" is now faster.
• "keys" on empty hash is now faster.
• "if (%foo)" has been optimized to be faster than "if (keys %foo)".
• The string repetition operator ("$str x $num") is now several times faster when $str has length one or $num is large.
• Reversing an array to itself (as in "@a = reverse @a") in void context now happens in-place and is several orders of magnitude faster than it used to be. It will also preserve non-existent elements whenever possible, i.e. for non magical arrays or tied arrays with "EXISTS" and "DELETE" methods.

Installation and Configuration Improvements

• perlapi, perlintern, perlmodlib and perltoc are now all generated at build time, rather than being shipped as part of the release.
• If "vendorlib" and "vendorarch" are the same, then they are only added to @INC once.
• $Config{usedevel} and the C-level "PERL_USE_DEVEL" are now defined if perl is built with "-Dusedevel".
• Configure will enable use of "-fstack-protector", to provide protection against stack-smashing attacks, if the compiler supports it.
• Configure will now determine the correct prototypes for re-entrant functions and for "gconvert" if you are using a C++ compiler rather than a C compiler.
• On Unix, if you build from a tree containing a git repository, the configuration process will note the commit hash you have checked out, for display in the output of "perl -v" and "perl -V". Unpushed local commits are automatically added to the list of local patches displayed by "perl -V".
• Perl now supports SystemTap's "dtrace" compatibility layer and an issue with linking "miniperl" has been fixed in the process.
• perldoc now uses "less -R" instead of "less" for improved behaviour in the face of "groff"'s new usage of ANSI escape codes.
• "perl -V" now reports use of the compile-time options "USE_PERL_ATOF" and "USE_ATTRIBUTES_FOR_PERLIO".
• As part of the flattening of ext, all extensions on all platforms are built by make_ext.pl. This replaces the Unix-specific ext/util/make_ext, VMS-specific make_ext.com and Win32-specific win32/buildext.pl.

Internal Changes

• The J.R.R. Tolkien quotes at the head of C source file have been checked and proper citations added, thanks to a patch from Tom Christiansen.
• The internal structure of the dual-life modules traditionally found in the lib/ and ext/ directories in the perl source has changed significantly. Where possible, dual-lifed modules have been extracted from lib/ and ext/.

  Dual-lifed modules maintained by Perl's developers as part of the Perl core now live in dist/. Dual-lifed modules maintained primarily on CPAN now live in cpan/. When reporting a bug in a module located under cpan/, please send your bug report directly to the module's bug tracker or author, rather than Perl's bug tracker.

• "\N{...}" now compiles better, always forces UTF-8 internal representation

  Perl's developers have fixed several problems with the recognition of "\N{...}" constructs. As part of this, perl will store any scalar or regex containing "\N{name}" or "\N{U+code point}" in its definition in UTF-8 format. (This was true previously for all occurrences of "\N{name}" that did not use a custom translator, but now it's always true.)

• Perl_magic_setmglob now knows about globs, fixing RT #71254.
• "SVt_RV" no longer exists. RVs are now stored in IVs.
• "Perl_vcroak()" now accepts a null first argument. In addition, a full audit was made of the "not NULL" compiler annotations, and those for several other internal functions were corrected.
• New macros "dSAVEDERRNO", "dSAVE_ERRNO", "SAVE_ERRNO", "RESTORE_ERRNO" have been added to formalise the temporary saving of the "errno" variable.
• The function "Perl_sv_insert_flags" has been added to augment "Perl_sv_insert".
• The function "Perl_newSV_type(type)" has been added, equivalent to "Perl_newSV()" followed by "Perl_sv_upgrade(type)".
• The function "Perl_newSVpvn_flags()" has been added, equivalent to "Perl_newSVpvn()" and then performing the action relevant to the flag.

  Two flag bits are currently supported.

• The function "Perl_croak_xs_usage" has been added as a wrapper to "Perl_croak".
• Perl now exports the functions "PerlIO_find_layer" and "PerlIO_list_alloc".
• "PL_na" has been exterminated from the core code, replaced by local STRLEN temporaries, or "*_nolen()" calls. Either approach is faster than "PL_na", which is a pointer dereference into the interpreter structure under ithreads, and a global variable otherwise.
• "Perl_mg_free()" used to leave freed memory accessible via "SvMAGIC()" on the scalar. It now updates the linked list to remove each piece of magic as it is freed.
• Under ithreads, the regex in "PL_reg_curpm" is now reference counted. This eliminates a lot of hackish workarounds to cope with it not being reference counted.
• "Perl_mg_magical()" would sometimes incorrectly turn on "SvRMAGICAL()". This has been fixed.
• The public IV and NV flags are now not set if the string value has trailing "garbage". This behaviour is consistent with not setting the public IV or NV flags if the value is out of range for the type.
• Uses of "Nullav", "Nullcv", "Nullhv", "Nullop", "Nullsv" etc have been replaced by "NULL" in the core code, and non-dual-life modules, as "NULL" is clearer to those unfamiliar with the core code.
• A macro MUTABLE_PTR(p) has been added, which on (non-pedantic) gcc will not cast away "const", returning a "void *". Macros "MUTABLE_SV(av)", "MUTABLE_SV(cv)" etc build on this, casting to "AV *" etc without casting away "const". This allows proper compile-time auditing of "const" correctness in the core, and helped picked up some errors (now fixed).
• Macros "mPUSHs()" and "mXPUSHs()" have been added, for pushing SVs on the stack and mortalizing them.
• Use of the private structure "mro_meta" has changed slightly. Nothing outside the core should be accessing this directly anyway.
• A new tool, Porting/expand-macro.pl has been added, that allows you to view how a C preprocessor macro would be expanded when compiled. This is handy when trying to decode the macro hell that is the perl guts.

Testing

New or Changed Diagnostics

  no warnings 'illegalproto';

Utility Changes

• h2ph now looks in "include-fixed" too, which is a recent addition to gcc's search path.
• h2xs no longer incorrectly treats enum values like macros. It also now handles C++ style comments ("//") properly in enums.
• perl5db.pl now supports "LVALUE" subroutines. Additionally, the debugger now correctly handles proxy constant subroutines, and subroutine stubs.
• perlbug now uses %Module::CoreList::bug_tracker to print out upstream bug tracker URLs. If a user identifies a particular module as the topic of their bug report and we're able to divine the URL for its upstream bug tracker, perlbug now provide a message to the user explaining that the core copies the CPAN version directly, and provide the URL for reporting the bug directly to the upstream author.

  perlbug no longer reports "Message sent" when it hasn't actually sent the message

• perlthanks is a new utility for sending non-bug-reports to the authors and maintainers of Perl. Getting nothing but bug reports can become a bit demoralising. If Perl 5.12 works well for you, please try out perlthanks. It will make the developers smile.
• Perl's developers have fixed bugs in a2p having to do with the "match()" operator in list context. Additionally, a2p no longer generates code that uses the $[ variable.

Selected Bug Fixes

• U+0FFFF is now a legal character in regular expressions.
• pp_qr now always returns a new regexp SV. Resolves RT #69852.

  Instead of returning a(nother) reference to the (pre-compiled) regexp in the optree, use reg_temp_copy() to create a copy of it, and return a reference to that. This resolves issues about Regexp::DESTROY not being called in a timely fashion (the original bug tracked by RT #69852), as well as bugs related to blessing regexps, and of assigning to regexps, as described in correspondence added to the ticket.

  It transpires that we also need to undo the SvPVX() sharing when ithreads cloning a Regexp SV, because mother_re is set to NULL, instead of a cloned copy of the mother_re. This change might fix bugs with regexps and threads in certain other situations, but as yet neither tests nor bug reports have indicated any problems, so it might not actually be an edge case that it's possible to reach.

• Several compilation errors and segfaults when perl was built with "-Dmad" were fixed.
• Fixes for lexer API changes in 5.11.2 which broke NYTProf's savesrc option.
• "-t" should only return TRUE for file handles connected to a TTY

  The Microsoft C version of "isatty()" returns TRUE for all character mode devices, including the /dev/null-style "nul" device and printers like "lpt1".

• Fixed a regression caused by commit fafafbaf which caused a panic during parameter passing [perl #70171]
• On systems which in-place edits without backup files, -i'*' now works as the documentation says it does [perl #70802]
• Saving and restoring magic flags no longer loses readonly flag.
• The malformed syntax "grep EXPR LIST" (note the missing comma) no longer causes abrupt and total failure.
• Regular expressions compiled with "qr{}" literals properly set "$'" when matching again.
• Using named subroutines with "sort" should no longer lead to bus errors [perl #71076]
• Numerous bugfixes catch small issues caused by the recently-added Lexer API.
• Smart match against @_ sometimes gave false negatives. [perl #71078]
• $@ may now be assigned a read-only value (without error or busting the stack).
• "sort" called recursively from within an active comparison subroutine no longer causes a bus error if run multiple times. [perl #71076]
• Tie::Hash::NamedCapture::* will not abort if passed bad input (RT #71828)
• @_ and $_ no longer leak under threads (RT #34342 and #41138, also #70602, #70974)
• "-I" on shebang line now adds directories in front of @INC as documented, and as does "-I" when specified on the command-line.
• "kill" is now fatal when called on non-numeric process identifiers. Previously, an "undef" process identifier would be interpreted as a request to kill process 0, which would terminate the current process group on POSIX systems. Since process identifiers are always integers, killing a non-numeric process is now fatal.
• 5.10.0 inadvertently disabled an optimisation, which caused a measurable performance drop in list assignment, such as is often used to assign function parameters from @_. The optimisation has been re-instated, and the performance regression fixed. (This fix is also present in 5.10.1)
• Fixed memory leak on "while (1) { map 1, 1 }" [RT #53038].
• Some potential coredumps in PerlIO fixed [RT #57322,54828].
• The debugger now works with lvalue subroutines.
• The debugger's "m" command was broken on modules that defined constants [RT #61222].
• "crypt" and string complement could return tainted values for untainted arguments [RT #59998].
• The "-i".suffix command-line switch now recreates the file using restricted permissions, before changing its mode to match the original file. This eliminates a potential race condition [RT #60904].
• On some Unix systems, the value in $? would not have the top bit set ("$? & 128") even if the child core dumped.
• Under some circumstances, $^R could incorrectly become undefined [RT #57042].
• In the XS API, various hash functions, when passed a pre-computed hash where the key is UTF-8, might result in an incorrect lookup.
• XS code including XSUB.h before perl.h gave a compile-time error [RT #57176].
• "$object->isa('Foo')" would report false if the package "Foo" didn't exist, even if the object's @ISA contained "Foo".
• Various bugs in the new-to 5.10.0 mro code, triggered by manipulating @ISA, have been found and fixed.
• Bitwise operations on references could crash the interpreter, e.g. "$x=\$y; $x |= "foo"" [RT #54956].
• Patterns including alternation might be sensitive to the internal UTF-8 representation, e.g.

      my $byte = chr(192);
      my $utf8 = chr(192); utf8::upgrade($utf8);
      $utf8 =~ /$byte|X}/i;       # failed in 5.10.0
      

• Within UTF8-encoded Perl source files (i.e. where "use utf8" is in effect), double-quoted literal strings could be corrupted where a "\xNN", "\0NNN" or "\N{}" is followed by a literal character with ordinal value greater than 255 [RT #59908].
• "B::Deparse" failed to correctly deparse various constructs: "readpipe STRING" [RT #62428], "CORE::require(STRING)" [RT #62488], "sub foo(_)" [RT #62484].
• Using "setpgrp" with no arguments could corrupt the perl stack.
• The block form of "eval" is now specifically trappable by "Safe" and "ops". Previously it was erroneously treated like string "eval".
• In 5.10.0, the two characters "[~" were sometimes parsed as the smart match operator ("~~") [RT #63854].
• In 5.10.0, the "*" quantifier in patterns was sometimes treated as "{0,32767}" [RT #60034, #60464]. For example, this match would fail:

      ("ab" x 32768) =~ /^(ab)*$/
      

• "shmget" was limited to a 32 bit segment size on a 64 bit OS [RT #63924].
• Using "next" or "last" to exit a "given" block no longer produces a spurious warning like the following:

      Exiting given via last at foo.pl line 123
      

• Assigning a format to a glob could corrupt the format; e.g.:

       *bar=*foo{FORMAT}; # foo format now bad
      

• Attempting to coerce a typeglob to a string or number could cause an assertion failure. The correct error message is now generated, "Can't coerce GLOB to $type".
• Under "use filetest 'access'", "-x" was using the wrong access mode. This has been fixed [RT #49003].
• "length" on a tied scalar that returned a Unicode value would not be correct the first time. This has been fixed.
• Using an array "tie" inside in array "tie" could SEGV. This has been fixed. [RT #51636]
• A race condition inside "PerlIOStdio_close()" has been identified and fixed. This used to cause various threading issues, including SEGVs.
• In "unpack", the use of "()" groups in scalar context was internally placing a list on the interpreter's stack, which manifested in various ways, including SEGVs. This is now fixed [RT #50256].
• Magic was called twice in "substr", "\&$x", "tie $x, $m" and "chop". These have all been fixed.
• A 5.10.0 optimisation to clear the temporary stack within the implicit loop of "s///ge" has been reverted, as it turned out to be the cause of obscure bugs in seemingly unrelated parts of the interpreter [commit ef0d4e17921ee3de].
• The line numbers for warnings inside "elsif" are now correct.
• The ".." operator now works correctly with ranges whose ends are at or close to the values of the smallest and largest integers.
• "binmode STDIN, ':raw'" could lead to segmentation faults on some platforms. This has been fixed [RT #54828].
• An off-by-one error meant that "index $str, ..." was effectively being executed as "index "$str\0", ...". This has been fixed [RT #53746].
• Various leaks associated with named captures in regexes have been fixed [RT #57024].
• A weak reference to a hash would leak. This was affecting "DBI" [RT #56908].
• Using (?|) in a regex could cause a segfault [RT #59734].
• Use of a UTF-8 "tr//" within a closure could cause a segfault [RT #61520].
• Calling "Perl_sv_chop()" or otherwise upgrading an SV could result in an unaligned 64-bit access on the SPARC architecture [RT #60574].
• In the 5.10.0 release, "inc_version_list" would incorrectly list "5.10.*" after "5.8.*"; this affected the @INC search order [RT #67628].
• In 5.10.0, "pack "a*", $tainted_value" returned a non-tainted value [RT #52552].
• In 5.10.0, "printf" and "sprintf" could produce the fatal error "panic: utf8_mg_pos_cache_update" when printing UTF-8 strings [RT #62666].
• In the 5.10.0 release, a dynamically created "AUTOLOAD" method might be missed (method cache issue) [RT #60220,60232].
• In the 5.10.0 release, a combination of "use feature" and "//ee" could cause a memory leak [RT #63110].
• "-C" on the shebang ("#!") line is once more permitted if it is also specified on the command line. "-C" on the shebang line used to be a silent no-op if it was not also on the command line, so perl 5.10.0 disallowed it, which broke some scripts. Now perl checks whether it is also on the command line and only dies if it is not [RT #67880].
• In 5.10.0, certain types of re-entrant regular expression could crash, or cause the following assertion failure [RT #60508]:

      Assertion rx->sublen >= (s - rx->subbeg) + i failed
      

• Perl now includes previously missing files from the Unicode Character Database.
• Perl now honors "TMPDIR" when opening an anonymous temporary file.

Platform Specific Changes

Known Problems

• Some CPANPLUS tests may fail if there is a functioning file ../../cpanp-run-perl outside your build directory. The failure shouldn't imply there's a problem with the actual functional software. The bug is already fixed in [RT #74188] and is scheduled for inclusion in perl-v5.12.1.
• "List::Util::first" misbehaves in the presence of a lexical $_ (typically introduced by "my $_" or implicitly by "given"). The variable which gets set for each iteration is the package variable $_, not the lexical $_ [RT #67694].

  A similar issue may occur in other modules that provide functions which take a block as their first argument, like

      foo { ... $_ ...} list
      

• Some regexes may run much more slowly when run in a child thread compared with the thread the pattern was compiled into [RT #55600].
• Things like ""\N{LATIN SMALL LIGATURE FF}" =~ /\N{LATIN SMALL LETTER F}+/" will appear to hang as they get into a very long running loop [RT #72998].
• Several porters have reported mysterious crashes when Perl's entire test suite is run after a build on certain Windows 2000 systems. When run by hand, the individual tests reportedly work fine.

Errata

•

This one is actually a change introduced in 5.10.0, but it was missed from that release's perldelta, so it is mentioned here instead.

A bugfix related to the handling of the "/m" modifier and "qr" resulted in a change of behaviour between 5.8.x and 5.10.0:

    # matches in 5.8.x, doesn't match in 5.10.0
    $re = qr/^bar/; "foo\nbar" =~ /$re/m;
    

Acknowledgements

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, AEvar Arnfjoerd` Bjarmason, Alan Grover, Alexandr Ciornii, Alex Davies, Alex Vandiver, Andreas Koenig, Andrew Rodland, andrew@sundale.net, 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 Gruenauer, 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, Renee Baecker, 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, Sebastien Aperghis-Tramoni, Sergio Durigan Junior, Shlomi Fish, Simon 'corecode' Schubert, Sisyphus, Slaven Rezic, Smylers, Steffen Mueller, 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 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 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 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.

SEE ALSO

The INSTALL file for how to build Perl.

The README file for general stuff.

The Artistic and Copying files for copyright information.

<http://dev.perl.org/perl5/errata.html> for a list of issues found after this release, as well as a list of CPAN modules known to be incompatible with this release.