NAME

DESCRIPTION

Notice

• "." no longer in @INC

  For security reasons, the current directory (".") is no longer included by default at the end of the module search path (@INC). This may have widespread implications for the building, testing and installing of modules, and for the execution of scripts. See the section "Removal of the current directory (".") from @INC" for the full details.

• "do" may now warn

  "do" now gives a deprecation warning when it fails to load a file which it would have loaded had "." been in @INC.

• In regular expression patterns, a literal left brace "{" should be escaped

  See "Unescaped literal "{" characters in regular expression patterns are no longer permissible".

Core Enhancements

    <<~EOF;
    <<~\EOF;
    <<~'EOF';
    <<~"EOF";
    <<~`EOF`;
    <<~ 'EOF';
    <<~ "EOF";
    <<~ `EOF`;

    if (1) {
      print <<~EOF;
        Hello there
        EOF
    }

    use experimental 'refaliasing', 'declared_refs';
    my \$a = \$b;

Security

Incompatible Changes

 qr/{fee|{fie/

    sub foo : lvalue { keys(%INC) }
    (foo) = 3; # death
    sub bar : lvalue { keys(@_) }
    (bar) = 3; # also an error

Deprecations

Performance Enhancements

• A hash in boolean context is now sometimes faster, e.g.

      if (!%h) { ... }
      

  This was already special-cased, but some cases were missed (such as "grep %$_, @AoH"), and even the ones which weren't have been improved.

• New Faster Hash Function on 64 bit builds

  We use a different hash function for short and long keys. This should improve performance and security, especially for long keys.

• readline is faster

  Reading from a file line-by-line with "readline()" or "<>" should now typically be faster due to a better implementation of the code that searches for the next newline character.

• Assigning one reference to another, e.g. "$ref1 = $ref2" has been optimized in some cases.
• Remove some exceptions to creating Copy-on-Write strings. The string buffer growth algorithm has been slightly altered so that you're less likely to encounter a string which can't be COWed.
• Better optimise array and hash assignment: where an array or hash appears in the LHS of a list assignment, such as "(..., @a) = (...);", it's likely to be considerably faster, especially if it involves emptying the array/hash. For example, this code runs about a third faster compared to Perl 5.24.0:

      my @a;
      for my $i (1..10_000_000) {
          @a = (1,2,3);
          @a = ();
      }
      

• Converting a single-digit string to a number is now substantially faster.
• The "split" builtin is now slightly faster in many cases: in particular for the two specially-handled forms

      my    @a = split ...;
      local @a = split ...;
      

• The rather slow implementation for the experimental subroutine signatures feature has been made much faster; it is now comparable in speed with the traditional "my ($a, $b, @c) = @_".
• Bareword constant strings are now permitted to take part in constant folding. They were originally exempted from constant folding in August 1999, during the development of Perl 5.6, to ensure that "use strict "subs"" would still apply to bareword constants. That has now been accomplished a different way, so barewords, like other constants, now gain the performance benefits of constant folding.

  This also means that void-context warnings on constant expressions of barewords now report the folded constant operand, rather than the operation; this matches the behaviour for non-bareword constants.

Modules and Pragmata

Documentation

Diagnostics

Utility Changes

Configuration and Compilation

• "-Ddefault_inc_excludes_dot" has added, and enabled by default.
• The "dtrace" build process has further changes [GH #15718] <https://github.com/Perl/perl5/issues/15718>:

• You can now disable perl's use of the "PERL_HASH_SEED" and "PERL_PERTURB_KEYS" environment variables by configuring perl with "-Accflags=NO_PERL_HASH_ENV".
• You can now disable perl's use of the "PERL_HASH_SEED_DEBUG" environment variable by configuring perl with "-Accflags=-DNO_PERL_HASH_SEED_DEBUG".
• Configure now zeroes out the alignment bytes when calculating the bytes for 80-bit "NaN" and "Inf" to make builds more reproducible. [GH #15725] <https://github.com/Perl/perl5/issues/15725>
• Since v5.18, for testing purposes we have included support for building perl with a variety of non-standard, and non-recommended hash functions. Since we do not recommend the use of these functions, we have removed them and their corresponding build options. Specifically this includes the following build options:

      PERL_HASH_FUNC_SDBM
      PERL_HASH_FUNC_DJB2
      PERL_HASH_FUNC_SUPERFAST
      PERL_HASH_FUNC_MURMUR3
      PERL_HASH_FUNC_ONE_AT_A_TIME
      PERL_HASH_FUNC_ONE_AT_A_TIME_OLD
      PERL_HASH_FUNC_MURMUR_HASH_64A
      PERL_HASH_FUNC_MURMUR_HASH_64B
      

• Remove "Warning: perl appears in your path"

  This install warning is more or less obsolete, since most platforms already will have a /usr/bin/perl or similar provided by the OS.

• Reduce verbosity of "make install.man"

  Previously, two progress messages were emitted for each manpage: one by installman itself, and one by the function in install_lib.pl that it calls to actually install the file. Disabling the second of those in each case saves over 750 lines of unhelpful output.

• Cleanup for "clang -Weverything" support. [GH #15683] <https://github.com/Perl/perl5/issues/15683>
• Configure: signbit scan was assuming too much, stop assuming negative 0.
• Various compiler warnings have been silenced.
• Several smaller changes have been made to remove impediments to compiling under C++11.
• Builds using "USE_PAD_RESET" now work again; this configuration had bit-rotted.
• A probe for "gai_strerror" was added to Configure that checks if the "gai_strerror()" routine is available and can be used to translate error codes returned by "getaddrinfo()" into human readable strings.
• Configure now aborts if both "-Duselongdouble" and "-Dusequadmath" are requested. [GH #14944] <https://github.com/Perl/perl5/issues/14944>
• Fixed a bug in which Configure could append "-quadmath" to the archname even if it was already present. [GH #15423] <https://github.com/Perl/perl5/issues/15423>
• Clang builds with "-DPERL_GLOBAL_STRUCT" or "-DPERL_GLOBAL_STRUCT_PRIVATE" have been fixed (by disabling Thread Safety Analysis for these configurations).
• make_ext.pl no longer updates a module's pm_to_blib file when no files require updates. This could cause dependencies, perlmain.c in particular, to be rebuilt unnecessarily. [GH #15060] <https://github.com/Perl/perl5/issues/15060>
• The output of "perl -V" has been reformatted so that each configuration and compile-time option is now listed one per line, to improve readability.
• Configure now builds "miniperl" and "generate_uudmap" if you invoke it with "-Dusecrosscompiler" but not "-Dtargethost=somehost". This means you can supply your target platform "config.sh", generate the headers and proceed to build your cross-target perl. [GH #15126] <https://github.com/Perl/perl5/issues/15126>
• Perl built with "-Accflags=-DPERL_TRACE_OPS" now only dumps the operator counts when the environment variable "PERL_TRACE_OPS" is set to a non-zero integer. This allows "make test" to pass on such a build.
• When building with GCC 6 and link-time optimization (the "-flto" option to "gcc"), Configure was treating all probed symbols as present on the system, regardless of whether they actually exist. This has been fixed. [GH #15322] <https://github.com/Perl/perl5/issues/15322>
• The t/test.pl library is used for internal testing of Perl itself, and also copied by several CPAN modules. Some of those modules must work on older versions of Perl, so t/test.pl must in turn avoid newer Perl features. Compatibility with Perl 5.8 was inadvertently removed some time ago; it has now been restored. [GH #15302] <https://github.com/Perl/perl5/issues/15302>
• The build process no longer emits an extra blank line before building each "simple" extension (those with only *.pm and *.pod files).

Testing

• A new test script, comp/parser_run.t, has been added that is like comp/parser.t but with test.pl included so that "runperl()" and the like are available for use.
• Tests for locales were erroneously using locales incompatible with Perl.
• Some parts of the test suite that try to exhaustively test edge cases in the regex implementation have been restricted to running for a maximum of five minutes. On slow systems they could otherwise take several hours, without significantly improving our understanding of the correctness of the code under test.
• A new internal facility allows analysing the time taken by the individual tests in Perl's own test suite; see Porting/harness-timer-report.pl.
• t/re/regexp_nonull.t has been added to test that the regular expression engine can handle scalars that do not have a null byte just past the end of the string.
• A new test script, t/op/decl-refs.t, has been added to test the new feature "Declaring a reference to a variable".
• A new test script, t/re/keep_tabs.t has been added to contain tests where "\t" characters should not be expanded into spaces.
• A new test script, t/re/anyof.t, has been added to test that the ANYOF nodes generated by bracketed character classes are as expected.
• There is now more extensive testing of the Unicode-related API macros and functions.
• Several of the longer running API test files have been split into multiple test files so that they can be run in parallel.
• t/harness now tries really hard not to run tests which are located outside of the Perl source tree. [GH #14578] <https://github.com/Perl/perl5/issues/14578>
• Prevent debugger tests (lib/perl5db.t) from failing due to the contents of $ENV{PERLDB_OPTS}. [GH #15782] <https://github.com/Perl/perl5/issues/15782>

Platform Support

Internal Changes

• A new API function "sv_setpv_bufsize()" allows simultaneously setting the length and the allocated size of the buffer in an "SV", growing the buffer if necessary.
• A new API macro "SvPVCLEAR()" sets its "SV" argument to an empty string, like Perl-space "$x = ''", but with several optimisations.
• Several new macros and functions for dealing with Unicode and UTF-8-encoded strings have been added to the API, as well as some changes in the functionality of existing functions (see "Unicode Support" in perlapi for more details):

• Perl is now built with the "PERL_OP_PARENT" compiler define enabled by default. To disable it, use the "PERL_NO_OP_PARENT" compiler define. This flag alters how the "op_sibling" field is used in "OP" structures, and has been available optionally since perl 5.22.

  See "Internal Changes" in perl5220delta for more details of what this build option does.

• Three new ops, "OP_ARGELEM", "OP_ARGDEFELEM", and "OP_ARGCHECK" have been added. These are intended principally to implement the individual elements of a subroutine signature, plus any overall checking required.
• The "OP_PUSHRE" op has been eliminated and the "OP_SPLIT" op has been changed from class "LISTOP" to "PMOP".

  Formerly the first child of a split would be a "pushre", which would have the "split"'s regex attached to it. Now the regex is attached directly to the "split" op, and the "pushre" has been eliminated.

• The "op_class()" API function has been added. This is like the existing "OP_CLASS()" macro, but can more accurately determine what struct an op has been allocated as. For example "OP_CLASS()" might return "OA_BASEOP_OR_UNOP" indicating that ops of this type are usually allocated as an "OP" or "UNOP"; while "op_class()" will return "OPclass_BASEOP" or "OPclass_UNOP" as appropriate.
• All parts of the internals now agree that the "sassign" op is a "BINOP"; previously it was listed as a "BASEOP" in regen/opcodes, which meant that several parts of the internals had to be special-cased to accommodate it. This oddity's original motivation was to handle code like "$x ||= 1"; that is now handled in a simpler way.
• The output format of the "op_dump()" function (as used by "perl -Dx") has changed: it now displays an "ASCII-art" tree structure, and shows more low-level details about each op, such as its address and class.
• The "PADOFFSET" type has changed from being unsigned to signed, and several pad-related variables such as "PL_padix" have changed from being of type "I32" to type "PADOFFSET".
• The "DEBUGGING"-mode output for regex compilation and execution has been enhanced.
• Several obscure SV flags have been eliminated, sometimes along with the macros which manipulate them: "SVpbm_VALID", "SVpbm_TAIL", "SvTAIL_on", "SvTAIL_off", "SVrepl_EVAL", "SvEVALED".
• An OP "op_private" flag has been eliminated: "OPpRUNTIME". This used to often get set on "PMOP" ops, but had become meaningless over time.

Selected Bug Fixes

• Perl no longer panics when switching into some locales on machines with buggy "strxfrm()" implementations in their libc. [GH #13768] <https://github.com/Perl/perl5/issues/13768>
• " $-{$name} " would leak an "AV" on each access if the regular expression had no named captures. The same applies to access to any hash tied with Tie::Hash::NamedCapture and "all => 1". [GH #15882] <https://github.com/Perl/perl5/issues/15882>
• Attempting to use the deprecated variable $# as the object in an indirect object method call could cause a heap use after free or buffer overflow. [GH #15599] <https://github.com/Perl/perl5/issues/15599>
• When checking for an indirect object method call, in some rare cases the parser could reallocate the line buffer but then continue to use pointers to the old buffer. [GH #15585] <https://github.com/Perl/perl5/issues/15585>
• Supplying a glob as the format argument to "formline" would cause an assertion failure. [GH #15862] <https://github.com/Perl/perl5/issues/15862>
• Code like " $value1 =~ qr/.../ ~~ $value2 " would have the match converted into a "qr//" operator, leaving extra elements on the stack to confuse any surrounding expression. [GH #15859] <https://github.com/Perl/perl5/issues/15859>
• Since v5.24 in some obscure cases, a regex which included code blocks from multiple sources (e.g., via embedded via "qr//" objects) could end up with the wrong current pad and crash or give weird results. [GH #15657] <https://github.com/Perl/perl5/issues/15657>
• Occasionally "local()"s in a code block within a patterns weren't being undone when the pattern matching backtracked over the code block. [GH #15056] <https://github.com/Perl/perl5/issues/15056>
• Using "substr()" to modify a magic variable could access freed memory in some cases. [GH #15871] <https://github.com/Perl/perl5/issues/15871>
• Under "use utf8", the entire source code is now checked for being UTF-8 well formed, not just quoted strings as before. [GH #14973] <https://github.com/Perl/perl5/issues/14973>.
• The range operator ".." on strings now handles its arguments correctly when in the scope of the "unicode_strings" feature. The previous behaviour was sufficiently unexpected that we believe no correct program could have made use of it.
• The "split" operator did not ensure enough space was allocated for its return value in scalar context. It could then write a single pointer immediately beyond the end of the memory block allocated for the stack. [GH #15749] <https://github.com/Perl/perl5/issues/15749>
• Using a large code point with the "W" pack template character with the current output position aligned at just the right point could cause a write of a single zero byte immediately beyond the end of an allocated buffer. [GH #15572] <https://github.com/Perl/perl5/issues/15572>
• Supplying a format's picture argument as part of the format argument list where the picture specifies modifying the argument could cause an access to the new freed compiled format. [GH #15566] <https://github.com/Perl/perl5/issues/15566>
• The sort() operator's built-in numeric comparison function didn't handle large integers that weren't exactly representable by a double. This now uses the same code used to implement the "<=>" operator. [GH #15768] <https://github.com/Perl/perl5/issues/15768>
• Fix issues with "/(?{ ... <<EOF })/" that broke Method::Signatures. [GH #15779] <https://github.com/Perl/perl5/issues/15779>
• Fixed an assertion failure with "chop" and "chomp", which could be triggered by "chop(@x =~ tr/1/1/)". [GH #15738] <https://github.com/Perl/perl5/issues/15738>.
• Fixed a comment skipping error in patterns under "/x"; it could stop skipping a byte early, which could be in the middle of a UTF-8 character. [GH #15790] <https://github.com/Perl/perl5/issues/15790>.
• perldb now ignores /dev/tty on non-Unix systems. [GH #12244] <https://github.com/Perl/perl5/issues/12244>;
• Fix assertion failure for "{}->$x" when $x isn't defined. [GH #15791] <https://github.com/Perl/perl5/issues/15791>.
• Fix an assertion error which could be triggered when a lookahead string in patterns exceeded a minimum length. [GH #15796] <https://github.com/Perl/perl5/issues/15796>.
• Only warn once per literal number about a misplaced "_". [GH #9989] <https://github.com/Perl/perl5/issues/9989>.
• The "tr///" parse code could be looking at uninitialized data after a perse error. [GH #15624] <https://github.com/Perl/perl5/issues/15624>.
• In a pattern match, a back-reference ("\1") to an unmatched capture could read back beyond the start of the string being matched. [GH #15634] <https://github.com/Perl/perl5/issues/15634>.
• "use re 'strict'" is supposed to warn if you use a range (such as "/(?[ [ X-Y ] ])/") whose start and end digit aren't from the same group of 10. It didn't do that for five groups of mathematical digits starting at "U+1D7E".
• A sub containing a "forward" declaration with the same name (e.g., "sub c { sub c; }") could sometimes crash or loop infinitely. [GH #15557] <https://github.com/Perl/perl5/issues/15557>
• A crash in executing a regex with a non-anchored UTF-8 substring against a target string that also used UTF-8 has been fixed. [GH #15628] <https://github.com/Perl/perl5/issues/15628>
• Previously, a shebang line like "#!perl -i u" could be erroneously interpreted as requesting the "-u" option. This has been fixed. [GH #15623] <https://github.com/Perl/perl5/issues/15623>
• The regex engine was previously producing incorrect results in some rare situations when backtracking past an alternation that matches only one thing; this showed up as capture buffers ($1, $2, etc.) erroneously containing data from regex execution paths that weren't actually executed for the final match. [GH #15666] <https://github.com/Perl/perl5/issues/15666>
• Certain regexes making use of the experimental "regex_sets" feature could trigger an assertion failure. This has been fixed. [GH #15620] <https://github.com/Perl/perl5/issues/15620>
• Invalid assignments to a reference constructor (e.g., "\eval=time") could sometimes crash in addition to giving a syntax error. [GH #14815] <https://github.com/Perl/perl5/issues/14815>
• The parser could sometimes crash if a bareword came after "evalbytes". [GH #15586] <https://github.com/Perl/perl5/issues/15586>
• Autoloading via a method call would warn erroneously ("Use of inherited AUTOLOAD for non-method") if there was a stub present in the package into which the invocant had been blessed. The warning is no longer emitted in such circumstances. [GH #9094] <https://github.com/Perl/perl5/issues/9094>
• The use of "splice" on arrays with non-existent elements could cause other operators to crash. [GH #15577] <https://github.com/Perl/perl5/issues/15577>
• A possible buffer overrun when a pattern contains a fixed utf8 substring. [GH #15534] <https://github.com/Perl/perl5/issues/15534>
• Fixed two possible use-after-free bugs in perl's lexer. [GH #15549] <https://github.com/Perl/perl5/issues/15549>
• Fixed a crash with "s///l" where it thought it was dealing with UTF-8 when it wasn't. [GH #15543] <https://github.com/Perl/perl5/issues/15543>
• Fixed a place where the regex parser was not setting the syntax error correctly on a syntactically incorrect pattern. [GH #15565] <https://github.com/Perl/perl5/issues/15565>
• The "&." operator (and the "&" operator, when it treats its arguments as strings) were failing to append a trailing null byte if at least one string was marked as utf8 internally. Many code paths (system calls, regexp compilation) still expect there to be a null byte in the string buffer just past the end of the logical string. An assertion failure was the result. [GH #15606] <https://github.com/Perl/perl5/issues/15606>
• Avoid a heap-after-use error in the parser when creating an error messge for a syntactically invalid heredoc. [GH #15527] <https://github.com/Perl/perl5/issues/15527>
• Fix a segfault when run with "-DC" options on DEBUGGING builds. [GH #15563] <https://github.com/Perl/perl5/issues/15563>
• Fixed the parser error handling in subroutine attributes for an '":attr(foo"' that does not have an ending '")"'.
• Fix the perl lexer to correctly handle a backslash as the last char in quoted-string context. This actually fixed two bugs, [GH #15546] <https://github.com/Perl/perl5/issues/15546> and [GH #15582] <https://github.com/Perl/perl5/issues/15582>.
• In the API function "gv_fetchmethod_pvn_flags", rework separator parsing to prevent possible string overrun with an invalid "len" argument. [GH #15598] <https://github.com/Perl/perl5/issues/15598>
• Problems with in-place array sorts: code like "@a = sort { ... } @a", where the source and destination of the sort are the same plain array, are optimised to do less copying around. Two side-effects of this optimisation were that the contents of @a as seen by sort routines were partially sorted; and under some circumstances accessing @a during the sort could crash the interpreter. Both these issues have been fixed, and Sort functions see the original value of @a. [GH #15387] <https://github.com/Perl/perl5/issues/15387>
• Non-ASCII string delimiters are now reported correctly in error messages for unterminated strings. [GH #15469] <https://github.com/Perl/perl5/issues/15469>
• "pack("p", ...)" used to emit its warning ("Attempt to pack pointer to temporary value") erroneously in some cases, but has been fixed.
• @DB::args is now exempt from "used once" warnings. The warnings only occurred under -w, because warnings.pm itself uses @DB::args multiple times.
• The use of built-in arrays or hash slices in a double-quoted string no longer issues a warning ("Possible unintended interpolation...") if the variable has not been mentioned before. This affected code like "qq|@DB::args|" and "qq|@SIG{'CHLD', 'HUP'}|". (The special variables "@-" and "@+" were already exempt from the warning.)
• "gethostent" and similar functions now perform a null check internally, to avoid crashing with the torsocks library. This was a regression from v5.22. [GH #15478] <https://github.com/Perl/perl5/issues/15478>
• "defined *{'!'}", "defined *{'['}", and "defined *{'-'}" no longer leak memory if the typeglob in question has never been accessed before.
• Mentioning the same constant twice in a row (which is a syntax error) no longer fails an assertion under debugging builds. This was a regression from v5.20. [GH #15017] <https://github.com/Perl/perl5/issues/15017>
• Many issues relating to "printf "%a"" of hexadecimal floating point were fixed. In addition, the "subnormals" (formerly known as "denormals") floating point numbers are now supported both with the plain IEEE 754 floating point numbers (64-bit or 128-bit) and the x86 80-bit "extended precision". Note that subnormal hexadecimal floating point literals will give a warning about "exponent underflow". [GH #15495] <https://github.com/Perl/perl5/issues/15495> [GH #15503] <https://github.com/Perl/perl5/issues/15503> [GH #15504] <https://github.com/Perl/perl5/issues/15504> [GH #15505] <https://github.com/Perl/perl5/issues/15505> [GH #15510] <https://github.com/Perl/perl5/issues/15510> [GH #15512] <https://github.com/Perl/perl5/issues/15512>
• A regression in v5.24 with "tr/\N{U+...}/foo/" when the code point was between 128 and 255 has been fixed. [GH #15475] <https://github.com/Perl/perl5/issues/15475>.
• Use of a string delimiter whose code point is above 2**31 now works correctly on platforms that allow this. Previously, certain characters, due to truncation, would be confused with other delimiter characters with special meaning (such as "?" in "m?...?"), resulting in inconsistent behaviour. Note that this is non-portable, and is based on Perl's extension to UTF-8, and is probably not displayable nor enterable by any editor. [GH #15477] <https://github.com/Perl/perl5/issues/15477>
• "@{x" followed by a newline where "x" represents a control or non-ASCII character no longer produces a garbled syntax error message or a crash. [GH #15518] <https://github.com/Perl/perl5/issues/15518>
• An assertion failure with "%: = 0" has been fixed. [GH #15358] <https://github.com/Perl/perl5/issues/15358>
• In Perl 5.18, the parsing of "$foo::$bar" was accidentally changed, such that it would be treated as "$foo."::".$bar". The previous behavior, which was to parse it as "$foo:: . $bar", has been restored. [GH #15408] <https://github.com/Perl/perl5/issues/15408>
• Since Perl 5.20, line numbers have been off by one when perl is invoked with the -x switch. This has been fixed. [GH #15413] <https://github.com/Perl/perl5/issues/15413>
• Vivifying a subroutine stub in a deleted stash (e.g., "delete $My::{"Foo::"}; \&My::Foo::foo") no longer crashes. It had begun crashing in Perl 5.18. [GH #15420] <https://github.com/Perl/perl5/issues/15420>
• Some obscure cases of subroutines and file handles being freed at the same time could result in crashes, but have been fixed. The crash was introduced in Perl 5.22. [GH #15435] <https://github.com/Perl/perl5/issues/15435>
• Code that looks for a variable name associated with an uninitialized value could cause an assertion failure in cases where magic is involved, such as $ISA[0][0]. This has now been fixed. [GH #15364] <https://github.com/Perl/perl5/issues/15364>
• A crash caused by code generating the warning "Subroutine STASH::NAME redefined" in cases such as "sub P::f{} undef *P::; *P::f =sub{};" has been fixed. In these cases, where the STASH is missing, the warning will now appear as "Subroutine NAME redefined". [GH #15368] <https://github.com/Perl/perl5/issues/15368>
• Fixed an assertion triggered by some code that handles deprecated behavior in formats, e.g., in cases like this:

      format STDOUT =
      @
      0"$x"
      

  [GH #15366] <https://github.com/Perl/perl5/issues/15366>

• A possible divide by zero in string transformation code on Windows has been avoided, fixing a crash when collating an empty string. [GH #15439] <https://github.com/Perl/perl5/issues/15439>
• Some regular expression parsing glitches could lead to assertion failures with regular expressions such as "/(?<=/" and "/(?<!/". This has now been fixed. [GH #15332] <https://github.com/Perl/perl5/issues/15332>
• " until ($x = 1) { ... } " and " ... until $x = 1 " now properly warn when syntax warnings are enabled. [GH #15138] <https://github.com/Perl/perl5/issues/15138>
• socket() now leaves the error code returned by the system in $! on failure. [GH #15383] <https://github.com/Perl/perl5/issues/15383>
• Assignment variants of any bitwise ops under the "bitwise" feature would crash if the left-hand side was an array or hash. [GH #15346] <https://github.com/Perl/perl5/issues/15346>
• "require" followed by a single colon (as in "foo() ? require : ..." is now parsed correctly as "require" with implicit $_, rather than "require """. [GH #15380] <https://github.com/Perl/perl5/issues/15380>
• Scalar "keys %hash" can now be assigned to consistently in all scalar lvalue contexts. Previously it worked for some contexts but not others.
• List assignment to "vec" or "substr" with an array or hash for its first argument used to result in crashes or "Can't coerce" error messages at run time, unlike scalar assignment, which would give an error at compile time. List assignment now gives a compile-time error, too. [GH #15370] <https://github.com/Perl/perl5/issues/15370>
• Expressions containing an "&&" or "||" operator (or their synonyms "and" and "or") were being compiled incorrectly in some cases. If the left-hand side consisted of either a negated bareword constant or a negated "do {}" block containing a constant expression, and the right-hand side consisted of a negated non-foldable expression, one of the negations was effectively ignored. The same was true of "if" and "unless" statement modifiers, though with the left-hand and right-hand sides swapped. This long-standing bug has now been fixed. [GH #15285] <https://github.com/Perl/perl5/issues/15285>
• "reset" with an argument no longer crashes when encountering stash entries other than globs. [GH #15314] <https://github.com/Perl/perl5/issues/15314>
• Assignment of hashes to, and deletion of, typeglobs named *:::::: no longer causes crashes. [GH #15307] <https://github.com/Perl/perl5/issues/15307>
• Perl wasn't correctly handling true/false values in the LHS of a list assign; specifically the truth values returned by boolean operators. This could trigger an assertion failure in something like the following:

      for ($x > $y) {
          ($_, ...) = (...); # here $_ is aliased to a truth value
      }
      

  This was a regression from v5.24. [GH #15690] <https://github.com/Perl/perl5/issues/15690>

• Assertion failure with user-defined Unicode-like properties. [GH #15696] <https://github.com/Perl/perl5/issues/15696>
• Fix error message for unclosed "\N{" in a regex. An unclosed "\N{" could give the wrong error message: "\N{NAME} must be resolved by the lexer".
• List assignment in list context where the LHS contained aggregates and where there were not enough RHS elements, used to skip scalar lvalues. Previously, "(($a,$b,@c,$d) = (1))" in list context returned "($a)"; now it returns "($a,$b,$d)". "(($a,$b,$c) = (1))" is unchanged: it still returns "($a,$b,$c)". This can be seen in the following:

      sub inc { $_++ for @_ }
      inc(($a,$b,@c,$d) = (10))
      

  Formerly, the values of "($a,$b,$d)" would be left as "(11,undef,undef)"; now they are "(11,1,1)".

• Code like this: "/(?{ s!!! })/" could trigger infinite recursion on the C stack (not the normal perl stack) when the last successful pattern in scope is itself. We avoid the segfault by simply forbidding the use of the empty pattern when it would resolve to the currently executing pattern. [GH #15669] <https://github.com/Perl/perl5/issues/15669>
• Avoid reading beyond the end of the line buffer in perl's lexer when there's a short UTF-8 character at the end. [GH #15531] <https://github.com/Perl/perl5/issues/15531>
• Alternations in regular expressions were sometimes failing to match a utf8 string against a utf8 alternate. [GH #15680] <https://github.com/Perl/perl5/issues/15680>
• Make "do "a\0b"" fail silently (and return "undef" and set $!) instead of throwing an error. [GH #15676] <https://github.com/Perl/perl5/issues/15676>
• "chdir" with no argument didn't ensure that there was stack space available for returning its result. [GH #15569] <https://github.com/Perl/perl5/issues/15569>
• All error messages related to "do" now refer to "do"; some formerly claimed to be from "require" instead.
• Executing "undef $x" where $x is tied or magical no longer incorrectly blames the variable for an uninitialized-value warning encountered by the tied/magical code.
• Code like "$x = $x . "a"" was incorrectly failing to yield a use of uninitialized value warning when $x was a lexical variable with an undefined value. That has now been fixed. [GH #15269] <https://github.com/Perl/perl5/issues/15269>
• "undef *_; shift" or "undef *_; pop" inside a subroutine, with no argument to "shift" or "pop", began crashing in Perl 5.14, but has now been fixed.
• "string$scalar->$*" now correctly prefers concatenation overloading to string overloading if "$scalar->$*" returns an overloaded object, bringing it into consistency with $$scalar.
• "/@0{0*->@*/*0" and similar contortions used to crash, but no longer do, but merely produce a syntax error. [GH #15333] <https://github.com/Perl/perl5/issues/15333>
• "do" or "require" with an argument which is a reference or typeglob which, when stringified, contains a null character, started crashing in Perl 5.20, but has now been fixed. [GH #15337] <https://github.com/Perl/perl5/issues/15337>
• Improve the error message for a missing "tie()" package/method. This brings the error messages in line with the ones used for normal method calls.
• Parsing bad POSIX charclasses no longer leaks memory. [GH #15382] <https://github.com/Perl/perl5/issues/15382>

Known Problems

•

G++ 6 handles subnormal (denormal) floating point values differently than gcc 6 or g++ 5 resulting in "flush-to-zero". The end result is that if you specify very small values using the hexadecimal floating point format, like "0x1.fffffffffffffp-1022", they become zeros. [GH #15990] <https://github.com/Perl/perl5/issues/15990>

Errata From Previous Releases

•

Fixed issues with recursive regexes. The behavior was fixed in Perl 5.24. [GH #14935] <https://github.com/Perl/perl5/issues/14935>

Obituary

It is with great sadness that we also note Kip Hampton's passing. Probably best known as the author of the Perl & XML column on XML.com, he was a core contributor to AxKit, an XML server platform that became an Apache Foundation project. He was a frequent speaker in the early days at OSCON, and most recently at YAPC::NA in Madison. He was frequently on irc.perl.org as ubu, generally in the #axkit-dahut community, the group responsible for YAPC::NA Asheville in 2011.

Kip and his constant contributions to the community will be greatly missed.

Acknowledgements

Excluding auto-generated files, documentation and release tools, there were approximately 230,000 lines of changes to 1,800 .pm, .t, .c and .h files.

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 5.26.0:

Aaron Crane, Abigail, AEvar Arnfjoerd` Bjarmason, Alex Vandiver, Andreas Koenig, Andreas Voegele, Andrew Fresh, Andy Lester, Aristotle Pagaltzis, Chad Granum, Chase Whitener, Chris 'BinGOs' Williams, Chris Lamb, Christian Hansen, Christian Millour, Colin Newell, Craig A. Berry, Dagfinn Ilmari Mannsaaker, Dan Collins, Daniel Dragan, Dave Cross, Dave Rolsky, David Golden, David H. Gutteridge, David Mitchell, Dominic Hargreaves, Doug Bell, E. Choroba, Ed Avis, Father Chrysostomos, Francois Perrad, Hauke D, H.Merijn Brand, Hugo van der Sanden, Ivan Pozdeev, James E Keenan, James Raspass, Jarkko Hietaniemi, Jerry D. Hedden, Jim Cromie, J. Nick Koston, John Lightsey, Karen Etheridge, Karl Williamson, Leon Timmermans, Lukas Mai, Matthew Horsfall, Maxwell Carey, Misty De Meo, Neil Bowers, Nicholas Clark, Nicolas R., Niko Tyni, Pali, Paul Marquess, Peter Avalos, Petr PisaX, Pino Toscano, Rafael Garcia-Suarez, Reini Urban, Renee Baecker, Ricardo Signes, Richard Levitte, Rick Delaney, Salvador Fandin~o, Samuel Thibault, Sawyer X, Sebastien Aperghis-Tramoni, Sergey Aleynikov, Shlomi Fish, Smylers, Stefan Seifert, Steffen Mueller, Stevan Little, Steve Hay, Steven Humphrey, Sullivan Beck, Theo Buehler, Thomas Sibley, Todd Rinaldo, Tomasz Konojacki, Tony Cook, Unicode Consortium, Yaroslav Kuzmin, Yves Orton, 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 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 see "SECURITY VULNERABILITY CONTACT INFORMATION" in perlsec for details of how to report the issue.

Give Thanks

    perlthanks

This will send an email to the Perl 5 Porters list with your show of thanks.

SEE ALSO

The INSTALL file for how to build Perl.

The README file for general stuff.

The Artistic and Copying files for copyright information.