Lexical subroutines are no longer experimental

Using the "lexical_subs" feature introduced in v5.18 no longer emits a warning. Existing code that disables the "experimental::lexical_subs" warning category that the feature previously used will continue to work. The "lexical_subs" feature has no effect; all Perl code can use lexical subroutines, regardless of what feature declarations are in scope.

Indented Here-documents

This adds a new modifier "~" to here-docs that tells the parser that it should look for "/^\s*$DELIM\n/" as the closing delimiter.

These syntaxes are all supported:

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

The "~" modifier will strip, from each line in the here-doc, the same whitespace that appears before the delimiter.

Newlines will be copied as-is, and lines that don't include the proper beginning whitespace will cause perl to croak.

For example:

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

prints "Hello there\n" with no leading whitespace.

New regular expression modifier "/xx"

Specifying two "x" characters to modify a regular expression pattern does everything that a single one does, but additionally TAB and SPACE characters within a bracketed character class are generally ignored and can be added to improve readability, like "/[ ^ A-Z d-f p-x ]/xx". Details are at "/x and /xx" in perlre.

"@{^CAPTURE}", "%{^CAPTURE}", and "%{^CAPTURE_ALL}"

"@{^CAPTURE}" exposes the capture buffers of the last match as an array. So $1 is "${^CAPTURE}[0]". This is a more efficient equivalent to code like "substr($matched_string,$-[0],$+[0]-$-[0])", and you don't have to keep track of the $matched_string either. This variable has no single character equivalent. Note that, like the other regex magic variables, the contents of this variable is dynamic; if you wish to store it beyond the lifetime of the match you must copy it to another array.

"%{^CAPTURE}" is equivalent to "%+" (i.e., named captures). Other than being more self-documenting there is no difference between the two forms.

"%{^CAPTURE_ALL}" is equivalent to "%-" (i.e., all named captures). Other than being more self-documenting there is no difference between the two forms.

Declaring a reference to a variable

As an experimental feature, Perl now allows the referencing operator to come after "my()", "state()", "our()", or "local()". This syntax must be enabled with "use feature 'declared_refs'". It is experimental, and will warn by default unless "no warnings 'experimental::refaliasing'" is in effect. It is intended mainly for use in assignments to references. For example:

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

See "Assigning to References" in perlref for more details.

Unicode 9.0 is now supported

A list of changes is at <http://www.unicode.org/versions/Unicode9.0.0/>. Modules that are shipped with core Perl but not maintained by p5p do not necessarily support Unicode 9.0. Unicode::Normalize does work on 9.0.

Use of "\p{script}" uses the improved Script_Extensions property

Unicode 6.0 introduced an improved form of the Script ("sc") property, and called it Script_Extensions ("scx"). Perl now uses this improved version when a property is specified as just "\p{script}". This should make programs more accurate when determining if a character is used in a given script, but there is a slight chance of breakage for programs that very specifically needed the old behavior. The meaning of compound forms, like "\p{sc=script}" are unchanged. See "Scripts" in perlunicode.

Perl can now do default collation in UTF-8 locales on platforms that support it

Some platforms natively do a reasonable job of collating and sorting in UTF-8 locales. Perl now works with those. For portability and full control, Unicode::Collate is still recommended, but now you may not need to do anything special to get good-enough results, depending on your application. See "Category "LC_COLLATE": Collation: Text Comparisons and Sorting" in perllocale.

Better locale collation of strings containing embedded "NUL" characters

In locales that have multi-level character weights, "NUL"s are now ignored at the higher priority ones. There are still some gotchas in some strings, though. See "Collation of strings containing embedded "NUL" characters" in perllocale.

"CORE" subroutines for hash and array functions callable via reference

The hash and array functions in the "CORE" namespace ("keys", "each", "values", "push", "pop", "shift", "unshift" and "splice") can now be called with ampersand syntax ("&CORE::keys(\%hash") and via reference ("my $k = \&CORE::keys; $k->(\%hash)"). Previously they could only be used when inlined.

New Hash Function For 64-bit Builds

We have switched to a hybrid hash function to better balance performance for short and long keys.

For short keys, 16 bytes and under, we use an optimised variant of One At A Time Hard, and for longer keys we use Siphash 1-3. For very long keys this is a big improvement in performance. For shorter keys there is a modest improvement.

Removal of the current directory (".") from @INC

The perl binary includes a default set of paths in @INC. Historically it has also included the current directory (".") as the final entry, unless run with taint mode enabled ("perl -T"). While convenient, this has security implications: for example, where a script attempts to load an optional module when its current directory is untrusted (such as /tmp), it could load and execute code from under that directory.

Starting with v5.26, "." is always removed by default, not just under tainting. This has major implications for installing modules and executing scripts.

The following new features have been added to help ameliorate these issues.

• Configure -Udefault_inc_excludes_dot

  There is a new Configure option, "default_inc_excludes_dot" (enabled by default) which builds a perl executable without "."; unsetting this option using "-U" reverts perl to the old behaviour. This may fix your path issues but will reintroduce all the security concerns, so don't build a perl executable like this unless you're really confident that such issues are not a concern in your environment.

• "PERL_USE_UNSAFE_INC"

  There is a new environment variable recognised by the perl interpreter. If this variable has the value 1 when the perl interpreter starts up, then "." will be automatically appended to @INC (except under tainting).

  This allows you restore the old perl interpreter behaviour on a case-by-case basis. But note that this is intended to be a temporary crutch, and this feature will likely be removed in some future perl version. It is currently set by the "cpan" utility and "Test::Harness" to ease installation of CPAN modules which have not been updated to handle the lack of dot. Once again, don't use this unless you are sure that this will not reintroduce any security concerns.

• A new deprecation warning issued by "do".

  While it is well-known that "use" and "require" use @INC to search for the file to load, many people don't realise that "do "file"" also searches @INC if the file is a relative path. With the removal of ".", a simple "do "file.pl"" will fail to read in and execute "file.pl" from the current directory. Since this is commonly expected behaviour, a new deprecation warning is now issued whenever "do" fails to load a file which it otherwise would have found if a dot had been in @INC.

Here are some things script and module authors may need to do to make their software work in the new regime.

• Script authors

  If the issue is within your own code (rather than within included modules), then you have two main options. Firstly, if you are confident that your script will only be run within a trusted directory (under which you expect to find trusted files and modules), then add "." back into the path; e.g.:

      BEGIN {
          my $dir = "/some/trusted/directory";
          chdir $dir or die "Can't chdir to $dir: $!\n";
          # safe now
          push @INC, '.';
      }
      use "Foo::Bar"; # may load /some/trusted/directory/Foo/Bar.pm
      do "config.pl"; # may load /some/trusted/directory/config.pl
      

  On the other hand, if your script is intended to be run from within untrusted directories (such as /tmp), then your script suddenly failing to load files may be indicative of a security issue. You most likely want to replace any relative paths with full paths; for example,

      do "foo_config.pl"
      

  might become

      do "$ENV{HOME}/foo_config.pl"
      

  If you are absolutely certain that you want your script to load and execute a file from the current directory, then use a "./" prefix; for example:

      do "./foo_config.pl"
      

• Installing and using CPAN modules

  If you install a CPAN module using an automatic tool like "cpan", then this tool will itself set the "PERL_USE_UNSAFE_INC" environment variable while building and testing the module, which may be sufficient to install a distribution which hasn't been updated to be dot-aware. If you want to install such a module manually, then you'll need to replace the traditional invocation:

      perl Makefile.PL && make && make test && make install
      

  with something like

      (export PERL_USE_UNSAFE_INC=1; \
       perl Makefile.PL && make && make test && make install)
      

  Note that this only helps build and install an unfixed module. It's possible for the tests to pass (since they were run under "PERL_USE_UNSAFE_INC=1"), but for the module itself to fail to perform correctly in production. In this case, you may have to temporarily modify your script until a fixed version of the module is released. For example:

      use Foo::Bar;
      {
          local @INC = (@INC, '.');
          # assuming read_config() needs '.' in @INC
          $config = Foo::Bar->read_config();
      }
      

  This is only rarely expected to be necessary. Again, if doing this, assess the resultant risks first.

• Module Authors

  If you maintain a CPAN distribution, it may need updating to run in a dotless environment. Although "cpan" and other such tools will currently set the "PERL_USE_UNSAFE_INC" during module build, this is a temporary workaround for the set of modules which rely on "." being in @INC for installation and testing, and this may mask deeper issues. It could result in a module which passes tests and installs, but which fails at run time.

  During build, test, and install, it will normally be the case that any perl processes will be executing directly within the root directory of the untarred distribution, or a known subdirectory of that, such as t/. It may well be that Makefile.PL or t/foo.t will attempt to include local modules and configuration files using their direct relative filenames, which will now fail.

  However, as described above, automatic tools like cpan will (for now) set the "PERL_USE_UNSAFE_INC" environment variable, which introduces dot during a build.

  This makes it likely that your existing build and test code will work, but this may mask issues with your code which only manifest when used after install. It is prudent to try and run your build process with that variable explicitly disabled:

      (export PERL_USE_UNSAFE_INC=0; \
       perl Makefile.PL && make && make test && make install)
      

  This is more likely to show up any potential problems with your module's build process, or even with the module itself. Fixing such issues will ensure both that your module can again be installed manually, and that it will still build once the "PERL_USE_UNSAFE_INC" crutch goes away.

  When fixing issues in tests due to the removal of dot from @INC, reinsertion of dot into @INC should be performed with caution, for this too may suppress real errors in your runtime code. You are encouraged wherever possible to apply the aforementioned approaches with explicit absolute/relative paths, or to relocate your needed files into a subdirectory and insert that subdirectory into @INC instead.

  If your runtime code has problems under the dotless @INC, then the comments above on how to fix for script authors will mostly apply here too. Bear in mind though that it is considered bad form for a module to globally add a dot to @INC, since it introduces both a security risk and hides issues of accidentally requiring dot in @INC, as explained above.

Escaped colons and relative paths in PATH

On Unix systems, Perl treats any relative paths in the "PATH" environment variable as tainted when starting a new process. Previously, it was allowing a backslash to escape a colon (unlike the OS), consequently allowing relative paths to be considered safe if the PATH was set to something like "/\:.". The check has been fixed to treat "." as tainted in that example.

New "-Di" switch is now required for PerlIO debugging output

This is used for debugging of code within PerlIO to avoid recursive calls. Previously this output would be sent to the file specified by the "PERLIO_DEBUG" environment variable if perl wasn't running setuid and the "-T" or "-t" switches hadn't been parsed yet.

If perl performed output at a point where it hadn't yet parsed its switches this could result in perl creating or overwriting the file named by "PERLIO_DEBUG" even when the "-T" switch had been supplied.

Perl now requires the "-Di" switch to be present before it will produce PerlIO debugging output. By default this is written to "stderr", but can optionally be redirected to a file by setting the "PERLIO_DEBUG" environment variable.

If perl is running setuid or the "-T" switch was supplied, "PERLIO_DEBUG" is ignored and the debugging output is sent to "stderr" as for any other "-D" switch.

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

You have to now say something like "\{" or "[{]" to specify to match a LEFT CURLY BRACKET; otherwise, it is a fatal pattern compilation error. This change will allow future extensions to the language.

These have been deprecated since v5.16, with a deprecation message raised for some uses starting in v5.22. Unfortunately, the code added to raise the message was buggy and failed to warn in some cases where it should have. Therefore, enforcement of this ban for these cases is deferred until Perl 5.30, but the code has been fixed to raise a default-on deprecation message for them in the meantime.

Some uses of literal "{" occur in contexts where we do not foresee the meaning ever being anything but the literal, such as the very first character in the pattern, or after a "|" meaning alternation. Thus

 qr/{fee|{fie/

matches either of the strings "{fee" or "{fie". To avoid forcing unnecessary code changes, these uses do not need to be escaped, and no warning is raised about them, and there are no current plans to change this.

But it is always correct to escape "{", and the simple rule to remember is to always do so.

See Unescaped left brace in regex is illegal here.

"scalar(%hash)" return signature changed

The value returned for "scalar(%hash)" will no longer show information about the buckets allocated in the hash. It will simply return the count of used keys. It is thus equivalent to "0+keys(%hash)".

A form of backward compatibility is provided via "Hash::Util::bucket_ratio()" which provides the same behavior as "scalar(%hash)" provided in Perl 5.24 and earlier.

"keys" returned from an lvalue subroutine

"keys" returned from an lvalue subroutine can no longer be assigned to in list context.

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

This makes the lvalue sub case consistent with "(keys %hash) = ..." and "(keys @_) = ...", which are also errors. [GH #15339] <https://github.com/Perl/perl5/issues/15339>

The "${^ENCODING}" facility has been removed

The special behaviour associated with assigning a value to this variable has been removed. As a consequence, the encoding pragma's default mode is no longer supported. If you still need to write your source code in encodings other than UTF-8, use a source filter such as Filter::Encoding on CPAN or encoding's "Filter" option.

"POSIX::tmpnam()" has been removed

The fundamentally unsafe "tmpnam()" interface was deprecated in Perl 5.22 and has now been removed. In its place, you can use, for example, the File::Temp interfaces.

require ::Foo::Bar is now illegal.

Formerly, "require ::Foo::Bar" would try to read /Foo/Bar.pm. Now any bareword require which starts with a double colon dies instead.

Literal control character variable names are no longer permissible

A variable name may no longer contain a literal control character under any circumstances. These previously were allowed in single-character names on ASCII platforms, but have been deprecated there since Perl 5.20. This affects things like "$\cT", where \cT is a literal control (such as a "NAK" or "NEGATIVE ACKNOWLEDGE" character) in the source code.

"NBSP" is no longer permissible in "\N{...}"

The name of a character may no longer contain non-breaking spaces. It has been deprecated to do so since Perl 5.22.

String delimiters that aren't stand-alone graphemes are now deprecated

For Perl to eventually allow string delimiters to be Unicode grapheme clusters (which look like a single character, but may be a sequence of several ones), we have to stop allowing a single character delimiter that isn't a grapheme by itself. These are unlikely to exist in actual code, as they would typically display as attached to the character in front of them.

"\cX" that maps to a printable is no longer deprecated

This means we have no plans to remove this feature. It still raises a warning, but only if syntax warnings are enabled. The feature was originally intended to be a way to express non-printable characters that don't have a mnemonic ("\t" and "\n" are mnemonics for two non-printable characters, but most non-printables don't have a mnemonic.) But the feature can be used to specify a few printable characters, though those are more clearly expressed as the printable itself. See <http://www.nntp.perl.org/group/perl.perl5.porters/2017/02/msg242944.html>.

Updated Modules and Pragmata

• IO::Compress has been upgraded from version 2.069 to 2.074.
• Archive::Tar has been upgraded from version 2.04 to 2.24.
• arybase has been upgraded from version 0.11 to 0.12.
• attributes has been upgraded from version 0.27 to 0.29.

  The deprecation message for the ":unique" and ":locked" attributes now mention that they will disappear in Perl 5.28.

• B has been upgraded from version 1.62 to 1.68.
• B::Concise has been upgraded from version 0.996 to 0.999.

  Its output is now more descriptive for "op_private" flags.

• B::Debug has been upgraded from version 1.23 to 1.24.
• B::Deparse has been upgraded from version 1.37 to 1.40.
• B::Xref has been upgraded from version 1.05 to 1.06.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• base has been upgraded from version 2.23 to 2.25.
• bignum has been upgraded from version 0.42 to 0.47.
• Carp has been upgraded from version 1.40 to 1.42.
• charnames has been upgraded from version 1.43 to 1.44.
• Compress::Raw::Bzip2 has been upgraded from version 2.069 to 2.074.
• Compress::Raw::Zlib has been upgraded from version 2.069 to 2.074.
• Config::Perl::V has been upgraded from version 0.25 to 0.28.
• CPAN has been upgraded from version 2.11 to 2.18.
• CPAN::Meta has been upgraded from version 2.150005 to 2.150010.
• Data::Dumper has been upgraded from version 2.160 to 2.167.

  The XS implementation now supports Deparse.

• DB_File has been upgraded from version 1.835 to 1.840.
• Devel::Peek has been upgraded from version 1.23 to 1.26.
• Devel::PPPort has been upgraded from version 3.32 to 3.35.
• Devel::SelfStubber has been upgraded from version 1.05 to 1.06.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• diagnostics has been upgraded from version 1.34 to 1.36.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• Digest has been upgraded from version 1.17 to 1.17_01.
• Digest::MD5 has been upgraded from version 2.54 to 2.55.
• Digest::SHA has been upgraded from version 5.95 to 5.96.
• DynaLoader has been upgraded from version 1.38 to 1.42.
• Encode has been upgraded from version 2.80 to 2.88.
• encoding has been upgraded from version 2.17 to 2.19.

  This module's default mode is no longer supported. It now dies when imported, unless the "Filter" option is being used.

• encoding::warnings has been upgraded from version 0.12 to 0.13.

  This module is no longer supported. It emits a warning to that effect and then does nothing.

• Errno has been upgraded from version 1.25 to 1.28.

  It now documents that using "%!" automatically loads Errno for you.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• ExtUtils::Embed has been upgraded from version 1.33 to 1.34.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• ExtUtils::MakeMaker has been upgraded from version 7.10_01 to 7.24.
• ExtUtils::Miniperl has been upgraded from version 1.05 to 1.06.
• ExtUtils::ParseXS has been upgraded from version 3.31 to 3.34.
• ExtUtils::Typemaps has been upgraded from version 3.31 to 3.34.
• feature has been upgraded from version 1.42 to 1.47.
• File::Copy has been upgraded from version 2.31 to 2.32.
• File::Fetch has been upgraded from version 0.48 to 0.52.
• File::Glob has been upgraded from version 1.26 to 1.28.

  It now Issues a deprecation message for "File::Glob::glob()".

• File::Spec has been upgraded from version 3.63 to 3.67.
• FileHandle has been upgraded from version 2.02 to 2.03.
• Filter::Simple has been upgraded from version 0.92 to 0.93.

  It no longer treats "no MyFilter" immediately following "use MyFilter" as end-of-file. [GH #11853] <https://github.com/Perl/perl5/issues/11853>

• Getopt::Long has been upgraded from version 2.48 to 2.49.
• Getopt::Std has been upgraded from version 1.11 to 1.12.
• Hash::Util has been upgraded from version 0.19 to 0.22.
• HTTP::Tiny has been upgraded from version 0.056 to 0.070.

  Internal 599-series errors now include the redirect history.

• I18N::LangTags has been upgraded from version 0.40 to 0.42.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• IO has been upgraded from version 1.36 to 1.38.
• IO::Socket::IP has been upgraded from version 0.37 to 0.38.
• IPC::Cmd has been upgraded from version 0.92 to 0.96.
• IPC::SysV has been upgraded from version 2.06_01 to 2.07.
• JSON::PP has been upgraded from version 2.27300 to 2.27400_02.
• lib has been upgraded from version 0.63 to 0.64.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• List::Util has been upgraded from version 1.42_02 to 1.46_02.
• Locale::Codes has been upgraded from version 3.37 to 3.42.
• Locale::Maketext has been upgraded from version 1.26 to 1.28.
• Locale::Maketext::Simple has been upgraded from version 0.21 to 0.21_01.
• Math::BigInt has been upgraded from version 1.999715 to 1.999806.
• Math::BigInt::FastCalc has been upgraded from version 0.40 to 0.5005.
• Math::BigRat has been upgraded from version 0.260802 to 0.2611.
• Math::Complex has been upgraded from version 1.59 to 1.5901.
• Memoize has been upgraded from version 1.03 to 1.03_01.
• Module::CoreList has been upgraded from version 5.20170420 to 5.20170530.
• Module::Load::Conditional has been upgraded from version 0.64 to 0.68.
• Module::Metadata has been upgraded from version 1.000031 to 1.000033.
• mro has been upgraded from version 1.18 to 1.20.
• Net::Ping has been upgraded from version 2.43 to 2.55.

  IPv6 addresses and "AF_INET6" sockets are now supported, along with several other enhancements.

• NEXT has been upgraded from version 0.65 to 0.67.
• Opcode has been upgraded from version 1.34 to 1.39.
• open has been upgraded from version 1.10 to 1.11.
• OS2::Process has been upgraded from version 1.11 to 1.12.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• overload has been upgraded from version 1.26 to 1.28.

  Its compilation speed has been improved slightly.

• parent has been upgraded from version 0.234 to 0.236.
• perl5db.pl has been upgraded from version 1.50 to 1.51.

  It now ignores /dev/tty on non-Unix systems. [GH #12244] <https://github.com/Perl/perl5/issues/12244>

• Perl::OSType has been upgraded from version 1.009 to 1.010.
• perlfaq has been upgraded from version 5.021010 to 5.021011.
• PerlIO has been upgraded from version 1.09 to 1.10.
• PerlIO::encoding has been upgraded from version 0.24 to 0.25.
• PerlIO::scalar has been upgraded from version 0.24 to 0.26.
• Pod::Checker has been upgraded from version 1.60 to 1.73.
• Pod::Functions has been upgraded from version 1.10 to 1.11.
• Pod::Html has been upgraded from version 1.22 to 1.2202.
• Pod::Perldoc has been upgraded from version 3.25_02 to 3.28.
• Pod::Simple has been upgraded from version 3.32 to 3.35.
• Pod::Usage has been upgraded from version 1.68 to 1.69.
• POSIX has been upgraded from version 1.65 to 1.76.

  This remedies several defects in making its symbols exportable. [GH #15260] <https://github.com/Perl/perl5/issues/15260>

  The "POSIX::tmpnam()" interface has been removed, see "POSIX::tmpnam() has been removed".

  The following deprecated functions have been removed:

      POSIX::isalnum
      POSIX::isalpha
      POSIX::iscntrl
      POSIX::isdigit
      POSIX::isgraph
      POSIX::islower
      POSIX::isprint
      POSIX::ispunct
      POSIX::isspace
      POSIX::isupper
      POSIX::isxdigit
      POSIX::tolower
      POSIX::toupper
      

  Trying to import POSIX subs that have no real implementations (like "POSIX::atend()") now fails at import time, instead of waiting until runtime.

• re has been upgraded from version 0.32 to 0.34

  This adds support for the new "/xx" regular expression pattern modifier, and a change to the "use re 'strict'" experimental feature. When "re 'strict'" is enabled, a warning now will be generated for all unescaped uses of the two characters "}" and "]" in regular expression patterns (outside bracketed character classes) that are taken literally. This brings them more in line with the ")" character which is always a metacharacter unless escaped. Being a metacharacter only sometimes, depending on an action at a distance, can lead to silently having the pattern mean something quite different than was intended, which the "re 'strict'" mode is intended to minimize.

• Safe has been upgraded from version 2.39 to 2.40.
• Scalar::Util has been upgraded from version 1.42_02 to 1.46_02.
• Storable has been upgraded from version 2.56 to 2.62.

  Fixes [GH #15714] <https://github.com/Perl/perl5/issues/15714>.

• Symbol has been upgraded from version 1.07 to 1.08.
• Sys::Syslog has been upgraded from version 0.33 to 0.35.
• Term::ANSIColor has been upgraded from version 4.04 to 4.06.
• Term::ReadLine has been upgraded from version 1.15 to 1.16.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• Test has been upgraded from version 1.28 to 1.30.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• Test::Harness has been upgraded from version 3.36 to 3.38.
• Test::Simple has been upgraded from version 1.001014 to 1.302073.
• Thread::Queue has been upgraded from version 3.09 to 3.12.
• Thread::Semaphore has been upgraded from 2.12 to 2.13.

  Added the "down_timed" method.

• threads has been upgraded from version 2.07 to 2.15.
• threads::shared has been upgraded from version 1.51 to 1.56.
• Tie::Hash::NamedCapture has been upgraded from version 0.09 to 0.10.
• Time::HiRes has been upgraded from version 1.9733 to 1.9741.

  It now builds on systems with C++11 compilers (such as G++ 6 and Clang++ 3.9).

  Now uses "clockid_t".

• Time::Local has been upgraded from version 1.2300 to 1.25.
• Unicode::Collate has been upgraded from version 1.14 to 1.19.
• Unicode::UCD has been upgraded from version 0.64 to 0.68.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• version has been upgraded from version 0.9916 to 0.9917.
• VMS::DCLsym has been upgraded from version 1.06 to 1.08.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

• warnings has been upgraded from version 1.36 to 1.37.
• XS::Typemap has been upgraded from version 0.14 to 0.15.
• XSLoader has been upgraded from version 0.21 to 0.27.

  Fixed a security hole in which binary files could be loaded from a path outside of @INC.

  It now uses 3-arg "open()" instead of 2-arg "open()". [GH #15721] <https://github.com/Perl/perl5/issues/15721>

New Documentation

perldeprecation

This file documents all upcoming deprecations, and some of the deprecations which already have been removed. The purpose of this documentation is two-fold: document what will disappear, and by which version, and serve as a guide for people dealing with code which has features that no longer work after an upgrade of their perl.

Changes to Existing Documentation

We have attempted to update the documentation to reflect the changes listed in this document. If you find any we have missed, send email to perlbug@perl.org <mailto:perlbug@perl.org>.

Additionally, all references to Usenet have been removed, and the following selected changes have been made:

perlfunc

• Removed obsolete text about "defined()" on aggregates that should have been deleted earlier, when the feature was removed.
• Corrected documentation of "eval()", and "evalbytes()".
• Clarified documentation of "seek()", "tell()" and "sysseek()" emphasizing that positions are in bytes and not characters. [GH #15438] <https://github.com/Perl/perl5/issues/15438>
• Clarified documentation of "sort()" concerning the variables $a and $b.
• In "split()" noted that certain pattern modifiers are legal, and added a caution about its use in Perls before v5.11.
• Removed obsolete documentation of "study()", noting that it is now a no-op.
• Noted that "vec()" doesn't work well when the string contains characters whose code points are above 255.

perlguts

•

Added advice on formatted printing of operands of "Size_t" and "SSize_t"

perlhack

•

Clarify what editor tab stop rules to use, and note that we are migrating away from using tabs, replacing them with sequences of SPACE characters.

perlhacktips

• Give another reason to use "cBOOL" to cast an expression to boolean.
• Note that the macros "TRUE" and "FALSE" are available to express boolean values.

perlinterp

•

perlinterp has been expanded to give a more detailed example of how to hunt around in the parser for how a given operator is handled.

perllocale

•

Some locales aren't compatible with Perl. Note that these can cause core dumps.

perlmod

•

Various clarifications have been added.

perlmodlib

•

Updated the site mirror list.

perlobj

• Added a section on calling methods using their fully qualified names.
• Do not discourage manual @ISA.

perlootut

•

Mention "Moo" more.

perlop

• Note that white space must be used for quoting operators if the delimiter is a word character (i.e., matches "\w").
• Clarify that in regular expression patterns delimited by single quotes, no variable interpolation is done.

perlre

• The first part was extensively rewritten to incorporate various basic points, that in earlier versions were mentioned in sort of an appendix on Version 8 regular expressions.
• Note that it is common to have the "/x" modifier and forget that this means that "#" has to be escaped.

perlretut

• Add introductory material.
• Note that a metacharacter occurring in a context where it can't mean that, silently loses its meta-ness and matches literally. "use re 'strict'" can catch some of these.

perlunicode

• Corrected the text about Unicode BYTE ORDER MARK handling.
• Updated the text to correspond with changes in Unicode UTS#18, concerning regular expressions, and Perl compatibility with what it says.

perlvar

•

Document @ISA. It was documented in other places, but not in perlvar.

New Diagnostics

New Errors

• A signature parameter must start with '$', '@' or '%'
• Bareword in require contains "%s"
• Bareword in require maps to empty filename
• Bareword in require maps to disallowed filename "%s"
• Bareword in require must not start with a double-colon: "%s"
• %s: command not found

  (A) You've accidentally run your script through bash or another shell instead of Perl. Check the "#!" line, or manually feed your script into Perl yourself. The "#!" line at the top of your file could look like:

    #!/usr/bin/perl
      

• %s: command not found: %s

  (A) You've accidentally run your script through zsh or another shell instead of Perl. Check the "#!" line, or manually feed your script into Perl yourself. The "#!" line at the top of your file could look like:

    #!/usr/bin/perl
      

• The experimental declared_refs feature is not enabled

  (F) To declare references to variables, as in "my \%x", you must first enable the feature:

      no warnings "experimental::declared_refs";
      use feature "declared_refs";
      

  See "Declaring a reference to a variable".

• Illegal character following sigil in a subroutine signature
• Indentation on line %d of here-doc doesn't match delimiter
• Infinite recursion via empty pattern.

  Using the empty pattern (which re-executes the last successfully-matched pattern) inside a code block in another regex, as in "/(?{ s!!new! })/", has always previously yielded a segfault. It now produces this error.

• Malformed UTF-8 string in "%s"
• Multiple slurpy parameters not allowed
• '#' not allowed immediately following a sigil in a subroutine signature
• panic: unknown OA_*: %x
• Unescaped left brace in regex is illegal here

  Unescaped left braces are now illegal in some contexts in regular expression patterns. In other contexts, they are still just deprecated; they will be illegal in Perl 5.30.

• Version control conflict marker

  (F) The parser found a line starting with "<<<<<<<", ">>>>>>>", or "=======". These may be left by a version control system to mark conflicts after a failed merge operation.

New Warnings

• Can't determine class of operator %s, assuming "BASEOP"
• Declaring references is experimental

  (S experimental::declared_refs) This warning is emitted if you use a reference constructor on the right-hand side of "my()", "state()", "our()", or "local()". Simply suppress the warning if you want to use the feature, but know that in doing so you are taking the risk of using an experimental feature which may change or be removed in a future Perl version:

      no warnings "experimental::declared_refs";
      use feature "declared_refs";
      $fooref = my \$foo;
      

  See "Declaring a reference to a variable".

• do "%s" failed, '.' is no longer in @INC

  Since "." is now removed from @INC by default, "do" will now trigger a warning recommending to fix the "do" statement.

• "File::Glob::glob()" will disappear in perl 5.30. Use "File::Glob::bsd_glob()" instead.
• Unescaped literal '%c' in regex; marked by <-- HERE in m/%s/
• Use of unassigned code point or non-standalone grapheme for a delimiter will be a fatal error starting in Perl 5.30

  See "Deprecations"

Changes to Existing Diagnostics

• When a "require" fails, we now do not provide @INC when the "require" is for a file instead of a module.
• When @INC is not scanned for a "require" call, we no longer display @INC to avoid confusion.
• Attribute "locked" is deprecated, and will disappear in Perl 5.28

  This existing warning has had the and will disappear text added in this release.

• Attribute "unique" is deprecated, and will disappear in Perl 5.28

  This existing warning has had the and will disappear text added in this release.

• Calling POSIX::%s() is deprecated

  This warning has been removed, as the deprecated functions have been removed from POSIX.

• Constants from lexical variables potentially modified elsewhere are deprecated. This will not be allowed in Perl 5.32

  This existing warning has had the this will not be allowed text added in this release.

• Deprecated use of "my()" in false conditional. This will be a fatal error in Perl 5.30

  This existing warning has had the this will be a fatal error text added in this release.

• "dump()" better written as "CORE::dump()". "dump()" will no longer be available in Perl 5.30

  This existing warning has had the no longer be available text added in this release.

• Experimental %s on scalar is now forbidden

  This message is now followed by more helpful text. [GH #15291] <https://github.com/Perl/perl5/issues/15291>

• Experimental "%s" subs not enabled

  This warning was been removed, as lexical subs are no longer experimental.

• Having more than one /%c regexp modifier is deprecated

  This deprecation warning has been removed, since "/xx" now has a new meaning.

• %s() is deprecated on ":utf8" handles. This will be a fatal error in Perl 5.30 .

  where "%s" is one of "sysread", "recv", "syswrite", or "send".

  This existing warning has had the this will be a fatal error text added in this release.

  This warning is now enabled by default, as all "deprecated" category warnings should be.

• $* is no longer supported. Its use will be fatal in Perl 5.30

  This existing warning has had the its use will be fatal text added in this release.

• $# is no longer supported. Its use will be fatal in Perl 5.30

  This existing warning has had the its use will be fatal text added in this release.

• Malformed UTF-8 character%s

  Details as to the exact problem have been added at the end of this message

• Missing or undefined argument to %s

  This warning used to warn about "require", even if it was actually "do" which being executed. It now gets the operation name right.

• NO-BREAK SPACE in a charnames alias definition is deprecated

  This warning has been removed as the behavior is now an error.

• Odd name/value argument for subroutine '%s'

  This warning now includes the name of the offending subroutine.

• Opening dirhandle %s also as a file. This will be a fatal error in Perl 5.28

  This existing warning has had the this will be a fatal error text added in this release.

• Opening filehandle %s also as a directory. This will be a fatal error in Perl 5.28

  This existing warning has had the this will be a fatal error text added in this release.

• panic: ck_split, type=%u

  panic: pp_split, pm=%p, s=%p

  These panic errors have been removed.

• Passing malformed UTF-8 to "%s" is deprecated

  This warning has been changed to the fatal Malformed UTF-8 string in "%s"

• Setting $/ to a reference to %s as a form of slurp is deprecated, treating as undef. This will be fatal in Perl 5.28

  This existing warning has had the this will be fatal text added in this release.

• "${^ENCODING}" is no longer supported. Its use will be fatal in Perl 5.28

  This warning used to be: "Setting "${^ENCODING}" is deprecated".

  The special action of the variable "${^ENCODING}" was formerly used to implement the "encoding" pragma. As of Perl 5.26, rather than being deprecated, assigning to this variable now has no effect except to issue the warning.

• Too few arguments for subroutine '%s'

  This warning now includes the name of the offending subroutine.

• Too many arguments for subroutine '%s'

  This warning now includes the name of the offending subroutine.

• Unescaped left brace in regex is deprecated here (and will be fatal in Perl 5.30), passed through in regex; marked by <-- HERE in m/%s/

  This existing warning has had the here (and will be fatal...) text added in this release.

• Unknown charname '' is deprecated. Its use will be fatal in Perl 5.28

  This existing warning has had the its use will be fatal text added in this release.

• Use of bare << to mean <<"" is deprecated. Its use will be fatal in Perl 5.28

  This existing warning has had the its use will be fatal text added in this release.

• Use of code point 0x%s is deprecated; the permissible max is 0x%s. This will be fatal in Perl 5.28

  This existing warning has had the this will be fatal text added in this release.

• Use of comma-less variable list is deprecated. Its use will be fatal in Perl 5.28

  This existing warning has had the its use will be fatal text added in this release.

• Use of inherited "AUTOLOAD" for non-method %s() is deprecated. This will be fatal in Perl 5.28

  This existing warning has had the this will be fatal text added in this release.

• Use of strings with code points over 0xFF as arguments to %s operator is deprecated. This will be a fatal error in Perl 5.28

  This existing warning has had the this will be a fatal error text added in this release.

c2ph and pstruct

•

These old utilities have long since superceded by h2xs, and are now gone from the distribution.

Porting/pod_lib.pl

• Removed spurious executable bit.
• Account for the possibility of DOS file endings.

Porting/sync-with-cpan

•

Many improvements.

perf/benchmarks

•

Tidy file, rename some symbols.

Porting/checkAUTHORS.pl

•

Replace obscure character range with "\w".

t/porting/regen.t

•

Try to be more helpful when tests fail.

utils/h2xs.PL

•

Avoid infinite loop for enums.

perlbug

•

Long lines in the message body are now wrapped at 900 characters, to stay well within the 1000-character limit imposed by SMTP mail transfer agents. This is particularly likely to be important for the list of arguments to Configure, which can readily exceed the limit if, for example, it names several non-default installation paths. This change also adds the first unit tests for perlbug. [perl #128020] <https://rt.perl.org/Public/Bug/Display.html?id=128020>

New Platforms

NetBSD/VAX

Perl now compiles under NetBSD on VAX machines. However, it's not possible for that platform to implement floating-point infinities and NaNs compatible with most modern systems, which implement the IEEE-754 floating point standard. The hexadecimal floating point ("0x...p[+-]n" literals, "printf %a") is not implemented, either. The "make test" passes 98% of tests.

Platform-Specific Notes

Darwin

EBCDIC

Several tests have been updated to work (or be skipped) on EBCDIC platforms.

HP-UX

The Net::Ping UDP test is now skipped on HP-UX.

Hurd

The hints for Hurd have been improved, enabling malloc wrap and reporting the GNU libc used (previously it was an empty string when reported).

VAX

VAX floating point formats are now supported on NetBSD.

VMS

Windows

Linux

Drop support for Linux a.out executable format. Linux has used ELF for over twenty years.

OpenBSD 6

OpenBSD 6 still does not support returning "pid", "gid", or "uid" with "SA_SIGINFO". Make sure to account for it.

FreeBSD

t/uni/overload.t: Skip hanging test on FreeBSD.

DragonFly BSD

DragonFly BSD now has support for "setproctitle()". [GH #15703] <https://github.com/Perl/perl5/issues/15703>.