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PERL5216DELTA(1pm)     Perl Programmers Reference Guide     PERL5216DELTA(1pm)


       perl5216delta - what is new for perl v5.21.6


       This document describes differences between the 5.21.5 release and the
       5.21.6 release.

       If you are upgrading from an earlier release such as 5.21.4, first read
       perl5215delta, which describes differences between 5.21.4 and 5.21.5.

Core Enhancements

   List form of pipe open implemented for Win32
       The list form of pipe:

         open my $fh, "-|", "program", @arguments;

       is now implemented on Win32.  It has the same limitations as "system
       LIST" on Win32, since the Win32 API doesn't accept program arguments as
       a list.

   Assignment to list repetition
       "(...) x ..." can now be used within a list that is assigned to, as
       long as the left-hand side is a valid lvalue.  This allows
       "(undef,undef,$foo) = that_function()" to be written as "((undef)x2,
       $foo) = that_function()".

   "close" now sets $!
       When an I/O error occurs, the fact that there has been an error is
       recorded in the handle.  "close" returns false for such a handle.
       Previously, the value of $! would be untouched by "close", so the
       common convention of writing "close $fh or die $!" did not work
       reliably.  Now the handle records the value of $!, too, and "close"
       restores it.


   Use of non-graphic characters in single-character variable names
       The syntax for single-character variable names is more lenient than for
       longer variable names, allowing the one-character name to be a
       punctuation character or even invisible (a non-graphic).  Perl v5.20
       deprecated the ASCII-range controls as such a name.  Now, all non-
       graphic characters that formerly were allowed are deprecated.  The
       practical effect of this occurs only when not under "use utf8", and
       affects just the C1 controls (code points 0x80 through 0xFF), NO-BREAK
       SPACE, and SOFT HYPHEN.

   Inlining of "sub () { $var }" with observable side-effects
       In many cases Perl makes sub () { $var } into an inlinable constant
       subroutine, capturing the value of $var at the time the "sub"
       expression is evaluated.  This can break the closure behaviour in those
       cases where $var is subsequently modified.  The subroutine won't return
       the new value.

       This usage is now deprecated in those cases where the variable could be
       modified elsewhere.  Perl detects those cases and emits a deprecation
       warning.  Such code will likely change in the future and stop producing
       a constant.

       If your variable is only modified in the place where it is declared,
       then Perl will continue to make the sub inlinable with no warnings.

           sub make_constant {
               my $var = shift;
               return sub () { $var }; # fine

           sub make_constant_deprecated {
               my $var;
               $var = shift;
               return sub () { $var }; # deprecated

           sub make_constant_deprecated2 {
               my $var = shift;
               log_that_value($var); # could modify $var
               return sub () { $var }; # deprecated

       In the second example above, detecting that $var is assigned to only
       once is too hard to detect.  That it happens in a spot other than the
       "my" declaration is enough for Perl to find it suspicious.

       This deprecation warning happens only for a simple variable for the
       body of the sub.  (A "BEGIN" block or "use" statement inside the sub is
       ignored, because it does not become part of the sub's body.)  For more
       complex cases, such as "sub () { do_something() if 0; $var }" the
       behaviour has changed such that inlining does not happen if the
       variable is modifiable elsewhere.  Such cases should be rare.

Performance Enhancements

       o   "(...)x1", "("constant")x0" and "($scalar)x0" are now optimised in
           list context.  If the right-hand argument is a constant 1, the
           repetition operator disappears.  If the right-hand argument is a
           constant 0, the whole expressions is optimised to the empty list,
           so long as the left-hand argument is a simple scalar or constant.
           "(foo())x0" is not optimised.

       o   "substr" assignment is now optimised into 4-argument "substr" at
           the end of a subroutine (or as the argument to "return").
           Previously, this optimisation only happened in void context.

       o   Assignment to lexical variables is often optimised away.  For
           instance, in "$lexical = chr $foo", the "chr" operator writes
           directly to the lexical variable instead of returning a value that
           gets copied.  This optimisation has been extended to "split", "x"
           and "vec" on the right-hand side.  It has also been made to work
           with state variable initialization.

       o   In "\L...", "\Q...", etc., the extra "stringify" op is now
           optimised away, making these just as fast as "lcfirst",
           "quotemeta", etc.

       o   Assignment to an empty list is now sometimes faster.  In
           particular, it never calls "FETCH" on tied arguments on the right-
           hand side, whereas it used to sometimes.

Modules and Pragmata

   Updated Modules and Pragmata
       o   B has been upgraded from version 1.52 to 1.53.

       o   B::Concise has been upgraded from version 0.994 to 0.995.

       o   B::Deparse has been upgraded from version 1.29 to 1.30.

           It now deparses "+sub : attr { ... }" correctly at the start of a
           statement.  Without the initial "+", "sub" would be a statement

           "BEGIN" blocks are now emitted in the right place most of the time,
           but the change unfortunately introduced a regression, in that
           "BEGIN" blocks occurring just before the end of the enclosing block
           may appear below it instead.  So this change may need to be
           reverted if it cannot be fixed before Perl 5.22.  [perl #77452]

           B::Deparse no longer puts erroneous "local" here and there, such as
           for "LIST = tr/a//d".  [perl #119815]

           Adjacent "use" statements are no longer accidentally nested if one
           contains a "do" block.  [perl #115066]

       o   B::Op_private has been upgraded from version 5.021005 to 5.021006.

           It now includes a hash named %ops_using, list all op types that use
           a particular private flag.

       o   CPAN::Meta has been upgraded from version 2.142690 to 2.143240.

       o   CPAN::Meta::Requirements has been upgraded from version 2.128 to

       o   Devel::Peek has been upgraded from version 1.18 to 1.19.

       o   Digest::SHA has been upgraded from version 5.92 to 5.93.

       o   DynaLoader has been upgraded from version 1.27 to 1.28.

       o   Encode has been upgraded from version 2.62 to 2.64.

       o   experimental has been upgraded from version 0.012 to 0.013.

       o   Exporter has been upgraded from version 5.71 to 5.72.

       o   ExtUtils::MakeMaker has been upgraded from version 6.98 to 7.02.

       o   ExtUtils::Manifest has been upgraded from version 1.68 to 1.69.

       o   ExtUtils::ParseXS has been upgraded from version 3.25 to 3.26.

       o   HTTP::Tiny has been upgraded from version 0.050 to 0.051.

       o   I18N::Langinfo has been upgraded from version 0.11 to 0.12.

       o   IO::Socket has been upgraded from version 1.37 to 1.38.

           Document the limitations of the connected() method.  [perl #123096]

       o   locale has been upgraded from version 1.04 to 1.05.

       o   Module::CoreList has been upgraded from version 5.20141020 to

       o   overload has been upgraded from version 1.23 to 1.24.

       o   PerlIO::encoding has been upgraded from version 0.19 to 0.20.

       o   PerlIO::scalar has been upgraded from version 0.19 to 0.20.

       o   POSIX has been upgraded from version 1.45 to 1.46.

       o   re has been upgraded from version 0.27 to 0.28.

       o   Test::Harness has been upgraded from version 3.33 to 3.34.

       o   Test::Simple has been upgraded from version 1.001008 to

       o   Unicode::UCD has been upgraded from version 0.58 to 0.59.

       o   warnings has been upgraded from version 1.28 to 1.29.

       o   XSLoader has been upgraded from version 0.18 to 0.19.


   Changes to Existing Documentation
       "Identifier parsing" in perldata

       o   The syntax of single-character variable names has been brought up-
           to-date and more fully explained.


       The following additions or changes have been made to diagnostic output,
       including warnings and fatal error messages.  For the complete list of
       diagnostic messages, see perldiag.

   New Diagnostics
       New Warnings

       o   Use of literal non-graphic characters in variable names is

       o   A new "locale" warning category has been created, with the
           following warning messages currently in it:

           o   Locale '%s' may not work well.%s

           o   Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".

       o   Warning: unable to close filehandle %s properly: %s

       o   The following two warnings for "tr///" used to be skipped if the
           transliteration contained wide characters, but now they occur
           regardless of whether there are wide characters or not:

           Useless use of /d modifier in transliteration operator

           Replacement list is longer than search list

   Changes to Existing Diagnostics
       o   Quantifier unexpected on zero-length expression in regex m/%s/.

           This message has had the "<-- HERE" marker removed, as it was
           always placed at the end of the regular expression, regardless of
           where the problem actually occurred.  [perl #122680]

       o   Setting $/ to a reference to %s as a form of slurp is deprecated,
           treating as undef

           This warning is now a default warning, like other deprecation

Configuration and Compilation

       o   Configure with "-Dmksymlinks" should now be faster. [perl #122002]

       o   As well as the gzip and bzip2 tarballs, this release has been made
           available as an xz utils compressed tarball.

Platform Support

   Platform-Specific Notes

       o   In the experimental ":win32" layer, a crash in "open" was fixed.
           Also opening "/dev/null", which works the Win32 Perl's normal
           ":unix" layer, was implemented for ":win32".  [perl #122224]

       o   A new makefile option, "USE_LONG_DOUBLE", has been added to the
           Windows dmake makefile for gcc builds only.  Set this to "define"
           if you want perl to use long doubles to give more accuracy and
           range for floating point numbers.

Internal Changes

       o   "screaminstr" has been removed. Although marked as public API, it
           is undocumented and has no usage in modern perl versions on CPAN
           Grep. Calling it has been fatal since 5.17.0.

       o   "newDEFSVOP", "block_start", "block_end" and "intro_my" have been
           added to the API.

       o   The internal "convert" function in op.c has been renamed
           "op_convert_list" and added to the API.

       o   "sv_magic" no longer forbids "ext" magic on read-only values.
           After all, perl can't know whether the custom magic will modify the
           SV or not.  [perl #123103]

       o   Starting in 5.21.6, accessing "CvPADLIST" in perlapi in an XSUB is
           forbidden.  CvPADLIST has be reused for a different internal
           purpose for XSUBs. Guard all CvPADLIST expressions with
           "CvISXSUB()" if your code doesn't already block XSUB CV*s from
           going through optree CV* expecting code.

Selected Bug Fixes

       o   fchmod() and futimes() now set $! when they fail due to being
           passed a closed file handle.  [perl #122703]

       o   Perl now comes with a corrected Unicode 7.0 for the erratum issued
           on October 21, 2014 (see
           <>), dealing with
           glyph shaping in Arabic.

       o   op_free() no longer crashes due to a stack overflow when freeing a
           deeply recursive op tree. [perl #108276]

       o   scalarvoid() would crash due to a stack overflow when processing a
           deeply recursive op tree. [perl #108276]

       o   In Perl 5.20.0, $^N accidentally had the internal UTF8 flag turned
           off if accessed from a code block within a regular expression,
           effectively UTF8-encoding the value.  This has been fixed.  [perl

       o   A failed "semctl" call no longer overwrites existing items on the
           stack, causing "(semctl(-1,0,0,0))[0]" to give an "uninitialized"

       o   "else{foo()}" with no space before "foo" is now better at assigning
           the right line number to that statement.  [perl #122695]

       o   Sometimes the assignment in "@array = split" gets optimised and
           "split" itself writes directly to the array.  This caused a bug,
           preventing this assignment from being used in lvalue context.  So
           "(@a=split//,"foo")=bar()" was an error.  (This bug probably goes
           back to Perl 3, when the optimisation was added.)  This
           optimisation, and the bug, started to happen in more cases in
           5.21.5.  It has now been fixed.  [perl #123057]

       o   When argument lists that fail the checks installed by subroutine
           signatures, the resulting error messages now give the file and line
           number of the caller, not of the called subroutine.  [perl #121374]

       o   Flip-flop operators (".." and "..." in scalar context) used to
           maintain a separate state for each recursion level (the number of
           times the enclosing sub was called recursively), contrary to the
           documentation.  Now each closure has one internal state for each
           flip-flop.  [perl #122829]

       o   "use", "no", statement labels, special blocks ("BEGIN") and pod are
           now permitted as the first thing in a "map" or "grep" block, the
           block after "print" or "say" (or other functions) returning a
           handle, and within "${...}", "@{...}", etc.  [perl #122782]

       o   The repetition operator "x" now propagates lvalue context to its
           left-hand argument when used in contexts like "foreach".  That
           allows "for(($#that_array)x2) { ... }" to work as expected if the
           loop modifies $_.

       o   "(...) x ..." in scalar context used to corrupt the stack if one
           operand were an object with "x" overloading, causing erratic
           behaviour.  [perl #121827]

       o   Assignment to a lexical scalar is often optimised away (as
           mentioned under "Performance Enhancements").  Various bugs related
           to this optimisation have been fixed.  Certain operators on the
           right-hand side would sometimes fail to assign the value at all or
           assign the wrong value, or would call STORE twice or not at all on
           tied variables.  The operators affected were "$foo++", "$foo--",
           and "-$foo" under "use integer", "chomp", "chr" and "setpgrp".

       o   List assignments were sometimes buggy if the same scalar ended up
           on both sides of the assignment due to used of "tied", "values" or
           "each".  The result would be the wrong value getting assigned.

       o   "setpgrp($nonzero)" (with one argument) was accidentally changed in
           5.16 to mean setpgrp(0).  This has been fixed.

       o   "__SUB__" could return the wrong value or even corrupt memory under
           the debugger (the -d switch) and in subs containing "eval $string".

       o   When "sub () { $var }" becomes inlinable, it now returns a
           different scalar each time, just as a non-inlinable sub would,
           though Perl still optimises the copy away in cases where it would
           make no observable difference.

       o   "my sub f () { $var }" and "sub () : attr { $var }" are no longer
           eligible for inlining.  The former would crash; the latter would
           just throw the attributes away.  An exception is made for the
           little-known ":method" attribute, which does nothing much.

       o   Inlining of subs with an empty prototype is now more consistent
           than before.  Previously, a sub with multiple statements, all but
           the last optimised away, would be inlinable only if it were an
           anonymous sub containing a string "eval" or "state" declaration or
           closing over an outer lexical variable (or any anonymous sub under
           the debugger).  Now any sub that gets folded to a single constant
           after statements have been optimised away is eligible for inlining.
           This applies to things like "sub () { jabber() if DEBUG; 42 }".

           Some subroutines with an explicit "return" were being made
           inlinable, contrary to the documentation,  Now "return" always
           prevents inlining.

       o   On some systems, such as VMS, "crypt" can return a non-ASCII
           string.  If a scalar assigned to had contained a UTF8 string
           previously, then "crypt" would not turn off the UTF8 flag, thus
           corrupting the return value.  This would happen with "$lexical =
           crypt ...".

       o   "crypt" no longer calls "FETCH" twice on a tied first argument.

       o   An unterminated here-doc on the last line of a quote-like operator
           ("qq[${ <<END }]", "/(?{ <<END })/") no longer causes a double
           free.  It started doing so in 5.18.

       o   Fixed two assertion failures introduced into "-DPERL_OP_PARENT"
           builds. [perl #108276]

Known Problems

       o   Builds on FreeBSD 10.x currently fail when compiling POSIX. A
           workaround is to specify "-Ui_fenv" when running "Configure".

Errata From Previous Releases

       o   Due to a mistake in the string-copying logic, copying the value of
           a state variable could instead steal the value and undefine the
           variable.  This bug, introduced in 5.20, would happen mostly for
           long strings (1250 chars or more), but could happen for any strings
           under builds with copy-on-write disabled.  [perl #123029]

           This bug was actually fixed in 5.21.5, but it was not until after
           that release that this bug, and the fact that it had been fixed,
           were discovered.

       o   If a named sub tries to access a scalar declared in an outer
           anonymous sub, the variable is not available, so the named sub gets
           its own undefined scalar.  In 5.10, attempts to take a reference to
           the variable ("\$that_variable") began returning a reference to a
           copy of it instead.  This was accidentally fixed in 5.21.4, but the
           bug and its fix were not noticed till now.


       Perl 5.21.6 represents approximately 4 weeks of development since Perl
       5.21.5 and contains approximately 60,000 lines of changes across 920
       files from 25 authors.

       Excluding auto-generated files, documentation and release tools, there
       were approximately 48,000 lines of changes to 630 .pm, .t, .c and .h

       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 5.21.6:

       Aaron Crane, Abigail, Andrew Fresh, Andy Dougherty, Brian Fraser, Chad
       Granum, Chris 'BinGOs' Williams, Craig A. Berry, Daniel Dragan, David
       Mitchell, Doug Bell, Father Chrysostomos, Glenn D. Golden, James E
       Keenan, Jarkko Hietaniemi, Jim Cromie, Karen Etheridge, Karl
       Williamson, Lukas Mai, Ricardo Signes, Shlomi Fish, Slaven Rezic, Steve
       Hay, Tony Cook, Yaroslav Kuzmin.

       The list above is almost certainly incomplete as it is automatically
       generated from version control history. In particular, it does not
       include the names of the (very much appreciated) contributors who
       reported issues to the Perl bug tracker.

       Many of the changes included in this version originated in the CPAN
       modules included in Perl's core. We're grateful to the entire CPAN
       community for helping Perl to flourish.

       For a more complete list of all of Perl's historical contributors,
       please see the AUTHORS file in the Perl source distribution.

Reporting Bugs

       If you find what you think is a bug, you might check the articles
       recently posted to the comp.lang.perl.misc newsgroup and the perl bug
       database at .  There may also be information at , the Perl Home Page.

       If you believe you have an unreported bug, please run the perlbug
       program included with your release.  Be sure to trim your bug down to a
       tiny but sufficient test case.  Your bug report, along with the output
       of "perl -V", will be sent off to to be analysed by
       the Perl porting team.

       If the bug you are reporting has security implications, which make it
       inappropriate to send to a publicly archived mailing list, then please
       send it to  This points to a closed
       subscription unarchived mailing list, which includes all the core
       committers, who will be able to help assess the impact of issues,
       figure out a resolution, and help co-ordinate the release of patches to
       mitigate or fix the problem across all platforms on which Perl is
       supported.  Please only use this address for security issues in the
       Perl core, not for modules independently distributed on CPAN.


       The Changes file for an explanation of how to view exhaustive details
       on what changed.

       The INSTALL file for how to build Perl.

       The README file for general stuff.

       The Artistic and Copying files for copyright information.

perl v5.22.0                      2015-05-13                PERL5216DELTA(1pm)

perl 5.22 - Generated Fri Aug 14 15:25:50 CDT 2015
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