This document describes differences between the 5.9.0 and the 5.9.1
       development releases. See perl590delta for the differences between
       5.8.0 and 5.9.0.

Incompatible Changes
   substr() lvalues are no longer fixed-length
       The lvalues returned by the three argument form of substr() used to be
       a "fixed length window" on the original string. In some cases this
       could cause surprising action at distance or other undefined behaviour.
       Now the length of the window adjusts itself to the length of the string
       assigned to it.

   The ":unique" attribute is only meaningful for globals
       Now applying ":unique" to lexical variables and to subroutines will
       result in a compilation error.

Core Enhancements
   Lexical $_
       The default variable $_ can now be lexicalized, by declaring it like
       any other lexical variable, with a simple

           my $_;

       The operations that default on $_ will use the lexically-scoped version
       of $_ when it exists, instead of the global $_.

       In a "map" or a "grep" block, if $_ was previously my'ed, then the $_
       inside the block is lexical as well (and scoped to the block).

       In a scope where $_ has been lexicalized, you can still have access to
       the global version of $_ by using $::_, or, more simply, by overriding
       the lexical declaration with "our $_".

   Tied hashes in scalar context
       As of perl 5.8.2/5.9.0, tied hashes did not return anything useful in
       scalar context, for example when used as boolean tests:

               if (%tied_hash) { ... }

       The old nonsensical behaviour was always to return false, regardless of
       whether the hash is empty or has elements.

       There is now an interface for the implementors of tied hashes to
       implement the behaviour of a hash in scalar context, via the SCALAR
       method (see perltie).  Without a SCALAR method, perl will try to guess
       whether the hash is empty, by testing if it's inside an iteration (in
       this case it can't be empty) or by calling FIRSTKEY.

       Formats were improved in several ways. A new field, "^*", can be used
       for variable-width, one-line-at-a-time text. Null characters are now
       handled correctly in picture lines. Using "@#" and "~~" together will
           statistics of children instead of parent when the selected style is

           The error messages produced by "Carp" now include spaces between
           the arguments in function argument lists: this makes long error
           messages appear more nicely in browsers and other tools.

           "Exporter" will now recognize grouping tags (such as ":name")
           anywhere in the import list, not only at the beginning.

           A function "again" is provided to resolve problems where modules in
           different directories wish to use FindBin.

           You can now weaken references to read only values.

           "cond_wait" has a new two argument form. "cond_timedwait" has been

Utility Changes
       "find2perl" now assumes "-print" as a default action. Previously, it
       needed to be specified explicitly.

       A new utility, "prove", makes it easy to run an individual regression
       test at the command line. "prove" is part of Test::Harness, which users
       of earlier Perl versions can install from CPAN.

       The perl debugger now supports a "save" command, to save the current
       history to a file, and an "i" command, which prints the inheritance
       tree of its argument (if the "Class::ISA" module is installed.)

       The documentation has been revised in places to produce more standard

       The long-existing feature of "/(?{...})/" regexps setting $_ and pos()
       is now documented.

Performance Enhancements
       Sorting arrays in place ("@a = sort @a") is now optimized to avoid
       making a temporary copy of the array.

       The operations involving case mapping on UTF-8 strings (uc(), lc(),
       "//i", etc.) have been greatly speeded up.

       Access to elements of lexical arrays via a numeric constant between 0
       and 255 is now faster. (This used to be only the case for global

Selected Bug Fixes
       chop() and chomp() used to mangle UTF-8 strings.  This has been fixed.

       sprintf() used to misbehave when the format string was in UTF-8. This
       is now fixed.

   Threading bugs
       Hashes with the ":unique" attribute weren't made read-only in new
       threads. They are now.

   More bugs
       "$a .. $b" will now work as expected when either $a or $b is "undef".

       Reading $^E now preserves $!. Previously, the C code implementing $^E
       did not preserve "errno", so reading $^E could cause "errno" and
       therefore $! to change unexpectedly.

       "strict" wasn't in effect in regexp-eval blocks ("/(?{...})/").

New or Changed Diagnostics
       A new deprecation warning, Deprecated use of my() in false conditional,
       has been added, to warn against the use of the dubious and deprecated

           my $x if 0;

       See perldiag.

       The fatal error DESTROY created new reference to dead object is now
       documented in perldiag.

       A new error, %ENV is aliased to %s, is produced when taint checks are
       enabled and when *ENV has been aliased (and thus doesn't reflect the
       program's environment anymore.)

Changed Internals
       These news matter to you only if you either write XS code or like to
       know about or hack Perl internals (using Devel::Peek or any of the
       "B::" modules counts), or like to run Perl with the "-D" option.

   Reordering of SVt_* constants
       The relative ordering of constants that define the various types of
       "SV" have changed; in particular, "SVt_PVGV" has been moved before
       "SVt_PVLV", "SVt_PVAV", "SVt_PVHV" and "SVt_PVCV".  This is unlikely to
       make any difference unless you have code that explicitly makes
       assumptions about that ordering. (The inheritance hierarchy of "B::*"
       objects has been changed to reflect this.)

   Removal of CPP symbols
       The C preprocessor symbols "PERL_PM_APIVERSION" and
       "PERL_XS_APIVERSION", which were supposed to give the version number of
       the oldest perl binary-compatible (resp. source-compatible) with the
       present one, were not used, and sometimes had misleading values. They
       have been removed.

       variable they are called for. Previously callbacks were only invoked in
       the "case $variable $define)" branch. This change should only affect
       platform maintainers writing configuration hints files.

       The portability and cleanliness of the Win32 makefiles has been

Known Problems
       There are still a couple of problems in the implementation of the
       lexical $_: it doesn't work inside "/(?{...})/" blocks and with regard
       to the reverse() built-in used without arguments. (See the TODO tests
       in t/op/mydef.t.)

   Platform Specific Problems
       The test ext/IPC/SysV/t/ipcsysv.t may fail on OpenBSD. This hasn't been
       diagnosed yet.

       On some configurations on AIX 5, one test in lib/Time/Local.t fails.
       When configured with long doubles, perl may fail tests 224-236 in
       t/op/pow.t on the same platform.

       For threaded builds, ext/threads/shared/t/wait.t has been reported to
       fail some tests on HP-UX 10.20.

To-do for perl 5.10.0
       This is a non-exhaustive, non-ordered, non-contractual and non-
       definitive list of things to do (or nice to have) for perl 5.10.0 :

       Clean up and finish support for assertions. See assertions.

       Reimplement the mechanism of lexical pragmas to be more extensible. Fix
       current pragmas that don't work well (or at all) with lexical scopes or
       in run-time eval(STRING) ("sort", "re", "encoding" for example). MJD
       has a preliminary patch that implements this.

       Fix (or rewrite) the implementation of the "/(?{...})/" closures.

       Conversions from byte strings to UTF-8 currently map high bit
       characters to Unicode without translation (or, depending on how you
       look at it, by implicitly assuming that the byte strings are in
       Latin-1). As perl assumes the C locale by default, upgrading a string
       to UTF-8 may change the meaning of its contents regarding character
       classes, case mapping, etc.  This should probably emit a warning (at

       Introduce a new special block, UNITCHECK, which is run at the end of a
       compilation unit (module, file, eval(STRING) block). This will
       correspond to the Perl 6 CHECK. Perl 5's CHECK cannot be changed or
       removed because the backend framework depends on it.

       Study the possibility of adding a new prototype character, "_", meaning
       "this argument defaults to $_".

       Make the peephole optimizer optional.
       A ponie.

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.

       The Changes file for 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 v5.14.2                      2011-09-26                   PERL591DELTA(1)
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