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PERL593DELTA(1)	       Perl Programmers Reference Guide	       PERL593DELTA(1)

       perl593delta - what is new for perl v5.9.3

       This document describes differences between the 5.9.2 and the 5.9.3
       development releases. See perl590delta, perl591delta and perl592delta
       for the differences between 5.8.0 and 5.9.2.

Incompatible Changes
   Parsing of "-f _"
       The identifier "_" is now forced to be a bareword after a filetest
       operator. This solves a number of misparsing issues when a global "_"
       subroutine is defined.

       "mkdir()" without arguments now defaults to $_.

   Magic goto and eval
       The construct "eval { goto &foo }" is now disallowed. (Note that the
       similar construct, but with "eval("")" instead, was already forbidden.)

   $# has been removed
       The deprecated $# variable (output format for numbers) has been
       removed. A new warning, "$# is no longer supported", has been added.

       The ":unique" attribute has been made a no-op, since its current
       implementation was fundamentally flawed and not threadsafe.

   Scoping of the "sort" pragma
       The "sort" pragma is now lexically scoped. Its effect used to be

Core Enhancements
   The "feature" pragma
       The "feature" pragma is used to enable new syntax that would break
       Perl's backwards-compatibility with older releases of the language.
       It's a lexical pragma, like "strict" or "warnings".

       Currently the following new features are available: "switch" (adds a
       switch statement), "~~" (adds a Perl 6-like smart match operator),
       "say" (adds a "say" built-in function), and "err" (adds an "err"
       keyword).  Those features are described below.

       Note that "err" low-precedence defined-or operator used to be enabled
       by default (although as a weak keyword, meaning that any function would
       override it). It's now only recognized when explicitly turned on (and
       is then a regular keyword).

       Those features, and the "feature" pragma itself, have been contributed
       by Robin Houston.

   Switch and Smart Match operator
       Perl 5 now has a switch statement. It's available when "use feature
       'switch'" is in effect. This feature introduces three new keywords,
       "given", "when", and "default":

	   given ($foo) {
	       when (/^abc/) { $abc = 1; }
	       when (/^def/) { $def = 1; }
	       when (/^xyz/) { $xyz = 1; }
	       default { $nothing = 1; }

       A more complete description of how Perl matches the switch variable
       against the "when" conditions is given in "Switch statements" in

       This kind of match is called smart match, and it's also possible to use
       it outside of switch statements, via the new "~~" operator (enabled via
       the "use feature '~~'" directive). See "Smart matching in detail" in

       say() is a new built-in, only available when "use feature 'say'" is in
       effect, that is similar to print(), but that implicitly appends a
       newline to the printed string. See "say" in perlfunc.

       Perl has now support for the "CLONE_SKIP" special subroutine. Like
       "CLONE", "CLONE_SKIP" is called once per package; however, it is called
       just before cloning starts, and in the context of the parent thread. If
       it returns a true value, then no objects of that class will be cloned.
       See perlmod for details. (Contributed by Dave Mitchell.)

       A new internal variable, "${^CHILD_ERROR_NATIVE}", gives the native
       status returned by the last pipe close, backtick command, successful
       call to wait() or waitpid(), or from the system() operator. See perlrun
       for details. (Contributed by Gisle Aas.)

       The support for assertions, introduced in perl 5.9.0, has been
       improved.  The syntax for the "-A" command-line switch has changed; it
       now accepts an optional module name, defaulting to
       "assertions::activate". See assertions and perlrun. (Contributed by
       Salvador Fandin~o Garcia.)

   Unicode Character Database 4.1.0
       The copy of the Unicode Character Database included in Perl 5.9 has
       been updated to 4.1.0.

   "no VERSION"
       You can now use "no" followed by a version number to specify that you
       want to use a version of perl older than the specified one.

   Recursive sort subs
       You can now use recursive subroutines with sort(), thanks to Robin

   Effect of pragmas in eval
       The compile-time value of the "%^H" hint variable can now propagate
       into eval("")uated code. This makes it more useful to implement lexical

       As a side-effect of this, the overloaded-ness of constants now
       propagates into eval("").

   New -E command-line switch
       -E is equivalent to -e, but it implicitly enables all optional features
       (like "use feature ":5.10"").

   "chdir", "chmod" and "chown" on filehandles
       "chdir", "chmod" and "chown" can now work on filehandles as well as
       filenames, if the system supports respectively "fchdir", "fchmod" and
       "fchown", thanks to a patch provided by Gisle Aas.

   OS groups
       $( and $) now return groups in the order where the OS returns them,
       thanks to Gisle Aas. This wasn't previously the case.

Modules and Pragmata
   New Core Modules
       ·   A new pragma, "feature", has been added; see above in "Core

       ·   "assertions::compat", also available on CPAN, allows the use of
	   assertions on perl versions prior to 5.9.0 (that is the first one
	   to natively support them).

       ·   "Math::BigInt::FastCalc" is an XS-enabled, and thus faster, version
	   of "Math::BigInt::Calc".

       ·   "Compress::Zlib" is an interface to the zlib compression library.
	   It comes with a bundled version of zlib, so having a working zlib
	   is not a prerequisite to install it. It's used by "Archive::Tar"
	   (see below).

       ·   "IO::Zlib" is an "IO::"-style interface to "Compress::Zlib".

       ·   "Archive::Tar" is a module to manipulate "tar" archives.

       ·   "Digest::SHA" is a module used to calculate many types of SHA
	   digests, has been included for SHA support in the CPAN module.

       ·   "ExtUtils::CBuilder" and "ExtUtils::ParseXS" have been added.

Utility Changes
       "ptar" is a pure perl implementation of "tar", that comes with

       "ptardiff" is a small script used to generate a diff between the
       contents of a tar archive and a directory tree. Like "ptar", it comes
       with "Archive::Tar".

       This command-line utility, used to print or to check SHA digests, comes
       with the new "Digest::SHA" module.

   "h2xs" enhancements
       "h2xs" implements a new option "--use-xsloader" to force use of
       "XSLoader" even in backwards compatible modules.

       The handling of authors' names that had apostrophes has been fixed.

       Any enums with negative values are now skipped.

   "perlivp" enhancements
       "perlivp" no longer checks for *.ph files by default.  Use the new "-a"
       option to run all tests.

   Perl Glossary
       The perlglossary manpage is a glossary of terms used in the Perl
       documentation, technical and otherwise, kindly provided by O'Reilly
       Media, Inc.

       perltodo now lists a rough roadmap to Perl 5.10.

Performance Enhancements
   XS-assisted SWASHGET
       Some pure-perl code that perl was using to retrieve Unicode properties
       and transliteration mappings has been reimplemented in XS.

   Constant subroutines
       The interpreter internals now support a far more memory efficient form
       of inlineable constants. Storing a reference to a constant value in a
       symbol table is equivalent to a full typeglob referencing a constant
       subroutine, but using about 400 bytes less memory. This proxy constant
       subroutine is automatically upgraded to a real typeglob with subroutine
       if necessary.  The approach taken is analogous to the existing space
       optimisation for subroutine stub declarations, which are stored as
       plain scalars in place of the full typeglob.

       Several of the core modules have been converted to use this feature for
       their system dependent constants - as a result "use POSIX;" now takes
       about 200K less memory.

       The new compilation flag "PERL_DONT_CREATE_GVSV", introduced as an
       option in perl 5.8.8, is turned on by default in perl 5.9.3. It
       prevents perl from creating an empty scalar with every new typeglob.
       See perl589delta for details.

   Weak references are cheaper
       Weak reference creation is now O(1) rather than O(n), courtesy of
       Nicholas Clark. Weak reference deletion remains O(n), but if deletion
       only happens at program exit, it may be skipped completely.

   sort() enhancements
       Salvador Fandin~o provided improvements to reduce the memory usage of
       "sort" and to speed up some cases.

Installation and Configuration Improvements
   Compilation improvements
       Parallel makes should work properly now, although there may still be
       problems if "make test" is instructed to run in parallel.

       Building with Borland's compilers on Win32 should work more smoothly.
       In particular Steve Hay has worked to side step many warnings emitted
       by their compilers and at least one C compiler internal error.

       Perl extensions on Windows now can be statically built into the Perl
       DLL, thanks to a work by Vadim Konovalov.

   New Or Improved Platforms
       Perl is being ported to Symbian OS. See perlsymbian for more

       The VMS port has been improved. See perlvms.

       DynaLoader::dl_unload_file() now works on Windows.

       Portability of Perl on various recent compilers on Windows has been
       improved (Borland C++, Visual C++ 7.0).

   New probes
       "Configure" will now detect "clearenv" and "unsetenv", thanks to a
       patch from Alan Burlison. It will also probe for "futimes" (and use it
       internally if available), and whether "sprintf" correctly returns the
       length of the formatted string.

   Module auxiliary files
       README files and changelogs for CPAN modules bundled with perl are no
       longer installed.

Selected Bug Fixes
   "defined $$x"
       "use strict "refs"" was ignoring taking a hard reference in an argument
       to defined(), as in :

	   use strict "refs";
	   my $x = "foo";
	   if (defined $$x) {...}

       This now correctly produces the run-time error "Can't use string as a
       SCALAR ref while "strict refs" in use". (However, "defined @$foo" and
       "defined %$foo" are still allowed. Those constructs are discouraged

   Calling CORE::require()
       CORE::require() and CORE::do() were always parsed as require() and do()
       when they were overridden. This is now fixed.

   Subscripts of slices
       You can now use a non-arrowed form for chained subscripts after a list
       slice, like in:

	   ({foo => "bar"})[0]{foo}

       This used to be a syntax error; a "->" was required.

   Remove over-optimisation
       Perl 5.9.2 introduced a change so that assignments of "undef" to a
       scalar, or of an empty list to an array or a hash, were optimised out.
       As this could cause problems when "goto" jumps were involved, this
       change was backed out.

   sprintf() fixes
       Using the sprintf() function with some formats could lead to a buffer
       overflow in some specific cases. This has been fixed, along with
       several other bugs, notably in bounds checking.

       In related fixes, it was possible for badly written code that did not
       follow the documentation of "Sys::Syslog" to have formatting
       vulnerabilities.	 "Sys::Syslog" has been changed to protect people from
       poor quality third party code.

   no warnings 'category' works correctly with -w
       Previously when running with warnings enabled globally via "-w",
       selective disabling of specific warning categories would actually turn
       off all warnings.  This is now fixed; now "no warnings 'io';" will only
       turn off warnings in the "io" class. Previously it would erroneously
       turn off all warnings.

   Smaller fixes
       ·   "FindBin" now works better with directories where access rights are
	   more restrictive than usual.

       ·   Several memory leaks in ithreads were closed. Also, ithreads were
	   made less memory-intensive.

       ·   Trailing spaces are now trimmed from $! and $^E.

       ·   Operations that require perl to read a process' list of groups,
	   such as reads of $( and $), now dynamically allocate memory rather
	   than using a fixed sized array. The fixed size array could cause C
	   stack exhaustion on systems configured to use large numbers of

       ·   "PerlIO::scalar" now works better with non-default $/ settings.

       ·   The "x" repetition operator is now able to operate on "qw//" lists.
	   This used to raise a syntax error.

       ·   The debugger now traces correctly execution in eval("")uated code
	   that contains #line directives.

       ·   The value of the "open" pragma is no longer ignored for three-
	   argument opens.

       ·   Perl will now use the C library calls "unsetenv" and "clearenv" if
	   present to delete keys from %ENV and delete %ENV entirely, thanks
	   to a patch from Alan Burlison.

   More Unicode Fixes
       ·   chr() on a negative value now gives "\x{FFFD}", the Unicode
	   replacement character, unless when the "bytes" pragma is in effect,
	   where the low eight bytes of the value are used.

       ·   Some case insensitive matches between UTF-8 encoded data and 8 bit
	   regexps, and vice versa, could give malformed character warnings.
	   These have been fixed by Dave Mitchell and Yves Orton.

       ·   "lcfirst" and "ucfirst" could corrupt the string for certain cases
	   where the length UTF-8 encoding of the string in lower case, upper
	   case or title case differed. This was fixed by Nicholas Clark.

New or Changed Diagnostics
   Attempt to set length of freed array
       This is a new warning, produced in situations like the following one:

	   $r = do {my @a; \$#a};
	   $$r = 503;

   Non-string passed as bitmask
       This is a new warning, produced when number has been passed as a
       argument to select(), instead of a bitmask.

	   # Wrong, will now warn
	   $rin = fileno(STDIN);
	   ($nfound,$timeleft) = select($rout=$rin, undef, undef, $timeout);

	   # Should be
	   $rin = '';
	   vec($rin,fileno(STDIN),1) = 1;
	   ($nfound,$timeleft) = select($rout=$rin, undef, undef, $timeout);

   Search pattern not terminated or ternary operator parsed as search pattern
       This syntax error indicates that the lexer couldn't find the final
       delimiter of a "?PATTERN?" construct. Mentioning the ternary operator
       in this error message makes syntax diagnostic easier.

   "%s" variable %s masks earlier declaration
       This warning is now emitted in more consistent cases; in short, when
       one of the declarations involved is a "my" variable:

	   my $x;   my $x;     # warns
	   my $x;  our $x;     # warns
	   our $x;  my $x;     # warns

       On the other hand, the following:

	   our $x; our $x;

       now gives a ""our" variable %s redeclared" warning.

   readdir()/closedir()/etc. attempted on invalid dirhandle
       These new warnings are now emitted when a dirhandle is used but is
       either closed or not really a dirhandle.

Changed Internals
       In general, the source code of perl has been refactored, tied up, and
       optimized in many places. Also, memory management and allocation has
       been improved in a couple of points.

       Andy Lester supplied many improvements to determine which function
       parameters and local variables could actually be declared "const" to
       the C compiler. Steve Peters provided new *_set macros and reworked the
       core to use these rather than assigning to macros in LVALUE context.

       Dave Mitchell improved the lexer debugging output under "-DT".

       A new file, mathoms.c, has been added. It contains functions that are
       no longer used in the perl core, but that remain available for binary
       or source compatibility reasons. However, those functions will not be
       compiled in if you add "-DNO_MATHOMS" in the compiler flags.

       The "AvFLAGS" macro has been removed.

       The "av_*()" functions, used to manipulate arrays, no longer accept
       null "AV*" parameters.

   B:: modules inheritance changed
       The inheritance hierarchy of "B::" modules has changed; "B::NV" now
       inherits from "B::SV" (it used to inherit from "B::IV").

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 v5.10.1			  2009-08-11		       PERL593DELTA(1)

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