This document describes differences between the 5.9.1 and the 5.9.2
       development releases. See perl590delta and perl591delta for the
       differences between 5.8.0 and 5.9.1.

Incompatible Changes
   Packing and UTF-8 strings
       The semantics of pack() and unpack() regarding UTF-8-encoded data has
       been changed. Processing is now by default character per character
       instead of byte per byte on the underlying encoding. Notably, code that
       used things like "pack("a*", $string)" to see through the encoding of
       string will now simply get back the original $string. Packed strings
       can also get upgraded during processing when you store upgraded
       characters. You can get the old behaviour by using "use bytes".

       To be consistent with pack(), the "C0" in unpack() templates indicates
       that the data is to be processed in character mode, i.e. character by
       character; on the contrary, "U0" in unpack() indicates UTF-8 mode,
       where the packed string is processed in its UTF-8-encoded Unicode form
       on a byte by byte basis. This is reversed with regard to perl 5.8.X.

       Moreover, "C0" and "U0" can also be used in pack() templates to specify
       respectively character and byte modes.

       "C0" and "U0" in the middle of a pack or unpack format now switch to
       the specified encoding mode, honoring parens grouping. Previously,
       parens were ignored.

       Also, there is a new pack() character format, "W", which is intended to
       replace the old "C". "C" is kept for unsigned chars coded as bytes in
       the strings internal representation. "W" represents unsigned (logical)
       character values, which can be greater than 255. It is therefore more
       robust when dealing with potentially UTF-8-encoded data (as "C" will
       wrap values outside the range 0..255, and not respect the string

       In practice, that means that pack formats are now encoding-neutral,
       except "C".

       For consistency, "A" in unpack() format now trims all Unicode
       whitespace from the end of the string. Before perl 5.9.2, it used to
       strip only the classical ASCII space characters.

       The internal dump output has been improved, so that non-printable
       characters such as newline and backspace are output in "\x" notation,
       rather than octal.

       The -C option can no longer be used on the "#!" line. It wasn't working
       there anyway.

Core Enhancements
   Malloc wrapping

   suidperl less insecure
       Paul Szabo has analysed and patched "suidperl" to remove existing known
       insecurities. Currently there are no known holes in "suidperl", but
       previous experience shows that we cannot be confident that these were
       the last. You may no longer invoke the set uid perl directly, so to
       preserve backwards compatibility with scripts that invoke
       #!/usr/bin/suidperl the only set uid binary is now "sperl5.9."n
       ("sperl5.9.2" for this release). "suidperl" is installed as a hard link
       to "perl"; both "suidperl" and "perl" will invoke "sperl5.9.2"
       automatically the set uid binary, so this change should be completely

       For new projects the core perl team would strongly recommend that you
       use dedicated, single purpose security tools such as "sudo" in
       preference to "suidperl".

       The "PERLIO_DEBUG" environment variable has no longer any effect for
       setuid scripts and for scripts run with -T.

       Moreover, with a thread-enabled perl, using "PERLIO_DEBUG" could lead
       to an internal buffer overflow. This has been fixed.

       In addition to bug fixes, "format"'s features have been enhanced. See

   Unicode Character Classes
       Perl's regular expression engine now contains support for matching on
       the intersection of two Unicode character classes. You can also now
       refer to user-defined character classes from within other user defined
       character classes.

   Byte-order modifiers for pack() and unpack()
       There are two new byte-order modifiers, ">" (big-endian) and "<"
       (little-endian), that can be appended to most pack() and unpack()
       template characters and groups to force a certain byte-order for that
       type or group.  See "pack" in perlfunc and perlpacktut for details.

   Byte count feature in pack()
       A new pack() template character, ".", returns the number of characters
       read so far.

   New variables
       A new variable, ${^RE_DEBUG_FLAGS}, controls what debug flags are in
       effect for the regular expression engine when running under "use re
       "debug"". See re for details.

       A new variable ${^UTF8LOCALE} indicates where a UTF-8 locale was
       detected by perl at startup.

Modules and Pragmata
   New modules
       The dual-lived modules which contain an "_" in their version number are
       actually ahead of the corresponding CPAN release.

           "B::Concise" was significantly improved.

           There is experimental support for Linux abstract Unix domain

           "syslog()" can now use numeric constants for facility names and
           priorities, in addition to strings.

           Detached threads are now also supported on Windows.

Utility Changes
       o   The "corelist" utility is now installed with perl (see "New
           modules" above).

       o   "h2ph" and "h2xs" have been made a bit more robust with regard to
           "modern" C code.

       o   Several bugs have been fixed in "find2perl", regarding "-exec" and
           "-eval". Also the options "-path", "-ipath" and "-iname" have been

       o   The Perl debugger can now save all debugger commands for sourcing
           later; notably, it can now emulate stepping backwards, by
           restarting and rerunning all bar the last command from a saved
           command history.

           It can also display the parent inheritance tree of a given class.

           Perl has a new -dt command-line flag, which enables threads support
           in the debugger.

Performance Enhancements
       o   Unicode case mappings ("/i", "lc", "uc", etc) are faster.

       o   "@a = sort @a" was optimized to do in-place sort. Likewise,
           "reverse sort ..." is now optimized to sort in reverse, avoiding
           the generation of a temporary intermediate list.

       o   Unnecessary assignments are optimised away in

             my $s = undef;
             my @a = ();
             my %h = ();

       o   "map" in scalar context is now optimized.

       o   The regexp engine now implements the trie optimization : it's able
       Perl should build on Interix and on GNU/kFreeBSD.

Selected Bug Fixes
       Most of those bugs were reported in the perl 5.8.x maintenance track.
       Notably, quite a few utf8 bugs were fixed, and several memory leaks
       were suppressed. The perl58Xdelta manpages have more details on them.

       Development-only bug fixes include :

       $Foo::_ was wrongly forced as $main::_.

New or Changed Diagnostics
       A new warning, "!=~ should be !~", is emitted to prevent this
       misspelling of the non-matching operator.

       The warning Newline in left-justified string has been removed.

       The error Too late for "-T" option has been reformulated to be more

       There is a new compilation error, Illegal declaration of subroutine,
       for an obscure case of syntax errors.

       The diagnostic output of Carp has been changed slightly, to add a space
       after the comma between arguments. This makes it much easier for tools
       such as web browsers to wrap it, but might confuse any automatic tools
       which perform detailed parsing of Carp output.

       "perl -V" has several improvements, making it more useable from shell
       scripts to get the value of configuration variables. See perlrun for

Changed Internals
       The perl core has been refactored and reorganised in several places.
       In short, this release will not be binary compatible with any previous
       perl release.

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

       Net::Ping might fail some tests on HP-UX 11.00 with the latest OS

       t/io/dup.t, t/io/open.t and lib/ExtUtils/t/Constant.t fail some tests
       on some BSD flavours.

Plans for the next release
       The current plan for perl 5.9.3 is to add CPANPLUS as a core module.
       More regular expression optimizations are also in the works.

       It is planned to release a development version of perl more frequently,
       i.e. each time something major changes.

       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                   PERL592DELTA(1)
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