perl561delta - Online in the Cloud

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NAME

perl561delta - what's new for perl v5.6.1

DESCRIPTION

This document describes differences between the 5.005 release and the 5.6.1 release.

Summary of changes between 5.6.0 and 5.6.1

This section contains a summary of the changes between the 5.6.0 release and the 5.6.1
release. More details about the changes mentioned here may be found in the Changes files
that accompany the Perl source distribution. See perlhack for pointers to online
resources where you can inspect the individual patches described by these changes.

Security Issues
suidperl will not run /bin/mail anymore, because some platforms have a /bin/mail that is
vulnerable to buffer overflow attacks.

Note that suidperl is neither built nor installed by default in any recent version of
perl. Use of suidperl is highly discouraged. If you think you need it, try alternatives
such as sudo first. See http://www.courtesan.com/sudo/ .

Core bug fixes
This is not an exhaustive list. It is intended to cover only the significant user-visible
changes.

"UNIVERSAL::isa()"
A bug in the caching mechanism used by "UNIVERSAL::isa()" that affected base.pm has
been fixed. The bug has existed since the 5.005 releases, but wasn't tickled by
base.pm in those releases.

Memory leaks
Various cases of memory leaks and attempts to access uninitialized memory have been
cured. See "Known Problems" below for further issues.

Numeric conversions
Numeric conversions did not recognize changes in the string value properly in certain
circumstances.

In other situations, large unsigned numbers (those above 2**31) could sometimes lose
their unsignedness, causing bogus results in arithmetic operations.

Integer modulus on large unsigned integers sometimes returned incorrect values.

Perl 5.6.0 generated "not a number" warnings on certain conversions where previous
versions didn't.

These problems have all been rectified.

Infinity is now recognized as a number.

qw(a\\b)
In Perl 5.6.0, qw(a\\b) produced a string with two backslashes instead of one, in a
departure from the behavior in previous versions. The older behavior has been
reinstated.

caller()
caller() could cause core dumps in certain situations. Carp was sometimes affected by
this problem.

Bugs in regular expressions
Pattern matches on overloaded values are now handled correctly.

Perl 5.6.0 parsed m/\x{ab}/ incorrectly, leading to spurious warnings. This has been
corrected.

The RE engine found in Perl 5.6.0 accidentally pessimised certain kinds of simple
pattern matches. These are now handled better.

Regular expression debug output (whether through "use re 'debug'" or via "-Dr") now
looks better.

Multi-line matches like ""a\nxb\n" =~ /(?!\A)x/m" were flawed. The bug has been
fixed.

Use of $& could trigger a core dump under some situations. This is now avoided.

Match variables $1 et al., weren't being unset when a pattern match was backtracking,
and the anomaly showed up inside "/...(?{ ... }).../" etc. These variables are now
tracked correctly.

pos() did not return the correct value within s///ge in earlier versions. This is now
handled correctly.

"slurp" mode
readline() on files opened in "slurp" mode could return an extra "" at the end in
certain situations. This has been corrected.

Autovivification of symbolic references to special variables
Autovivification of symbolic references of special variables described in perlvar (as
in "${$num}") was accidentally disabled. This works again now.

Lexical warnings
Lexical warnings now propagate correctly into "eval "..."".

"use warnings qw(FATAL all)" did not work as intended. This has been corrected.

Lexical warnings could leak into other scopes in some situations. This is now fixed.

warnings::enabled() now reports the state of $^W correctly if the caller isn't using
lexical warnings.

Spurious warnings and errors
Perl 5.6.0 could emit spurious warnings about redefinition of dl_error() when
statically building extensions into perl. This has been corrected.

"our" variables could result in bogus "Variable will not stay shared" warnings. This
is now fixed.

"our" variables of the same name declared in two sibling blocks resulted in bogus
warnings about "redeclaration" of the variables. The problem has been corrected.

glob()
Compatibility of the builtin glob() with old csh-based glob has been improved with the
addition of GLOB_ALPHASORT option. See "File::Glob".

File::Glob::glob() has been renamed to File::Glob::bsd_glob() because the name clashes
with the builtin glob(). The older name is still available for compatibility, but is
deprecated.

Spurious syntax errors generated in certain situations, when glob() caused File::Glob
to be loaded for the first time, have been fixed.

Tainting
Some cases of inconsistent taint propagation (such as within hash values) have been
fixed.

The tainting behavior of sprintf() has been rationalized. It does not taint the
result of floating point formats anymore, making the behavior consistent with that of
string interpolation.

sort()
Arguments to sort() weren't being provided the right wantarray() context. The
comparison block is now run in scalar context, and the arguments to be sorted are
always provided list context.

sort() is also fully reentrant, in the sense that the sort function can itself call
sort(). This did not work reliably in previous releases.

#line directives
#line directives now work correctly when they appear at the very beginning of "eval
"..."".

Subroutine prototypes
The (\&) prototype now works properly.

map()
map() could get pathologically slow when the result list it generates is larger than
the source list. The performance has been improved for common scenarios.

Debugger
Debugger exit code now reflects the script exit code.

Condition "0" in breakpoints is now treated correctly.

The "d" command now checks the line number.

$. is no longer corrupted by the debugger.

All debugger output now correctly goes to the socket if RemotePort is set.

PERL5OPT
PERL5OPT can be set to more than one switch group. Previously, it used to be limited
to one group of options only.

chop()
chop(@list) in list context returned the characters chopped in reverse order. This
has been reversed to be in the right order.

Unicode support
Unicode support has seen a large number of incremental improvements, but continues to
be highly experimental. It is not expected to be fully supported in the 5.6.x
maintenance releases.

substr(), join(), repeat(), reverse(), quotemeta() and string concatenation were all
handling Unicode strings incorrectly in Perl 5.6.0. This has been corrected.

Support for "tr///CU" and "tr///UC" etc., have been removed since we realized the
interface is broken. For similar functionality, see "pack" in perlfunc.

The Unicode Character Database has been updated to version 3.0.1 with additions made
available to the public as of August 30, 2000.

The Unicode character classes \p{Blank} and \p{SpacePerl} have been added. "Blank" is
like C isblank(), that is, it contains only "horizontal whitespace" (the space
character is, the newline isn't), and the "SpacePerl" is the Unicode equivalent of
"\s" (\p{Space} isn't, since that includes the vertical tabulator character, whereas
"\s" doesn't.)

If you are experimenting with Unicode support in perl, the development versions of
Perl may have more to offer. In particular, I/O layers are now available in the
development track, but not in the maintenance track, primarily to do backward
compatibility issues. Unicode support is also evolving rapidly on a daily basis in
the development track--the maintenance track only reflects the most conservative of
these changes.

64-bit support
Support for 64-bit platforms has been improved, but continues to be experimental. The
level of support varies greatly among platforms.

Compiler
The B Compiler and its various backends have had many incremental improvements, but
they continue to remain highly experimental. Use in production environments is
discouraged.

The perlcc tool has been rewritten so that the user interface is much more like that
of a C compiler.

The perlbc tools has been removed. Use "perlcc -B" instead.

Lvalue subroutines
There have been various bugfixes to support lvalue subroutines better. However, the
feature still remains experimental.

IO::Socket
IO::Socket::INET failed to open the specified port if the service name was not known.
It now correctly uses the supplied port number as is.

File::Find
File::Find now chdir()s correctly when chasing symbolic links.

xsubpp
xsubpp now tolerates embedded POD sections.

"no Module;"
"no Module;" does not produce an error even if Module does not have an unimport()
method. This parallels the behavior of "use" vis-a-vis "import".

Tests
A large number of tests have been added.

Core features
untie() will now call an UNTIE() hook if it exists. See perltie for details.

The "-DT" command line switch outputs copious tokenizing information. See perlrun.

Arrays are now always interpolated in double-quotish strings. Previously, "foo@bar.com"
used to be a fatal error at compile time, if an array @bar was not used or declared. This
transitional behavior was intended to help migrate perl4 code, and is deemed to be no
longer useful. See "Arrays now always interpolate into double-quoted strings".

keys(), each(), pop(), push(), shift(), splice() and unshift() can all be overridden now.

"my __PACKAGE__ $obj" now does the expected thing.

Configuration issues
On some systems (IRIX and Solaris among them) the system malloc is demonstrably better.
While the defaults haven't been changed in order to retain binary compatibility with
earlier releases, you may be better off building perl with "Configure -Uusemymalloc ..."
as discussed in the INSTALL file.

"Configure" has been enhanced in various ways:

· Minimizes use of temporary files.

· By default, does not link perl with libraries not used by it, such as the various dbm
libraries. SunOS 4.x hints preserve behavior on that platform.

· Support for pdp11-style memory models has been removed due to obsolescence.

· Building outside the source tree is supported on systems that have symbolic links.
This is done by running

sh /path/to/source/Configure -Dmksymlinks ...
make all test install

in a directory other than the perl source directory. See INSTALL.

· "Configure -S" can be run non-interactively.

Documentation
README.aix, README.solaris and README.macos have been added. README.posix-bc has been
renamed to README.bs2000. These are installed as perlaix, perlsolaris, perlmacos, and
perlbs2000 respectively.

The following pod documents are brand new:

perlclib Internal replacements for standard C library functions
perldebtut Perl debugging tutorial
perlebcdic Considerations for running Perl on EBCDIC platforms
perlnewmod Perl modules: preparing a new module for distribution
perlrequick Perl regular expressions quick start
perlretut Perl regular expressions tutorial
perlutil utilities packaged with the Perl distribution

The INSTALL file has been expanded to cover various issues, such as 64-bit support.

A longer list of contributors has been added to the source distribution. See the file
"AUTHORS".

Numerous other changes have been made to the included documentation and FAQs.

Bundled modules
The following modules have been added.

B::Concise
Walks Perl syntax tree, printing concise info about ops. See B::Concise.

File::Temp
Returns name and handle of a temporary file safely. See File::Temp.

Pod::LaTeX
Converts Pod data to formatted LaTeX. See Pod::LaTeX.

Pod::Text::Overstrike
Converts POD data to formatted overstrike text. See Pod::Text::Overstrike.

The following modules have been upgraded.

CGI CGI v2.752 is now included.

CPAN
CPAN v1.59_54 is now included.

Class::Struct
Various bugfixes have been added.

DB_File
DB_File v1.75 supports newer Berkeley DB versions, among other improvements.

Devel::Peek
Devel::Peek has been enhanced to support dumping of memory statistics, when perl is
built with the included malloc().

File::Find
File::Find now supports pre and post-processing of the files in order to sort() them,
etc.

Getopt::Long
Getopt::Long v2.25 is included.

IO::Poll
Various bug fixes have been included.

IPC::Open3
IPC::Open3 allows use of numeric file descriptors.

Math::BigFloat
The fmod() function supports modulus operations. Various bug fixes have also been
included.

Math::Complex
Math::Complex handles inf, NaN etc., better.

Net::Ping
ping() could fail on odd number of data bytes, and when the echo service isn't
running. This has been corrected.

Opcode
A memory leak has been fixed.

Pod::Parser
Version 1.13 of the Pod::Parser suite is included.

Pod::Text
Pod::Text and related modules have been upgraded to the versions in podlators suite
v2.08.

SDBM_File
On dosish platforms, some keys went missing because of lack of support for files with
"holes". A workaround for the problem has been added.

Sys::Syslog
Various bug fixes have been included.

Tie::RefHash
Now supports Tie::RefHash::Nestable to automagically tie hashref values.

Tie::SubstrHash
Various bug fixes have been included.

Platform-specific improvements
The following new ports are now available.

NCR MP-RAS
NonStop-UX

Perl now builds under Amdahl UTS.

Perl has also been verified to build under Amiga OS.

Support for EPOC has been much improved. See README.epoc.

Building perl with -Duseithreads or -Duse5005threads now works under HP-UX 10.20
(previously it only worked under 10.30 or later). You will need a thread library package
installed. See README.hpux.

Long doubles should now work under Linux.

Mac OS Classic is now supported in the mainstream source package. See README.macos.

Support for MPE/iX has been updated. See README.mpeix.

Support for OS/2 has been improved. See "os2/Changes" and README.os2.

Dynamic loading on z/OS (formerly OS/390) has been improved. See README.os390.

Support for VMS has seen many incremental improvements, including better support for
operators like backticks and system(), and better %ENV handling. See "README.vms" and
perlvms.

Support for Stratus VOS has been improved. See "vos/Changes" and README.vos.

Support for Windows has been improved.

· fork() emulation has been improved in various ways, but still continues to be
experimental. See perlfork for known bugs and caveats.

· %SIG has been enabled under USE_ITHREADS, but its use is completely unsupported under
all configurations.

· Borland C++ v5.5 is now a supported compiler that can build Perl. However, the
generated binaries continue to be incompatible with those generated by the other
supported compilers (GCC and Visual C++).

· Non-blocking waits for child processes (or pseudo-processes) are supported via
"waitpid($pid, &POSIX::WNOHANG)".

· A memory leak in accept() has been fixed.

· wait(), waitpid() and backticks now return the correct exit status under Windows 9x.

· Trailing new %ENV entries weren't propagated to child processes. This is now fixed.

· Current directory entries in %ENV are now correctly propagated to child processes.

· Duping socket handles with open(F, ">&MYSOCK") now works under Windows 9x.

· The makefiles now provide a single switch to bulk-enable all the features enabled in
ActiveState ActivePerl (a popular binary distribution).

· Win32::GetCwd() correctly returns C:\ instead of C: when at the drive root. Other
bugs in chdir() and Cwd::cwd() have also been fixed.

· fork() correctly returns undef and sets EAGAIN when it runs out of pseudo-process
handles.

· ExtUtils::MakeMaker now uses $ENV{LIB} to search for libraries.

· UNC path handling is better when perl is built to support fork().

· A handle leak in socket handling has been fixed.

· send() works from within a pseudo-process.

Unless specifically qualified otherwise, the remainder of this document covers changes
between the 5.005 and 5.6.0 releases.

Core Enhancements

Interpreter cloning, threads, and concurrency
Perl 5.6.0 introduces the beginnings of support for running multiple interpreters
concurrently in different threads. In conjunction with the perl_clone() API call, which
can be used to selectively duplicate the state of any given interpreter, it is possible to
compile a piece of code once in an interpreter, clone that interpreter one or more times,
and run all the resulting interpreters in distinct threads.

On the Windows platform, this feature is used to emulate fork() at the interpreter level.
See perlfork for details about that.

This feature is still in evolution. It is eventually meant to be used to selectively
clone a subroutine and data reachable from that subroutine in a separate interpreter and
run the cloned subroutine in a separate thread. Since there is no shared data between the
interpreters, little or no locking will be needed (unless parts of the symbol table are
explicitly shared). This is obviously intended to be an easy-to-use replacement for the
existing threads support.

Support for cloning interpreters and interpreter concurrency can be enabled using the
-Dusethreads Configure option (see win32/Makefile for how to enable it on Windows.) The
resulting perl executable will be functionally identical to one that was built with
-Dmultiplicity, but the perl_clone() API call will only be available in the former.

-Dusethreads enables the cpp macro USE_ITHREADS by default, which in turn enables Perl
source code changes that provide a clear separation between the op tree and the data it
operates with. The former is immutable, and can therefore be shared between an
interpreter and all of its clones, while the latter is considered local to each
interpreter, and is therefore copied for each clone.

Note that building Perl with the -Dusemultiplicity Configure option is adequate if you
wish to run multiple independent interpreters concurrently in different threads.
-Dusethreads only provides the additional functionality of the perl_clone() API call and
other support for running cloned interpreters concurrently.

NOTE: This is an experimental feature. Implementation details are
subject to change.

Lexically scoped warning categories
You can now control the granularity of warnings emitted by perl at a finer level using the
"use warnings" pragma. warnings and perllexwarn have copious documentation on this
feature.

Unicode and UTF-8 support
Perl now uses UTF-8 as its internal representation for character strings. The "utf8" and
"bytes" pragmas are used to control this support in the current lexical scope. See
perlunicode, utf8 and bytes for more information.

This feature is expected to evolve quickly to support some form of I/O disciplines that
can be used to specify the kind of input and output data (bytes or characters). Until
that happens, additional modules from CPAN will be needed to complete the toolkit for
dealing with Unicode.

NOTE: This should be considered an experimental feature. Implementation
details are subject to change.

Support for interpolating named characters
The new "\N" escape interpolates named characters within strings. For example, "Hi!
\N{WHITE SMILING FACE}" evaluates to a string with a Unicode smiley face at the end.

"our" declarations
An "our" declaration introduces a value that can be best understood as a lexically scoped
symbolic alias to a global variable in the package that was current where the variable was
declared. This is mostly useful as an alternative to the "vars" pragma, but also provides
the opportunity to introduce typing and other attributes for such variables. See "our" in
perlfunc.

Support for strings represented as a vector of ordinals
Literals of the form "v1.2.3.4" are now parsed as a string composed of characters with the
specified ordinals. This is an alternative, more readable way to construct (possibly
Unicode) strings instead of interpolating characters, as in "\x{1}\x{2}\x{3}\x{4}". The
leading "v" may be omitted if there are more than two ordinals, so 1.2.3 is parsed the
same as "v1.2.3".

Strings written in this form are also useful to represent version "numbers". It is easy
to compare such version "numbers" (which are really just plain strings) using any of the
usual string comparison operators "eq", "ne", "lt", "gt", etc., or perform bitwise string
operations on them using "|", "&", etc.

In conjunction with the new $^V magic variable (which contains the perl version as a
string), such literals can be used as a readable way to check if you're running a
particular version of Perl:

# this will parse in older versions of Perl also
if ($^V and $^V gt v5.6.0) {
# new features supported
}

"require" and "use" also have some special magic to support such literals. They will be
interpreted as a version rather than as a module name:

require v5.6.0; # croak if $^V lt v5.6.0
use v5.6.0; # same, but croaks at compile-time

Alternatively, the "v" may be omitted if there is more than one dot:

require 5.6.0;
use 5.6.0;

Also, "sprintf" and "printf" support the Perl-specific format flag %v to print ordinals of
characters in arbitrary strings:

printf "v%vd", $^V; # prints current version, such as "v5.5.650"
printf "%*vX", ":", $addr; # formats IPv6 address
printf "%*vb", " ", $bits; # displays bitstring

See "Scalar value constructors" in perldata for additional information.

Improved Perl version numbering system
Beginning with Perl version 5.6.0, the version number convention has been changed to a
"dotted integer" scheme that is more commonly found in open source projects.

Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc. The next
development series following v5.6.0 will be numbered v5.7.x, beginning with v5.7.0, and
the next major production release following v5.6.0 will be v5.8.0.

The English module now sets $PERL_VERSION to $^V (a string value) rather than $] (a
numeric value). (This is a potential incompatibility. Send us a report via perlbug if
you are affected by this.)

The v1.2.3 syntax is also now legal in Perl. See "Support for strings represented as a
vector of ordinals" for more on that.

To cope with the new versioning system's use of at least three significant digits for each
version component, the method used for incrementing the subversion number has also changed
slightly. We assume that versions older than v5.6.0 have been incrementing the subversion
component in multiples of 10. Versions after v5.6.0 will increment them by 1. Thus,
using the new notation, 5.005_03 is the "same" as v5.5.30, and the first maintenance
version following v5.6.0 will be v5.6.1 (which should be read as being equivalent to a
floating point value of 5.006_001 in the older format, stored in $]).

New syntax for declaring subroutine attributes
Formerly, if you wanted to mark a subroutine as being a method call or as requiring an
automatic lock() when it is entered, you had to declare that with a "use attrs" pragma in
the body of the subroutine. That can now be accomplished with declaration syntax, like
this:

sub mymethod : locked method;
...
sub mymethod : locked method {
...
}

sub othermethod :locked :method;
...
sub othermethod :locked :method {
...
}

(Note how only the first ":" is mandatory, and whitespace surrounding the ":" is
optional.)

AutoSplit.pm and SelfLoader.pm have been updated to keep the attributes with the stubs
they provide. See attributes.

File and directory handles can be autovivified
Similar to how constructs such as "$x->[0]" autovivify a reference, handle constructors
(open(), opendir(), pipe(), socketpair(), sysopen(), socket(), and accept()) now
autovivify a file or directory handle if the handle passed to them is an uninitialized
scalar variable. This allows the constructs such as "open(my $fh, ...)" and "open(local
$fh,...)" to be used to create filehandles that will conveniently be closed automatically
when the scope ends, provided there are no other references to them. This largely
eliminates the need for typeglobs when opening filehandles that must be passed around, as
in the following example:

sub myopen {
open my $fh, "@_"
or die "Can't open '@_': $!";
return $fh;
}

{
my $f = myopen("</etc/motd");
print <$f>;
# $f implicitly closed here
}

open() with more than two arguments
If open() is passed three arguments instead of two, the second argument is used as the
mode and the third argument is taken to be the file name. This is primarily useful for
protecting against unintended magic behavior of the traditional two-argument form. See
"open" in perlfunc.

64-bit support
Any platform that has 64-bit integers either

(1) natively as longs or ints
(2) via special compiler flags
(3) using long long or int64_t

is able to use "quads" (64-bit integers) as follows:

· constants (decimal, hexadecimal, octal, binary) in the code

· arguments to oct() and hex()

· arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)

· printed as such

· pack() and unpack() "q" and "Q" formats

· in basic arithmetics: + - * / % (NOTE: operating close to the limits of the integer
values may produce surprising results)

· in bit arithmetics: & | ^ ~ << >> (NOTE: these used to be forced to be 32 bits wide
but now operate on the full native width.)

· vec()

Note that unless you have the case (a) you will have to configure and compile Perl using
the -Duse64bitint Configure flag.

NOTE: The Configure flags -Duselonglong and -Duse64bits have been
deprecated. Use -Duse64bitint instead.

There are actually two modes of 64-bitness: the first one is achieved using Configure
-Duse64bitint and the second one using Configure -Duse64bitall. The difference is that
the first one is minimal and the second one maximal. The first works in more places than
the second.

The "use64bitint" does only as much as is required to get 64-bit integers into Perl (this
may mean, for example, using "long longs") while your memory may still be limited to 2
gigabytes (because your pointers could still be 32-bit). Note that the name "64bitint"
does not imply that your C compiler will be using 64-bit "int"s (it might, but it doesn't
have to): the "use64bitint" means that you will be able to have 64 bits wide scalar
values.

The "use64bitall" goes all the way by attempting to switch also integers (if it can),
longs (and pointers) to being 64-bit. This may create an even more binary incompatible
Perl than -Duse64bitint: the resulting executable may not run at all in a 32-bit box, or
you may have to reboot/reconfigure/rebuild your operating system to be 64-bit aware.

Natively 64-bit systems like Alpha and Cray need neither -Duse64bitint nor -Duse64bitall.

Last but not least: note that due to Perl's habit of always using floating point numbers,
the quads are still not true integers. When quads overflow their limits
(0...18_446_744_073_709_551_615 unsigned,
-9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they are silently promoted
to floating point numbers, after which they will start losing precision (in their lower
digits).

NOTE: 64-bit support is still experimental on most platforms.
Existing support only covers the LP64 data model. In particular, the
LLP64 data model is not yet supported. 64-bit libraries and system
APIs on many platforms have not stabilized--your mileage may vary.

Large file support
If you have filesystems that support "large files" (files larger than 2 gigabytes), you
may now also be able to create and access them from Perl.

NOTE: The default action is to enable large file support, if
available on the platform.

If the large file support is on, and you have a Fcntl constant O_LARGEFILE, the
O_LARGEFILE is automatically added to the flags of sysopen().

Beware that unless your filesystem also supports "sparse files" seeking to umpteen
petabytes may be inadvisable.

Note that in addition to requiring a proper file system to do large files you may also
need to adjust your per-process (or your per-system, or per-process-group, or per-user-
group) maximum filesize limits before running Perl scripts that try to handle large files,
especially if you intend to write such files.

Finally, in addition to your process/process group maximum filesize limits, you may have
quota limits on your filesystems that stop you (your user id or your user group id) from
using large files.

Adjusting your process/user/group/file system/operating system limits is outside the scope
of Perl core language. For process limits, you may try increasing the limits using your
shell's limits/limit/ulimit command before running Perl. The BSD::Resource extension (not
included with the standard Perl distribution) may also be of use, it offers the
getrlimit/setrlimit interface that can be used to adjust process resource usage limits,
including the maximum filesize limit.

Long doubles
In some systems you may be able to use long doubles to enhance the range and precision of
your double precision floating point numbers (that is, Perl's numbers). Use Configure
-Duselongdouble to enable this support (if it is available).

"more bits"
You can "Configure -Dusemorebits" to turn on both the 64-bit support and the long double
support.

Enhanced support for sort() subroutines
Perl subroutines with a prototype of "($$)", and XSUBs in general, can now be used as sort
subroutines. In either case, the two elements to be compared are passed as normal
parameters in @_. See "sort" in perlfunc.

For unprototyped sort subroutines, the historical behavior of passing the elements to be
compared as the global variables $a and $b remains unchanged.

"sort $coderef @foo" allowed
sort() did not accept a subroutine reference as the comparison function in earlier
versions. This is now permitted.

File globbing implemented internally
Perl now uses the File::Glob implementation of the glob() operator automatically. This
avoids using an external csh process and the problems associated with it.

NOTE: This is currently an experimental feature. Interfaces and
implementation are subject to change.

Support for CHECK blocks
In addition to "BEGIN", "INIT", "END", "DESTROY" and "AUTOLOAD", subroutines named "CHECK"
are now special. These are queued up during compilation and behave similar to END blocks,
except they are called at the end of compilation rather than at the end of execution.
They cannot be called directly.

POSIX character class syntax [: :] supported
For example to match alphabetic characters use /[[:alpha:]]/. See perlre for details.

Better pseudo-random number generator
In 5.005_0x and earlier, perl's rand() function used the C library rand(3) function. As
of 5.005_52, Configure tests for drand48(), random(), and rand() (in that order) and picks
the first one it finds.

These changes should result in better random numbers from rand().

Improved "qw//" operator
The "qw//" operator is now evaluated at compile time into a true list instead of being
replaced with a run time call to "split()". This removes the confusing misbehaviour of
"qw//" in scalar context, which had inherited that behaviour from split().

Thus:

$foo = ($bar) = qw(a b c); print "$foo|$bar\n";

now correctly prints "3|a", instead of "2|a".

Better worst-case behavior of hashes
Small changes in the hashing algorithm have been implemented in order to improve the
distribution of lower order bits in the hashed value. This is expected to yield better
performance on keys that are repeated sequences.

pack() format 'Z' supported
The new format type 'Z' is useful for packing and unpacking null-terminated strings. See
"pack" in perlfunc.

pack() format modifier '!' supported
The new format type modifier '!' is useful for packing and unpacking native shorts, ints,
and longs. See "pack" in perlfunc.

pack() and unpack() support counted strings
The template character '/' can be used to specify a counted string type to be packed or
unpacked. See "pack" in perlfunc.

Comments in pack() templates
The '#' character in a template introduces a comment up to end of the line. This
facilitates documentation of pack() templates.

Weak references
In previous versions of Perl, you couldn't cache objects so as to allow them to be deleted
if the last reference from outside the cache is deleted. The reference in the cache would
hold a reference count on the object and the objects would never be destroyed.

Another familiar problem is with circular references. When an object references itself,
its reference count would never go down to zero, and it would not get destroyed until the
program is about to exit.

Weak references solve this by allowing you to "weaken" any reference, that is, make it not
count towards the reference count. When the last non-weak reference to an object is
deleted, the object is destroyed and all the weak references to the object are
automatically undef-ed.

To use this feature, you need the Devel::WeakRef package from CPAN, which contains
additional documentation.

NOTE: This is an experimental feature. Details are subject to change.

Binary numbers supported
Binary numbers are now supported as literals, in s?printf formats, and "oct()":

$answer = 0b101010;
printf "The answer is: %b\n", oct("0b101010");

Lvalue subroutines
Subroutines can now return modifiable lvalues. See "Lvalue subroutines" in perlsub.

NOTE: This is an experimental feature. Details are subject to change.

Some arrows may be omitted in calls through references
Perl now allows the arrow to be omitted in many constructs involving subroutine calls
through references. For example, "$foo[10]->('foo')" may now be written
"$foo[10]('foo')". This is rather similar to how the arrow may be omitted from
"$foo[10]->{'foo'}". Note however, that the arrow is still required for
"foo(10)->('bar')".

Boolean assignment operators are legal lvalues
Constructs such as "($a ||= 2) += 1" are now allowed.

exists() is supported on subroutine names
The exists() builtin now works on subroutine names. A subroutine is considered to exist
if it has been declared (even if implicitly). See "exists" in perlfunc for examples.

exists() and delete() are supported on array elements
The exists() and delete() builtins now work on simple arrays as well. The behavior is
similar to that on hash elements.

exists() can be used to check whether an array element has been initialized. This avoids
autovivifying array elements that don't exist. If the array is tied, the EXISTS() method
in the corresponding tied package will be invoked.

delete() may be used to remove an element from the array and return it. The array element
at that position returns to its uninitialized state, so that testing for the same element
with exists() will return false. If the element happens to be the one at the end, the
size of the array also shrinks up to the highest element that tests true for exists(), or
0 if none such is found. If the array is tied, the DELETE() method in the corresponding
tied package will be invoked.

See "exists" in perlfunc and "delete" in perlfunc for examples.

Pseudo-hashes work better
Dereferencing some types of reference values in a pseudo-hash, such as "$ph->{foo}[1]",
was accidentally disallowed. This has been corrected.

When applied to a pseudo-hash element, exists() now reports whether the specified value
exists, not merely if the key is valid.

delete() now works on pseudo-hashes. When given a pseudo-hash element or slice it deletes
the values corresponding to the keys (but not the keys themselves). See "Pseudo-hashes:
Using an array as a hash" in perlref.

Pseudo-hash slices with constant keys are now optimized to array lookups at compile-time.

List assignments to pseudo-hash slices are now supported.

The "fields" pragma now provides ways to create pseudo-hashes, via fields::new() and
fields::phash(). See fields.

NOTE: The pseudo-hash data type continues to be experimental.
Limiting oneself to the interface elements provided by the
fields pragma will provide protection from any future changes.

Automatic flushing of output buffers
fork(), exec(), system(), qx//, and pipe open()s now flush buffers of all files opened for
output when the operation was attempted. This mostly eliminates confusing buffering
mishaps suffered by users unaware of how Perl internally handles I/O.

This is not supported on some platforms like Solaris where a suitably correct
implementation of fflush(NULL) isn't available.

Better diagnostics on meaningless filehandle operations
Constructs such as "open(<FH>)" and "close(<FH>)" are compile time errors. Attempting to
read from filehandles that were opened only for writing will now produce warnings (just as
writing to read-only filehandles does).

Where possible, buffered data discarded from duped input filehandle
"open(NEW, "<&OLD")" now attempts to discard any data that was previously read and
buffered in "OLD" before duping the handle. On platforms where doing this is allowed, the
next read operation on "NEW" will return the same data as the corresponding operation on
"OLD". Formerly, it would have returned the data from the start of the following disk
block instead.

eof() has the same old magic as <>
"eof()" would return true if no attempt to read from "<>" had yet been made. "eof()" has
been changed to have a little magic of its own, it now opens the "<>" files.

binmode() can be used to set :crlf and :raw modes
binmode() now accepts a second argument that specifies a discipline for the handle in
question. The two pseudo-disciplines ":raw" and ":crlf" are currently supported on DOS-
derivative platforms. See "binmode" in perlfunc and open.

"-T" filetest recognizes UTF-8 encoded files as "text"
The algorithm used for the "-T" filetest has been enhanced to correctly identify UTF-8
content as "text".

system(), backticks and pipe open now reflect exec() failure
On Unix and similar platforms, system(), qx() and open(FOO, "cmd |") etc., are implemented
via fork() and exec(). When the underlying exec() fails, earlier versions did not report
the error properly, since the exec() happened to be in a different process.

The child process now communicates with the parent about the error in launching the
external command, which allows these constructs to return with their usual error value and
set $!.

Improved diagnostics
Line numbers are no longer suppressed (under most likely circumstances) during the global
destruction phase.

Diagnostics emitted from code running in threads other than the main thread are now
accompanied by the thread ID.

Embedded null characters in diagnostics now actually show up. They used to truncate the
message in prior versions.

$foo::a and $foo::b are now exempt from "possible typo" warnings only if sort() is
encountered in package "foo".

Unrecognized alphabetic escapes encountered when parsing quote constructs now generate a
warning, since they may take on new semantics in later versions of Perl.

Many diagnostics now report the internal operation in which the warning was provoked, like
so:

Use of uninitialized value in concatenation (.) at (eval 1) line 1.
Use of uninitialized value in print at (eval 1) line 1.

Diagnostics that occur within eval may also report the file and line number where the
eval is located, in addition to the eval sequence number and the line number within the
evaluated text itself. For example:

Not enough arguments for scalar at (eval 4)[newlib/perl5db.pl:1411] line 2, at EOF

Diagnostics follow STDERR
Diagnostic output now goes to whichever file the "STDERR" handle is pointing at, instead
of always going to the underlying C runtime library's "stderr".

More consistent close-on-exec behavior
On systems that support a close-on-exec flag on filehandles, the flag is now set for any
handles created by pipe(), socketpair(), socket(), and accept(), if that is warranted by
the value of $^F that may be in effect. Earlier versions neglected to set the flag for
handles created with these operators. See "pipe" in perlfunc, "socketpair" in perlfunc,
"socket" in perlfunc, "accept" in perlfunc, and "$^F" in perlvar.

syswrite() ease-of-use
The length argument of "syswrite()" has become optional.

Better syntax checks on parenthesized unary operators
Expressions such as:

print defined(&foo,&bar,&baz);
print uc("foo","bar","baz");
undef($foo,&bar);

used to be accidentally allowed in earlier versions, and produced unpredictable behaviour.
Some produced ancillary warnings when used in this way; others silently did the wrong
thing.

The parenthesized forms of most unary operators that expect a single argument now ensure
that they are not called with more than one argument, making the cases shown above syntax
errors. The usual behaviour of:

print defined &foo, &bar, &baz;
print uc "foo", "bar", "baz";
undef $foo, &bar;

remains unchanged. See perlop.

Bit operators support full native integer width
The bit operators (& | ^ ~ << >>) now operate on the full native integral width (the exact
size of which is available in $Config{ivsize}). For example, if your platform is either
natively 64-bit or if Perl has been configured to use 64-bit integers, these operations
apply to 8 bytes (as opposed to 4 bytes on 32-bit platforms). For portability, be sure to
mask off the excess bits in the result of unary "~", e.g., "~$x & 0xffffffff".

Improved security features
More potentially unsafe operations taint their results for improved security.

The "passwd" and "shell" fields returned by the getpwent(), getpwnam(), and getpwuid() are
now tainted, because the user can affect their own encrypted password and login shell.

The variable modified by shmread(), and messages returned by msgrcv() (and its object-
oriented interface IPC::SysV::Msg::rcv) are also tainted, because other untrusted
processes can modify messages and shared memory segments for their own nefarious purposes.

More functional bareword prototype (*)
Bareword prototypes have been rationalized to enable them to be used to override builtins
that accept barewords and interpret them in a special way, such as "require" or "do".

Arguments prototyped as "*" will now be visible within the subroutine as either a simple
scalar or as a reference to a typeglob. See "Prototypes" in perlsub.

"require" and "do" may be overridden
"require" and "do 'file'" operations may be overridden locally by importing subroutines of
the same name into the current package (or globally by importing them into the
CORE::GLOBAL:: namespace). Overriding "require" will also affect "use", provided the
override is visible at compile-time. See "Overriding Built-in Functions" in perlsub.

$^X variables may now have names longer than one character
Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax error. Now variable
names that begin with a control character may be arbitrarily long. However, for
compatibility reasons, these variables must be written with explicit braces, as "${^XY}"
for example. "${^XYZ}" is synonymous with ${"\cXYZ"}. Variable names with more than one
control character, such as "${^XY^Z}", are illegal.

The old syntax has not changed. As before, `^X' may be either a literal control-X
character or the two-character sequence `caret' plus `X'. When braces are omitted, the
variable name stops after the control character. Thus "$^XYZ" continues to be synonymous
with "$^X . "YZ"" as before.

As before, lexical variables may not have names beginning with control characters. As
before, variables whose names begin with a control character are always forced to be in
package `main'. All such variables are reserved for future extensions, except those that
begin with "^_", which may be used by user programs and are guaranteed not to acquire
special meaning in any future version of Perl.

New variable $^C reflects "-c" switch
$^C has a boolean value that reflects whether perl is being run in compile-only mode (i.e.
via the "-c" switch). Since BEGIN blocks are executed under such conditions, this
variable enables perl code to determine whether actions that make sense only during normal
running are warranted. See perlvar.

New variable $^V contains Perl version as a string
$^V contains the Perl version number as a string composed of characters whose ordinals
match the version numbers, i.e. v5.6.0. This may be used in string comparisons.

See "Support for strings represented as a vector of ordinals" for an example.

Optional Y2K warnings
If Perl is built with the cpp macro "PERL_Y2KWARN" defined, it emits optional warnings
when concatenating the number 19 with another number.

This behavior must be specifically enabled when running Configure. See INSTALL and
README.Y2K.

Arrays now always interpolate into double-quoted strings
In double-quoted strings, arrays now interpolate, no matter what. The behavior in earlier
versions of perl 5 was that arrays would interpolate into strings if the array had been
mentioned before the string was compiled, and otherwise Perl would raise a fatal compile-
time error. In versions 5.000 through 5.003, the error was

Literal @example now requires backslash

In versions 5.004_01 through 5.6.0, the error was

In string, @example now must be written as \@example

The idea here was to get people into the habit of writing "fred\@example.com" when they
wanted a literal "@" sign, just as they have always written "Give me back my \$5" when
they wanted a literal "$" sign.

Starting with 5.6.1, when Perl now sees an "@" sign in a double-quoted string, it always
attempts to interpolate an array, regardless of whether or not the array has been used or
declared already. The fatal error has been downgraded to an optional warning:

Possible unintended interpolation of @example in string

This warns you that "fred@example.com" is going to turn into "fred.com" if you don't
backslash the "@". See http://perl.plover.com/at-error.html for more details about the
history here.

@- and @+ provide starting/ending offsets of regex submatches
The new magic variables @- and @+ provide the starting and ending offsets, respectively,
of $&, $1, $2, etc. See perlvar for details.

Modules and Pragmata

Modules
attributes
While used internally by Perl as a pragma, this module also provides a way to fetch
subroutine and variable attributes. See attributes.

B The Perl Compiler suite has been extensively reworked for this release. More of the
standard Perl test suite passes when run under the Compiler, but there is still a
significant way to go to achieve production quality compiled executables.

NOTE: The Compiler suite remains highly experimental. The
generated code may not be correct, even when it manages to execute
without errors.

Benchmark
Overall, Benchmark results exhibit lower average error and better timing accuracy.

You can now run tests for n seconds instead of guessing the right number of tests to
run: e.g., timethese(-5, ...) will run each code for at least 5 CPU seconds. Zero as
the "number of repetitions" means "for at least 3 CPU seconds". The output format has
also changed. For example:

use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})

will now output something like this:

Benchmark: running a, b, each for at least 5 CPU seconds...
a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)

New features: "each for at least N CPU seconds...", "wallclock secs", and the "@
operations/CPU second (n=operations)".

timethese() now returns a reference to a hash of Benchmark objects containing the test
results, keyed on the names of the tests.

timethis() now returns the iterations field in the Benchmark result object instead of
0.

timethese(), timethis(), and the new cmpthese() (see below) can also take a format
specifier of 'none' to suppress output.

A new function countit() is just like timeit() except that it takes a TIME instead of
a COUNT.

A new function cmpthese() prints a chart comparing the results of each test returned
from a timethese() call. For each possible pair of tests, the percentage speed
difference (iters/sec or seconds/iter) is shown.

For other details, see Benchmark.

ByteLoader
The ByteLoader is a dedicated extension to generate and run Perl bytecode. See
ByteLoader.

constant
References can now be used.

The new version also allows a leading underscore in constant names, but disallows a
double leading underscore (as in "__LINE__"). Some other names are disallowed or
warned against, including BEGIN, END, etc. Some names which were forced into main::
used to fail silently in some cases; now they're fatal (outside of main::) and an
optional warning (inside of main::). The ability to detect whether a constant had
been set with a given name has been added.

See constant.

charnames
This pragma implements the "\N" string escape. See charnames.

Data::Dumper
A "Maxdepth" setting can be specified to avoid venturing too deeply into deep data
structures. See Data::Dumper.

The XSUB implementation of Dump() is now automatically called if the "Useqq" setting
is not in use.

Dumping "qr//" objects works correctly.

DB "DB" is an experimental module that exposes a clean abstraction to Perl's debugging
API.

DB_File
DB_File can now be built with Berkeley DB versions 1, 2 or 3. See
"ext/DB_File/Changes".

Devel::DProf
Devel::DProf, a Perl source code profiler has been added. See Devel::DProf and
dprofpp.

Devel::Peek
The Devel::Peek module provides access to the internal representation of Perl
variables and data. It is a data debugging tool for the XS programmer.

Dumpvalue
The Dumpvalue module provides screen dumps of Perl data.

DynaLoader
DynaLoader now supports a dl_unload_file() function on platforms that support
unloading shared objects using dlclose().

Perl can also optionally arrange to unload all extension shared objects loaded by
Perl. To enable this, build Perl with the Configure option
"-Accflags=-DDL_UNLOAD_ALL_AT_EXIT". (This maybe useful if you are using Apache with
mod_perl.)

English
$PERL_VERSION now stands for $^V (a string value) rather than for $] (a numeric
value).

Env Env now supports accessing environment variables like PATH as array variables.

Fcntl
More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for large file (more
than 4GB) access (NOTE: the O_LARGEFILE is automatically added to sysopen() flags if
large file support has been configured, as is the default), Free/Net/OpenBSD locking
behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the combined mask of
O_RDONLY, O_WRONLY, and O_RDWR. The seek()/sysseek() constants SEEK_SET, SEEK_CUR,
and SEEK_END are available via the ":seek" tag. The chmod()/stat() S_IF* constants
and S_IS* functions are available via the ":mode" tag.

File::Compare
A compare_text() function has been added, which allows custom comparison functions.
See File::Compare.

File::Find
File::Find now works correctly when the wanted() function is either autoloaded or is a
symbolic reference.

A bug that caused File::Find to lose track of the working directory when pruning top-
level directories has been fixed.

File::Find now also supports several other options to control its behavior. It can
follow symbolic links if the "follow" option is specified. Enabling the "no_chdir"
option will make File::Find skip changing the current directory when walking
directories. The "untaint" flag can be useful when running with taint checks enabled.

See File::Find.

File::Glob
This extension implements BSD-style file globbing. By default, it will also be used
for the internal implementation of the glob() operator. See File::Glob.

File::Spec
New methods have been added to the File::Spec module: devnull() returns the name of
the null device (/dev/null on Unix) and tmpdir() the name of the temp directory
(normally /tmp on Unix). There are now also methods to convert between absolute and
relative filenames: abs2rel() and rel2abs(). For compatibility with operating systems
that specify volume names in file paths, the splitpath(), splitdir(), and catdir()
methods have been added.

File::Spec::Functions
The new File::Spec::Functions modules provides a function interface to the File::Spec
module. Allows shorthand

$fullname = catfile($dir1, $dir2, $file);

instead of

$fullname = File::Spec->catfile($dir1, $dir2, $file);

Getopt::Long
Getopt::Long licensing has changed to allow the Perl Artistic License as well as the
GPL. It used to be GPL only, which got in the way of non-GPL applications that wanted
to use Getopt::Long.

Getopt::Long encourages the use of Pod::Usage to produce help messages. For example:

use Getopt::Long;
use Pod::Usage;
my $man = 0;
my $help = 0;
GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
pod2usage(1) if $help;
pod2usage(-exitstatus => 0, -verbose => 2) if $man;

__END__

=head1 NAME

sample - Using Getopt::Long and Pod::Usage

=head1 SYNOPSIS

sample [options] [file ...]

Options:
-help brief help message
-man full documentation

=head1 OPTIONS

=over 8

=item B<-help>

Print a brief help message and exits.

=item B<-man>

Prints the manual page and exits.

=back

=head1 DESCRIPTION

B<This program> will read the given input file(s) and do something
useful with the contents thereof.

=cut

See Pod::Usage for details.

A bug that prevented the non-option call-back <> from being specified as the first
argument has been fixed.

To specify the characters < and > as option starters, use ><. Note, however, that
changing option starters is strongly deprecated.

IO write() and syswrite() will now accept a single-argument form of the call, for
consistency with Perl's syswrite().

You can now create a TCP-based IO::Socket::INET without forcing a connect attempt.
This allows you to configure its options (like making it non-blocking) and then call
connect() manually.

A bug that prevented the IO::Socket::protocol() accessor from ever returning the
correct value has been corrected.

IO::Socket::connect now uses non-blocking IO instead of alarm() to do connect
timeouts.

IO::Socket::accept now uses select() instead of alarm() for doing timeouts.

IO::Socket::INET->new now sets $! correctly on failure. $@ is still set for backwards
compatibility.

JPL Java Perl Lingo is now distributed with Perl. See jpl/README for more information.

lib "use lib" now weeds out any trailing duplicate entries. "no lib" removes all named
entries.

Math::BigInt
The bitwise operations "<<", ">>", "&", "|", and "~" are now supported on bigints.

Math::Complex
The accessor methods Re, Im, arg, abs, rho, and theta can now also act as mutators
(accessor $z->Re(), mutator $z->Re(3)).

The class method "display_format" and the corresponding object method
"display_format", in addition to accepting just one argument, now can also accept a
parameter hash. Recognized keys of a parameter hash are "style", which corresponds to
the old one parameter case, and two new parameters: "format", which is a
printf()-style format string (defaults usually to "%.15g", you can revert to the
default by setting the format string to "undef") used for both parts of a complex
number, and "polar_pretty_print" (defaults to true), which controls whether an attempt
is made to try to recognize small multiples and rationals of pi (2pi, pi/2) at the
argument (angle) of a polar complex number.

The potentially disruptive change is that in list context both methods now return the
parameter hash, instead of only the value of the "style" parameter.

Math::Trig
A little bit of radial trigonometry (cylindrical and spherical), radial coordinate
conversions, and the great circle distance were added.

Pod::Parser, Pod::InputObjects
Pod::Parser is a base class for parsing and selecting sections of pod documentation
from an input stream. This module takes care of identifying pod paragraphs and
commands in the input and hands off the parsed paragraphs and commands to user-defined
methods which are free to interpret or translate them as they see fit.

Pod::InputObjects defines some input objects needed by Pod::Parser, and for advanced
users of Pod::Parser that need more about a command besides its name and text.

As of release 5.6.0 of Perl, Pod::Parser is now the officially sanctioned "base parser
code" recommended for use by all pod2xxx translators. Pod::Text (pod2text) and
Pod::Man (pod2man) have already been converted to use Pod::Parser and efforts to
convert Pod::HTML (pod2html) are already underway. For any questions or comments
about pod parsing and translating issues and utilities, please use the
pod-people@perl.org mailing list.

For further information, please see Pod::Parser and Pod::InputObjects.

Pod::Checker, podchecker
This utility checks pod files for correct syntax, according to perlpod. Obvious
errors are flagged as such, while warnings are printed for mistakes that can be
handled gracefully. The checklist is not complete yet. See Pod::Checker.

Pod::ParseUtils, Pod::Find
These modules provide a set of gizmos that are useful mainly for pod translators.
Pod::Find traverses directory structures and returns found pod files, along with their
canonical names (like "File::Spec::Unix"). Pod::ParseUtils contains Pod::List (useful
for storing pod list information), Pod::Hyperlink (for parsing the contents of "L<>"
sequences) and Pod::Cache (for caching information about pod files, e.g., link nodes).

Pod::Select, podselect
Pod::Select is a subclass of Pod::Parser which provides a function named "podselect()"
to filter out user-specified sections of raw pod documentation from an input stream.
podselect is a script that provides access to Pod::Select from other scripts to be
used as a filter. See Pod::Select.

Pod::Usage, pod2usage
Pod::Usage provides the function "pod2usage()" to print usage messages for a Perl
script based on its embedded pod documentation. The pod2usage() function is generally
useful to all script authors since it lets them write and maintain a single source
(the pods) for documentation, thus removing the need to create and maintain redundant
usage message text consisting of information already in the pods.

There is also a pod2usage script which can be used from other kinds of scripts to
print usage messages from pods (even for non-Perl scripts with pods embedded in
comments).

For details and examples, please see Pod::Usage.

Pod::Text and Pod::Man
Pod::Text has been rewritten to use Pod::Parser. While pod2text() is still available
for backwards compatibility, the module now has a new preferred interface. See
Pod::Text for the details. The new Pod::Text module is easily subclassed for tweaks
to the output, and two such subclasses (Pod::Text::Termcap for man-page-style bold and
underlining using termcap information, and Pod::Text::Color for markup with ANSI color
sequences) are now standard.

pod2man has been turned into a module, Pod::Man, which also uses Pod::Parser. In the
process, several outstanding bugs related to quotes in section headers, quoting of
code escapes, and nested lists have been fixed. pod2man is now a wrapper script
around this module.

SDBM_File
An EXISTS method has been added to this module (and sdbm_exists() has been added to
the underlying sdbm library), so one can now call exists on an SDBM_File tied hash and
get the correct result, rather than a runtime error.

A bug that may have caused data loss when more than one disk block happens to be read
from the database in a single FETCH() has been fixed.

Sys::Syslog
Sys::Syslog now uses XSUBs to access facilities from syslog.h so it no longer requires
syslog.ph to exist.

Sys::Hostname
Sys::Hostname now uses XSUBs to call the C library's gethostname() or uname() if they
exist.

Term::ANSIColor
Term::ANSIColor is a very simple module to provide easy and readable access to the
ANSI color and highlighting escape sequences, supported by most ANSI terminal
emulators. It is now included standard.

Time::Local
The timelocal() and timegm() functions used to silently return bogus results when the
date fell outside the machine's integer range. They now consistently croak() if the
date falls in an unsupported range.

Win32
The error return value in list context has been changed for all functions that return
a list of values. Previously these functions returned a list with a single element
"undef" if an error occurred. Now these functions return the empty list in these
situations. This applies to the following functions:

Win32::FsType
Win32::GetOSVersion

The remaining functions are unchanged and continue to return "undef" on error even in
list context.

The Win32::SetLastError(ERROR) function has been added as a complement to the
Win32::GetLastError() function.

The new Win32::GetFullPathName(FILENAME) returns the full absolute pathname for
FILENAME in scalar context. In list context it returns a two-element list containing
the fully qualified directory name and the filename. See Win32.

XSLoader
The XSLoader extension is a simpler alternative to DynaLoader. See XSLoader.

DBM Filters
A new feature called "DBM Filters" has been added to all the DBM modules--DB_File,
GDBM_File, NDBM_File, ODBM_File, and SDBM_File. DBM Filters add four new methods to
each DBM module:

filter_store_key
filter_store_value
filter_fetch_key
filter_fetch_value

These can be used to filter key-value pairs before the pairs are written to the
database or just after they are read from the database. See perldbmfilter for further
information.

Pragmata
"use attrs" is now obsolete, and is only provided for backward-compatibility. It's been
replaced by the "sub : attributes" syntax. See "Subroutine Attributes" in perlsub and
attributes.

Lexical warnings pragma, "use warnings;", to control optional warnings. See perllexwarn.

"use filetest" to control the behaviour of filetests ("-r" "-w" ...). Currently only one
subpragma implemented, "use filetest 'access';", that uses access(2) or equivalent to
check permissions instead of using stat(2) as usual. This matters in filesystems where
there are ACLs (access control lists): the stat(2) might lie, but access(2) knows better.

The "open" pragma can be used to specify default disciplines for handle constructors (e.g.
open()) and for qx//. The two pseudo-disciplines ":raw" and ":crlf" are currently
supported on DOS-derivative platforms (i.e. where binmode is not a no-op). See also
"binmode() can be used to set :crlf and :raw modes".

Utility Changes

dprofpp
"dprofpp" is used to display profile data generated using "Devel::DProf". See dprofpp.

find2perl
The "find2perl" utility now uses the enhanced features of the File::Find module. The
-depth and -follow options are supported. Pod documentation is also included in the
script.

h2xs
The "h2xs" tool can now work in conjunction with "C::Scan" (available from CPAN) to
automatically parse real-life header files. The "-M", "-a", "-k", and "-o" options are
new.

perlcc
"perlcc" now supports the C and Bytecode backends. By default, it generates output from
the simple C backend rather than the optimized C backend.

Support for non-Unix platforms has been improved.

perldoc
"perldoc" has been reworked to avoid possible security holes. It will not by default let
itself be run as the superuser, but you may still use the -U switch to try to make it drop
privileges first.

The Perl Debugger
Many bug fixes and enhancements were added to perl5db.pl, the Perl debugger. The help
documentation was rearranged. New commands include "< ?", "> ?", and "{ ?" to list out
current actions, "man docpage" to run your doc viewer on some perl docset, and support for
quoted options. The help information was rearranged, and should be viewable once again if
you're using less as your pager. A serious security hole was plugged--you should
immediately remove all older versions of the Perl debugger as installed in previous
releases, all the way back to perl3, from your system to avoid being bitten by this.

Improved Documentation

Many of the platform-specific README files are now part of the perl installation. See
perl for the complete list.

perlapi.pod
The official list of public Perl API functions.

perlboot.pod
A tutorial for beginners on object-oriented Perl.

perlcompile.pod
An introduction to using the Perl Compiler suite.

perldbmfilter.pod
A howto document on using the DBM filter facility.

perldebug.pod
All material unrelated to running the Perl debugger, plus all low-level guts-like
details that risked crushing the casual user of the debugger, have been relocated from
the old manpage to the next entry below.

perldebguts.pod
This new manpage contains excessively low-level material not related to the Perl
debugger, but slightly related to debugging Perl itself. It also contains some arcane
internal details of how the debugging process works that may only be of interest to
developers of Perl debuggers.

perlfork.pod
Notes on the fork() emulation currently available for the Windows platform.

perlfilter.pod
An introduction to writing Perl source filters.

perlhack.pod
Some guidelines for hacking the Perl source code.

perlintern.pod
A list of internal functions in the Perl source code. (List is currently empty.)

perllexwarn.pod
Introduction and reference information about lexically scoped warning categories.

perlnumber.pod
Detailed information about numbers as they are represented in Perl.

perlopentut.pod
A tutorial on using open() effectively.

perlreftut.pod
A tutorial that introduces the essentials of references.

perltootc.pod
A tutorial on managing class data for object modules.

perltodo.pod
Discussion of the most often wanted features that may someday be supported in Perl.

perlunicode.pod
An introduction to Unicode support features in Perl.

Performance enhancements

Simple sort() using { $a <=> $b } and the like are optimized
Many common sort() operations using a simple inlined block are now optimized for faster
performance.

Optimized assignments to lexical variables
Certain operations in the RHS of assignment statements have been optimized to directly set
the lexical variable on the LHS, eliminating redundant copying overheads.

Faster subroutine calls
Minor changes in how subroutine calls are handled internally provide marginal improvements
in performance.

delete(), each(), values() and hash iteration are faster
The hash values returned by delete(), each(), values() and hashes in a list context are
the actual values in the hash, instead of copies. This results in significantly better
performance, because it eliminates needless copying in most situations.

Installation and Configuration Improvements

-Dusethreads means something different
The -Dusethreads flag now enables the experimental interpreter-based thread support by
default. To get the flavor of experimental threads that was in 5.005 instead, you need to
run Configure with "-Dusethreads -Duse5005threads".

As of v5.6.0, interpreter-threads support is still lacking a way to create new threads
from Perl (i.e., "use Thread;" will not work with interpreter threads). "use Thread;"
continues to be available when you specify the -Duse5005threads option to Configure, bugs
and all.

NOTE: Support for threads continues to be an experimental feature.
Interfaces and implementation are subject to sudden and drastic changes.

New Configure flags
The following new flags may be enabled on the Configure command line by running Configure
with "-Dflag".

usemultiplicity
usethreads useithreads (new interpreter threads: no Perl API yet)
usethreads use5005threads (threads as they were in 5.005)

use64bitint (equal to now deprecated 'use64bits')
use64bitall

uselongdouble
usemorebits
uselargefiles
usesocks (only SOCKS v5 supported)

Threadedness and 64-bitness now more daring
The Configure options enabling the use of threads and the use of 64-bitness are now more
daring in the sense that they no more have an explicit list of operating systems of known
threads/64-bit capabilities. In other words: if your operating system has the necessary
APIs and datatypes, you should be able just to go ahead and use them, for threads by
Configure -Dusethreads, and for 64 bits either explicitly by Configure -Duse64bitint or
implicitly if your system has 64-bit wide datatypes. See also "64-bit support".

Long Doubles
Some platforms have "long doubles", floating point numbers of even larger range than
ordinary "doubles". To enable using long doubles for Perl's scalars, use -Duselongdouble.

-Dusemorebits
You can enable both -Duse64bitint and -Duselongdouble with -Dusemorebits. See also
"64-bit support".

-Duselargefiles
Some platforms support system APIs that are capable of handling large files (typically,
files larger than two gigabytes). Perl will try to use these APIs if you ask for
-Duselargefiles.

See "Large file support" for more information.

installusrbinperl
You can use "Configure -Uinstallusrbinperl" which causes installperl to skip installing
perl also as /usr/bin/perl. This is useful if you prefer not to modify /usr/bin for some
reason or another but harmful because many scripts assume to find Perl in /usr/bin/perl.

SOCKS support
You can use "Configure -Dusesocks" which causes Perl to probe for the SOCKS proxy protocol
library (v5, not v4). For more information on SOCKS, see:

http://www.socks.nec.com/

"-A" flag
You can "post-edit" the Configure variables using the Configure "-A" switch. The editing
happens immediately after the platform specific hints files have been processed but before
the actual configuration process starts. Run "Configure -h" to find out the full "-A"
syntax.

Enhanced Installation Directories
The installation structure has been enriched to improve the support for maintaining
multiple versions of perl, to provide locations for vendor-supplied modules, scripts, and
manpages, and to ease maintenance of locally-added modules, scripts, and manpages. See
the section on Installation Directories in the INSTALL file for complete details. For
most users building and installing from source, the defaults should be fine.

If you previously used "Configure -Dsitelib" or "-Dsitearch" to set special values for
library directories, you might wish to consider using the new "-Dsiteprefix" setting
instead. Also, if you wish to re-use a config.sh file from an earlier version of perl,
you should be sure to check that Configure makes sensible choices for the new directories.
See INSTALL for complete details.

gcc automatically tried if 'cc' does not seem to be working
In many platforms the vendor-supplied 'cc' is too stripped-down to build Perl (basically,
the 'cc' doesn't do ANSI C). If this seems to be the case and the 'cc' does not seem to
be the GNU C compiler 'gcc', an automatic attempt is made to find and use 'gcc' instead.

Platform specific changes

Supported platforms
· The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread extension.

· GNU/Hurd is now supported.

· Rhapsody/Darwin is now supported.

· EPOC is now supported (on Psion 5).

· The cygwin port (formerly cygwin32) has been greatly improved.

DOS
· Perl now works with djgpp 2.02 (and 2.03 alpha).

· Environment variable names are not converted to uppercase any more.

· Incorrect exit codes from backticks have been fixed.

· This port continues to use its own builtin globbing (not File::Glob).

OS390 (OpenEdition MVS)
Support for this EBCDIC platform has not been renewed in this release. There are
difficulties in reconciling Perl's standardization on UTF-8 as its internal representation
for characters with the EBCDIC character set, because the two are incompatible.

It is unclear whether future versions will renew support for this platform, but the
possibility exists.

VMS
Numerous revisions and extensions to configuration, build, testing, and installation
process to accommodate core changes and VMS-specific options.

Expand %ENV-handling code to allow runtime mapping to logical names, CLI symbols, and CRTL
environ array.

Extension of subprocess invocation code to accept filespecs as command "verbs".

Add to Perl command line processing the ability to use default file types and to recognize
Unix-style "2>&1".

Expansion of File::Spec::VMS routines, and integration into ExtUtils::MM_VMS.

Extension of ExtUtils::MM_VMS to handle complex extensions more flexibly.

Barewords at start of Unix-syntax paths may be treated as text rather than only as logical
names.

Optional secure translation of several logical names used internally by Perl.

Miscellaneous bugfixing and porting of new core code to VMS.

Thanks are gladly extended to the many people who have contributed VMS patches, testing,
and ideas.

Win32
Perl can now emulate fork() internally, using multiple interpreters running in different
concurrent threads. This support must be enabled at build time. See perlfork for
detailed information.

When given a pathname that consists only of a drivename, such as "A:", opendir() and
stat() now use the current working directory for the drive rather than the drive root.

The builtin XSUB functions in the Win32:: namespace are documented. See Win32.

$^X now contains the full path name of the running executable.

A Win32::GetLongPathName() function is provided to complement Win32::GetFullPathName() and
Win32::GetShortPathName(). See Win32.

POSIX::uname() is supported.

system(1,...) now returns true process IDs rather than process handles. kill() accepts
any real process id, rather than strictly return values from system(1,...).

For better compatibility with Unix, "kill(0, $pid)" can now be used to test whether a
process exists.

The "Shell" module is supported.

Better support for building Perl under command.com in Windows 95 has been added.

Scripts are read in binary mode by default to allow ByteLoader (and the filter mechanism
in general) to work properly. For compatibility, the DATA filehandle will be set to text
mode if a carriage return is detected at the end of the line containing the __END__ or
__DATA__ token; if not, the DATA filehandle will be left open in binary mode. Earlier
versions always opened the DATA filehandle in text mode.

The glob() operator is implemented via the "File::Glob" extension, which supports glob
syntax of the C shell. This increases the flexibility of the glob() operator, but there
may be compatibility issues for programs that relied on the older globbing syntax. If you
want to preserve compatibility with the older syntax, you might want to run perl with
"-MFile::DosGlob". For details and compatibility information, see File::Glob.

Significant bug fixes

<HANDLE> on empty files
With $/ set to "undef", "slurping" an empty file returns a string of zero length (instead
of "undef", as it used to) the first time the HANDLE is read after $/ is set to "undef".
Further reads yield "undef".

This means that the following will append "foo" to an empty file (it used to do nothing):

perl -0777 -pi -e 's/^/foo/' empty_file

The behaviour of:

perl -pi -e 's/^/foo/' empty_file

is unchanged (it continues to leave the file empty).

"eval '...'" improvements
Line numbers (as reflected by caller() and most diagnostics) within "eval '...'" were
often incorrect where here documents were involved. This has been corrected.

Lexical lookups for variables appearing in "eval '...'" within functions that were
themselves called within an "eval '...'" were searching the wrong place for lexicals. The
lexical search now correctly ends at the subroutine's block boundary.

The use of "return" within "eval {...}" caused $@ not to be reset correctly when no
exception occurred within the eval. This has been fixed.

Parsing of here documents used to be flawed when they appeared as the replacement
expression in "eval 's/.../.../e'". This has been fixed.

All compilation errors are true errors
Some "errors" encountered at compile time were by necessity generated as warnings followed
by eventual termination of the program. This enabled more such errors to be reported in a
single run, rather than causing a hard stop at the first error that was encountered.

The mechanism for reporting such errors has been reimplemented to queue compile-time
errors and report them at the end of the compilation as true errors rather than as
warnings. This fixes cases where error messages leaked through in the form of warnings
when code was compiled at run time using "eval STRING", and also allows such errors to be
reliably trapped using "eval "..."".

Implicitly closed filehandles are safer
Sometimes implicitly closed filehandles (as when they are localized, and Perl
automatically closes them on exiting the scope) could inadvertently set $? or $!. This
has been corrected.

Behavior of list slices is more consistent
When taking a slice of a literal list (as opposed to a slice of an array or hash), Perl
used to return an empty list if the result happened to be composed of all undef values.

The new behavior is to produce an empty list if (and only if) the original list was empty.
Consider the following example:

@a = (1,undef,undef,2)[2,1,2];

The old behavior would have resulted in @a having no elements. The new behavior ensures
it has three undefined elements.

Note in particular that the behavior of slices of the following cases remains unchanged:

@a = ()[1,2];
@a = (getpwent)[7,0];
@a = (anything_returning_empty_list())[2,1,2];
@a = @b[2,1,2];
@a = @c{'a','b','c'};

See perldata.

"(\$)" prototype and $foo{a}
A scalar reference prototype now correctly allows a hash or array element in that slot.

"goto &sub" and AUTOLOAD
The "goto &sub" construct works correctly when &sub happens to be autoloaded.

"-bareword" allowed under "use integer"
The autoquoting of barewords preceded by "-" did not work in prior versions when the
"integer" pragma was enabled. This has been fixed.

Failures in DESTROY()
When code in a destructor threw an exception, it went unnoticed in earlier versions of
Perl, unless someone happened to be looking in $@ just after the point the destructor
happened to run. Such failures are now visible as warnings when warnings are enabled.

Locale bugs fixed
printf() and sprintf() previously reset the numeric locale back to the default "C" locale.
This has been fixed.

Numbers formatted according to the local numeric locale (such as using a decimal comma
instead of a decimal dot) caused "isn't numeric" warnings, even while the operations
accessing those numbers produced correct results. These warnings have been discontinued.

Memory leaks
The "eval 'return sub {...}'" construct could sometimes leak memory. This has been fixed.

Operations that aren't filehandle constructors used to leak memory when used on invalid
filehandles. This has been fixed.

Constructs that modified @_ could fail to deallocate values in @_ and thus leak memory.
This has been corrected.

Spurious subroutine stubs after failed subroutine calls
Perl could sometimes create empty subroutine stubs when a subroutine was not found in the
package. Such cases stopped later method lookups from progressing into base packages.
This has been corrected.

Taint failures under "-U"
When running in unsafe mode, taint violations could sometimes cause silent failures. This
has been fixed.

END blocks and the "-c" switch
Prior versions used to run BEGIN and END blocks when Perl was run in compile-only mode.
Since this is typically not the expected behavior, END blocks are not executed anymore
when the "-c" switch is used, or if compilation fails.

See "Support for CHECK blocks" for how to run things when the compile phase ends.

Potential to leak DATA filehandles
Using the "__DATA__" token creates an implicit filehandle to the file that contains the
token. It is the program's responsibility to close it when it is done reading from it.

This caveat is now better explained in the documentation. See perldata.

New or Changed Diagnostics

"%s" variable %s masks earlier declaration in same %s
(W misc) A "my" or "our" variable has been redeclared in the current scope or
statement, effectively eliminating all access to the previous instance. This is
almost always a typographical error. Note that the earlier variable will still exist
until the end of the scope or until all closure referents to it are destroyed.

"my sub" not yet implemented
(F) Lexically scoped subroutines are not yet implemented. Don't try that yet.

"our" variable %s redeclared
(W misc) You seem to have already declared the same global once before in the current
lexical scope.

'!' allowed only after types %s
(F) The '!' is allowed in pack() and unpack() only after certain types. See "pack" in
perlfunc.

/ cannot take a count
(F) You had an unpack template indicating a counted-length string, but you have also
specified an explicit size for the string. See "pack" in perlfunc.

/ must be followed by a, A or Z
(F) You had an unpack template indicating a counted-length string, which must be
followed by one of the letters a, A or Z to indicate what sort of string is to be
unpacked. See "pack" in perlfunc.

/ must be followed by a*, A* or Z*
(F) You had a pack template indicating a counted-length string, Currently the only
things that can have their length counted are a*, A* or Z*. See "pack" in perlfunc.

/ must follow a numeric type
(F) You had an unpack template that contained a '#', but this did not follow some
numeric unpack specification. See "pack" in perlfunc.

/%s/: Unrecognized escape \\%c passed through
(W regexp) You used a backslash-character combination which is not recognized by Perl.
This combination appears in an interpolated variable or a "'"-delimited regular
expression. The character was understood literally.

/%s/: Unrecognized escape \\%c in character class passed through
(W regexp) You used a backslash-character combination which is not recognized by Perl
inside character classes. The character was understood literally.

/%s/ should probably be written as "%s"
(W syntax) You have used a pattern where Perl expected to find a string, as in the
first argument to "join". Perl will treat the true or false result of matching the
pattern against $_ as the string, which is probably not what you had in mind.

%s() called too early to check prototype
(W prototype) You've called a function that has a prototype before the parser saw a
definition or declaration for it, and Perl could not check that the call conforms to
the prototype. You need to either add an early prototype declaration for the
subroutine in question, or move the subroutine definition ahead of the call to get
proper prototype checking. Alternatively, if you are certain that you're calling the
function correctly, you may put an ampersand before the name to avoid the warning.
See perlsub.

%s argument is not a HASH or ARRAY element
(F) The argument to exists() must be a hash or array element, such as:

$foo{$bar}
$ref->{"susie"}[12]

%s argument is not a HASH or ARRAY element or slice
(F) The argument to delete() must be either a hash or array element, such as:

$foo{$bar}
$ref->{"susie"}[12]

or a hash or array slice, such as:

@foo[$bar, $baz, $xyzzy]
@{$ref->[12]}{"susie", "queue"}

%s argument is not a subroutine name
(F) The argument to exists() for "exists &sub" must be a subroutine name, and not a
subroutine call. "exists &sub()" will generate this error.

%s package attribute may clash with future reserved word: %s
(W reserved) A lowercase attribute name was used that had a package-specific handler.
That name might have a meaning to Perl itself some day, even though it doesn't yet.
Perhaps you should use a mixed-case attribute name, instead. See attributes.

(in cleanup) %s
(W misc) This prefix usually indicates that a DESTROY() method raised the indicated
exception. Since destructors are usually called by the system at arbitrary points
during execution, and often a vast number of times, the warning is issued only once
for any number of failures that would otherwise result in the same message being
repeated.

Failure of user callbacks dispatched using the "G_KEEPERR" flag could also result in
this warning. See "G_KEEPERR" in perlcall.

<> should be quotes
(F) You wrote "require <file>" when you should have written "require 'file'".

Attempt to join self
(F) You tried to join a thread from within itself, which is an impossible task. You
may be joining the wrong thread, or you may need to move the join() to some other
thread.

Bad evalled substitution pattern
(F) You've used the /e switch to evaluate the replacement for a substitution, but perl
found a syntax error in the code to evaluate, most likely an unexpected right brace
'}'.

Bad realloc() ignored
(S) An internal routine called realloc() on something that had never been malloc()ed
in the first place. Mandatory, but can be disabled by setting environment variable
"PERL_BADFREE" to 1.

Bareword found in conditional
(W bareword) The compiler found a bareword where it expected a conditional, which
often indicates that an || or && was parsed as part of the last argument of the
previous construct, for example:

open FOO || die;

It may also indicate a misspelled constant that has been interpreted as a bareword:

use constant TYPO => 1;
if (TYOP) { print "foo" }

The "strict" pragma is useful in avoiding such errors.

Binary number > 0b11111111111111111111111111111111 non-portable
(W portable) The binary number you specified is larger than 2**32-1 (4294967295) and
therefore non-portable between systems. See perlport for more on portability
concerns.

Bit vector size > 32 non-portable
(W portable) Using bit vector sizes larger than 32 is non-portable.

Buffer overflow in prime_env_iter: %s
(W internal) A warning peculiar to VMS. While Perl was preparing to iterate over
%ENV, it encountered a logical name or symbol definition which was too long, so it was
truncated to the string shown.

Can't check filesystem of script "%s"
(P) For some reason you can't check the filesystem of the script for nosuid.

Can't declare class for non-scalar %s in "%s"
(S) Currently, only scalar variables can declared with a specific class qualifier in a
"my" or "our" declaration. The semantics may be extended for other types of variables
in future.

Can't declare %s in "%s"
(F) Only scalar, array, and hash variables may be declared as "my" or "our" variables.
They must have ordinary identifiers as names.

Can't ignore signal CHLD, forcing to default
(W signal) Perl has detected that it is being run with the SIGCHLD signal (sometimes
known as SIGCLD) disabled. Since disabling this signal will interfere with proper
determination of exit status of child processes, Perl has reset the signal to its
default value. This situation typically indicates that the parent program under which
Perl may be running (e.g., cron) is being very careless.

Can't modify non-lvalue subroutine call
(F) Subroutines meant to be used in lvalue context should be declared as such, see
"Lvalue subroutines" in perlsub.

Can't read CRTL environ
(S) A warning peculiar to VMS. Perl tried to read an element of %ENV from the CRTL's
internal environment array and discovered the array was missing. You need to figure
out where your CRTL misplaced its environ or define PERL_ENV_TABLES (see perlvms) so
that environ is not searched.

Can't remove %s: %s, skipping file
(S) You requested an inplace edit without creating a backup file. Perl was unable to
remove the original file to replace it with the modified file. The file was left
unmodified.

Can't return %s from lvalue subroutine
(F) Perl detected an attempt to return illegal lvalues (such as temporary or readonly
values) from a subroutine used as an lvalue. This is not allowed.

Can't weaken a nonreference
(F) You attempted to weaken something that was not a reference. Only references can
be weakened.

Character class [:%s:] unknown
(F) The class in the character class [: :] syntax is unknown. See perlre.

Character class syntax [%s] belongs inside character classes
(W unsafe) The character class constructs [: :], [= =], and [. .] go inside character
classes, the [] are part of the construct, for example: /[012[:alpha:]345]/. Note
that [= =] and [. .] are not currently implemented; they are simply placeholders for
future extensions.

Constant is not %s reference
(F) A constant value (perhaps declared using the "use constant" pragma) is being
dereferenced, but it amounts to the wrong type of reference. The message indicates
the type of reference that was expected. This usually indicates a syntax error in
dereferencing the constant value. See "Constant Functions" in perlsub and constant.

constant(%s): %s
(F) The parser found inconsistencies either while attempting to define an overloaded
constant, or when trying to find the character name specified in the "\N{...}" escape.
Perhaps you forgot to load the corresponding "overload" or "charnames" pragma? See
charnames and overload.

CORE::%s is not a keyword
(F) The CORE:: namespace is reserved for Perl keywords.

defined(@array) is deprecated
(D) defined() is not usually useful on arrays because it checks for an undefined
scalar value. If you want to see if the array is empty, just use "if (@array) { # not
empty }" for example.

defined(%hash) is deprecated
(D) defined() is not usually useful on hashes because it checks for an undefined
scalar value. If you want to see if the hash is empty, just use "if (%hash) { # not
empty }" for example.

Did not produce a valid header
See Server error.

(Did you mean "local" instead of "our"?)
(W misc) Remember that "our" does not localize the declared global variable. You have
declared it again in the same lexical scope, which seems superfluous.

Document contains no data
See Server error.

entering effective %s failed
(F) While under the "use filetest" pragma, switching the real and effective uids or
gids failed.

false [] range "%s" in regexp
(W regexp) A character class range must start and end at a literal character, not
another character class like "\d" or "[:alpha:]". The "-" in your false range is
interpreted as a literal "-". Consider quoting the "-", "\-". See perlre.

Filehandle %s opened only for output
(W io) You tried to read from a filehandle opened only for writing. If you intended
it to be a read/write filehandle, you needed to open it with "+<" or "+>" or "+>>"
instead of with "<" or nothing. If you intended only to read from the file, use "<".
See "open" in perlfunc.

flock() on closed filehandle %s
(W closed) The filehandle you're attempting to flock() got itself closed some time
before now. Check your logic flow. flock() operates on filehandles. Are you
attempting to call flock() on a dirhandle by the same name?

Global symbol "%s" requires explicit package name
(F) You've said "use strict vars", which indicates that all variables must either be
lexically scoped (using "my"), declared beforehand using "our", or explicitly
qualified to say which package the global variable is in (using "::").

Hexadecimal number > 0xffffffff non-portable
(W portable) The hexadecimal number you specified is larger than 2**32-1 (4294967295)
and therefore non-portable between systems. See perlport for more on portability
concerns.

Ill-formed CRTL environ value "%s"
(W internal) A warning peculiar to VMS. Perl tried to read the CRTL's internal
environ array, and encountered an element without the "=" delimiter used to separate
keys from values. The element is ignored.

Ill-formed message in prime_env_iter: |%s|
(W internal) A warning peculiar to VMS. Perl tried to read a logical name or CLI
symbol definition when preparing to iterate over %ENV, and didn't see the expected
delimiter between key and value, so the line was ignored.

Illegal binary digit %s
(F) You used a digit other than 0 or 1 in a binary number.

Illegal binary digit %s ignored
(W digit) You may have tried to use a digit other than 0 or 1 in a binary number.
Interpretation of the binary number stopped before the offending digit.

Illegal number of bits in vec
(F) The number of bits in vec() (the third argument) must be a power of two from 1 to
32 (or 64, if your platform supports that).

Integer overflow in %s number
(W overflow) The hexadecimal, octal or binary number you have specified either as a
literal or as an argument to hex() or oct() is too big for your architecture, and has
been converted to a floating point number. On a 32-bit architecture the largest
hexadecimal, octal or binary number representable without overflow is 0xFFFFFFFF,
037777777777, or 0b11111111111111111111111111111111 respectively. Note that Perl
transparently promotes all numbers to a floating point representation
internally--subject to loss of precision errors in subsequent operations.

Invalid %s attribute: %s
The indicated attribute for a subroutine or variable was not recognized by Perl or by
a user-supplied handler. See attributes.

Invalid %s attributes: %s
The indicated attributes for a subroutine or variable were not recognized by Perl or
by a user-supplied handler. See attributes.

invalid [] range "%s" in regexp
The offending range is now explicitly displayed.

Invalid separator character %s in attribute list
(F) Something other than a colon or whitespace was seen between the elements of an
attribute list. If the previous attribute had a parenthesised parameter list, perhaps
that list was terminated too soon. See attributes.

Invalid separator character %s in subroutine attribute list
(F) Something other than a colon or whitespace was seen between the elements of a
subroutine attribute list. If the previous attribute had a parenthesised parameter
list, perhaps that list was terminated too soon.

leaving effective %s failed
(F) While under the "use filetest" pragma, switching the real and effective uids or
gids failed.

Lvalue subs returning %s not implemented yet
(F) Due to limitations in the current implementation, array and hash values cannot be
returned in subroutines used in lvalue context. See "Lvalue subroutines" in perlsub.

Method %s not permitted
See Server error.

Missing %sbrace%s on \N{}
(F) Wrong syntax of character name literal "\N{charname}" within double-quotish
context.

Missing command in piped open
(W pipe) You used the "open(FH, "| command")" or "open(FH, "command |")" construction,
but the command was missing or blank.

Missing name in "my sub"
(F) The reserved syntax for lexically scoped subroutines requires that they have a
name with which they can be found.

No %s specified for -%c
(F) The indicated command line switch needs a mandatory argument, but you haven't
specified one.

No package name allowed for variable %s in "our"
(F) Fully qualified variable names are not allowed in "our" declarations, because that
doesn't make much sense under existing semantics. Such syntax is reserved for future
extensions.

No space allowed after -%c
(F) The argument to the indicated command line switch must follow immediately after
the switch, without intervening spaces.

no UTC offset information; assuming local time is UTC
(S) A warning peculiar to VMS. Perl was unable to find the local timezone offset, so
it's assuming that local system time is equivalent to UTC. If it's not, define the
logical name SYS$TIMEZONE_DIFFERENTIAL to translate to the number of seconds which
need to be added to UTC to get local time.

Octal number > 037777777777 non-portable
(W portable) The octal number you specified is larger than 2**32-1 (4294967295) and
therefore non-portable between systems. See perlport for more on portability
concerns.

See also perlport for writing portable code.

panic: del_backref
(P) Failed an internal consistency check while trying to reset a weak reference.

panic: kid popen errno read
(F) forked child returned an incomprehensible message about its errno.

panic: magic_killbackrefs
(P) Failed an internal consistency check while trying to reset all weak references to
an object.

Parentheses missing around "%s" list
(W parenthesis) You said something like

my $foo, $bar = @_;

when you meant

my ($foo, $bar) = @_;

Remember that "my", "our", and "local" bind tighter than comma.

Possible unintended interpolation of %s in string
(W ambiguous) It used to be that Perl would try to guess whether you wanted an array
interpolated or a literal @. It no longer does this; arrays are now always
interpolated into strings. This means that if you try something like:

print "fred@example.com";

and the array @example doesn't exist, Perl is going to print "fred.com", which is
probably not what you wanted. To get a literal "@" sign in a string, put a backslash
before it, just as you would to get a literal "$" sign.

Possible Y2K bug: %s
(W y2k) You are concatenating the number 19 with another number, which could be a
potential Year 2000 problem.

pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead
(W deprecated) You have written something like this:

sub doit
{
use attrs qw(locked);
}

You should use the new declaration syntax instead.

sub doit : locked
{
...

The "use attrs" pragma is now obsolete, and is only provided for backward-
compatibility. See "Subroutine Attributes" in perlsub.

Premature end of script headers
See Server error.

Repeat count in pack overflows
(F) You can't specify a repeat count so large that it overflows your signed integers.
See "pack" in perlfunc.

Repeat count in unpack overflows
(F) You can't specify a repeat count so large that it overflows your signed integers.
See "unpack" in perlfunc.

realloc() of freed memory ignored
(S) An internal routine called realloc() on something that had already been freed.

Reference is already weak
(W misc) You have attempted to weaken a reference that is already weak. Doing so has
no effect.

setpgrp can't take arguments
(F) Your system has the setpgrp() from BSD 4.2, which takes no arguments, unlike POSIX
setpgid(), which takes a process ID and process group ID.

Strange *+?{} on zero-length expression
(W regexp) You applied a regular expression quantifier in a place where it makes no
sense, such as on a zero-width assertion. Try putting the quantifier inside the
assertion instead. For example, the way to match "abc" provided that it is followed
by three repetitions of "xyz" is "/abc(?=(?:xyz){3})/", not "/abc(?=xyz){3}/".

switching effective %s is not implemented
(F) While under the "use filetest" pragma, we cannot switch the real and effective
uids or gids.

This Perl can't reset CRTL environ elements (%s)
This Perl can't set CRTL environ elements (%s=%s)
(W internal) Warnings peculiar to VMS. You tried to change or delete an element of
the CRTL's internal environ array, but your copy of Perl wasn't built with a CRTL that
contained the setenv() function. You'll need to rebuild Perl with a CRTL that does,
or redefine PERL_ENV_TABLES (see perlvms) so that the environ array isn't the target
of the change to %ENV which produced the warning.

Too late to run %s block
(W void) A CHECK or INIT block is being defined during run time proper, when the
opportunity to run them has already passed. Perhaps you are loading a file with
"require" or "do" when you should be using "use" instead. Or perhaps you should put
the "require" or "do" inside a BEGIN block.

Unknown open() mode '%s'
(F) The second argument of 3-argument open() is not among the list of valid modes:
"<", ">", ">>", "+<", "+>", "+>>", "-|", "|-".

Unknown process %x sent message to prime_env_iter: %s
(P) An error peculiar to VMS. Perl was reading values for %ENV before iterating over
it, and someone else stuck a message in the stream of data Perl expected. Someone's
very confused, or perhaps trying to subvert Perl's population of %ENV for nefarious
purposes.

Unrecognized escape \\%c passed through
(W misc) You used a backslash-character combination which is not recognized by Perl.
The character was understood literally.

Unterminated attribute parameter in attribute list
(F) The lexer saw an opening (left) parenthesis character while parsing an attribute
list, but the matching closing (right) parenthesis character was not found. You may
need to add (or remove) a backslash character to get your parentheses to balance. See
attributes.

Unterminated attribute list
(F) The lexer found something other than a simple identifier at the start of an
attribute, and it wasn't a semicolon or the start of a block. Perhaps you terminated
the parameter list of the previous attribute too soon. See attributes.

Unterminated attribute parameter in subroutine attribute list
(F) The lexer saw an opening (left) parenthesis character while parsing a subroutine
attribute list, but the matching closing (right) parenthesis character was not found.
You may need to add (or remove) a backslash character to get your parentheses to
balance.

Unterminated subroutine attribute list
(F) The lexer found something other than a simple identifier at the start of a
subroutine attribute, and it wasn't a semicolon or the start of a block. Perhaps you
terminated the parameter list of the previous attribute too soon.

Value of CLI symbol "%s" too long
(W misc) A warning peculiar to VMS. Perl tried to read the value of an %ENV element
from a CLI symbol table, and found a resultant string longer than 1024 characters.
The return value has been truncated to 1024 characters.

Version number must be a constant number
(P) The attempt to translate a "use Module n.n LIST" statement into its equivalent
"BEGIN" block found an internal inconsistency with the version number.

New tests

lib/attrs
Compatibility tests for "sub : attrs" vs the older "use attrs".

lib/env
Tests for new environment scalar capability (e.g., "use Env qw($BAR);").

lib/env-array
Tests for new environment array capability (e.g., "use Env qw(@PATH);").

lib/io_const
IO constants (SEEK_*, _IO*).

lib/io_dir
Directory-related IO methods (new, read, close, rewind, tied delete).

lib/io_multihomed
INET sockets with multi-homed hosts.

lib/io_poll
IO poll().

lib/io_unix
UNIX sockets.

op/attrs
Regression tests for "my ($x,@y,%z) : attrs" and <sub : attrs>.

op/filetest
File test operators.

op/lex_assign
Verify operations that access pad objects (lexicals and temporaries).

op/exists_sub
Verify "exists &sub" operations.

Incompatible Changes

Perl Source Incompatibilities
Beware that any new warnings that have been added or old ones that have been enhanced are
not considered incompatible changes.

Since all new warnings must be explicitly requested via the "-w" switch or the "warnings"
pragma, it is ultimately the programmer's responsibility to ensure that warnings are
enabled judiciously.

CHECK is a new keyword
All subroutine definitions named CHECK are now special. See "/"Support for CHECK
blocks"" for more information.

Treatment of list slices of undef has changed
There is a potential incompatibility in the behavior of list slices that are comprised
entirely of undefined values. See "Behavior of list slices is more consistent".

Format of $English::PERL_VERSION is different
The English module now sets $PERL_VERSION to $^V (a string value) rather than $] (a
numeric value). This is a potential incompatibility. Send us a report via perlbug if
you are affected by this.

See "Improved Perl version numbering system" for the reasons for this change.

Literals of the form 1.2.3 parse differently
Previously, numeric literals with more than one dot in them were interpreted as a
floating point number concatenated with one or more numbers. Such "numbers" are now
parsed as strings composed of the specified ordinals.

For example, "print 97.98.99" used to output 97.9899 in earlier versions, but now
prints "abc".

See "Support for strings represented as a vector of ordinals".

Possibly changed pseudo-random number generator
Perl programs that depend on reproducing a specific set of pseudo-random numbers may
now produce different output due to improvements made to the rand() builtin. You can
use "sh Configure -Drandfunc=rand" to obtain the old behavior.

See "Better pseudo-random number generator".

Hashing function for hash keys has changed
Even though Perl hashes are not order preserving, the apparently random order
encountered when iterating on the contents of a hash is actually determined by the
hashing algorithm used. Improvements in the algorithm may yield a random order that
is different from that of previous versions, especially when iterating on hashes.

See "Better worst-case behavior of hashes" for additional information.

"undef" fails on read only values
Using the "undef" operator on a readonly value (such as $1) has the same effect as
assigning "undef" to the readonly value--it throws an exception.

Close-on-exec bit may be set on pipe and socket handles
Pipe and socket handles are also now subject to the close-on-exec behavior determined
by the special variable $^F.

See "More consistent close-on-exec behavior".

Writing "$$1" to mean "${$}1" is unsupported
Perl 5.004 deprecated the interpretation of $$1 and similar within interpolated
strings to mean "$$ . "1"", but still allowed it.

In Perl 5.6.0 and later, "$$1" always means "${$1}".

delete(), each(), values() and "\(%h)"
operate on aliases to values, not copies

delete(), each(), values() and hashes (e.g. "\(%h)") in a list context return the
actual values in the hash, instead of copies (as they used to in earlier versions).
Typical idioms for using these constructs copy the returned values, but this can make
a significant difference when creating references to the returned values. Keys in the
hash are still returned as copies when iterating on a hash.

See also "delete(), each(), values() and hash iteration are faster".

vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS
vec() generates a run-time error if the BITS argument is not a valid power-of-two
integer.

Text of some diagnostic output has changed
Most references to internal Perl operations in diagnostics have been changed to be
more descriptive. This may be an issue for programs that may incorrectly rely on the
exact text of diagnostics for proper functioning.

"%@" has been removed
The undocumented special variable "%@" that used to accumulate "background" errors
(such as those that happen in DESTROY()) has been removed, because it could
potentially result in memory leaks.

Parenthesized not() behaves like a list operator
The "not" operator now falls under the "if it looks like a function, it behaves like a
function" rule.

As a result, the parenthesized form can be used with "grep" and "map". The following
construct used to be a syntax error before, but it works as expected now:

grep not($_), @things;

On the other hand, using "not" with a literal list slice may not work. The following
previously allowed construct:

print not (1,2,3)[0];

needs to be written with additional parentheses now:

print not((1,2,3)[0]);

The behavior remains unaffected when "not" is not followed by parentheses.

Semantics of bareword prototype "(*)" have changed
The semantics of the bareword prototype "*" have changed. Perl 5.005 always coerced
simple scalar arguments to a typeglob, which wasn't useful in situations where the
subroutine must distinguish between a simple scalar and a typeglob. The new behavior
is to not coerce bareword arguments to a typeglob. The value will always be visible
as either a simple scalar or as a reference to a typeglob.

See "More functional bareword prototype (*)".

Semantics of bit operators may have changed on 64-bit platforms
If your platform is either natively 64-bit or if Perl has been configured to used
64-bit integers, i.e., $Config{ivsize} is 8, there may be a potential incompatibility
in the behavior of bitwise numeric operators (& | ^ ~ << >>). These operators used to
strictly operate on the lower 32 bits of integers in previous versions, but now
operate over the entire native integral width. In particular, note that unary "~"
will produce different results on platforms that have different $Config{ivsize}. For
portability, be sure to mask off the excess bits in the result of unary "~", e.g.,
"~$x & 0xffffffff".

See "Bit operators support full native integer width".

More builtins taint their results
As described in "Improved security features", there may be more sources of taint in a
Perl program.

To avoid these new tainting behaviors, you can build Perl with the Configure option
"-Accflags=-DINCOMPLETE_TAINTS". Beware that the ensuing perl binary may be insecure.

C Source Incompatibilities
"PERL_POLLUTE"
Release 5.005 grandfathered old global symbol names by providing preprocessor macros
for extension source compatibility. As of release 5.6.0, these preprocessor
definitions are not available by default. You need to explicitly compile perl with
"-DPERL_POLLUTE" to get these definitions. For extensions still using the old
symbols, this option can be specified via MakeMaker:

perl Makefile.PL POLLUTE=1

"PERL_IMPLICIT_CONTEXT"
This new build option provides a set of macros for all API functions such that an
implicit interpreter/thread context argument is passed to every API function. As a
result of this, something like "sv_setsv(foo,bar)" amounts to a macro invocation that
actually translates to something like "Perl_sv_setsv(my_perl,foo,bar)". While this is
generally expected to not have any significant source compatibility issues, the
difference between a macro and a real function call will need to be considered.

This means that there is a source compatibility issue as a result of this if your
extensions attempt to use pointers to any of the Perl API functions.

Note that the above issue is not relevant to the default build of Perl, whose
interfaces continue to match those of prior versions (but subject to the other options
described here).

See "Background and PERL_IMPLICIT_CONTEXT" in perlguts for detailed information on the
ramifications of building Perl with this option.

NOTE: PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
with one of -Dusethreads, -Dusemultiplicity, or both. It is not
intended to be enabled by users at this time.

"PERL_POLLUTE_MALLOC"
Enabling Perl's malloc in release 5.005 and earlier caused the namespace of the
system's malloc family of functions to be usurped by the Perl versions, since by
default they used the same names. Besides causing problems on platforms that do not
allow these functions to be cleanly replaced, this also meant that the system versions
could not be called in programs that used Perl's malloc. Previous versions of Perl
have allowed this behaviour to be suppressed with the HIDEMYMALLOC and EMBEDMYMALLOC
preprocessor definitions.

As of release 5.6.0, Perl's malloc family of functions have default names distinct
from the system versions. You need to explicitly compile perl with
"-DPERL_POLLUTE_MALLOC" to get the older behaviour. HIDEMYMALLOC and EMBEDMYMALLOC
have no effect, since the behaviour they enabled is now the default.

Note that these functions do not constitute Perl's memory allocation API. See "Memory
Allocation" in perlguts for further information about that.

Compatible C Source API Changes
"PATCHLEVEL" is now "PERL_VERSION"
The cpp macros "PERL_REVISION", "PERL_VERSION", and "PERL_SUBVERSION" are now
available by default from perl.h, and reflect the base revision, patchlevel, and
subversion respectively. "PERL_REVISION" had no prior equivalent, while
"PERL_VERSION" and "PERL_SUBVERSION" were previously available as "PATCHLEVEL" and
"SUBVERSION".

The new names cause less pollution of the cpp namespace and reflect what the numbers
have come to stand for in common practice. For compatibility, the old names are still
supported when patchlevel.h is explicitly included (as required before), so there is
no source incompatibility from the change.

Binary Incompatibilities
In general, the default build of this release is expected to be binary compatible for
extensions built with the 5.005 release or its maintenance versions. However, specific
platforms may have broken binary compatibility due to changes in the defaults used in
hints files. Therefore, please be sure to always check the platform-specific README files
for any notes to the contrary.

The usethreads or usemultiplicity builds are not binary compatible with the corresponding
builds in 5.005.

On platforms that require an explicit list of exports (AIX, OS/2 and Windows, among
others), purely internal symbols such as parser functions and the run time opcodes are not
exported by default. Perl 5.005 used to export all functions irrespective of whether they
were considered part of the public API or not.

For the full list of public API functions, see perlapi.

Known Problems

Localizing a tied hash element may leak memory
As of the 5.6.1 release, there is a known leak when code such as this is executed:

use Tie::Hash;
tie my %tie_hash => 'Tie::StdHash';

...

local($tie_hash{Foo}) = 1; # leaks

Known test failures
· 64-bit builds

Subtest #15 of lib/b.t may fail under 64-bit builds on platforms such as HP-UX PA64
and Linux IA64. The issue is still being investigated.

The lib/io_multihomed test may hang in HP-UX if Perl has been configured to be 64-bit.
Because other 64-bit platforms do not hang in this test, HP-UX is suspect. All other
tests pass in 64-bit HP-UX. The test attempts to create and connect to "multihomed"
sockets (sockets which have multiple IP addresses).

Note that 64-bit support is still experimental.

· Failure of Thread tests

The subtests 19 and 20 of lib/thr5005.t test are known to fail due to fundamental
problems in the 5.005 threading implementation. These are not new failures--Perl
5.005_0x has the same bugs, but didn't have these tests. (Note that support for
5.005-style threading remains experimental.)

· NEXTSTEP 3.3 POSIX test failure

In NEXTSTEP 3.3p2 the implementation of the strftime(3) in the operating system
libraries is buggy: the %j format numbers the days of a month starting from zero,
which, while being logical to programmers, will cause the subtests 19 to 27 of the
lib/posix test may fail.

· Tru64 (aka Digital UNIX, aka DEC OSF/1) lib/sdbm test failure with gcc

If compiled with gcc 2.95 the lib/sdbm test will fail (dump core). The cure is to use
the vendor cc, it comes with the operating system and produces good code.

EBCDIC platforms not fully supported
In earlier releases of Perl, EBCDIC environments like OS390 (also known as Open Edition
MVS) and VM-ESA were supported. Due to changes required by the UTF-8 (Unicode) support,
the EBCDIC platforms are not supported in Perl 5.6.0.

The 5.6.1 release improves support for EBCDIC platforms, but they are not fully supported
yet.

UNICOS/mk CC failures during Configure run
In UNICOS/mk the following errors may appear during the Configure run:

Guessing which symbols your C compiler and preprocessor define...
CC-20 cc: ERROR File = try.c, Line = 3
...
bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K
...
4 errors detected in the compilation of "try.c".

The culprit is the broken awk of UNICOS/mk. The effect is fortunately rather mild: Perl
itself is not adversely affected by the error, only the h2ph utility coming with Perl, and
that is rather rarely needed these days.

Arrow operator and arrays
When the left argument to the arrow operator "->" is an array, or the "scalar" operator
operating on an array, the result of the operation must be considered erroneous. For
example:

@x->[2]
scalar(@x)->[2]

These expressions will get run-time errors in some future release of Perl.

Experimental features
As discussed above, many features are still experimental. Interfaces and implementation
of these features are subject to change, and in extreme cases, even subject to removal in
some future release of Perl. These features include the following:

Threads
Unicode
64-bit support
Lvalue subroutines
Weak references
The pseudo-hash data type
The Compiler suite
Internal implementation of file globbing
The DB module
The regular expression code constructs:
"(?{ code })" and "(??{ code })"

Obsolete Diagnostics

Character class syntax [: :] is reserved for future extensions
(W) Within regular expression character classes ([]) the syntax beginning with "[:"
and ending with ":]" is reserved for future extensions. If you need to represent
those character sequences inside a regular expression character class, just quote the
square brackets with the backslash: "\[:" and ":\]".

Ill-formed logical name |%s| in prime_env_iter
(W) A warning peculiar to VMS. A logical name was encountered when preparing to
iterate over %ENV which violates the syntactic rules governing logical names. Because
it cannot be translated normally, it is skipped, and will not appear in %ENV. This
may be a benign occurrence, as some software packages might directly modify logical
name tables and introduce nonstandard names, or it may indicate that a logical name
table has been corrupted.

In string, @%s now must be written as \@%s
The description of this error used to say:

(Someday it will simply assume that an unbackslashed @
interpolates an array.)

That day has come, and this fatal error has been removed. It has been replaced by a
non-fatal warning instead. See "Arrays now always interpolate into double-quoted
strings" for details.

Probable precedence problem on %s
(W) The compiler found a bareword where it expected a conditional, which often
indicates that an || or && was parsed as part of the last argument of the previous
construct, for example:

open FOO || die;

regexp too big
(F) The current implementation of regular expressions uses shorts as address offsets
within a string. Unfortunately this means that if the regular expression compiles to
longer than 32767, it'll blow up. Usually when you want a regular expression this
big, there is a better way to do it with multiple statements. See perlre.

Use of "$$<digit>" to mean "${$}<digit>" is deprecated
(D) Perl versions before 5.004 misinterpreted any type marker followed by "$" and a
digit. For example, "$$0" was incorrectly taken to mean "${$}0" instead of "${$0}".
This bug is (mostly) fixed in Perl 5.004.

However, the developers of Perl 5.004 could not fix this bug completely, because at
least two widely-used modules depend on the old meaning of "$$0" in a string. So Perl
5.004 still interprets "$$<digit>" in the old (broken) way inside strings; but it
generates this message as a warning. And in Perl 5.005, this special treatment will
cease.

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. There may also be information at http://www.perl.com/ ,
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 perlbug@perl.org to be
analysed by the Perl porting team.

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