perl561delta - what's new for perl v5.6.1
This document describes differences between the 5.005 release and the 5.6.1 release.
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.
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/ .
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.
Various cases of memory leaks and attempts to access uninitialized memory have been cured. See "Known Problems" below for further issues.
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.
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() could cause core dumps in certain situations. Carp was sometimes affected by this problem.
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.
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 of special variables described in perlvar (as in ${$num}) was accidentally disabled. This works again now.
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.
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.
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.
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.
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 now work correctly when they appear at the very beginning of eval "...".
The (\&) prototype now works properly.
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 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 can be set to more than one switch group. Previously, it used to be limited to one group of options only.
chop(@list) in list context returned the characters chopped in reverse order. This has been reversed to be in the right order.
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.
Support for 64-bit platforms has been improved, but continues to be experimental. The level of support varies greatly among platforms.
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.
There have been various bugfixes to support lvalue subroutines better. However, the feature still remains experimental.
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 now chdir()s correctly when chasing symbolic links.
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.
A large number of tests have been added.
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, "[email protected]" 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.
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 installin a directory other than the perl source directory. See INSTALL.
Configure -S can be run non-interactively.
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 distributionThe 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.
The following modules have been added.
Walks Perl syntax tree, printing concise info about ops. See B::Concise.
Returns name and handle of a temporary file safely. See File::Temp.
Converts Pod data to formatted LaTeX. See Pod::LaTeX.
Converts POD data to formatted overstrike text. See Pod::Text::Overstrike.
The following modules have been upgraded.
CGI v2.752 is now included.
CPAN v1.59_54 is now included.
Various bugfixes have been added.
DB_File v1.75 supports newer Berkeley DB versions, among other improvements.
Devel::Peek has been enhanced to support dumping of memory statistics, when perl is built with the included malloc().
File::Find now supports pre and post-processing of the files in order to sort() them, etc.
Getopt::Long v2.25 is included.
Various bug fixes have been included.
IPC::Open3 allows use of numeric file descriptors.
The fmod() function supports modulus operations. Various bug fixes have also been included.
Math::Complex handles inf, NaN etc., better.
ping() could fail on odd number of data bytes, and when the echo service isn't running. This has been corrected.
A memory leak has been fixed.
Version 1.13 of the Pod::Parser suite is included.
Pod::Text and related modules have been upgraded to the versions in podlators suite v2.08.
On dosish platforms, some keys went missing because of lack of support for files with "holes". A workaround for the problem has been added.
Various bug fixes have been included.
Now supports Tie::RefHash::Nestable to automagically tie hashref values.
Various bug fixes have been included.
The following new ports are now available.
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.
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.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.
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.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.
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.
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-timeAlternatively, 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 bitstringSee "Scalar value constructors" in perldata for additional information.
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 $]).
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.
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
}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.
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_tis 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 ints (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.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.
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).
You can "Configure -Dusemorebits" to turn on both the 64-bit support and the long double support.
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 allowedsort() did not accept a subroutine reference as the comparison function in earlier versions. This is now permitted.
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.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.
For example to match alphabetic characters use /[[:alpha:]]/. See perlre for details.
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().
qw// operatorThe 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".
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.
The new format type 'Z' is useful for packing and unpacking null-terminated strings. See "pack" in perlfunc.
The new format type modifier '!' is useful for packing and unpacking native shorts, ints, and longs. See "pack" in perlfunc.
The template character '/' can be used to specify a counted string type to be packed or unpacked. See "pack" in perlfunc.
The '#' character in a template introduces a comment up to end of the line. This facilitates documentation of pack() templates.
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 are now supported as literals, in s?printf formats, and oct():
$answer = 0b101010;
printf "The answer is: %b\n", oct("0b101010");Subroutines can now return modifiable lvalues. See "Lvalue subroutines" in perlsub.
NOTE: This is an experimental feature. Details are subject to change.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 $foo[10]->{'foo'}. Note however, that the arrow is still required for foo(10)->('bar').
Constructs such as ($a ||= 2) += 1 are now allowed.
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.
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.
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.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.
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).
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() 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() 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".
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 $!.
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 EOFDiagnostic output now goes to whichever file the STDERR handle is pointing at, instead of always going to the underlying C runtime library's stderr.
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.
The length argument of syswrite() has become optional.
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.
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.
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.
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 overriddenrequire 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.
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 $^X . "YZ" as before.
As before, lexical variables may not have names beginning with control characters. As before, variables whose names begin with a control character are always forced to be in package `main'. All such variables are reserved for future extensions, except those that begin with ^_, which may be used by user programs and are guaranteed not to acquire special meaning in any future version of Perl.
-c switch$^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.
$^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.
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.