perl561delta - what's new for perl v5.6.x
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 [Toc] [Back] 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 [Toc] [Back]
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.courte-
san.com/sudo/ .
Core bug fixes [Toc] [Back]
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/b}/ 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 ""a0b0 =~ /(?!0
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 {Blank}
and
{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 "{Space} isn't, since that includes the vertical
tabulator character, whereas "oesn'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 [Toc] [Back]
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.
Configuration issues [Toc] [Back]
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:
o Minimizes use of temporary files.
o 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.
o Support for pdp11-style memory models has been removed
due to obsolescence.
o 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.
o "Configure -S" can be run non-interactively.
Documentation [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
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.
o fork() emulation has been improved in various ways,
but still continues to be experimental. See perlfork
for known bugs and caveats.
o %SIG has been enabled under USE_ITHREADS, but its use
is completely unsupported under all configurations.
o 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++).
o Non-blocking waits for child processes (or pseudo-processes)
are supported via "waitpid($pid, &POSIX::WNOHANG)".
o A memory leak in accept() has been fixed.
o wait(), waitpid() and backticks now return the correct
exit status under Windows 9x.
o Trailing new %ENV entries weren't propagated to child
processes. This is now fixed.
o Current directory entries in %ENV are now correctly
propagated to child processes.
o Duping socket handles with open(F, ">&MYSOCK") now
works under Windows 9x.
o The makefiles now provide a single switch to bulkenable
all the features enabled in ActiveState
ActivePerl (a popular binary distribution).
o Win32::GetCwd() correctly returns C: instead of C:
when at the drive root. Other bugs in chdir() and
Cwd::cwd() have also been fixed.
o fork() correctly returns undef and sets EAGAIN when it
runs out of pseudo-process handles.
o ExtUtils::MakeMaker now uses $ENV{LIB} to search for
libraries.
o UNC path handling is better when perl is built to support
fork().
o A handle leak in socket handling has been fixed.
o 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.
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 inde-
pendent 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 [Toc] [Back]
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 [Toc] [Back]
The new "scape interpolates named characters within
strings. For example, "Hi! HITE 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 [Toc] [Back]
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 "". 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 [Toc] [Back]
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 $]).
New syntax for declaring subroutine attributes [Toc] [Back]
Formerly, if you wanted to mark a subroutine as being a
method call or as requiring an automatic lock() when it is
entered, you had to declare that with a "use attrs" pragma
in the body of the subroutine. That can now be accomplished
with declaration syntax, like this:
sub mymethod : locked method ;
...
sub mymethod : locked method {
...
}
sub othermethod :locked :method ;
...
sub othermethod :locked :method {
...
}
(Note how only the first ":" is mandatory, and whitespace
surrounding the ":" is optional.)
AutoSplit.pm and SelfLoader.pm have been updated to keep
the attributes with the stubs they provide. See
attributes.
File and directory handles can be autovivified [Toc] [Back]
Similar to how constructs such as "$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:
o constants (decimal, hexadecimal, octal, binary) in the
code
o arguments to oct() and hex()
o arguments to print(), printf() and sprintf() (flag
prefixes ll, L, q)
o printed as such
o pack() and unpack() "q" and "Q" formats
o in basic arithmetics: + - * / % (NOTE: operating close
to the limits of the integer values may produce surprising
results)
o in bit arithmetics: & | ^ ~ << >> (NOTE: these used to
be forced to be 32 bits wide but now operate on the
full native width.)
o 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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
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 "$foo|$bar0;
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 [Toc] [Back]
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()":
$answer = 0b101010;
printf "The answer is: %b0, oct("0b101010");
Lvalue subroutines [Toc] [Back]
Subroutines can now return modifiable lvalues. See
"Lvalue subroutines" in perlsub.
NOTE: This is an experimental feature. Details are
subject to change.
Some arrows may be omitted in calls through references [Toc] [Back]
Perl now allows the arrow to be omitted in many constructs
involving subroutine calls through references. For example,
"$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 [Toc] [Back]
Constructs such as "($a ||= 2) += 1" are now allowed.
exists() is supported on subroutine names
The exists() builtin now works on subroutine names. A
subroutine is considered to exist if it has been declared
(even if implicitly). See "exists" in perlfunc for examples.
exists() and delete() are supported on array elements
The exists() and delete() builtins now work on simple
arrays as well. The behavior is similar to that on hash
elements.
exists() can be used to check whether an array element has
been initialized. This avoids autovivifying array elements
that don't exist. If the array is tied, the
EXISTS() method in the corresponding tied package will be
invoked.
delete() may be used to remove an element from the array
and return it. The array element at that position returns
to its uninitialized state, so that testing for the same
element with exists() will return false. If the element
happens to be the one at the end, the size of the array
also shrinks up to the highest element that tests true for
exists(), or 0 if none such is found. If the array is
tied, the DELETE() method in the corresponding tied package
will be invoked.
See "exists" in perlfunc and "delete" in perlfunc for
examples.
Pseudo-hashes work better [Toc] [Back]
Dereferencing some types of reference values in a
pseudo-hash, such as "$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 pseudohash
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 [Toc] [Back]
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 [Toc] [Back]
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 pseudodisciplines
":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() fail-
ure
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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
More potentially unsafe operations taint their results for
improved security.
The "passwd" and "shell" fields returned by the getp-
went(), getpwnam(), and getpwuid() ar
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