PERL561DELTA(1) Perl Programmers Reference Guide PERL561DELTA(1)
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.
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 "..."".
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.
"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, "[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
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
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.
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.
· 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.
"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 $] (a numeric value). (This is
a potential incompatibility. Send us a report via perlbug if you are affected by this.)
Formerly, if you wanted to mark a subroutine as being a method call or as requiring an automatic lock() when
it is entered, you had to declare that with a "use attrs" pragma in the body of the subroutine. That can now
be accomplished with declaration syntax, like this:
sub mymethod : locked method;
...
sub mymethod : locked method {
...
}
sub othermethod :locked :method;
...
sub othermethod :locked :method {
...
}
(Note how only the first ":" is mandatory, and whitespace surrounding the ":" is optional.)
AutoSplit.pm and SelfLoader.pm have been updated to keep the attributes with the stubs they provide. See
attributes.
File and directory handles can be autovivified
Similar to how constructs such as "$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:
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
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
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
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
"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".
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
@- 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.
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
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.
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
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.
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.
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.
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.
/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,
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".
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.
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.
/%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
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.
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
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.
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 "[email protected]";
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"
(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().
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
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
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
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
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.
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 [email protected] to be analysed by the Perl porting team.
SEE ALSO
The Changes file for exhaustive details on what changed.
The INSTALL file for how to build Perl.
The README file for general stuff.
The Artistic and Copying files for copyright information.
HISTORY
Written by Gurusamy Sarathy <[email protected]>, with many contributions from The Perl Porters.
Send omissions or corrections to <[email protected]>.
perl v5.16.3 2013-03-04 PERL561DELTA(1)
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