PERL561DELTA(1) Perl Programmers Reference Guide PERL561DELTA(1)
NAME
perl561delta - what's new for perl v5.6.x
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 point-
ers 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 tick-
led 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 pre-
vious versions didn't.
These problems have all been rectified.
Infinity is now recognized as a number.
qw(a\\b)
In Perl 5.6.0, qw(a\\b) produced a string with two backslashes instead of one,
in a departure from the behavior in previous versions. The older behavior has
been reinstated.
caller()
caller() could cause core dumps in certain situations. Carp was sometimes
affected by this problem.
Bugs in regular expressions
Pattern matches on overloaded values are now handled correctly.
Perl 5.6.0 parsed m/\x{ab}/ incorrectly, leading to spurious warnings. This
has been corrected.
The RE engine found in Perl 5.6.0 accidentally pessimised certain kinds of sim-
ple pattern matches. These are now handled better.
Regular expression debug output (whether through "use re 'debug'" or via "-Dr")
now looks better.
Multi-line matches like ""a\nxb\n" =~ /(?!\A)x/m" were flawed. The bug has
been fixed.
Use of $& could trigger a core dump under some situations. This is now
avoided.
Match variables $1 et al., weren't being unset when a pattern match was back-
tracking, and the anomaly showed up inside "/...(?{ ... }).../" etc. These
variables are now tracked correctly.
pos() did not return the correct value within s///ge in earlier versions. This
is now handled correctly.
"slurp" mode
readline() on files opened in "slurp" mode could return an extra "" at the end
in certain situations. This has been corrected.
Autovivification of symbolic references to special variables
Autovivification of symbolic references of special variables described in perl-
var (as in "${$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 cor-
rected.
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 compat-
ibility, but is deprecated.
Spurious syntax errors generated in certain situations, when glob() caused
File::Glob to be loaded for the first time, have been fixed.
Tainting
Some cases of inconsistent taint propagation (such as within hash values) have
been fixed.
The tainting behavior of sprintf() has been rationalized. It does not taint
the result of floating point formats anymore, making the behavior consistent
with that of string interpolation.
sort()
Arguments to sort() weren't being provided the right wantarray() context. The
comparison block is now run in scalar context, and the arguments to be sorted
are always provided list context.
sort() is also fully reentrant, in the sense that the sort function can itself
call sort(). This did not work reliably in previous releases.
#line directives
#line directives now work correctly when they appear at the very beginning of
"eval "..."".
Subroutine prototypes
The (\&) prototype now works properly.
map()
map() could get pathologically slow when the result list it generates is larger
than the source list. The performance has been improved for common scenarios.
Debugger
Debugger exit code now reflects the script exit code.
Condition "0" in breakpoints is now treated correctly.
The "d" command now checks the line number.
$. is no longer corrupted by the debugger.
All debugger output now correctly goes to the socket if RemotePort is set.
PERL5OPT
PERL5OPT can be set to more than one switch group. Previously, it used to be
limited to one group of options only.
chop()
chop(@list) in list context returned the characters chopped in reverse order.
This has been reversed to be in the right order.
Unicode support
Unicode support has seen a large number of incremental improvements, but con-
tinues 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 back-
ward 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 experimen-
tal. 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 environ-
ments 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. How-
ever, the feature still remains experimental.
IO::Socket
IO::Socket::INET failed to open the specified port if the service name was not
known. It now correctly uses the supplied port number as is.
File::Find
File::Find now chdir()s correctly when chasing symbolic links.
xsubpp
xsubpp now tolerates embedded POD sections.
"no Module;"
"no Module;" does not produce an error even if Module does not have an unim-
port() method. This parallels the behavior of "use" vis-a-vis "import".
Tests
A large number of tests have been added.
Core features
untie() will now call an UNTIE() hook if it exists. See perltie for details.
The "-DT" command line switch outputs copious tokenizing information. See perlrun.
Arrays are now always interpolated in double-quotish strings. Previously,
"foo AT bar.com" used to be a fatal error at compile time, if an array @bar was not
used or declared. This transitional behavior was intended to help migrate perl4
code, and is deemed to be no longer useful. See "Arrays now always interpolate
into double-quoted strings".
keys(), each(), pop(), push(), shift(), splice() and unshift() can all be overrid-
den 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 compati-
bility 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 vari-
ous 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, perl-
macos, and perlbs2000 respectively.
The following pod documents are brand new:
perlclib Internal replacements for standard C library functions
perldebtut Perl debugging tutorial
perlebcdic Considerations for running Perl on EBCDIC platforms
perlnewmod Perl modules: preparing a new module for distribution
perlrequick Perl regular expressions quick start
perlretut Perl regular expressions tutorial
perlutil utilities packaged with the Perl distribution
The INSTALL file has been expanded to cover various issues, such as 64-bit support.
A longer list of contributors has been added to the source distribution. See the
file "AUTHORS".
Numerous other changes have been made to the included documentation and FAQs.
Bundled modules
The following modules have been added.
B::Concise
Walks Perl syntax tree, printing concise info about ops. See B::Concise.
File::Temp
Returns name and handle of a temporary file safely. See File::Temp.
Pod::LaTeX
Converts Pod data to formatted LaTeX. See Pod::LaTeX.
Pod::Text::Overstrike
Converts POD data to formatted overstrike text. See Pod::Text::Overstrike.
The following modules have been upgraded.
CGI CGI v2.752 is now included.
CPAN
CPAN v1.59_54 is now included.
Class::Struct
Various bugfixes have been added.
DB_File
DB_File v1.75 supports newer Berkeley DB versions, among other improvements.
Devel::Peek
Devel::Peek has been enhanced to support dumping of memory statistics, when
perl is built with the included malloc().
File::Find
File::Find now supports pre and post-processing of the files in order to sort()
them, etc.
Getopt::Long
Getopt::Long v2.25 is included.
IO::Poll
Various bug fixes have been included.
IPC::Open3
IPC::Open3 allows use of numeric file descriptors.
Math::BigFloat
The fmod() function supports modulus operations. Various bug fixes have also
been included.
Math::Complex
Math::Complex handles inf, NaN etc., better.
Net::Ping
ping() could fail on odd number of data bytes, and when the echo service isn't
running. This has been corrected.
Opcode
A memory leak has been fixed.
Pod::Parser
Version 1.13 of the Pod::Parser suite is included.
Pod::Text
Pod::Text and related modules have been upgraded to the versions in podlators
suite v2.08.
SDBM_File
On dosish platforms, some keys went missing because of lack of support for
files with "holes". A workaround for the problem has been added.
Sys::Syslog
Various bug fixes have been included.
Tie::RefHash
Now supports Tie::RefHash::Nestable to automagically tie hashref values.
Tie::SubstrHash
Various bug fixes have been included.
Platform-specific improvements
The following new ports are now available.
NCR MP-RAS
NonStop-UX
Perl now builds under Amdahl UTS.
Perl has also been verified to build under Amiga OS.
Support for EPOC has been much improved. See README.epoc.
Building perl with -Duseithreads or -Duse5005threads now works under HP-UX 10.20
(previously it only worked under 10.30 or later). You will need a thread library
package installed. See README.hpux.
Long doubles should now work under Linux.
Mac OS Classic is now supported in the mainstream source package. See
README.macos.
Support for MPE/iX has been updated. See README.mpeix.
Support for OS/2 has been improved. See "os2/Changes" and README.os2.
Dynamic loading on z/OS (formerly OS/390) has been improved. See README.os390.
Support for VMS has seen many incremental improvements, including better support
for operators like backticks and system(), and better %ENV handling. See
"README.vms" and perlvms.
Support for Stratus VOS has been improved. See "vos/Changes" and README.vos.
Support for Windows has been improved.
? fork() emulation has been improved in various ways, but still continues to be
experimental. See perlfork for known bugs and caveats.
? %SIG has been enabled under USE_ITHREADS, but its use is completely unsupported
under all configurations.
? Borland C++ v5.5 is now a supported compiler that can build Perl. However, the
generated binaries continue to be incompatible with those generated by the
other supported compilers (GCC and Visual C++).
? Non-blocking waits for child processes (or pseudo-processes) are supported via
"waitpid($pid, &POSIX::WNOHANG)".
? A memory leak in accept() has been fixed.
? wait(), waitpid() and backticks now return the correct exit status under Win-
dows 9x.
? Trailing new %ENV entries weren't propagated to child processes. This is now
fixed.
? Current directory entries in %ENV are now correctly propagated to child pro-
cesses.
? Duping socket handles with open(F, ">&MYSOCK") now works under Windows 9x.
? The makefiles now provide a single switch to bulk-enable all the features
enabled in ActiveState ActivePerl (a popular binary distribution).
? Win32::GetCwd() correctly returns C:\ instead of C: when at the drive root.
Other bugs in chdir() and Cwd::cwd() have also been fixed.
? fork() correctly returns undef and sets EAGAIN when it runs out of pseudo-pro-
cess 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 inter-
preter 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 selec-
tively 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 Win-
dows.) 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 concur-
rently.
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 documenta-
tion on this feature.
Unicode and UTF-8 support
Perl now uses UTF-8 as its internal representation for character strings. The
"utf8" and "bytes" pragmas are used to control this support in the current lexical
scope. See perlunicode, utf8 and bytes for more information.
This feature is expected to evolve quickly to support some form of I/O disciplines
that can be used to specify the kind of input and output data (bytes or charac-
ters). Until that happens, additional modules from CPAN will be needed to complete
the toolkit for dealing with Unicode.
NOTE: This should be considered an experimental feature. Implementation
details are subject to change.
Support for interpolating named characters
The new "\N" escape interpolates named characters within strings. For example,
"Hi! \N{WHITE SMILING FACE}" evaluates to a string with a Unicode smiley face at
the end.
"our" declarations
An "our" declaration introduces a value that can be best understood as a lexically
scoped symbolic alias to a global variable in the package that was current where
the variable was declared. This is mostly useful as an alternative to the "vars"
pragma, but also provides the opportunity to introduce typing and other attributes
for such variables. See "our" in perlfunc.
Support for strings represented as a vector of ordinals
Literals of the form "v1.2.3.4" are now parsed as a string composed of characters
with the specified ordinals. This is an alternative, more readable way to con-
struct (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 per-
form 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 perl-
bug if you are affected by this.)
The v1.2.3 syntax is also now legal in Perl. See "Support for strings represented
as a vector of ordinals" for more on that.
To cope with the new versioning system's use of at least three significant digits
for each version component, the method used for incrementing the subversion number
has also changed slightly. We assume that versions older than v5.6.0 have been
incrementing the subversion component in multiples of 10. Versions after v5.6.0
will increment them by 1. Thus, using the new notation, 5.005_03 is the "same" as
v5.5.30, and the first maintenance version following v5.6.0 will be v5.6.1 (which
should be read as being equivalent to a floating point value of 5.006_001 in the
older format, stored in $]).
New syntax for declaring subroutine attributes
Formerly, if you wanted to mark a subroutine as being a method call or as requiring
an automatic lock() when it is entered, you had to declare that with a "use attrs"
pragma in the body of the subroutine. That can now be accomplished with declara-
tion syntax, like this:
sub mymethod : locked method;
...
sub mymethod : locked method {
...
}
sub othermethod :locked :method;
...
sub othermethod :locked :method {
...
}
(Note how only the first ":" is mandatory, and whitespace surrounding the ":" is
optional.)
AutoSplit.pm and SelfLoader.pm have been updated to keep the attributes with the
stubs they provide. See attributes.
File and directory handles can be autovivified
Similar to how constructs such as "$x->[0]" autovivify a reference, handle con-
structors (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 conve-
niently be closed automatically when the scope ends, provided there are no other
references to them. This largely eliminates the need for typeglobs when opening
filehandles that must be passed around, as in the following example:
sub myopen {
open my $fh, "@_"
or die "Can't open '@_': $!";
return $fh;
}
{
my $f = myopen("</etc/motd");
print <$f>;
# $f implicitly closed here
}
open() with more than two arguments
If open() is passed three arguments instead of two, the second argument is used as
the mode and the third argument is taken to be the file name. This is primarily
useful for protecting against unintended magic behavior of the traditional two-
argument form. See "open" in perlfunc.
64-bit support
Any platform that has 64-bit integers either
(1) natively as longs or ints
(2) via special compiler flags
(3) using long long or int64_t
is able to use "quads" (64-bit integers) as follows:
? constants (decimal, hexadecimal, octal, binary) in the code
? arguments to oct() and hex()
? arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)
? printed as such
? pack() and unpack() "q" and "Q" formats
? in basic arithmetics: + - * / % (NOTE: operating close to the limits of the
integer values may produce surprising results)
? in bit arithmetics: & | ^ ~ << >> (NOTE: these used to be forced to be 32 bits
wide but now operate on the full native width.)
? vec()
Note that unless you have the case (a) you will have to configure and compile Perl
using the -Duse64bitint Configure flag.
NOTE: The Configure flags -Duselonglong and -Duse64bits have been
deprecated. Use -Duse64bitint instead.
There are actually two modes of 64-bitness: the first one is achieved using Config-
ure -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 sys-
tem to be 64-bit aware.
Natively 64-bit systems like Alpha and Cray need neither -Duse64bitint nor
-Duse64bitall.
Last but not least: note that due to Perl's habit of always using floating point
numbers, the quads are still not true integers. When quads overflow their limits
(0...18_446_744_073_709_551_615 unsigned,
-9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they are silently
promoted to floating point numbers, after which they will start losing precision
(in their lower digits).
NOTE: 64-bit support is still experimental on most platforms.
Existing support only covers the LP64 data model. In particular, the
LLP64 data model is not yet supported. 64-bit libraries and system
APIs on many platforms have not stabilized--your mileage may vary.
Large file support
If you have filesystems that support "large files" (files larger than 2 gigabytes),
you may now also be able to create and access them from Perl.
NOTE: The default action is to enable large file support, if
available on the platform.
If the large file support is on, and you have a Fcntl constant O_LARGEFILE, the
O_LARGEFILE is automatically added to the flags of sysopen().
Beware that unless your filesystem also supports "sparse files" seeking to umpteen
petabytes may be inadvisable.
Note that in addition to requiring a proper file system to do large files you may
also need to adjust your per-process (or your per-system, or per-process-group, or
per-user-group) maximum filesize limits before running Perl scripts that try to
handle large files, especially if you intend to write such files.
Finally, in addition to your process/process group maximum filesize limits, you may
have quota limits on your filesystems that stop you (your user id or your user
group id) from using large files.
Adjusting your process/user/group/file system/operating system limits is outside
the scope of Perl core language. For process limits, you may try increasing the
limits using your shell's limits/limit/ulimit command before running Perl. The
BSD::Resource extension (not included with the standard Perl distribution) may also
be of use, it offers the getrlimit/setrlimit interface that can be used to adjust
process resource usage limits, including the maximum filesize limit.
Long doubles
In some systems you may be able to use long doubles to enhance the range and preci-
sion 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) func-
tion. 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 mis-
behaviour of "qw//" in scalar context, which had inherited that behaviour from
split().
Thus:
$foo = ($bar) = qw(a b c); print "$foo|$bar\n";
now correctly prints "3|a", instead of "2|a".
Better worst-case behavior of hashes
Small changes in the hashing algorithm have been implemented in order to improve
the distribution of lower order bits in the hashed value. This is expected to
yield better performance on keys that are repeated sequences.
pack() format 'Z' supported
The new format type 'Z' is useful for packing and unpacking null-terminated
strings. See "pack" in perlfunc.
pack() format modifier '!' supported
The new format type modifier '!' is useful for packing and unpacking native shorts,
ints, and longs. See "pack" in perlfunc.
pack() and unpack() support counted strings
The template character '/' can be used to specify a counted string type to be
packed or unpacked. See "pack" in perlfunc.
Comments in pack() templates
The '#' character in a template introduces a comment up to end of the line. This
facilitates documentation of pack() templates.
Weak references
In previous versions of Perl, you couldn't cache objects so as to allow them to be
deleted if the last reference from outside the cache is deleted. The reference in
the cache would hold a reference count on the object and the objects would never be
destroyed.
Another familiar problem is with circular references. When an object references
itself, its reference count would never go down to zero, and it would not get
destroyed until the program is about to exit.
Weak references solve this by allowing you to "weaken" any reference, that is, make
it not count towards the reference count. When the last non-weak reference to an
object is deleted, the object is destroyed and all the weak references to the
object are automatically undef-ed.
To use this feature, you need the Devel::WeakRef package from CPAN, which contains
additional documentation.
NOTE: This is an experimental feature. Details are subject to change.
Binary numbers supported
Binary numbers are now supported as literals, in s?printf formats, and "oct()":
$answer = 0b101010;
printf "The answer is: %b\n", oct("0b101010");
Lvalue subroutines
Subroutines can now return modifiable lvalues. See "Lvalue subroutines" in perl-
sub.
NOTE: This is an experimental feature. Details are subject to change.
Some arrows may be omitted in calls through references
Perl now allows the arrow to be omitted in many constructs involving subroutine
calls through references. For example, "$foo[10]->('foo')" may now be written
"$foo[10]('foo')". This is rather similar to how the arrow may be omitted from
"$foo[10]->{'foo'}". Note however, that the arrow is still required for
"foo(10)->('bar')".
Boolean assignment operators are legal lvalues
Constructs such as "($a ||= 2) += 1" are now allowed.
exists() is supported on subroutine names
The exists() builtin now works on subroutine names. A subroutine is considered to
exist if it has been declared (even if implicitly). See "exists" in perlfunc for
examples.
exists() and delete() are supported on array elements
The exists() and delete() builtins now work on simple arrays as well. The behavior
is similar to that on hash elements.
exists() can be used to check whether an array element has been initialized. This
avoids autovivifying array elements that don't exist. If the array is tied, the
EXISTS() method in the corresponding tied package will be invoked.
delete() may be used to remove an element from the array and return it. The array
element at that position returns to its uninitialized state, so that testing for
the same element with exists() will return false. If the element happens to be the
one at the end, the size of the array also shrinks up to the highest element that
tests true for exists(), or 0 if none such is found. If the array is tied, the
DELETE() method in the corresponding tied package will be invoked.
See "exists" in perlfunc and "delete" in perlfunc for examples.
Pseudo-hashes work better
Dereferencing some types of reference values in a pseudo-hash, such as
"$ph->{foo}[1]", was accidentally disallowed. This has been corrected.
When applied to a pseudo-hash element, exists() now reports whether the specified
value exists, not merely if the key is valid.
delete() now works on pseudo-hashes. When given a pseudo-hash element or slice it
deletes the values corresponding to the keys (but not the keys themselves). See
"Pseudo-hashes: Using an array as a hash" in perlref.
Pseudo-hash slices with constant keys are now optimized to array lookups at com-
pile-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 confus-
ing 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 pro-
duce 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 corre-
sponding 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 ver-
sions did not report the error properly, since the exec() happened to be in a dif-
ferent process.
The child process now communicates with the parent about the error in launching the
external command, which allows these constructs to return with their usual error
value and set $!.
Improved diagnostics
Line numbers are no longer suppressed (under most likely circumstances) during the
global destruction phase.
Diagnostics emitted from code running in threads other than the main thread are now
accompanied by the thread ID.
Embedded null characters in diagnostics now actually show up. They used to trun-
cate the message in prior versions.
$foo::a and $foo::b are now exempt from "possible typo" warnings only if sort() is
encountered in package "foo".
Unrecognized alphabetic escapes encountered when parsing quote constructs now gen-
erate 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 pro-
voked, 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 $Config{ivsize}). For example, if your
platform is either natively 64-bit or if Perl has been configured to use 64-bit
integers, these operations apply to 8 bytes (as opposed to 4 bytes on 32-bit plat-
forms). For portability, be sure to mask off the excess bits in the result of
unary "~", e.g., "~$x & 0xffffffff".
Improved security features
More potentially unsafe operations taint their results for improved security.
The "passwd" and "shell" fields returned by the getpwent(), getpwnam(), and getp-
wuid() are now tainted, because the user can affect their own encrypted password
and login shell.
The variable modified by shmread(), and messages returned by msgrcv() (and its
object-oriented interface IPC::SysV::Msg::rcv) are also tainted, because other
untrusted processes can modify messages and shared memory segments for their own
nefarious purposes.
More functional bareword prototype (*)
Bareword prototypes have been rationalized to enable them to be used to override
builtins that accept barewords and interpret them in a special way, such as
"require" or "do".
Arguments prototyped as "*" will now be visible within the subroutine as either a
simple scalar or as a reference to a typeglob. See "Prototypes" in perlsub.
"require" and "do" may be overridden
"require" and "do 'file'" operations may be overridden locally by importing subrou-
tines of the same name into the current package (or globally by importing them into
the CORE::GLOBAL:: namespace). Overriding "require" will also affect "use", pro-
vided 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 $^XY was a syntax error. Now vari-
able names that begin with a control character may be arbitrarily long. However,
for compatibility reasons, these variables must be written with explicit braces, as
"${^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 guar-
anteed 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 condi-
tions, 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
$^V contains the Perl version number as a string composed of characters whose ordi-
nals match the version numbers, i.e. v5.6.0. This may be used in string compar-
isons.
See "Support for strings represented as a vector of ordinals" for an example.
Optional Y2K warnings
If Perl is built with the cpp macro "PERL_Y2KWARN" defined, it emits optional warn-
ings when concatenating the number 19 with another number.
This behavior must be specifically enabled when running Configure. See INSTALL and
README.Y2K.
Arrays now always interpolate into double-quoted strings
In double-quoted strings, arrays now interpolate, no matter what. The behavior in
earlier versions of perl 5 was that arrays would interpolate into strings if the
array had been mentioned before the string was compiled, and otherwise Perl would
raise a fatal compile-time error. In versions 5.000 through 5.003, the error was
Literal @example now requires backslash
In versions 5.004_01 through 5.6.0, the error was
In string, @example now must be written as \@example
The idea here was to get people into the habit of writing "fred\@example.com" when
they wanted a literal "@" sign, just as they have always written "Give me back my
\$5" when they wanted a literal "$" sign.
Starting with 5.6.1, when Perl now sees an "@" sign in a double-quoted string, it
always attempts to interpolate an array, regardless of whether or not the array has
been used or declared already. The fatal error has been downgraded to an optional
warning:
Possible unintended interpolation of @example in string
This warns you that "fred AT example.com" is going to turn into "fred.com" if you
don't backslash the "@". See http://www.plover.com/~mjd/perl/at-error.html for
more details about the history here.
@- and @+ provide starting/ending offsets of regex submatches
The new magic variables @- and @+ provide the starting and ending offsets, respec-
tively, of $&, $1, $2, etc. See perlvar for details.
Modules and Pragmata
Modules
attributes
While used internally by Perl as a pragma, this module also provides a way to
fetch subroutine and variable attributes. See attributes.
B The Perl Compiler suite has been extensively reworked for this release. More
of the standard Perl testsuite passes when run under the Compiler, but there is
still a significant way to go to achieve production quality compiled executa-
bles.
NOTE: The Compiler suite remains highly experimental. The
generated code may not be correct, even when it manages to execute
without errors.
Benchmark
Overall, Benchmark results exhibit lower average error and better timing accu-
racy.
You can now run tests for n seconds instead of guessing the right number of
tests to run: e.g., timethese(-5, ...) will run each code for at least 5 CPU
seconds. Zero as the "number of repetitions" means "for at least 3 CPU sec-
onds". The output format has also changed. For example:
use Benchmark;$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 per-
centage speed difference (iters/sec or seconds/iter) is shown.
For other details, see Benchmark.
ByteLoader
The ByteLoader is a dedicated extension to generate and run Perl bytecode. See
ByteLoader.
constant
References can now be used.
The new version also allows a leading underscore in constant names, but disal-
lows a double leading underscore (as in "__LINE__"). Some other names are dis-
allowed or warned against, including BEGIN, END, etc. Some names which were
forced into main:: used to fail silently in some cases; now they're fatal (out-
side of main::) and an optional warning (inside of main::). The ability to
detect whether a constant had been set with a given name has been added.
See constant.
charnames
This pragma implements the "\N" string escape. See charnames.
Data::Dumper
A "Maxdepth" setting can be specified to avoid venturing too deeply into deep
data structures. See Data::Dumper.
The XSUB implementation of Dump() is now automatically called if the "Useqq"
setting is not in use.
Dumping "qr//" objects works correctly.
DB "DB" is an experimental module that exposes a clean abstraction to Perl's
debugging API.
DB_File
DB_File can now be built with Berkeley DB versions 1, 2 or 3. See
"ext/DB_File/Changes".
Devel::DProf
Devel::DProf, a Perl source code profiler has been added. See Devel::DProf and
dprofpp.
Devel::Peek
The Devel::Peek module provides access to the internal representation of Perl
variables and data. It is a data debugging tool for the XS programmer.
Dumpvalue
The Dumpvalue module provides screen dumps of Perl data.
DynaLoader
DynaLoader now supports a dl_unload_file() function on platforms that support
unloading shared objects using dlclose().
Perl can also optionally arrange to unload all extension shared objects loaded
by Perl. To enable this, build Perl with the Configure option
"-Accflags=-DDL_UNLOAD_ALL_AT_EXIT". (This maybe useful if you are using
Apache with mod_perl.)
English
$PERL_VERSION now stands for $^V (a string value) rather than for $] (a numeric
value).
Env Env now supports accessing environment variables like PATH as array variables.
Fcntl
More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for large file
(more than 4GB) access (NOTE: the O_LARGEFILE is automatically added to
sysopen() flags if large file support has been configured, as is the default),
Free/Net/OpenBSD locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and
O_ACCMODE: the combined mask of O_RDONLY, O_WRONLY, and O_RDWR. The
seek()/sysseek() constants SEEK_SET, SEEK_CUR, and SEEK_END are available via
the ":seek" tag. The chmod()/stat() S_IF* constants and S_IS* functions are
available via the ":mode" tag.
File::Compare
A compare_text() function has been added, which allows custom comparison func-
tions. 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 prun-
ing top-level directories has been fixed.
File::Find now also supports several other options to control its behavior. It
can follow symbolic links if the "follow" option is specified. Enabling the
"no_chdir" option will make File::Find skip changing the current directory when
walking directories. The "untaint" flag can be useful when running with taint
checks enabled.
See File::Find.
File::Glob
This extension implements BSD-style file globbing. By default, it will also be
used for the internal implementation of the glob() operator. See File::Glob.
File::Spec
New methods have been added to the File::Spec module: devnull() returns the
name of the null device (/dev/null on Unix) and tmpdir() the name of the temp
directory (normally /tmp on Unix). There are now also methods to convert
between absolute and relative filenames: abs2rel() and rel2abs(). For compati-
bility 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 applica-
tions that wanted to use Getopt::Long.
Getopt::Long encourages the use of Pod::Usage to produce help messages. For
example:
use Getopt::Long;
use Pod::Usage;
my $man = 0;
my $help = 0;
GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
pod2usage(1) if $help;
pod2usage(-exitstatus => 0, -verbose => 2) if $man;
__END__
=head1 NAME
sample - Using Getopt::Long and Pod::Usage
=head1 SYNOPSIS
sample [options] [file ...]
Options:
-help brief help message
-man full documentation
=head1 OPTIONS
=over 8
=item B<-help>
Print a brief help message and exits.
=item B<-man>
Prints the manual page and exits.
=back
=head1 DESCRIPTION
B<This program> will read the given input file(s) and do something
useful with the contents thereof.
=cut
See Pod::Usage for details.
A bug that prevented the non-option call-back <> from being specified as the
first argument has been fixed.
To specify the characters < and > as option starters, use ><. Note, however,
that changing option starters is strongly deprecated.
IO write() and syswrite() will now accept a single-argument form of the call, for
consistency with Perl's syswrite().
You can now create a TCP-based IO::Socket::INET without forcing a connect
attempt. This allows you to configure its options (like making it non-block-
ing) 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 informa-
tion.
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 big-
ints.
Math::Complex
The accessor methods Re, Im, arg, abs, rho, and theta can now also act as muta-
tors (accessor $z->Re(), mutator $z->Re(3)).
The class method "display_format" and the corresponding object method "dis-
play_format", in addition to accepting just one argument, now can also accept a
parameter hash. Recognized keys of a parameter hash are "style", which corre-
sponds 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 coordi-
nate 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 documen-
tation from an input stream. This module takes care of identifying pod para-
graphs and commands in the input and hands off the parsed paragraphs and com-
mands to user-defined methods which are free to interpret or translate them as
they see fit.
Pod::InputObjects defines some input objects needed by Pod::Parser, and for
advanced users of Pod::Parser that need more about a command besides its name
and text.
As of release 5.6.0 of Perl, Pod::Parser is now the officially sanctioned "base
parser code" recommended for use by all pod2xxx translators. Pod::Text
(pod2text) and Pod::Man (pod2man) have already been converted to use
Pod::Parser and efforts to convert Pod::HTML (pod2html) are already underway.
For any questions or comments about pod parsing and translating issues and
utilities, please use the pod-people AT perl.org mailing list.
For further information, please see Pod::Parser and Pod::InputObjects.
Pod::Checker, podchecker
This utility checks pod files for correct syntax, according to perlpod. Obvi-
ous 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 transla-
tors. 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 "pods-
elect()" 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::Term-
cap for man-page-style bold and underlining using termcap information, and
Pod::Text::Color for markup with ANSI color sequences) are now standard.
pod2man has been turned into a module, Pod::Man, which also uses Pod::Parser.
In the process, several outstanding bugs related to quotes in section headers,
quoting of code escapes, and nested lists have been fixed. pod2man is now a
wrapper script around this module.
SDBM_File
An EXISTS method has been added to this module (and sdbm_exists() has been
added to the underlying sdbm library), so one can now call exists on an
SDBM_File tied hash and get the correct result, rather than a runtime error.
A bug that may have caused data loss when more than one disk block happens to
be read from the database in a single FETCH() has been fixed.
Sys::Syslog
Sys::Syslog now uses XSUBs to access facilities from syslog.h so it no longer
requires syslog.ph to exist.
Sys::Hostname
Sys::Hostname now uses XSUBs to call the C library's gethostname() or uname()
if they exist.
Term::ANSIColor
Term::ANSIColor is a very simple module to provide easy and readable access to
the ANSI color and highlighting escape sequences, supported by most ANSI termi-
nal emulators. It is now included standard.
Time::Local
The timelocal() and timegm() functions used to silently return bogus results
when the date fell outside the machine's integer range. They now consistently
croak() if the date falls in an unsupported range.
Win32
The error return value in list context has been changed for all functions that
return a list of values. Previously these functions returned a list with a
single element "undef" if an error occurred. Now these functions return the
empty list in these situations. This applies to the following functions:
Win32::FsType
Win32::GetOSVersion
The remaining functions are unchanged and continue to return "undef" on error
even in list context.
The Win32::SetLastError(ERROR) function has been added as a complement to the
Win32::GetLastError() function.
The new Win32::GetFullPathName(FILENAME) returns the full absolute pathname for
FILENAME in scalar context. In list context it returns a two-element list con-
taining 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 mod-
ules--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 per-
llexwarn.
"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 construc-
tors (e.g. open()) and for qx//. The two pseudo-disciplines ":raw" and ":crlf" are
currently supported on DOS-derivative platforms (i.e. where binmode is not a
no-op). See also "binmode() can be used to set :crlf and :raw modes".
Utility Changes
dprofpp
"dprofpp" is used to display profile data generated using "Devel::DProf". See
dprofpp.
find2perl
The "find2perl" utility now uses the enhanced features of the File::Find module.
The -depth and -follow options are supported. Pod documentation is also included
in the script.
h2xs
The "h2xs" tool can now work in conjunction with "C::Scan" (available from CPAN) to
automatically parse real-life header files. The "-M", "-a", "-k", and "-o" options
are new.
perlcc
"perlcc" now supports the C and Bytecode backends. By default, it generates output
from the simple C backend rather than the optimized C backend.
Support for non-Unix platforms has been improved.
perldoc
"perldoc" has been reworked to avoid possible security holes. It will not by
default let itself be run as the superuser, but you may still use the -U switch to
try to make it drop privileges first.
The Perl Debugger
Many bug fixes and enhancements were added to perl5db.pl, the Perl debugger. The
help documentation was rearranged. New commands include "< ?", "> ?", and "{ ?" to
list out current actions, "man docpage" to run your doc viewer on some perl docset,
and support for quoted options. The help information was rearranged, and should be
viewable once again if you're using less as your pager. A serious security hole
was plugged--you should immediately remove all older versions of the Perl debugger
as installed in previous releases, all the way back to perl3, from your system to
avoid being bitten by this.
Improved Documentation
Many of the platform-specific README files are now part of the perl installation.
See perl for the complete list.
perlapi.pod
The official list of public Perl API functions.
perlboot.pod
A tutorial for beginners on object-oriented Perl.
perlcompile.pod
An introduction to using the Perl Compiler suite.
perldbmfilter.pod
A howto document on using the DBM filter facility.
perldebug.pod
All material unrelated to running the Perl debugger, plus all low-level guts-
like details that risked crushing the casual user of the debugger, have been
relocated from the old manpage to the next entry below.
perldebguts.pod
This new manpage contains excessively low-level material not related to the
Perl debugger, but slightly related to debugging Perl itself. It also contains
some arcane internal details of how the debugging process works that may only
be of interest to developers of Perl debuggers.
perlfork.pod
Notes on the fork() emulation currently available for the Windows platform.
perlfilter.pod
An introduction to writing Perl source filters.
perlhack.pod
Some guidelines for hacking the Perl source code.
perlintern.pod
A list of internal functions in the Perl source code. (List is currently
empty.)
perllexwarn.pod
Introduction and reference information about lexically scoped warning cate-
gories.
perlnumber.pod
Detailed information about numbers as they are represented in Perl.
perlopentut.pod
A tutorial on using open() effectively.
perlreftut.pod
A tutorial that introduces the essentials of references.
perltootc.pod
A tutorial on managing class data for object modules.
perltodo.pod
Discussion of the most often wanted features that may someday be supported in
Perl.
perlunicode.pod
An introduction to Unicode support features in Perl.
Performance enhancements
Simple sort() using { $a <=> $b } and the like are optimized
Many common sort() operations using a simple inlined block are now optimized for
faster performance.
Optimized assignments to lexical variables
Certain operations in the RHS of assignment statements have been optimized to
directly set the lexical variable on the LHS, eliminating redundant copying over-
heads.
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 signifi-
cantly better performance, because it eliminates needless copying in most situa-
tions.
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 sys-
tems of known threads/64-bit capabilities. In other words: if your operating sys-
tem has the necessary APIs and datatypes, you should be able just to go ahead and
use them, for threads by Configure -Dusethreads, and for 64 bits either explicitly
by Configure -Duse64bitint or implicitly if your system has 64-bit wide datatypes.
See also "64-bit support".
Long Doubles
Some platforms have "long doubles", floating point numbers of even larger range
than ordinary "doubles". To enable using long doubles for Perl's scalars, use
-Duselongdouble.
-Dusemorebits
You can enable both -Duse64bitint and -Duselongdouble with -Dusemorebits. See also
"64-bit support".
-Duselargefiles
Some platforms support system APIs that are capable of handling large files (typi-
cally, files larger than two gigabytes). Perl will try to use these APIs if you
ask for -Duselargefiles.
See "Large file support" for more information.
installusrbinperl
You can use "Configure -Uinstallusrbinperl" which causes installperl to skip
installing perl also as /usr/bin/perl. This is useful if you prefer not to modify
/usr/bin for some reason or another but harmful because many scripts assume to find
Perl in /usr/bin/perl.
SOCKS support
You can use "Configure -Dusesocks" which causes Perl to probe for the SOCKS proxy
protocol library (v5, not v4). For more information on SOCKS, see:
http://www.socks.nec.com/
"-A" flag
You can "post-edit" the Configure variables using the Configure "-A" switch. The
editing happens immediately after the platform specific hints files have been pro-
cessed 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 ver-
sion 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 exten-
sion.
? 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 repre-
sentation for characters with the EBCDIC character set, because the two are incom-
patible.
It is unclear whether future versions will renew support for this platform, but the
possibility exists.
VMS
Numerous revisions and extensions to configuration, build, testing, and installa-
tion process to accommodate core changes and VMS-specific options.
Expand %ENV-handling code to allow runtime mapping to logical names, CLI symbols,
and CRTL environ array.
Extension of subprocess invocation code to accept filespecs as command "verbs".
Add to Perl command line processing the ability to use default file types and to
recognize Unix-style "2>&1".
Expansion of File::Spec::VMS routines, and integration into ExtUtils::MM_VMS.
Extension of ExtUtils::MM_VMS to handle complex extensions more flexibly.
Barewords at start of Unix-syntax paths may be treated as text rather than only as
logical names.
Optional secure translation of several logical names used internally by Perl.
Miscellaneous bugfixing and porting of new core code to VMS.
Thanks are gladly extended to the many people who have contributed VMS patches,
testing, and ideas.
Win32
Perl can now emulate fork() internally, using multiple interpreters running in dif-
ferent concurrent threads. This support must be enabled at build time. See perl-
fork 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::GetFullPath-
Name() 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 glob-
bing syntax. If you want to preserve compatibility with the older syntax, you
might want to run perl with "-MFile::DosGlob". For details and compatibility
information, see File::Glob.
Significant bug fixes
<HANDLE> on empty files
With $/ set to "undef", "slurping" an empty file returns a string of zero length
(instead of "undef", as it used to) the first time the HANDLE is read after $/ is
set to "undef". Further reads yield "undef".
This means that the following will append "foo" to an empty file (it used to do
nothing):
perl -0777 -pi -e 's/^/foo/' empty_file
The behaviour of:
perl -pi -e 's/^/foo/' empty_file
is unchanged (it continues to leave the file empty).
"eval '...'" improvements
Line numbers (as reflected by caller() and most diagnostics) within "eval '...'"
were often incorrect where here documents were involved. This has been corrected.
Lexical lookups for variables appearing in "eval '...'" within functions that were
themselves called within an "eval '...'" were searching the wrong place for lexi-
cals. 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 auto-
matically closes them on exiting the scope) could inadvertently set $? or $!. This
has been corrected.
Behavior of list slices is more consistent
When taking a slice of a literal list (as opposed to a slice of an array or hash),
Perl used to return an empty list if the result happened to be composed of all
undef values.
The new behavior is to produce an empty list if (and only if) the original list was
empty. Consider the following example:
@a = (1,undef,undef,2)[2,1,2];
The old behavior would have resulted in @a having no elements. The new behavior
ensures it has three undefined elements.
Note in particular that the behavior of slices of the following cases remains
unchanged:
@a = ()[1,2];
@a = (getpwent)[7,0];
@a = (anything_returning_empty_list())[2,1,2];
@a = @b[2,1,2];
@a = @c{'a','b','c'};
See perldata.
"(\$)" prototype and $foo{a}
A scalar reference prototype now correctly allows a hash or array element in that
slot.
"goto &sub" and AUTOLOAD
The "goto &sub" construct works correctly when &sub happens to be autoloaded.
"-bareword" allowed under "use integer"
The autoquoting of barewords preceded by "-" did not work in prior versions when
the "integer" pragma was enabled. This has been fixed.
Failures in DESTROY()
When code in a destructor threw an exception, it went unnoticed in earlier versions
of Perl, unless someone happened to be looking in $@ just after the point the
destructor happened to run. Such failures are now visible as warnings when
warnings are enabled.
Locale bugs fixed
printf() and sprintf() previously reset the numeric locale back to the default "C"
locale. This has been fixed.
Numbers formatted according to the local numeric locale (such as using a decimal
comma instead of a decimal dot) caused "isn't numeric" warnings, even while the
operations accessing those numbers produced correct results. These warnings have
been discontinued.
Memory leaks
The "eval 'return sub {...}'" construct could sometimes leak memory. This has been
fixed.
Operations that aren't filehandle constructors used to leak memory when used on
invalid filehandles. This has been fixed.
Constructs that modified @_ could fail to deallocate values in @_ and thus leak
memory. This has been corrected.
Spurious subroutine stubs after failed subroutine calls
Perl could sometimes create empty subroutine stubs when a subroutine was not found
in the package. Such cases stopped later method lookups from progressing into base
packages. This has been corrected.
Taint failures under "-U"
When running in unsafe mode, taint violations could sometimes cause silent fail-
ures. 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 exe-
cuted anymore when the "-c" switch is used, or if compilation fails.
See "Support for CHECK blocks" for how to run things when the compile phase ends.
Potential to leak DATA filehandles
Using the "__DATA__" token creates an implicit filehandle to the file that contains
the token. It is the program's responsibility to close it when it is done reading
from it.
This caveat is now better explained in the documentation. See perldata.
New or Changed Diagnostics
"%s" variable %s masks earlier declaration in same %s
(W misc) A "my" or "our" variable has been redeclared in the current scope or
statement, effectively eliminating all access to the previous instance. This
is almost always a typographical error. Note that the earlier variable will
still exist until the end of the scope or until all closure referents to it are
destroyed.
"my sub" not yet implemented
(F) Lexically scoped subroutines are not yet implemented. Don't try that yet.
"our" variable %s redeclared
(W misc) You seem to have already declared the same global once before in the
current lexical scope.
'!' allowed only after types %s
(F) The '!' is allowed in pack() and unpack() only after certain types. See
"pack" in perlfunc.
/ cannot take a count
(F) You had an unpack template indicating a counted-length string, but you have
also specified an explicit size for the string. See "pack" in perlfunc.
/ must be followed by a, A or Z
(F) You had an unpack template indicating a counted-length string, which must
be followed by one of the letters a, A or Z to indicate what sort of string is
to be unpacked. See "pack" in perlfunc.
/ must be followed by a*, A* or Z*
(F) You had a pack template indicating a counted-length string, Currently the
only things that can have their length counted are a*, A* or Z*. See "pack" in
perlfunc.
/ must follow a numeric type
(F) You had an unpack template that contained a '#', but this did not follow
some numeric unpack specification. See "pack" in perlfunc.
/%s/: Unrecognized escape \\%c passed through
(W regexp) You used a backslash-character combination which is not recognized
by Perl. This combination appears in an interpolated variable or a "'"-delim-
ited 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 declara-
tion 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 indi-
cated exception. Since destructors are usually called by the system at arbi-
trary points during execution, and often a vast number of times, the warning is
issued only once for any number of failures that would otherwise result in the
same message being repeated.
Failure of user callbacks dispatched using the "G_KEEPERR" flag could also
result in this warning. See "G_KEEPERR" in perlcall.
<> should be quotes
(F) You wrote "require <file>" when you should have written "require 'file'".
Attempt to join self
(F) You tried to join a thread from within itself, which is an impossible task.
You may be joining the wrong thread, or you may need to move the join() to some
other thread.
Bad evalled substitution pattern
(F) You've used the /e switch to evaluate the replacement for a substitution,
but perl found a syntax error in the code to evaluate, most likely an unex-
pected right brace '}'.
Bad realloc() ignored
(S) An internal routine called realloc() on something that had never been mal-
loc()ed in the first place. Mandatory, but can be disabled by setting environ-
ment 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 bare-
word:
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 quali-
fier 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 inter-
fere with proper determination of exit status of child processes, Perl has
reset the signal to its default value. This situation typically indicates that
the parent program under which Perl may be running (e.g., cron) is being very
careless.
Can't modify non-lvalue subroutine call
(F) Subroutines meant to be used in lvalue context should be declared as such,
see "Lvalue subroutines" in perlsub.
Can't read CRTL environ
(S) A warning peculiar to VMS. Perl tried to read an element of %ENV from the
CRTL's internal environment array and discovered the array was missing. You
need to figure out where your CRTL misplaced its environ or define
PERL_ENV_TABLES (see perlvms) so that environ is not searched.
Can't remove %s: %s, skipping file
(S) You requested an inplace edit without creating a backup file. Perl was
unable to remove the original file to replace it with the modified file. The
file was left unmodified.
Can't return %s from lvalue subroutine
(F) Perl detected an attempt to return illegal lvalues (such as temporary or
readonly values) from a subroutine used as an lvalue. This is not allowed.
Can't weaken a nonreference
(F) You attempted to weaken something that was not a reference. Only refer-
ences can be weakened.
Character class [:%s:] unknown
(F) The class in the character class [: :] syntax is unknown. See perlre.
Character class syntax [%s] belongs inside character classes
(W unsafe) The character class constructs [: :], [= =], and [. .] go inside
character classes, the [] are part of the construct, for example:
/[012[:alpha:]345]/. Note that [= =] and [. .] are not currently implemented;
they are simply placeholders for future extensions.
Constant is not %s reference
(F) A constant value (perhaps declared using the "use constant" pragma) is
being dereferenced, but it amounts to the wrong type of reference. The message
indicates the type of reference that was expected. This usually indicates a
syntax error in dereferencing the constant value. See "Constant Functions" in
perlsub and constant.
constant(%s): %s
(F) The parser found inconsistencies either while attempting to define an over-
loaded 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 unde-
fined 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 unde-
fined scalar value. If you want to see if the hash is empty, just use "if
(%hash) { # not empty }" for example.
Did not produce a valid header
See Server error.
(Did you mean "local" instead of "our"?)
(W misc) Remember that "our" does not localize the declared global variable.
You have declared it again in the same lexical scope, which seems superfluous.
Document contains no data
See Server error.
entering effective %s failed
(F) While under the "use filetest" pragma, switching the real and effective
uids or gids failed.
false [] range "%s" in regexp
(W regexp) A character class range must start and end at a literal character,
not another character class like "\d" or "[:alpha:]". The "-" in your false
range is interpreted as a literal "-". Consider quoting the "-", "\-". See
perlre.
Filehandle %s opened only for output
(W io) You tried to read from a filehandle opened only for writing. If you
intended it to be a read/write filehandle, you needed to open it with "+<" or
"+>" or "+>>" instead of with "<" or nothing. If you intended only to read
from the file, use "<". See "open" in perlfunc.
flock() on closed filehandle %s
(W closed) The filehandle you're attempting to flock() got itself closed some
time before now. Check your logic flow. flock() operates on filehandles. Are
you attempting to call flock() on a dirhandle by the same name?
Global symbol "%s" requires explicit package name
(F) You've said "use strict vars", which indicates that all variables must
either be lexically scoped (using "my"), declared beforehand using "our", or
explicitly qualified to say which package the global variable is in (using
"::").
Hexadecimal number > 0xffffffff non-portable
(W portable) The hexadecimal number you specified is larger than 2**32-1
(4294967295) and therefore non-portable between systems. See perlport for more
on portability concerns.
Ill-formed CRTL environ value "%s"
(W internal) A warning peculiar to VMS. Perl tried to read the CRTL's internal
environ array, and encountered an element without the "=" delimiter used to
separate keys from values. The element is ignored.
Ill-formed message in prime_env_iter: |%s|
(W internal) A warning peculiar to VMS. Perl tried to read a logical name or
CLI symbol definition when preparing to iterate over %ENV, and didn't see the
expected delimiter between key and value, so the line was ignored.
Illegal binary digit %s
(F) You used a digit other than 0 or 1 in a binary number.
Illegal binary digit %s ignored
(W digit) You may have tried to use a digit other than 0 or 1 in a binary num-
ber. 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 architec-
ture, and has been converted to a floating point number. On a 32-bit architec-
ture 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 subse-
quent operations.
Invalid %s attribute: %s
The indicated attribute for a subroutine or variable was not recognized by Perl
or by a user-supplied handler. See attributes.
Invalid %s attributes: %s
The indicated attributes for a subroutine or variable were not recognized by
Perl or by a user-supplied handler. See attributes.
invalid [] range "%s" in regexp
The offending range is now explicitly displayed.
Invalid separator character %s in attribute list
(F) Something other than a colon or whitespace was seen between the elements of
an attribute list. If the previous attribute had a parenthesised parameter
list, perhaps that list was terminated too soon. See attributes.
Invalid separator character %s in subroutine attribute list
(F) Something other than a colon or whitespace was seen between the elements of
a subroutine attribute list. If the previous attribute had a parenthesised
parameter list, perhaps that list was terminated too soon.
leaving effective %s failed
(F) While under the "use filetest" pragma, switching the real and effective
uids or gids failed.
Lvalue subs returning %s not implemented yet
(F) Due to limitations in the current implementation, array and hash values
cannot be returned in subroutines used in lvalue context. See "Lvalue subrou-
tines" in perlsub.
Method %s not permitted
See Server error.
Missing %sbrace%s on \N{}
(F) Wrong syntax of character name literal "\N{charname}" within double-quotish
context.
Missing command in piped open
(W pipe) You used the "open(FH, "| command")" or "open(FH, "command |")" con-
struction, but the command was missing or blank.
Missing name in "my sub"
(F) The reserved syntax for lexically scoped subroutines requires that they
have a name with which they can be found.
No %s specified for -%c
(F) The indicated command line switch needs a mandatory argument, but you
haven't specified one.
No package name allowed for variable %s in "our"
(F) Fully qualified variable names are not allowed in "our" declarations,
because that doesn't make much sense under existing semantics. Such syntax is
reserved for future extensions.
No space allowed after -%c
(F) The argument to the indicated command line switch must follow immediately
after the switch, without intervening spaces.
no UTC offset information; assuming local time is UTC
(S) A warning peculiar to VMS. Perl was unable to find the local timezone off-
set, 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 num-
ber 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 portabil-
ity concerns.
See also perlport for writing portable code.
panic: del_backref
(P) Failed an internal consistency check while trying to reset a weak refer-
ence.
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 refer-
ences to an object.
Parentheses missing around "%s" list
(W parenthesis) You said something like
my $foo, $bar = @_;
when you meant
my ($foo, $bar) = @_;
Remember that "my", "our", and "local" bind tighter than comma.
Possible unintended interpolation of %s in string
(W ambiguous) It used to be that Perl would try to guess whether you wanted an
array interpolated or a literal @. It no longer does this; arrays are now
always interpolated into strings. This means that if you try something like:
print "fred AT example.com";
and the array @example doesn't exist, Perl is going to print "fred.com", which
is probably not what you wanted. To get a literal "@" sign in a string, put a
backslash before it, just as you would to get a literal "$" sign.
Possible Y2K bug: %s
(W y2k) You are concatenating the number 19 with another number, which could be
a potential Year 2000 problem.
pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead
(W deprecated) You have written something like this:
sub doit
{
use attrs qw(locked);
}
You should use the new declaration syntax instead.
sub doit : locked
{
...
The "use attrs" pragma is now obsolete, and is only provided for backward-com-
patibility. 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 effec-
tive uids or gids.