PERL56DELTA(1) Perl Programmers Reference Guide PERL56DELTA(1)
NAME
perl56delta - what's new for perl v5.6.0
DESCRIPTION
This document describes differences between the 5.005 release and the
5.6.0 release.
Core Enhancements
Interpreter cloning, threads, and concurrency
Perl 5.6.0 introduces the beginnings of support for running multiple
interpreters concurrently in different threads. In conjunction with the
perl_clone() API call, which can be used to selectively duplicate the
state of any given interpreter, it is possible to compile a piece of
code once in an interpreter, clone that interpreter one or more times,
and run all the resulting interpreters in distinct threads.
On the Windows platform, this feature is used to emulate fork() at the
interpreter level. See perlfork for details about that.
This feature is still in evolution. It is eventually meant to be used
to selectively clone a subroutine and data reachable from that
subroutine in a separate interpreter and run the cloned subroutine in a
separate thread. Since there is no shared data between the
interpreters, little or no locking will be needed (unless parts of the
symbol table are explicitly shared). This is obviously intended to be
an easy-to-use replacement for the existing threads support.
Support for cloning interpreters and interpreter concurrency can be
enabled using the -Dusethreads Configure option (see win32/Makefile for
how to enable it on Windows.) The resulting perl executable will be
functionally identical to one that was built with -Dmultiplicity, but
the perl_clone() API call will only be available in the former.
-Dusethreads enables the cpp macro USE_ITHREADS by default, which in
turn enables Perl source code changes that provide a clear separation
between the op tree and the data it operates with. The former is
immutable, and can therefore be shared between an interpreter and all of
its clones, while the latter is considered local to each interpreter,
and is therefore copied for each clone.
Note that building Perl with the -Dusemultiplicity Configure option is
adequate if you wish to run multiple independent interpreters
concurrently in different threads. -Dusethreads only provides the
additional functionality of the perl_clone() API call and other support
for running cloned interpreters concurrently.
NOTE: This is an experimental feature. Implementation details are
subject to change.
Lexically scoped warning categories
You can now control the granularity of warnings emitted by perl at a
finer level using the "use warnings" pragma. warnings and perllexwarn
have copious documentation on this feature.
Unicode and UTF-8 support
Perl now uses UTF-8 as its internal representation for character
strings. The "utf8" and "bytes" pragmas are used to control this
support in the current lexical scope. See perlunicode, utf8 and bytes
for more information.
This feature is expected to evolve quickly to support some form of I/O
disciplines that can be used to specify the kind of input and output
data (bytes or characters). Until that happens, additional modules from
CPAN will be needed to complete the toolkit for dealing with Unicode.
NOTE: This should be considered an experimental feature. Implementation
details are subject to change.
Support for interpolating named characters
The new "\N" escape interpolates named characters within strings. For
example, "Hi! \N{WHITE SMILING FACE}" evaluates to a string with a
unicode smiley face at the end.
"our" declarations
An "our" declaration introduces a value that can be best understood as a
lexically scoped symbolic alias to a global variable in the package that
was current where the variable was declared. This is mostly useful as
an alternative to the "vars" pragma, but also provides the opportunity
to introduce typing and other attributes for such variables. See "our"
in perlfunc.
Support for strings represented as a vector of ordinals
Literals of the form "v1.2.3.4" are now parsed as a string composed of
characters with the specified ordinals. This is an alternative, more
readable way to construct (possibly unicode) strings instead of
interpolating characters, as in "\x{1}\x{2}\x{3}\x{4}". The leading "v"
may be omitted if there are more than two ordinals, so 1.2.3 is parsed
the same as "v1.2.3".
Strings written in this form are also useful to represent version
"numbers". It is easy to compare such version "numbers" (which are
really just plain strings) using any of the usual string comparison
operators "eq", "ne", "lt", "gt", etc., or perform bitwise string
operations on them using "|", "&", etc.
In conjunction with the new $^V magic variable (which contains the perl
version as a string), such literals can be used as a readable way to
check if you're running a particular version of Perl:
# this will parse in older versions of Perl also
if ($^V and $^V gt v5.6.0) {
# new features supported
}
"require" and "use" also have some special magic to support such
literals, but this particular usage should be avoided because it leads
to misleading error messages under versions of Perl which don't support
vector strings. Using a true version number will ensure correct
behavior in all versions of Perl:
require 5.006; # run time check for v5.6
use 5.006_001; # compile time check for v5.6.1
Also, "sprintf" and "printf" support the Perl-specific format flag %v to
print ordinals of characters in arbitrary strings:
printf "v%vd", $^V; # prints current version, such as "v5.5.650"
printf "%*vX", ":", $addr; # formats IPv6 address
printf "%*vb", " ", $bits; # displays bitstring
See "Scalar value constructors" in perldata for additional information.
Improved Perl version numbering system
Beginning with Perl version 5.6.0, the version number convention has
been changed to a "dotted integer" scheme that is more commonly found in
open source projects.
Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc.
The next development series following v5.6.0 will be numbered v5.7.x,
beginning with v5.7.0, and the next major production release following
v5.6.0 will be v5.8.0.
The English module now sets $PERL_VERSION to $^V (a string value) rather
than $] (a numeric value). (This is a potential incompatibility. Send
us a report via perlbug if you are affected by this.)
The v1.2.3 syntax is also now legal in Perl. See "Support for strings
represented as a vector of ordinals" for more on that.
To cope with the new versioning system's use of at least three
significant digits for each version component, the method used for
incrementing the subversion number has also changed slightly. We assume
that versions older than v5.6.0 have been incrementing the subversion
component in multiples of 10. Versions after v5.6.0 will increment them
by 1. Thus, using the new notation, 5.005_03 is the "same" as v5.5.30,
and the first maintenance version following v5.6.0 will be v5.6.1 (which
should be read as being equivalent to a floating point value of
5.006_001 in the older format, stored in $]).
New syntax for declaring subroutine attributes
Formerly, if you wanted to mark a subroutine as being a method call or
as requiring an automatic lock() when it is entered, you had to declare
that with a "use attrs" pragma in the body of the subroutine. That can
now be accomplished with declaration syntax, like this:
sub mymethod : locked method;
...
sub mymethod : locked method {
...
}
sub othermethod :locked :method;
...
sub othermethod :locked :method {
...
}
(Note how only the first ":" is mandatory, and whitespace surrounding
the ":" is optional.)
AutoSplit.pm and SelfLoader.pm have been updated to keep the attributes
with the stubs they provide. See attributes.
File and directory handles can be autovivified
Similar to how constructs such as "$x->[0]" autovivify a reference,
handle constructors (open(), opendir(), pipe(), socketpair(), sysopen(),
socket(), and accept()) now autovivify a file or directory handle if the
handle passed to them is an uninitialized scalar variable. This allows
the constructs such as "open(my $fh, ...)" and "open(local $fh,...)" to
be used to create filehandles that will conveniently be closed
automatically when the scope ends, provided there are no other
references to them. This largely eliminates the need for typeglobs when
opening filehandles that must be passed around, as in the following
example:
sub myopen {
open my $fh, "@_"
or die "Can't open '@_': $!";
return $fh;
}
{
my $f = myopen("</etc/motd");
print <$f>;
# $f implicitly closed here
}
open() with more than two arguments
If open() is passed three arguments instead of two, the second argument
is used as the mode and the third argument is taken to be the file name.
This is primarily useful for protecting against unintended magic
behavior of the traditional two-argument form. See "open" in perlfunc.
64-bit support
Any platform that has 64-bit integers either
(1) natively as longs or ints
(2) via special compiler flags
(3) using long long or int64_t
is able to use "quads" (64-bit integers) as follows:
• constants (decimal, hexadecimal, octal, binary) in the code
• arguments to oct() and hex()
• arguments to print(), printf() and sprintf() (flag prefixes ll, L,
q)
• printed as such
• pack() and unpack() "q" and "Q" formats
• in basic arithmetics: + - * / % (NOTE: operating close to the limits
of the integer values may produce surprising results)
• in bit arithmetics: & | ^ ~ << >> (NOTE: these used to be forced to
be 32 bits wide but now operate on the full native width.)
• vec()
Note that unless you have the case (a) you will have to configure and
compile Perl using the -Duse64bitint Configure flag.
NOTE: The Configure flags -Duselonglong and -Duse64bits have been
deprecated. Use -Duse64bitint instead.
There are actually two modes of 64-bitness: the first one is achieved
using Configure -Duse64bitint and the second one using Configure
-Duse64bitall. The difference is that the first one is minimal and the
second one maximal. The first works in more places than the second.
The "use64bitint" does only as much as is required to get 64-bit
integers into Perl (this may mean, for example, using "long longs")
while your memory may still be limited to 2 gigabytes (because your
pointers could still be 32-bit). Note that the name "64bitint" does not
imply that your C compiler will be using 64-bit "int"s (it might, but it
doesn't have to): the "use64bitint" means that you will be able to have
64 bits wide scalar values.
The "use64bitall" goes all the way by attempting to switch also integers
(if it can), longs (and pointers) to being 64-bit. This may create an
even more binary incompatible Perl than -Duse64bitint: the resulting
executable may not run at all in a 32-bit box, or you may have to
reboot/reconfigure/rebuild your operating system to be 64-bit aware.
Natively 64-bit systems like Alpha and Cray need neither -Duse64bitint
nor -Duse64bitall.
Last but not least: note that due to Perl's habit of always using
floating point numbers, the quads are still not true integers. When
quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
-9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they are
silently promoted to floating point numbers, after which they will start
losing precision (in their lower digits).
NOTE: 64-bit support is still experimental on most platforms.
Existing support only covers the LP64 data model. In particular, the
LLP64 data model is not yet supported. 64-bit libraries and system
APIs on many platforms have not stabilized--your mileage may vary.
Large file support
If you have filesystems that support "large files" (files larger than 2
gigabytes), you may now also be able to create and access them from
Perl.
NOTE: The default action is to enable large file support, if
available on the platform.
If the large file support is on, and you have a Fcntl constant
O_LARGEFILE, the O_LARGEFILE is automatically added to the flags of
sysopen().
Beware that unless your filesystem also supports "sparse files" seeking
to umpteen petabytes may be inadvisable.
Note that in addition to requiring a proper file system to do large
files you may also need to adjust your per-process (or your per-system,
or per-process-group, or per-user-group) maximum filesize limits before
running Perl scripts that try to handle large files, especially if you
intend to write such files.
Finally, in addition to your process/process group maximum filesize
limits, you may have quota limits on your filesystems that stop you
(your user id or your user group id) from using large files.
Adjusting your process/user/group/file system/operating system limits is
outside the scope of Perl core language. For process limits, you may
try increasing the limits using your shell's limits/limit/ulimit command
before running Perl. The BSD::Resource extension (not included with the
standard Perl distribution) may also be of use, it offers the
getrlimit/setrlimit interface that can be used to adjust process
resource usage limits, including the maximum filesize limit.
Long doubles
In some systems you may be able to use long doubles to enhance the range
and precision of your double precision floating point numbers (that is,
Perl's numbers). Use Configure -Duselongdouble to enable this support
(if it is available).
"more bits"
You can "Configure -Dusemorebits" to turn on both the 64-bit support and
the long double support.
Enhanced support for sort() subroutines
Perl subroutines with a prototype of "($$)", and XSUBs in general, can
now be used as sort subroutines. In either case, the two elements to be
compared are passed as normal parameters in @_. See "sort" in perlfunc.
For unprototyped sort subroutines, the historical behavior of passing
the elements to be compared as the global variables $a and $b remains
unchanged.
"sort $coderef @foo" allowed
sort() did not accept a subroutine reference as the comparison function
in earlier versions. This is now permitted.
File globbing implemented internally
Perl now uses the File::Glob implementation of the glob() operator
automatically. This avoids using an external csh process and the
problems associated with it.
NOTE: This is currently an experimental feature. Interfaces and
implementation are subject to change.
Support for CHECK blocks
In addition to "BEGIN", "INIT", "END", "DESTROY" and "AUTOLOAD",
subroutines named "CHECK" are now special. These are queued up during
compilation and behave similar to END blocks, except they are called at
the end of compilation rather than at the end of execution. They cannot
be called directly.
POSIX character class syntax [: :] supported
For example to match alphabetic characters use /[[:alpha:]]/. See
perlre for details.
Better pseudo-random number generator
In 5.005_0x and earlier, perl's rand() function used the C library
rand(3) function. As of 5.005_52, Configure tests for drand48(),
random(), and rand() (in that order) and picks the first one it finds.
These changes should result in better random numbers from rand().
Improved "qw//" operator
The "qw//" operator is now evaluated at compile time into a true list
instead of being replaced with a run time call to split(). This removes
the confusing misbehaviour of "qw//" in scalar context, which had
inherited that behaviour from split().
Thus:
$foo = ($bar) = qw(a b c); print "$foo|$bar\n";
now correctly prints "3|a", instead of "2|a".
Better worst-case behavior of hashes
Small changes in the hashing algorithm have been implemented in order to
improve the distribution of lower order bits in the hashed value. This
is expected to yield better performance on keys that are repeated
sequences.
pack() format 'Z' supported
The new format type 'Z' is useful for packing and unpacking null-
terminated strings. See "pack" in perlfunc.
pack() format modifier '!' supported
The new format type modifier '!' is useful for packing and unpacking
native shorts, ints, and longs. See "pack" in perlfunc.
pack() and unpack() support counted strings
The template character '/' can be used to specify a counted string type
to be packed or unpacked. See "pack" in perlfunc.
Comments in pack() templates
The '#' character in a template introduces a comment up to end of the
line. This facilitates documentation of pack() templates.
Weak references
In previous versions of Perl, you couldn't cache objects so as to allow
them to be deleted if the last reference from outside the cache is
deleted. The reference in the cache would hold a reference count on the
object and the objects would never be destroyed.
Another familiar problem is with circular references. When an object
references itself, its reference count would never go down to zero, and
it would not get destroyed until the program is about to exit.
Weak references solve this by allowing you to "weaken" any reference,
that is, make it not count towards the reference count. When the last
non-weak reference to an object is deleted, the object is destroyed and
all the weak references to the object are automatically undef-ed.
To use this feature, you need the Devel::WeakRef package from CPAN,
which contains additional documentation.
NOTE: This is an experimental feature. Details are subject to change.
Binary numbers supported
Binary numbers are now supported as literals, in s?printf formats, and
oct():
$answer = 0b101010;
printf "The answer is: %b\n", oct("0b101010");
Lvalue subroutines
Subroutines can now return modifiable lvalues. See "Lvalue subroutines"
in perlsub.
NOTE: This is an experimental feature. Details are subject to change.
Some arrows may be omitted in calls through references
Perl now allows the arrow to be omitted in many constructs involving
subroutine calls through references. For example, "$foo[10]->('foo')"
may now be written "$foo[10]('foo')". This is rather similar to how the
arrow may be omitted from "$foo[10]->{'foo'}". Note however, that the
arrow is still required for "foo(10)->('bar')".
Boolean assignment operators are legal lvalues
Constructs such as "($a ||= 2) += 1" are now allowed.
exists() is supported on subroutine names
The exists() builtin now works on subroutine names. A subroutine is
considered to exist if it has been declared (even if implicitly). See
"exists" in perlfunc for examples.
exists() and delete() are supported on array elements
The exists() and delete() builtins now work on simple arrays as well.
The behavior is similar to that on hash elements.
exists() can be used to check whether an array element has been
initialized. This avoids autovivifying array elements that don't exist.
If the array is tied, the EXISTS() method in the corresponding tied
package will be invoked.
delete() may be used to remove an element from the array and return it.
The array element at that position returns to its uninitialized state,
so that testing for the same element with exists() will return false.
If the element happens to be the one at the end, the size of the array
also shrinks up to the highest element that tests true for exists(), or
0 if none such is found. If the array is tied, the DELETE() method in
the corresponding tied package will be invoked.
See "exists" in perlfunc and "delete" in perlfunc for examples.
Pseudo-hashes work better
Dereferencing some types of reference values in a pseudo-hash, such as
"$ph->{foo}[1]", was accidentally disallowed. This has been corrected.
When applied to a pseudo-hash element, exists() now reports whether the
specified value exists, not merely if the key is valid.
delete() now works on pseudo-hashes. When given a pseudo-hash element
or slice it deletes the values corresponding to the keys (but not the
keys themselves). See "Pseudo-hashes: Using an array as a hash" in
perlref.
Pseudo-hash slices with constant keys are now optimized to array lookups
at compile-time.
List assignments to pseudo-hash slices are now supported.
The "fields" pragma now provides ways to create pseudo-hashes, via
fields::new() and fields::phash(). See fields.
NOTE: The pseudo-hash data type continues to be experimental.
Limiting oneself to the interface elements provided by the
fields pragma will provide protection from any future changes.
Automatic flushing of output buffers
fork(), exec(), system(), qx//, and pipe open()s now flush buffers of
all files opened for output when the operation was attempted. This
mostly eliminates confusing buffering mishaps suffered by users unaware
of how Perl internally handles I/O.
This is not supported on some platforms like Solaris where a suitably
correct implementation of fflush(NULL) isn't available.
Better diagnostics on meaningless filehandle operations
Constructs such as open(<FH>) and close(<FH>) are compile time errors.
Attempting to read from filehandles that were opened only for writing
will now produce warnings (just as writing to read-only filehandles
does).
Where possible, buffered data discarded from duped input filehandle
"open(NEW, "<&OLD")" now attempts to discard any data that was
previously read and buffered in "OLD" before duping the handle. On
platforms where doing this is allowed, the next read operation on "NEW"
will return the same data as the corresponding operation on "OLD".
Formerly, it would have returned the data from the start of the
following disk block instead.
eof() has the same old magic as <>
eof() would return true if no attempt to read from "<>" had yet been
made. eof() has been changed to have a little magic of its own, it now
opens the "<>" files.
binmode() can be used to set :crlf and :raw modes
binmode() now accepts a second argument that specifies a discipline for
the handle in question. The two pseudo-disciplines ":raw" and ":crlf"
are currently supported on DOS-derivative platforms. See "binmode" in
perlfunc and open.
"-T" filetest recognizes UTF-8 encoded files as "text"
The algorithm used for the "-T" filetest has been enhanced to correctly
identify UTF-8 content as "text".
system(), backticks and pipe open now reflect exec() failure
On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
etc., are implemented via fork() and exec(). When the underlying exec()
fails, earlier versions did not report the error properly, since the
exec() happened to be in a different process.
The child process now communicates with the parent about the error in
launching the external command, which allows these constructs to return
with their usual error value and set $!.
Improved diagnostics
Line numbers are no longer suppressed (under most likely circumstances)
during the global destruction phase.
Diagnostics emitted from code running in threads other than the main
thread are now accompanied by the thread ID.
Embedded null characters in diagnostics now actually show up. They used
to truncate the message in prior versions.
$foo::a and $foo::b are now exempt from "possible typo" warnings only if
sort() is encountered in package "foo".
Unrecognized alphabetic escapes encountered when parsing quote
constructs now generate a warning, since they may take on new semantics
in later versions of Perl.
Many diagnostics now report the internal operation in which the warning
was provoked, like so:
Use of uninitialized value in concatenation (.) at (eval 1) line 1.
Use of uninitialized value in print at (eval 1) line 1.
Diagnostics that occur within eval may also report the file and line
number where the eval is located, in addition to the eval sequence
number and the line number within the evaluated text itself. For
example:
Not enough arguments for scalar at (eval 4)[newlib/perl5db.pl:1411] line 2, at EOF
Diagnostics follow STDERR
Diagnostic output now goes to whichever file the "STDERR" handle is
pointing at, instead of always going to the underlying C runtime
library's "stderr".
More consistent close-on-exec behavior
On systems that support a close-on-exec flag on filehandles, the flag is
now set for any handles created by pipe(), socketpair(), socket(), and
accept(), if that is warranted by the value of $^F that may be in
effect. Earlier versions neglected to set the flag for handles created
with these operators. See "pipe" in perlfunc, "socketpair" in perlfunc,
"socket" in perlfunc, "accept" in perlfunc, and "$^F" in perlvar.
syswrite() ease-of-use
The length argument of syswrite() has become optional.
Better syntax checks on parenthesized unary operators
Expressions such as:
print defined(&foo,&bar,&baz);
print uc("foo","bar","baz");
undef($foo,&bar);
used to be accidentally allowed in earlier versions, and produced
unpredictable behaviour. Some produced ancillary warnings when used in
this way; others silently did the wrong thing.
The parenthesized forms of most unary operators that expect a single
argument now ensure that they are not called with more than one
argument, making the cases shown above syntax errors. The usual
behaviour of:
print defined &foo, &bar, &baz;
print uc "foo", "bar", "baz";
undef $foo, &bar;
remains unchanged. See perlop.
Bit operators support full native integer width
The bit operators (& | ^ ~ << >>) now operate on the full native
integral width (the exact size of which is available in
$Config{ivsize}). For example, if your platform is either natively
64-bit or if Perl has been configured to use 64-bit integers, these
operations apply to 8 bytes (as opposed to 4 bytes on 32-bit platforms).
For portability, be sure to mask off the excess bits in the result of
unary "~", e.g., "~$x & 0xffffffff".
Improved security features
More potentially unsafe operations taint their results for improved
security.
The "passwd" and "shell" fields returned by the getpwent(), getpwnam(),
and getpwuid() are now tainted, because the user can affect their own
encrypted password and login shell.
The variable modified by shmread(), and messages returned by msgrcv()
(and its object-oriented interface IPC::SysV::Msg::rcv) are also
tainted, because other untrusted processes can modify messages and
shared memory segments for their own nefarious purposes.
More functional bareword prototype (*)
Bareword prototypes have been rationalized to enable them to be used to
override builtins that accept barewords and interpret them in a special
way, such as "require" or "do".
Arguments prototyped as "*" will now be visible within the subroutine as
either a simple scalar or as a reference to a typeglob. See
"Prototypes" in perlsub.
"require" and "do" may be overridden
"require" and "do 'file'" operations may be overridden locally by
importing subroutines of the same name into the current package (or
globally by importing them into the CORE::GLOBAL:: namespace).
Overriding "require" will also affect "use", provided the override is
visible at compile-time. See "Overriding Built-in Functions" in
perlsub.
$^X variables may now have names longer than one character
Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax error.
Now variable names that begin with a control character may be
arbitrarily long. However, for compatibility reasons, these variables
must be written with explicit braces, as "${^XY}" for example.
"${^XYZ}" is synonymous with ${"\cXYZ"}. Variable names with more than
one control character, such as "${^XY^Z}", are illegal.
The old syntax has not changed. As before, `^X' may be either a literal
control-X character or the two-character sequence `caret' plus `X'.
When braces are omitted, the variable name stops after the control
character. Thus "$^XYZ" continues to be synonymous with "$^X . "YZ"" as
before.
As before, lexical variables may not have names beginning with control
characters. As before, variables whose names begin with a control
character are always forced to be in package `main'. All such variables
are reserved for future extensions, except those that begin with "^_",
which may be used by user programs and are guaranteed not to acquire
special meaning in any future version of Perl.
New variable $^C reflects "-c" switch
$^C has a boolean value that reflects whether perl is being run in
compile-only mode (i.e. via the "-c" switch). Since BEGIN blocks are
executed under such conditions, this variable enables perl code to
determine whether actions that make sense only during normal running are
warranted. See perlvar.
New variable $^V contains Perl version as a string
$^V contains the Perl version number as a string composed of characters
whose ordinals match the version numbers, i.e. v5.6.0. This may be used
in string comparisons.
See "Support for strings represented as a vector of ordinals" for an
example.
Optional Y2K warnings
If Perl is built with the cpp macro "PERL_Y2KWARN" defined, it emits
optional warnings when concatenating the number 19 with another number.
This behavior must be specifically enabled when running Configure. See
INSTALL and README.Y2K.
Arrays now always interpolate into double-quoted strings
In double-quoted strings, arrays now interpolate, no matter what. The
behavior in earlier versions of perl 5 was that arrays would interpolate
into strings if the array had been mentioned before the string was
compiled, and otherwise Perl would raise a fatal compile-time error. In
versions 5.000 through 5.003, the error was
Literal @example now requires backslash
In versions 5.004_01 through 5.6.0, the error was
In string, @example now must be written as \@example
The idea here was to get people into the habit of writing
"fred\@example.com" when they wanted a literal "@" sign, just as they
have always written "Give me back my \$5" when they wanted a literal "$"
sign.
Starting with 5.6.1, when Perl now sees an "@" sign in a double-quoted
string, it always attempts to interpolate an array, regardless of
whether or not the array has been used or declared already. The fatal
error has been downgraded to an optional warning:
Possible unintended interpolation of @example in string
This warns you that "fred@example.com" is going to turn into "fred.com"
if you don't backslash the "@". See
http://perl.plover.com/at-error.html for more details about the history
here.
@- and @+ provide starting/ending offsets of regex matches
The new magic variables @- and @+ provide the starting and ending
offsets, respectively, of $&, $1, $2, etc. See perlvar for details.
Modules and Pragmata
Modules
attributes
While used internally by Perl as a pragma, this module also provides
a way to fetch subroutine and variable attributes. See attributes.
B The Perl Compiler suite has been extensively reworked for this
release. More of the standard Perl test suite passes when run under
the Compiler, but there is still a significant way to go to achieve
production quality compiled executables.
NOTE: The Compiler suite remains highly experimental. The
generated code may not be correct, even when it manages to execute
without errors.
Benchmark
Overall, Benchmark results exhibit lower average error and better
timing accuracy.
You can now run tests for n seconds instead of guessing the right
number of tests to run: e.g., timethese(-5, ...) will run each code
for at least 5 CPU seconds. Zero as the "number of repetitions"
means "for at least 3 CPU seconds". The output format has also
changed. For example:
use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
will now output something like this:
Benchmark: running a, b, each for at least 5 CPU seconds...
a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
New features: "each for at least N CPU seconds...", "wallclock
secs", and the "@ operations/CPU second (n=operations)".
timethese() now returns a reference to a hash of Benchmark objects
containing the test results, keyed on the names of the tests.
timethis() now returns the iterations field in the Benchmark result
object instead of 0.
timethese(), timethis(), and the new cmpthese() (see below) can also
take a format specifier of 'none' to suppress output.
A new function countit() is just like timeit() except that it takes
a TIME instead of a COUNT.
A new function cmpthese() prints a chart comparing the results of
each test returned from a timethese() call. For each possible pair
of tests, the percentage speed difference (iters/sec or
seconds/iter) is shown.
For other details, see Benchmark.
ByteLoader
The ByteLoader is a dedicated extension to generate and run Perl
bytecode. See ByteLoader.
constant
References can now be used.
The new version also allows a leading underscore in constant names,
but disallows a double leading underscore (as in "__LINE__"). Some
other names are disallowed or warned against, including BEGIN, END,
etc. Some names which were forced into main:: used to fail silently
in some cases; now they're fatal (outside of main::) and an optional
warning (inside of main::). The ability to detect whether a
constant had been set with a given name has been added.
See constant.
charnames
This pragma implements the "\N" string escape. See charnames.
Data::Dumper
A "Maxdepth" setting can be specified to avoid venturing too deeply
into deep data structures. See Data::Dumper.
The XSUB implementation of Dump() is now automatically called if the
"Useqq" setting is not in use.
Dumping "qr//" objects works correctly.
DB "DB" is an experimental module that exposes a clean abstraction to
Perl's debugging API.
DB_File
DB_File can now be built with Berkeley DB versions 1, 2 or 3. See
"ext/DB_File/Changes".
Devel::DProf
Devel::DProf, a Perl source code profiler has been added. See
Devel::DProf and dprofpp.
Devel::Peek
The Devel::Peek module provides access to the internal
representation of Perl variables and data. It is a data debugging
tool for the XS programmer.
Dumpvalue
The Dumpvalue module provides screen dumps of Perl data.
DynaLoader
DynaLoader now supports a dl_unload_file() function on platforms
that support unloading shared objects using dlclose().
Perl can also optionally arrange to unload all extension shared
objects loaded by Perl. To enable this, build Perl with the
Configure option "-Accflags=-DDL_UNLOAD_ALL_AT_EXIT". (This maybe
useful if you are using Apache with mod_perl.)
English
$PERL_VERSION now stands for $^V (a string value) rather than for $]
(a numeric value).
Env Env now supports accessing environment variables like PATH as array
variables.
Fcntl
More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
large file (more than 4GB) access (NOTE: the O_LARGEFILE is
automatically added to sysopen() flags if large file support has
been configured, as is the default), Free/Net/OpenBSD locking
behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the
combined mask of O_RDONLY, O_WRONLY, and O_RDWR. The
seek()/sysseek() constants SEEK_SET, SEEK_CUR, and SEEK_END are
available via the ":seek" tag. The chmod()/stat() S_IF* constants
and S_IS* functions are available via the ":mode" tag.
File::Compare
A compare_text() function has been added, which allows custom
comparison functions. See File::Compare.
File::Find
File::Find now works correctly when the wanted() function is either
autoloaded or is a symbolic reference.
A bug that caused File::Find to lose track of the working directory
when pruning top-level directories has been fixed.
File::Find now also supports several other options to control its
behavior. It can follow symbolic links if the "follow" option is
specified. Enabling the "no_chdir" option will make File::Find skip
changing the current directory when walking directories. The
"untaint" flag can be useful when running with taint checks enabled.
See File::Find.
File::Glob
This extension implements BSD-style file globbing. By default, it
will also be used for the internal implementation of the glob()
operator. See File::Glob.
File::Spec
New methods have been added to the File::Spec module: devnull()
returns the name of the null device (/dev/null on Unix) and tmpdir()
the name of the temp directory (normally /tmp on Unix). There are
now also methods to convert between absolute and relative filenames:
abs2rel() and rel2abs(). For compatibility with operating systems
that specify volume names in file paths, the splitpath(),
splitdir(), and catdir() methods have been added.
File::Spec::Functions
The new File::Spec::Functions modules provides a function interface
to the File::Spec module. Allows shorthand
$fullname = catfile($dir1, $dir2, $file);
instead of
$fullname = File::Spec->catfile($dir1, $dir2, $file);
Getopt::Long
Getopt::Long licensing has changed to allow the Perl Artistic
License as well as the GPL. It used to be GPL only, which got in the
way of non-GPL applications that wanted to use Getopt::Long.
Getopt::Long encourages the use of Pod::Usage to produce help
messages. For example:
use Getopt::Long;
use Pod::Usage;
my $man = 0;
my $help = 0;
GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
pod2usage(1) if $help;
pod2usage(-exitstatus => 0, -verbose => 2) if $man;
__END__
=head1 NAME
sample - Using Getopt::Long and Pod::Usage
=head1 SYNOPSIS
sample [options] [file ...]
Options:
-help brief help message
-man full documentation
=head1 OPTIONS
=over 8
=item B<-help>
Print a brief help message and exits.
=item B<-man>
Prints the manual page and exits.
=back
=head1 DESCRIPTION
B<This program> will read the given input file(s) and do something
useful with the contents thereof.
=cut
See Pod::Usage for details.
A bug that prevented the non-option call-back <> from being
specified as the first argument has been fixed.
To specify the characters < and > as option starters, use ><. Note,
however, that changing option starters is strongly deprecated.
IO write() and syswrite() will now accept a single-argument form of the
call, for consistency with Perl's syswrite().
You can now create a TCP-based IO::Socket::INET without forcing a
connect attempt. This allows you to configure its options (like
making it non-blocking) and then call connect() manually.
A bug that prevented the IO::Socket::protocol() accessor from ever
returning the correct value has been corrected.
IO::Socket::connect now uses non-blocking IO instead of alarm() to
do connect timeouts.
IO::Socket::accept now uses select() instead of alarm() for doing
timeouts.
IO::Socket::INET->new now sets $! correctly on failure. $@ is still
set for backwards compatibility.
JPL Java Perl Lingo is now distributed with Perl. See jpl/README for
more information.
lib "use lib" now weeds out any trailing duplicate entries. "no lib"
removes all named entries.
Math::BigInt
The bitwise operations "<<", ">>", "&", "|", and "~" are now
supported on bigints.
Math::Complex
The accessor methods Re, Im, arg, abs, rho, and theta can now also
act as mutators (accessor $z->Re(), mutator $z->Re(3)).
The class method "display_format" and the corresponding object
method "display_format", in addition to accepting just one argument,
now can also accept a parameter hash. Recognized keys of a
parameter hash are "style", which corresponds to the old one
parameter case, and two new parameters: "format", which is a
printf()-style format string (defaults usually to "%.15g", you can
revert to the default by setting the format string to "undef") used
for both parts of a complex number, and "polar_pretty_print"
(defaults to true), which controls whether an attempt is made to try
to recognize small multiples and rationals of pi (2pi, pi/2) at the
argument (angle) of a polar complex number.
The potentially disruptive change is that in list context both
methods now return the parameter hash, instead of only the value of
the "style" parameter.
Math::Trig
A little bit of radial trigonometry (cylindrical and spherical),
radial coordinate conversions, and the great circle distance were
added.
Pod::Parser, Pod::InputObjects
Pod::Parser is a base class for parsing and selecting sections of
pod documentation from an input stream. This module takes care of
identifying pod paragraphs and commands in the input and hands off
the parsed paragraphs and commands to user-defined methods which are
free to interpret or translate them as they see fit.
Pod::InputObjects defines some input objects needed by Pod::Parser,
and for advanced users of Pod::Parser that need more about a command
besides its name and text.
As of release 5.6.0 of Perl, Pod::Parser is now the officially
sanctioned "base parser code" recommended for use by all pod2xxx
translators. Pod::Text (pod2text) and Pod::Man (pod2man) have
already been converted to use Pod::Parser and efforts to convert
Pod::HTML (pod2html) are already underway. For any questions or
comments about pod parsing and translating issues and utilities,
please use the pod-people@perl.org mailing list.
For further information, please see Pod::Parser and
Pod::InputObjects.
Pod::Checker, podchecker
This utility checks pod files for correct syntax, according to
perlpod. Obvious errors are flagged as such, while warnings are
printed for mistakes that can be handled gracefully. The checklist
is not complete yet. See Pod::Checker.
Pod::ParseUtils, Pod::Find
These modules provide a set of gizmos that are useful mainly for pod
translators. Pod::Find traverses directory structures and returns
found pod files, along with their canonical names (like
"File::Spec::Unix"). Pod::ParseUtils contains Pod::List (useful for
storing pod list information), Pod::Hyperlink (for parsing the
contents of "L<>" sequences) and Pod::Cache (for caching information
about pod files, e.g., link nodes).
Pod::Select, podselect
Pod::Select is a subclass of Pod::Parser which provides a function
named "podselect()" to filter out user-specified sections of raw pod
documentation from an input stream. podselect is a script that
provides access to Pod::Select from other scripts to be used as a
filter. See Pod::Select.
Pod::Usage, pod2usage
Pod::Usage provides the function "pod2usage()" to print usage
messages for a Perl script based on its embedded pod documentation.
The pod2usage() function is generally useful to all script authors
since it lets them write and maintain a single source (the pods) for
documentation, thus removing the need to create and maintain
redundant usage message text consisting of information already in
the pods.
There is also a pod2usage script which can be used from other kinds
of scripts to print usage messages from pods (even for non-Perl
scripts with pods embedded in comments).
For details and examples, please see Pod::Usage.
Pod::Text and Pod::Man
Pod::Text has been rewritten to use Pod::Parser. While pod2text()
is still available for backwards compatibility, the module now has a
new preferred interface. See Pod::Text for the details. The new
Pod::Text module is easily subclassed for tweaks to the output, and
two such subclasses (Pod::Text::Termcap for man-page-style bold and
underlining using termcap information, and Pod::Text::Color for
markup with ANSI color sequences) are now standard.
pod2man has been turned into a module, Pod::Man, which also uses
Pod::Parser. In the process, several outstanding bugs related to
quotes in section headers, quoting of code escapes, and nested lists
have been fixed. pod2man is now a wrapper script around this
module.
SDBM_File
An EXISTS method has been added to this module (and sdbm_exists()
has been added to the underlying sdbm library), so one can now call
exists on an SDBM_File tied hash and get the correct result, rather
than a runtime error.
A bug that may have caused data loss when more than one disk block
happens to be read from the database in a single FETCH() has been
fixed.
Sys::Syslog
Sys::Syslog now uses XSUBs to access facilities from syslog.h so it
no longer requires syslog.ph to exist.
Sys::Hostname
Sys::Hostname now uses XSUBs to call the C library's gethostname()
or uname() if they exist.
Term::ANSIColor
Term::ANSIColor is a very simple module to provide easy and readable
access to the ANSI color and highlighting escape sequences,
supported by most ANSI terminal emulators. It is now included
standard.
Time::Local
The timelocal() and timegm() functions used to silently return bogus
results when the date fell outside the machine's integer range.
They now consistently croak() if the date falls in an unsupported
range.
Win32
The error return value in list context has been changed for all
functions that return a list of values. Previously these functions
returned a list with a single element "undef" if an error occurred.
Now these functions return the empty list in these situations. This
applies to the following functions:
Win32::FsType
Win32::GetOSVersion
The remaining functions are unchanged and continue to return "undef"
on error even in list context.
The Win32::SetLastError(ERROR) function has been added as a
complement to the Win32::GetLastError() function.
The new Win32::GetFullPathName(FILENAME) returns the full absolute
pathname for FILENAME in scalar context. In list context it returns
a two-element list containing the fully qualified directory name and
the filename. See Win32.
XSLoader
The XSLoader extension is a simpler alternative to DynaLoader. See
XSLoader.
DBM Filters
A new feature called "DBM Filters" has been added to all the DBM
modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
DBM Filters add four new methods to each DBM module:
filter_store_key
filter_store_value
filter_fetch_key
filter_fetch_value
These can be used to filter key-value pairs before the pairs are
written to the database or just after they are read from the
database. See perldbmfilter for further information.
Pragmata
"use attrs" is now obsolete, and is only provided for backward-
compatibility. It's been replaced by the "sub : attributes" syntax.
See "Subroutine Attributes" in perlsub and attributes.
Lexical warnings pragma, "use warnings;", to control optional warnings.
See perllexwarn.
"use filetest" to control the behaviour of filetests ("-r" "-w" ...).
Currently only one subpragma implemented, "use filetest 'access';", that
uses access(2) or equivalent to check permissions instead of using
stat(2) as usual. This matters in filesystems where there are ACLs
(access control lists): the stat(2) might lie, but access(2) knows
better.
The "open" pragma can be used to specify default disciplines for handle
constructors (e.g. open()) and for qx//. The two pseudo-disciplines
":raw" and ":crlf" are currently supported on DOS-derivative platforms
(i.e. where binmode is not a no-op). See also "binmode() can be used to
set :crlf and :raw modes".
Utility Changes
dprofpp
"dprofpp" is used to display profile data generated using
"Devel::DProf". See dprofpp.
find2perl
The "find2perl" utility now uses the enhanced features of the File::Find
module. The -depth and -follow options are supported. Pod
documentation is also included in the script.
h2xs
The "h2xs" tool can now work in conjunction with "C::Scan" (available
from CPAN) to automatically parse real-life header files. The "-M",
"-a", "-k", and "-o" options are new.
perlcc
"perlcc" now supports the C and Bytecode backends. By default, it
generates output from the simple C backend rather than the optimized C
backend.
Support for non-Unix platforms has been improved.
perldoc
"perldoc" has been reworked to avoid possible security holes. It will
not by default let itself be run as the superuser, but you may still use
the -U switch to try to make it drop privileges first.
The Perl Debugger
Many bug fixes and enhancements were added to perl5db.pl, the Perl
debugger. The help documentation was rearranged. New commands include
"< ?", "> ?", and "{ ?" to list out current actions, "man docpage" to
run your doc viewer on some perl docset, and support for quoted options.
The help information was rearranged, and should be viewable once again
if you're using less as your pager. A serious security hole was
plugged--you should immediately remove all older versions of the Perl
debugger as installed in previous releases, all the way back to perl3,
from your system to avoid being bitten by this.
Improved Documentation
Many of the platform-specific README files are now part of the perl
installation. See perl for the complete list.
perlapi.pod
The official list of public Perl API functions.
perlboot.pod
A tutorial for beginners on object-oriented Perl.
perlcompile.pod
An introduction to using the Perl Compiler suite.
perldbmfilter.pod
A howto document on using the DBM filter facility.
perldebug.pod
All material unrelated to running the Perl debugger, plus all low-
level guts-like details that risked crushing the casual user of the
debugger, have been relocated from the old manpage to the next entry
below.
perldebguts.pod
This new manpage contains excessively low-level material not related
to the Perl debugger, but slightly related to debugging Perl itself.
It also contains some arcane internal details of how the debugging
process works that may only be of interest to developers of Perl
debuggers.
perlfork.pod
Notes on the fork() emulation currently available for the Windows
platform.
perlfilter.pod
An introduction to writing Perl source filters.
perlhack.pod
Some guidelines for hacking the Perl source code.
perlintern.pod
A list of internal functions in the Perl source code. (List is
currently empty.)
perllexwarn.pod
Introduction and reference information about lexically scoped
warning categories.
perlnumber.pod
Detailed information about numbers as they are represented in Perl.
perlopentut.pod
A tutorial on using open() effectively.
perlreftut.pod
A tutorial that introduces the essentials of references.
perltootc.pod
A tutorial on managing class data for object modules.
perltodo.pod
Discussion of the most often wanted features that may someday be
supported in Perl.
perlunicode.pod
An introduction to Unicode support features in Perl.
Performance enhancements
Simple sort() using { $a <=> $b } and the like are optimized
Many common sort() operations using a simple inlined block are now
optimized for faster performance.
Optimized assignments to lexical variables
Certain operations in the RHS of assignment statements have been
optimized to directly set the lexical variable on the LHS, eliminating
redundant copying overheads.
Faster subroutine calls
Minor changes in how subroutine calls are handled internally provide
marginal improvements in performance.
delete(), each(), values() and hash iteration are faster
The hash values returned by delete(), each(), values() and hashes in a
list context are the actual values in the hash, instead of copies. This
results in significantly better performance, because it eliminates
needless copying in most situations.
Installation and Configuration Improvements
-Dusethreads means something different
The -Dusethreads flag now enables the experimental interpreter-based
thread support by default. To get the flavor of experimental threads
that was in 5.005 instead, you need to run Configure with "-Dusethreads
-Duse5005threads".
As of v5.6.0, interpreter-threads support is still lacking a way to
create new threads from Perl (i.e., "use Thread;" will not work with
interpreter threads). "use Thread;" continues to be available when you
specify the -Duse5005threads option to Configure, bugs and all.
NOTE: Support for threads continues to be an experimental feature.
Interfaces and implementation are subject to sudden and drastic changes.
New Configure flags
The following new flags may be enabled on the Configure command line by
running Configure with "-Dflag".
usemultiplicity
usethreads useithreads (new interpreter threads: no Perl API yet)
usethreads use5005threads (threads as they were in 5.005)
use64bitint (equal to now deprecated 'use64bits')
use64bitall
uselongdouble
usemorebits
uselargefiles
usesocks (only SOCKS v5 supported)
Threadedness and 64-bitness now more daring
The Configure options enabling the use of threads and the use of
64-bitness are now more daring in the sense that they no more have an
explicit list of operating systems of known threads/64-bit capabilities.
In other words: if your operating system has the necessary APIs and
datatypes, you should be able just to go ahead and use them, for threads
by Configure -Dusethreads, and for 64 bits either explicitly by
Configure -Duse64bitint or implicitly if your system has 64-bit wide
datatypes. See also "64-bit support".
Long Doubles
Some platforms have "long doubles", floating point numbers of even
larger range than ordinary "doubles". To enable using long doubles for
Perl's scalars, use -Duselongdouble.
-Dusemorebits
You can enable both -Duse64bitint and -Duselongdouble with
-Dusemorebits. See also "64-bit support".
-Duselargefiles
Some platforms support system APIs that are capable of handling large
files (typically, files larger than two gigabytes). Perl will try to
use these APIs if you ask for -Duselargefiles.
See "Large file support" for more information.
installusrbinperl
You can use "Configure -Uinstallusrbinperl" which causes installperl to
skip installing perl also as /usr/bin/perl. This is useful if you
prefer not to modify /usr/bin for some reason or another but harmful
because many scripts assume to find Perl in /usr/bin/perl.
SOCKS support
You can use "Configure -Dusesocks" which causes Perl to probe for the
SOCKS proxy protocol library (v5, not v4). For more information on
SOCKS, see:
http://www.socks.nec.com/
"-A" flag
You can "post-edit" the Configure variables using the Configure "-A"
switch. The editing happens immediately after the platform specific
hints files have been processed but before the actual configuration
process starts. Run "Configure -h" to find out the full "-A" syntax.
Enhanced Installation Directories
The installation structure has been enriched to improve the support for
maintaining multiple versions of perl, to provide locations for vendor-
supplied modules, scripts, and manpages, and to ease maintenance of
locally-added modules, scripts, and manpages. See the section on
Installation Directories in the INSTALL file for complete details. For
most users building and installing from source, the defaults should be
fine.
If you previously used "Configure -Dsitelib" or "-Dsitearch" to set
special values for library directories, you might wish to consider using
the new "-Dsiteprefix" setting instead. Also, if you wish to re-use a
config.sh file from an earlier version of perl, you should be sure to
check that Configure makes sensible choices for the new directories.
See INSTALL for complete details.
Platform specific changes
Supported platforms
• The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the
Thread extension.
• GNU/Hurd is now supported.
• Rhapsody/Darwin is now supported.
• EPOC is now supported (on Psion 5).
• The cygwin port (formerly cygwin32) has been greatly improved.
DOS
• Perl now works with djgpp 2.02 (and 2.03 alpha).
• Environment variable names are not converted to uppercase any more.
• Incorrect exit codes from backticks have been fixed.
• This port continues to use its own builtin globbing (not
File::Glob).
OS390 (OpenEdition MVS)
Support for this EBCDIC platform has not been renewed in this release.
There are difficulties in reconciling Perl's standardization on UTF-8 as
its internal representation for characters with the EBCDIC character
set, because the two are incompatible.
It is unclear whether future versions will renew support for this
platform, but the possibility exists.
VMS
Numerous revisions and extensions to configuration, build, testing, and
installation process to accommodate core changes and VMS-specific
options.
Expand %ENV-handling code to allow runtime mapping to logical names, CLI
symbols, and CRTL environ array.
Extension of subprocess invocation code to accept filespecs as command
"verbs".
Add to Perl command line processing the ability to use default file
types and to recognize Unix-style "2>&1".
Expansion of File::Spec::VMS routines, and integration into
ExtUtils::MM_VMS.
Extension of ExtUtils::MM_VMS to handle complex extensions more
flexibly.
Barewords at start of Unix-syntax paths may be treated as text rather
than only as logical names.
Optional secure translation of several logical names used internally by
Perl.
Miscellaneous bugfixing and porting of new core code to VMS.
Thanks are gladly extended to the many people who have contributed VMS
patches, testing, and ideas.
Win32
Perl can now emulate fork() internally, using multiple interpreters
running in different concurrent threads. This support must be enabled
at build time. See perlfork for detailed information.
When given a pathname that consists only of a drivename, such as "A:",
opendir() and stat() now use the current working directory for the drive
rather than the drive root.
The builtin XSUB functions in the Win32:: namespace are documented. See
Win32.
$^X now contains the full path name of the running executable.
A Win32::GetLongPathName() function is provided to complement
Win32::GetFullPathName() and Win32::GetShortPathName(). See Win32.
POSIX::uname() is supported.
system(1,...) now returns true process IDs rather than process handles.
kill() accepts any real process id, rather than strictly return values
from system(1,...).
For better compatibility with Unix, "kill(0, $pid)" can now be used to
test whether a process exists.
The "Shell" module is supported.
Better support for building Perl under command.com in Windows 95 has
been added.
Scripts are read in binary mode by default to allow ByteLoader (and the
filter mechanism in general) to work properly. For compatibility, the
DATA filehandle will be set to text mode if a carriage return is
detected at the end of the line containing the __END__ or __DATA__
token; if not, the DATA filehandle will be left open in binary mode.
Earlier versions always opened the DATA filehandle in text mode.
The glob() operator is implemented via the "File::Glob" extension, which
supports glob syntax of the C shell. This increases the flexibility of
the glob() operator, but there may be compatibility issues for programs
that relied on the older globbing syntax. If you want to preserve
compatibility with the older syntax, you might want to run perl with
"-MFile::DosGlob". For details and compatibility information, see
File::Glob.
Significant bug fixes
<HANDLE> on empty files
With $/ set to "undef", "slurping" an empty file returns a string of
zero length (instead of "undef", as it used to) the first time the
HANDLE is read after $/ is set to "undef". Further reads yield "undef".
This means that the following will append "foo" to an empty file (it
used to do nothing):
perl -0777 -pi -e 's/^/foo/' empty_file
The behaviour of:
perl -pi -e 's/^/foo/' empty_file
is unchanged (it continues to leave the file empty).
"eval '...'" improvements
Line numbers (as reflected by caller() and most diagnostics) within
"eval '...'" were often incorrect where here documents were involved.
This has been corrected.
Lexical lookups for variables appearing in "eval '...'" within functions
that were themselves called within an "eval '...'" were searching the
wrong place for lexicals. The lexical search now correctly ends at the
subroutine's block boundary.
The use of "return" within "eval {...}" caused $@ not to be reset
correctly when no exception occurred within the eval. This has been
fixed.
Parsing of here documents used to be flawed when they appeared as the
replacement expression in "eval 's/.../.../e'". This has been fixed.
All compilation errors are true errors
Some "errors" encountered at compile time were by necessity generated as
warnings followed by eventual termination of the program. This enabled
more such errors to be reported in a single run, rather than causing a
hard stop at the first error that was encountered.
The mechanism for reporting such errors has been reimplemented to queue
compile-time errors and report them at the end of the compilation as
true errors rather than as warnings. This fixes cases where error
messages leaked through in the form of warnings when code was compiled
at run time using "eval STRING", and also allows such errors to be
reliably trapped using "eval "..."".
Implicitly closed filehandles are safer
Sometimes implicitly closed filehandles (as when they are localized, and
Perl automatically closes them on exiting the scope) could inadvertently
set $? or $!. This has been corrected.
Behavior of list slices is more consistent
When taking a slice of a literal list (as opposed to a slice of an array
or hash), Perl used to return an empty list if the result happened to be
composed of all undef values.
The new behavior is to produce an empty list if (and only if) the
original list was empty. Consider the following example:
@a = (1,undef,undef,2)[2,1,2];
The old behavior would have resulted in @a having no elements. The new
behavior ensures it has three undefined elements.
Note in particular that the behavior of slices of the following cases
remains unchanged:
@a = ()[1,2];
@a = (getpwent)[7,0];
@a = (anything_returning_empty_list())[2,1,2];
@a = @b[2,1,2];
@a = @c{'a','b','c'};
See perldata.
"(\$)" prototype and $foo{a}
A scalar reference prototype now correctly allows a hash or array
element in that slot.
"goto &sub" and AUTOLOAD
The "goto &sub" construct works correctly when &sub happens to be
autoloaded.
"-bareword" allowed under "use integer"
The autoquoting of barewords preceded by "-" did not work in prior
versions when the "integer" pragma was enabled. This has been fixed.
Failures in DESTROY()
When code in a destructor threw an exception, it went unnoticed in
earlier versions of Perl, unless someone happened to be looking in $@
just after the point the destructor happened to run. Such failures are
now visible as warnings when warnings are enabled.
Locale bugs fixed
printf() and sprintf() previously reset the numeric locale back to the
default "C" locale. This has been fixed.
Numbers formatted according to the local numeric locale (such as using a
decimal comma instead of a decimal dot) caused "isn't numeric" warnings,
even while the operations accessing those numbers produced correct
results. These warnings have been discontinued.
Memory leaks
The "eval 'return sub {...}'" construct could sometimes leak memory.
This has been fixed.
Operations that aren't filehandle constructors used to leak memory when
used on invalid filehandles. This has been fixed.
Constructs that modified @_ could fail to deallocate values in @_ and
thus leak memory. This has been corrected.
Spurious subroutine stubs after failed subroutine calls
Perl could sometimes create empty subroutine stubs when a subroutine was
not found in the package. Such cases stopped later method lookups from
progressing into base packages. This has been corrected.
Taint failures under "-U"
When running in unsafe mode, taint violations could sometimes cause
silent failures. This has been fixed.
END blocks and the "-c" switch
Prior versions used to run BEGIN and END blocks when Perl was run in
compile-only mode. Since this is typically not the expected behavior,
END blocks are not executed anymore when the "-c" switch is used, or if
compilation fails.
See "Support for CHECK blocks" for how to run things when the compile
phase ends.
Potential to leak DATA filehandles
Using the "__DATA__" token creates an implicit filehandle to the file
that contains the token. It is the program's responsibility to close it
when it is done reading from it.
This caveat is now better explained in the documentation. See perldata.
New or Changed Diagnostics
"%s" variable %s masks earlier declaration in same %s
(W misc) A "my" or "our" variable has been redeclared in the current
scope or statement, effectively eliminating all access to the
previous instance. This is almost always a typographical error.
Note that the earlier variable will still exist until the end of the
scope or until all closure referents to it are destroyed.
"my sub" not yet implemented
(F) Lexically scoped subroutines are not yet implemented. Don't try
that yet.
"our" variable %s redeclared
(W misc) You seem to have already declared the same global once
before in the current lexical scope.
'!' allowed only after types %s
(F) The '!' is allowed in pack() and unpack() only after certain
types. See "pack" in perlfunc.
/ cannot take a count
(F) You had an unpack template indicating a counted-length string,
but you have also specified an explicit size for the string. See
"pack" in perlfunc.
/ must be followed by a, A or Z
(F) You had an unpack template indicating a counted-length string,
which must be followed by one of the letters a, A or Z to indicate
what sort of string is to be unpacked. See "pack" in perlfunc.
/ must be followed by a*, A* or Z*
(F) You had a pack template indicating a counted-length string,
Currently the only things that can have their length counted are a*,
A* or Z*. See "pack" in perlfunc.
/ must follow a numeric type
(F) You had an unpack template that contained a '#', but this did
not follow some numeric unpack specification. See "pack" in
perlfunc.
/%s/: Unrecognized escape \\%c passed through
(W regexp) You used a backslash-character combination which is not
recognized by Perl. This combination appears in an interpolated
variable or a "'"-delimited regular expression. The character was
understood literally.
/%s/: Unrecognized escape \\%c in character class passed through
(W regexp) You used a backslash-character combination which is not
recognized by Perl inside character classes. The character was
understood literally.
/%s/ should probably be written as "%s"
(W syntax) You have used a pattern where Perl expected to find a
string, as in the first argument to "join". Perl will treat the
true or false result of matching the pattern against $_ as the
string, which is probably not what you had in mind.
%s() called too early to check prototype
(W prototype) You've called a function that has a prototype before
the parser saw a definition or declaration for it, and Perl could
not check that the call conforms to the prototype. You need to
either add an early prototype declaration for the subroutine in
question, or move the subroutine definition ahead of the call to get
proper prototype checking. Alternatively, if you are certain that
you're calling the function correctly, you may put an ampersand
before the name to avoid the warning. See perlsub.
%s argument is not a HASH or ARRAY element
(F) The argument to exists() must be a hash or array element, such
as:
$foo{$bar}
$ref->{"susie"}[12]
%s argument is not a HASH or ARRAY element or slice
(F) The argument to delete() must be either a hash or array element,
such as:
$foo{$bar}
$ref->{"susie"}[12]
or a hash or array slice, such as:
@foo[$bar, $baz, $xyzzy]
@{$ref->[12]}{"susie", "queue"}
%s argument is not a subroutine name
(F) The argument to exists() for "exists &sub" must be a subroutine
name, and not a subroutine call. "exists &sub()" will generate this
error.
%s package attribute may clash with future reserved word: %s
(W reserved) A lowercase attribute name was used that had a package-
specific handler. That name might have a meaning to Perl itself
some day, even though it doesn't yet. Perhaps you should use a
mixed-case attribute name, instead. See attributes.
(in cleanup) %s
(W misc) This prefix usually indicates that a DESTROY() method
raised the indicated exception. Since destructors are usually
called by the system at arbitrary points during execution, and often
a vast number of times, the warning is issued only once for any
number of failures that would otherwise result in the same message
being repeated.
Failure of user callbacks dispatched using the "G_KEEPERR" flag
could also result in this warning. See "G_KEEPERR" in perlcall.
<> should be quotes
(F) You wrote "require <file>" when you should have written "require
'file'".
Attempt to join self
(F) You tried to join a thread from within itself, which is an
impossible task. You may be joining the wrong thread, or you may
need to move the join() to some other thread.
Bad evalled substitution pattern
(F) You've used the /e switch to evaluate the replacement for a
substitution, but perl found a syntax error in the code to evaluate,
most likely an unexpected right brace '}'.
Bad realloc() ignored
(S) An internal routine called realloc() on something that had never
been malloc()ed in the first place. Mandatory, but can be disabled
by setting environment variable "PERL_BADFREE" to 1.
Bareword found in conditional
(W bareword) The compiler found a bareword where it expected a
conditional, which often indicates that an || or && was parsed as
part of the last argument of the previous construct, for example:
open FOO || die;
It may also indicate a misspelled constant that has been interpreted
as a bareword:
use constant TYPO => 1;
if (TYOP) { print "foo" }
The "strict" pragma is useful in avoiding such errors.
Binary number > 0b11111111111111111111111111111111 non-portable
(W portable) The binary number you specified is larger than 2**32-1
(4294967295) and therefore non-portable between systems. See
perlport for more on portability concerns.
Bit vector size > 32 non-portable
(W portable) Using bit vector sizes larger than 32 is non-portable.
Buffer overflow in prime_env_iter: %s
(W internal) A warning peculiar to VMS. While Perl was preparing to
iterate over %ENV, it encountered a logical name or symbol
definition which was too long, so it was truncated to the string
shown.
Can't check filesystem of script "%s"
(P) For some reason you can't check the filesystem of the script for
nosuid.
Can't declare class for non-scalar %s in "%s"
(S) Currently, only scalar variables can declared with a specific
class qualifier in a "my" or "our" declaration. The semantics may
be extended for other types of variables in future.
Can't declare %s in "%s"
(F) Only scalar, array, and hash variables may be declared as "my"
or "our" variables. They must have ordinary identifiers as names.
Can't ignore signal CHLD, forcing to default
(W signal) Perl has detected that it is being run with the SIGCHLD
signal (sometimes known as SIGCLD) disabled. Since disabling this
signal will interfere with proper determination of exit status of
child processes, Perl has reset the signal to its default value.
This situation typically indicates that the parent program under
which Perl may be running (e.g., cron) is being very careless.
Can't modify non-lvalue subroutine call
(F) Subroutines meant to be used in lvalue context should be
declared as such, see "Lvalue subroutines" in perlsub.
Can't read CRTL environ
(S) A warning peculiar to VMS. Perl tried to read an element of
%ENV from the CRTL's internal environment array and discovered the
array was missing. You need to figure out where your CRTL misplaced
its environ or define PERL_ENV_TABLES (see perlvms) so that environ
is not searched.
Can't remove %s: %s, skipping file
(S) You requested an inplace edit without creating a backup file.
Perl was unable to remove the original file to replace it with the
modified file. The file was left unmodified.
Can't return %s from lvalue subroutine
(F) Perl detected an attempt to return illegal lvalues (such as
temporary or readonly values) from a subroutine used as an lvalue.
This is not allowed.
Can't weaken a nonreference
(F) You attempted to weaken something that was not a reference.
Only references can be weakened.
Character class [:%s:] unknown
(F) The class in the character class [: :] syntax is unknown. See
perlre.
Character class syntax [%s] belongs inside character classes
(W unsafe) The character class constructs [: :], [= =], and [. .]
go inside character classes, the [] are part of the construct, for
example: /[012[:alpha:]345]/. Note that [= =] and [. .] are not
currently implemented; they are simply placeholders for future
extensions.
Constant is not %s reference
(F) A constant value (perhaps declared using the "use constant"
pragma) is being dereferenced, but it amounts to the wrong type of
reference. The message indicates the type of reference that was
expected. This usually indicates a syntax error in dereferencing the
constant value. See "Constant Functions" in perlsub and constant.
constant(%s): %s
(F) The parser found inconsistencies either while attempting to
define an overloaded constant, or when trying to find the character
name specified in the "\N{...}" escape. Perhaps you forgot to load
the corresponding "overload" or "charnames" pragma? See charnames
and overload.
CORE::%s is not a keyword
(F) The CORE:: namespace is reserved for Perl keywords.
defined(@array) is deprecated
(D) defined() is not usually useful on arrays because it checks for
an undefined scalar value. If you want to see if the array is
empty, just use "if (@array) { # not empty }" for example.
defined(%hash) is deprecated
(D) defined() is not usually useful on hashes because it checks for
an undefined scalar value. If you want to see if the hash is empty,
just use "if (%hash) { # not empty }" for example.
Did not produce a valid header
See Server error.
(Did you mean "local" instead of "our"?)
(W misc) Remember that "our" does not localize the declared global
variable. You have declared it again in the same lexical scope,
which seems superfluous.
Document contains no data
See Server error.
entering effective %s failed
(F) While under the "use filetest" pragma, switching the real and
effective uids or gids failed.
false [] range "%s" in regexp
(W regexp) A character class range must start and end at a literal
character, not another character class like "\d" or "[:alpha:]".
The "-" in your false range is interpreted as a literal "-".
Consider quoting the "-", "\-". See perlre.
Filehandle %s opened only for output
(W io) You tried to read from a filehandle opened only for writing.
If you intended it to be a read/write filehandle, you needed to open
it with "+<" or "+>" or "+>>" instead of with "<" or nothing. If
you intended only to read from the file, use "<". See "open" in
perlfunc.
flock() on closed filehandle %s
(W closed) The filehandle you're attempting to flock() got itself
closed some time before now. Check your logic flow. flock()
operates on filehandles. Are you attempting to call flock() on a
dirhandle by the same name?
Global symbol "%s" requires explicit package name
(F) You've said "use strict vars", which indicates that all
variables must either be lexically scoped (using "my"), declared
beforehand using "our", or explicitly qualified to say which package
the global variable is in (using "::").
Hexadecimal number > 0xffffffff non-portable
(W portable) The hexadecimal number you specified is larger than
2**32-1 (4294967295) and therefore non-portable between systems.
See perlport for more on portability concerns.
Ill-formed CRTL environ value "%s"
(W internal) A warning peculiar to VMS. Perl tried to read the
CRTL's internal environ array, and encountered an element without
the "=" delimiter used to separate keys from values. The element is
ignored.
Ill-formed message in prime_env_iter: |%s|
(W internal) A warning peculiar to VMS. Perl tried to read a
logical name or CLI symbol definition when preparing to iterate over
%ENV, and didn't see the expected delimiter between key and value,
so the line was ignored.
Illegal binary digit %s
(F) You used a digit other than 0 or 1 in a binary number.
Illegal binary digit %s ignored
(W digit) You may have tried to use a digit other than 0 or 1 in a
binary number. Interpretation of the binary number stopped before
the offending digit.
Illegal number of bits in vec
(F) The number of bits in vec() (the third argument) must be a power
of two from 1 to 32 (or 64, if your platform supports that).
Integer overflow in %s number
(W overflow) The hexadecimal, octal or binary number you have
specified either as a literal or as an argument to hex() or oct() is
too big for your architecture, and has been converted to a floating
point number. On a 32-bit architecture the largest hexadecimal,
octal or binary number representable without overflow is 0xFFFFFFFF,
037777777777, or 0b11111111111111111111111111111111 respectively.
Note that Perl transparently promotes all numbers to a floating
point representation internally--subject to loss of precision errors
in subsequent operations.
Invalid %s attribute: %s
The indicated attribute for a subroutine or variable was not
recognized by Perl or by a user-supplied handler. See attributes.
Invalid %s attributes: %s
The indicated attributes for a subroutine or variable were not
recognized by Perl or by a user-supplied handler. See attributes.
invalid [] range "%s" in regexp
The offending range is now explicitly displayed.
Invalid separator character %s in attribute list
(F) Something other than a colon or whitespace was seen between the
elements of an attribute list. If the previous attribute had a
parenthesised parameter list, perhaps that list was terminated too
soon. See attributes.
Invalid separator character %s in subroutine attribute list
(F) Something other than a colon or whitespace was seen between the
elements of a subroutine attribute list. If the previous attribute
had a parenthesised parameter list, perhaps that list was terminated
too soon.
leaving effective %s failed
(F) While under the "use filetest" pragma, switching the real and
effective uids or gids failed.
Lvalue subs returning %s not implemented yet
(F) Due to limitations in the current implementation, array and hash
values cannot be returned in subroutines used in lvalue context.
See "Lvalue subroutines" in perlsub.
Method %s not permitted
See Server error.
Missing %sbrace%s on \N{}
(F) Wrong syntax of character name literal "\N{charname}" within
double-quotish context.
Missing command in piped open
(W pipe) You used the "open(FH, "| command")" or "open(FH, "command
|")" construction, but the command was missing or blank.
Missing name in "my sub"
(F) The reserved syntax for lexically scoped subroutines requires
that they have a name with which they can be found.
No %s specified for -%c
(F) The indicated command line switch needs a mandatory argument,
but you haven't specified one.
No package name allowed for variable %s in "our"
(F) Fully qualified variable names are not allowed in "our"
declarations, because that doesn't make much sense under existing
semantics. Such syntax is reserved for future extensions.
No space allowed after -%c
(F) The argument to the indicated command line switch must follow
immediately after the switch, without intervening spaces.
no UTC offset information; assuming local time is UTC
(S) A warning peculiar to VMS. Perl was unable to find the local
timezone offset, so it's assuming that local system time is
equivalent to UTC. If it's not, define the logical name
SYS$TIMEZONE_DIFFERENTIAL to translate to the number of seconds
which need to be added to UTC to get local time.
Octal number > 037777777777 non-portable
(W portable) The octal number you specified is larger than 2**32-1
(4294967295) and therefore non-portable between systems. See
perlport for more on portability concerns.
See also perlport for writing portable code.
panic: del_backref
(P) Failed an internal consistency check while trying to reset a
weak reference.
panic: kid popen errno read
(F) forked child returned an incomprehensible message about its
errno.
panic: magic_killbackrefs
(P) Failed an internal consistency check while trying to reset all
weak references to an object.
Parentheses missing around "%s" list
(W parenthesis) You said something like
my $foo, $bar = @_;
when you meant
my ($foo, $bar) = @_;
Remember that "my", "our", and "local" bind tighter than comma.
Possible unintended interpolation of %s in string
(W ambiguous) It used to be that Perl would try to guess whether you
wanted an array interpolated or a literal @. It no longer does
this; arrays are now always interpolated into strings. This means
that if you try something like:
print "fred@example.com";
and the array @example doesn't exist, Perl is going to print
"fred.com", which is probably not what you wanted. To get a literal
"@" sign in a string, put a backslash before it, just as you would
to get a literal "$" sign.
Possible Y2K bug: %s
(W y2k) You are concatenating the number 19 with another number,
which could be a potential Year 2000 problem.
pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead
(W deprecated) You have written something like this:
sub doit
{
use attrs qw(locked);
}
You should use the new declaration syntax instead.
sub doit : locked
{
...
The "use attrs" pragma is now obsolete, and is only provided for
backward-compatibility. See "Subroutine Attributes" in perlsub.
Premature end of script headers
See Server error.
Repeat count in pack overflows
(F) You can't specify a repeat count so large that it overflows your
signed integers. See "pack" in perlfunc.
Repeat count in unpack overflows
(F) You can't specify a repeat count so large that it overflows your
signed integers. See "unpack" in perlfunc.
realloc() of freed memory ignored
(S) An internal routine called realloc() on something that had
already been freed.
Reference is already weak
(W misc) You have attempted to weaken a reference that is already
weak. Doing so has no effect.
setpgrp can't take arguments
(F) Your system has the setpgrp() from BSD 4.2, which takes no
arguments, unlike POSIX setpgid(), which takes a process ID and
process group ID.
Strange *+?{} on zero-length expression
(W regexp) You applied a regular expression quantifier in a place
where it makes no sense, such as on a zero-width assertion. Try
putting the quantifier inside the assertion instead. For example,
the way to match "abc" provided that it is followed by three
repetitions of "xyz" is "/abc(?=(?:xyz){3})/", not
"/abc(?=xyz){3}/".
switching effective %s is not implemented
(F) While under the "use filetest" pragma, we cannot switch the real
and effective uids or gids.
This Perl can't reset CRTL environ elements (%s)
This Perl can't set CRTL environ elements (%s=%s)
(W internal) Warnings peculiar to VMS. You tried to change or
delete an element of the CRTL's internal environ array, but your
copy of Perl wasn't built with a CRTL that contained the setenv()
function. You'll need to rebuild Perl with a CRTL that does, or
redefine PERL_ENV_TABLES (see perlvms) so that the environ array
isn't the target of the change to %ENV which produced the warning.
Too late to run %s block
(W void) A CHECK or INIT block is being defined during run time
proper, when the opportunity to run them has already passed.
Perhaps you are loading a file with "require" or "do" when you
should be using "use" instead. Or perhaps you should put the
"require" or "do" inside a BEGIN block.
Unknown open() mode '%s'
(F) The second argument of 3-argument open() is not among the list
of valid modes: "<", ">", ">>", "+<", "+>", "+>>", "-|", "|-".
Unknown process %x sent message to prime_env_iter: %s
(P) An error peculiar to VMS. Perl was reading values for %ENV
before iterating over it, and someone else stuck a message in the
stream of data Perl expected. Someone's very confused, or perhaps
trying to subvert Perl's population of %ENV for nefarious purposes.
Unrecognized escape \\%c passed through
(W misc) You used a backslash-character combination which is not
recognized by Perl. The character was understood literally.
Unterminated attribute parameter in attribute list
(F) The lexer saw an opening (left) parenthesis character while
parsing an attribute list, but the matching closing (right)
parenthesis character was not found. You may need to add (or
remove) a backslash character to get your parentheses to balance.
See attributes.
Unterminated attribute list
(F) The lexer found something other than a simple identifier at the
start of an attribute, and it wasn't a semicolon or the start of a
block. Perhaps you terminated the parameter list of the previous
attribute too soon. See attributes.
Unterminated attribute parameter in subroutine attribute list
(F) The lexer saw an opening (left) parenthesis character while
parsing a subroutine attribute list, but the matching closing
(right) parenthesis character was not found. You may need to add
(or remove) a backslash character to get your parentheses to
balance.
Unterminated subroutine attribute list
(F) The lexer found something other than a simple identifier at the
start of a subroutine attribute, and it wasn't a semicolon or the
start of a block. Perhaps you terminated the parameter list of the
previous attribute too soon.
Value of CLI symbol "%s" too long
(W misc) A warning peculiar to VMS. Perl tried to read the value of
an %ENV element from a CLI symbol table, and found a resultant
string longer than 1024 characters. The return value has been
truncated to 1024 characters.
Version number must be a constant number
(P) The attempt to translate a "use Module n.n LIST" statement into
its equivalent "BEGIN" block found an internal inconsistency with
the version number.
New tests
lib/attrs
Compatibility tests for "sub : attrs" vs the older "use attrs".
lib/env
Tests for new environment scalar capability (e.g., "use Env
qw($BAR);").
lib/env-array
Tests for new environment array capability (e.g., "use Env
qw(@PATH);").
lib/io_const
IO constants (SEEK_*, _IO*).
lib/io_dir
Directory-related IO methods (new, read, close, rewind, tied
delete).
lib/io_multihomed
INET sockets with multi-homed hosts.
lib/io_poll
IO poll().
lib/io_unix
UNIX sockets.
op/attrs
Regression tests for "my ($x,@y,%z) : attrs" and <sub : attrs>.
op/filetest
File test operators.
op/lex_assign
Verify operations that access pad objects (lexicals and
temporaries).
op/exists_sub
Verify "exists &sub" operations.
Incompatible Changes
Perl Source Incompatibilities
Beware that any new warnings that have been added or old ones that have
been enhanced are not considered incompatible changes.
Since all new warnings must be explicitly requested via the "-w" switch
or the "warnings" pragma, it is ultimately the programmer's
responsibility to ensure that warnings are enabled judiciously.
CHECK is a new keyword
All subroutine definitions named CHECK are now special. See
"/"Support for CHECK blocks"" for more information.
Treatment of list slices of undef has changed
There is a potential incompatibility in the behavior of list slices
that consist entirely of undefined values. See "Behavior of list
slices is more consistent".
Format of $English::PERL_VERSION is different
The English module now sets $PERL_VERSION to $^V (a string value)
rather than $] (a numeric value). This is a potential
incompatibility. Send us a report via perlbug if you are affected
by this.
See "Improved Perl version numbering system" for the reasons for
this change.
Literals of the form 1.2.3 parse differently
Previously, numeric literals with more than one dot in them were
interpreted as a floating point number concatenated with one or more
numbers. Such "numbers" are now parsed as strings composed of the
specified ordinals.
For example, "print 97.98.99" used to output 97.9899 in earlier
versions, but now prints "abc".
See "Support for strings represented as a vector of ordinals".
Possibly changed pseudo-random number generator
Perl programs that depend on reproducing a specific set of pseudo-
random numbers may now produce different output due to improvements
made to the rand() builtin. You can use "sh Configure
-Drandfunc=rand" to obtain the old behavior.
See "Better pseudo-random number generator".
Hashing function for hash keys has changed
Even though Perl hashes are not order preserving, the apparently
random order encountered when iterating on the contents of a hash is
actually determined by the hashing algorithm used. Improvements in
the algorithm may yield a random order that is different from that
of previous versions, especially when iterating on hashes.
See "Better worst-case behavior of hashes" for additional
information.
"undef" fails on read only values
Using the "undef" operator on a readonly value (such as $1) has the
same effect as assigning "undef" to the readonly value--it throws an
exception.
Close-on-exec bit may be set on pipe and socket handles
Pipe and socket handles are also now subject to the close-on-exec
behavior determined by the special variable $^F.
See "More consistent close-on-exec behavior".
Writing "$$1" to mean "${$}1" is unsupported
Perl 5.004 deprecated the interpretation of $$1 and similar within
interpolated strings to mean "$$ . "1"", but still allowed it.
In Perl 5.6.0 and later, "$$1" always means "${$1}".
delete(), each(), values() and "\(%h)"
operate on aliases to values, not copies
delete(), each(), values() and hashes (e.g. "\(%h)") in a list
context return the actual values in the hash, instead of copies (as
they used to in earlier versions). Typical idioms for using these
constructs copy the returned values, but this can make a significant
difference when creating references to the returned values. Keys in
the hash are still returned as copies when iterating on a hash.
See also "delete(), each(), values() and hash iteration are faster".
vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS
vec() generates a run-time error if the BITS argument is not a valid
power-of-two integer.
Text of some diagnostic output has changed
Most references to internal Perl operations in diagnostics have been
changed to be more descriptive. This may be an issue for programs
that may incorrectly rely on the exact text of diagnostics for
proper functioning.
"%@" has been removed
The undocumented special variable "%@" that used to accumulate
"background" errors (such as those that happen in DESTROY()) has
been removed, because it could potentially result in memory leaks.
Parenthesized not() behaves like a list operator
The "not" operator now falls under the "if it looks like a function,
it behaves like a function" rule.
As a result, the parenthesized form can be used with "grep" and
"map". The following construct used to be a syntax error before,
but it works as expected now:
grep not($_), @things;
On the other hand, using "not" with a literal list slice may not
work. The following previously allowed construct:
print not (1,2,3)[0];
needs to be written with additional parentheses now:
print not((1,2,3)[0]);
The behavior remains unaffected when "not" is not followed by
parentheses.
Semantics of bareword prototype "(*)" have changed
The semantics of the bareword prototype "*" have changed. Perl
5.005 always coerced simple scalar arguments to a typeglob, which
wasn't useful in situations where the subroutine must distinguish
between a simple scalar and a typeglob. The new behavior is to not
coerce bareword arguments to a typeglob. The value will always be
visible as either a simple scalar or as a reference to a typeglob.
See "More functional bareword prototype (*)".
Semantics of bit operators may have changed on 64-bit platforms
If your platform is either natively 64-bit or if Perl has been
configured to used 64-bit integers, i.e., $Config{ivsize} is 8,
there may be a potential incompatibility in the behavior of bitwise
numeric operators (& | ^ ~ << >>). These operators used to strictly
operate on the lower 32 bits of integers in previous versions, but
now operate over the entire native integral width. In particular,
note that unary "~" will produce different results on platforms that
have different $Config{ivsize}. For portability, be sure to mask
off the excess bits in the result of unary "~", e.g., "~$x &
0xffffffff".
See "Bit operators support full native integer width".
More builtins taint their results
As described in "Improved security features", there may be more
sources of taint in a Perl program.
To avoid these new tainting behaviors, you can build Perl with the
Configure option "-Accflags=-DINCOMPLETE_TAINTS". Beware that the
ensuing perl binary may be insecure.
C Source Incompatibilities
"PERL_POLLUTE"
Release 5.005 grandfathered old global symbol names by providing
preprocessor macros for extension source compatibility. As of
release 5.6.0, these preprocessor definitions are not available by
default. You need to explicitly compile perl with "-DPERL_POLLUTE"
to get these definitions. For extensions still using the old
symbols, this option can be specified via MakeMaker:
perl Makefile.PL POLLUTE=1
"PERL_IMPLICIT_CONTEXT"
This new build option provides a set of macros for all API functions
such that an implicit interpreter/thread context argument is passed
to every API function. As a result of this, something like
"sv_setsv(foo,bar)" amounts to a macro invocation that actually
translates to something like "Perl_sv_setsv(my_perl,foo,bar)".
While this is generally expected to not have any significant source
compatibility issues, the difference between a macro and a real
function call will need to be considered.
This means that there is a source compatibility issue as a result of
this if your extensions attempt to use pointers to any of the Perl
API functions.
Note that the above issue is not relevant to the default build of
Perl, whose interfaces continue to match those of prior versions
(but subject to the other options described here).
See "Background and PERL_IMPLICIT_CONTEXT" in perlguts for detailed
information on the ramifications of building Perl with this option.
NOTE: PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
with one of -Dusethreads, -Dusemultiplicity, or both. It is not
intended to be enabled by users at this time.
"PERL_POLLUTE_MALLOC"
Enabling Perl's malloc in release 5.005 and earlier caused the
namespace of the system's malloc family of functions to be usurped
by the Perl versions, since by default they used the same names.
Besides causing problems on platforms that do not allow these
functions to be cleanly replaced, this also meant that the system
versions could not be called in programs that used Perl's malloc.
Previous versions of Perl have allowed this behaviour to be
suppressed with the HIDEMYMALLOC and EMBEDMYMALLOC preprocessor
definitions.
As of release 5.6.0, Perl's malloc family of functions have default
names distinct from the system versions. You need to explicitly
compile perl with "-DPERL_POLLUTE_MALLOC" to get the older
behaviour. HIDEMYMALLOC and EMBEDMYMALLOC have no effect, since the
behaviour they enabled is now the default.
Note that these functions do not constitute Perl's memory allocation
API. See "Memory Allocation" in perlguts for further information
about that.
Compatible C Source API Changes
"PATCHLEVEL" is now "PERL_VERSION"
The cpp macros "PERL_REVISION", "PERL_VERSION", and
"PERL_SUBVERSION" are now available by default from perl.h, and
reflect the base revision, patchlevel, and subversion respectively.
"PERL_REVISION" had no prior equivalent, while "PERL_VERSION" and
"PERL_SUBVERSION" were previously available as "PATCHLEVEL" and
"SUBVERSION".
The new names cause less pollution of the cpp namespace and reflect
what the numbers have come to stand for in common practice. For
compatibility, the old names are still supported when patchlevel.h
is explicitly included (as required before), so there is no source
incompatibility from the change.
Binary Incompatibilities
In general, the default build of this release is expected to be binary
compatible for extensions built with the 5.005 release or its
maintenance versions. However, specific platforms may have broken
binary compatibility due to changes in the defaults used in hints files.
Therefore, please be sure to always check the platform-specific README
files for any notes to the contrary.
The usethreads or usemultiplicity builds are not binary compatible with
the corresponding builds in 5.005.
On platforms that require an explicit list of exports (AIX, OS/2 and
Windows, among others), purely internal symbols such as parser functions
and the run time opcodes are not exported by default. Perl 5.005 used
to export all functions irrespective of whether they were considered
part of the public API or not.
For the full list of public API functions, see perlapi.
Known Problems
Thread test failures
The subtests 19 and 20 of lib/thr5005.t test are known to fail due to
fundamental problems in the 5.005 threading implementation. These are
not new failures--Perl 5.005_0x has the same bugs, but didn't have these
tests.
EBCDIC platforms not supported
In earlier releases of Perl, EBCDIC environments like OS390 (also known
as Open Edition MVS) and VM-ESA were supported. Due to changes required
by the UTF-8 (Unicode) support, the EBCDIC platforms are not supported
in Perl 5.6.0.
In 64-bit HP-UX the lib/io_multihomed test may hang
The lib/io_multihomed test may hang in HP-UX if Perl has been configured
to be 64-bit. Because other 64-bit platforms do not hang in this test,
HP-UX is suspect. All other tests pass in 64-bit HP-UX. The test
attempts to create and connect to "multihomed" sockets (sockets which
have multiple IP addresses).
NEXTSTEP 3.3 POSIX test failure
In NEXTSTEP 3.3p2 the implementation of the strftime(3) in the operating
system libraries is buggy: the %j format numbers the days of a month
starting from zero, which, while being logical to programmers, will
cause the subtests 19 to 27 of the lib/posix test may fail.
Tru64 (aka Digital UNIX, aka DEC OSF/1) lib/sdbm test failure with gcc
If compiled with gcc 2.95 the lib/sdbm test will fail (dump core). The
cure is to use the vendor cc, it comes with the operating system and
produces good code.
UNICOS/mk CC failures during Configure run
In UNICOS/mk the following errors may appear during the Configure run:
Guessing which symbols your C compiler and preprocessor define...
CC-20 cc: ERROR File = try.c, Line = 3
...
bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K
...
4 errors detected in the compilation of "try.c".
The culprit is the broken awk of UNICOS/mk. The effect is fortunately
rather mild: Perl itself is not adversely affected by the error, only
the h2ph utility coming with Perl, and that is rather rarely needed
these days.
Arrow operator and arrays
When the left argument to the arrow operator "->" is an array, or the
"scalar" operator operating on an array, the result of the operation
must be considered erroneous. For example:
@x->[2]
scalar(@x)->[2]
These expressions will get run-time errors in some future release of
Perl.
Experimental features
As discussed above, many features are still experimental. Interfaces
and implementation of these features are subject to change, and in
extreme cases, even subject to removal in some future release of Perl.
These features include the following:
Threads
Unicode
64-bit support
Lvalue subroutines
Weak references
The pseudo-hash data type
The Compiler suite
Internal implementation of file globbing
The DB module
The regular expression code constructs:
"(?{ code })" and "(??{ code })"
Obsolete Diagnostics
Character class syntax [: :] is reserved for future extensions
(W) Within regular expression character classes ([]) the syntax
beginning with "[:" and ending with ":]" is reserved for future
extensions. If you need to represent those character sequences
inside a regular expression character class, just quote the square
brackets with the backslash: "\[:" and ":\]".
Ill-formed logical name |%s| in prime_env_iter
(W) A warning peculiar to VMS. A logical name was encountered when
preparing to iterate over %ENV which violates the syntactic rules
governing logical names. Because it cannot be translated normally,
it is skipped, and will not appear in %ENV. This may be a benign
occurrence, as some software packages might directly modify logical
name tables and introduce nonstandard names, or it may indicate that
a logical name table has been corrupted.
In string, @%s now must be written as \@%s
The description of this error used to say:
(Someday it will simply assume that an unbackslashed @
interpolates an array.)
That day has come, and this fatal error has been removed. It has
been replaced by a non-fatal warning instead. See "Arrays now
always interpolate into double-quoted strings" for details.
Probable precedence problem on %s
(W) The compiler found a bareword where it expected a conditional,
which often indicates that an || or && was parsed as part of the
last argument of the previous construct, for example:
open FOO || die;
regexp too big
(F) The current implementation of regular expressions uses shorts as
address offsets within a string. Unfortunately this means that if
the regular expression compiles to longer than 32767, it'll blow up.
Usually when you want a regular expression this big, there is a
better way to do it with multiple statements. See perlre.
Use of "$$<digit>" to mean "${$}<digit>" is deprecated
(D) Perl versions before 5.004 misinterpreted any type marker
followed by "$" and a digit. For example, "$$0" was incorrectly
taken to mean "${$}0" instead of "${$0}". This bug is (mostly)
fixed in Perl 5.004.
However, the developers of Perl 5.004 could not fix this bug
completely, because at least two widely-used modules depend on the
old meaning of "$$0" in a string. So Perl 5.004 still interprets
"$$<digit>" in the old (broken) way inside strings; but it generates
this message as a warning. And in Perl 5.005, this special
treatment will cease.
Reporting Bugs
If you find what you think is a bug, you might check the articles
recently posted to the comp.lang.perl.misc newsgroup. There may also be
information at http://www.perl.com/perl/ , the Perl Home Page.
If you believe you have an unreported bug, please run the perlbug
program included with your release. Be sure to trim your bug down to a
tiny but sufficient test case. Your bug report, along with the output
of "perl -V", will be sent off to perlbug@perl.org to be analysed by the
Perl porting team.
SEE ALSO
The Changes file for exhaustive details on what changed.
The INSTALL file for how to build Perl.
The README file for general stuff.
The Artistic and Copying files for copyright information.
HISTORY
Written by Gurusamy Sarathy <gsar@activestate.com>, with many
contributions from The Perl Porters.
Send omissions or corrections to <perlbug@perl.org>.
perl v5.40.1 2026-08-30 PERL56DELTA(1)
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