perl56delta - what's new for perl v5.6.0
This document describes differences between the 5.005
release and the 5.6.0 release.
Interpreter cloning, threads, and concurrency
Perl 5.6.0 introduces the beginnings of support for running
multiple interpreters concurrently in different
threads. In conjunction with the perl_clone() API call,
which can be used to selectively duplicate the state of
any given interpreter, it is possible to compile a piece
of code once in an interpreter, clone that interpreter one
or more times, and run all the resulting interpreters in
distinct threads.
On the Windows platform, this feature is used to emulate
fork() at the interpreter level. See perlfork for details
about that.
This feature is still in evolution. It is eventually
meant to be used to selectively clone a subroutine and
data reachable from that subroutine in a separate interpreter
and run the cloned subroutine in a separate thread.
Since there is no shared data between the interpreters,
little or no locking will be needed (unless parts of the
symbol table are explicitly shared). This is obviously
intended to be an easy-to-use replacement for the existing
threads support.
Support for cloning interpreters and interpreter concurrency
can be enabled using the -Dusethreads Configure
option (see win32/Makefile for how to enable it on Windows.)
The resulting perl executable will be functionally
identical to one that was built with -Dmultiplicity, but
the perl_clone() API call will only be available in the
former.
-Dusethreads enables the cpp macro USE_ITHREADS by
default, which in turn enables Perl source code changes
that provide a clear separation between the op tree and
the data it operates with. The former is immutable, and
can therefore be shared between an interpreter and all of
its clones, while the latter is considered local to each
interpreter, and is therefore copied for each clone.
Note that building Perl with the -Dusemultiplicity Configure
option is adequate if you wish to run multiple inde-
pendent interpreters concurrently in different threads.
-Dusethreads only provides the additional functionality of
the perl_clone() API call and other support for running
cloned interpreters concurrently.
NOTE: This is an experimental feature. Implementation
details are
subject to change.
Lexically scoped warning categories [Toc] [Back]
You can now control the granularity of warnings emitted by
perl at a finer level using the "use warnings" pragma.
warnings and perllexwarn have copious documentation on
this feature.
Unicode and UTF-8 support [Toc] [Back]
Perl now uses UTF-8 as its internal representation for
character strings. The "utf8" and "bytes" pragmas are
used to control this support in the current lexical scope.
See perlunicode, utf8 and bytes for more information.
This feature is expected to evolve quickly to support some
form of I/O disciplines that can be used to specify the
kind of input and output data (bytes or characters).
Until that happens, additional modules from CPAN will be
needed to complete the toolkit for dealing with Unicode.
NOTE: This should be considered an experimental feature. Implementation
details are subject to change.
Support for interpolating named characters [Toc] [Back]
The new "scape interpolates named characters within
strings. For example, "Hi! HITE SMILING FACE}" evaluates
to a string with a unicode smiley face at the end.
"our" declarations
An "our" declaration introduces a value that can be best
understood as a lexically scoped symbolic alias to a
global variable in the package that was current where the
variable was declared. This is mostly useful as an alternative
to the "vars" pragma, but also provides the opportunity
to introduce typing and other attributes for such
variables. See "our" in perlfunc.
Support for strings represented as a vector of ordinals [Toc] [Back]
Literals of the form "v1.2.3.4" are now parsed as a string
composed of characters with the specified ordinals. This
is an alternative, more readable way to construct (possibly
unicode) strings instead of interpolating characters,
as in "". The leading "v" may be
omitted if there are more than two ordinals, so 1.2.3 is
parsed the same as "v1.2.3".
Strings written in this form are also useful to represent
version "numbers". It is easy to compare such version
"numbers" (which are really just plain strings) using any
of the usual string comparison operators "eq", "ne", "lt",
"gt", etc., or perform bitwise string operations on them
using "|", "&", etc.
In conjunction with the new $^V magic variable (which contains
the perl version as a string), such literals can be
used as a readable way to check if you're running a particular
version of Perl:
# this will parse in older versions of Perl also
if ($^V and $^V gt v5.6.0) {
# new features supported
}
"require" and "use" also have some special magic to support
such literals, 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 [Toc] [Back]
Beginning with Perl version 5.6.0, the version number convention
has been changed to a "dotted integer" scheme that
is more commonly found in open source projects.
Maintenance versions of v5.6.0 will be released as v5.6.1,
v5.6.2 etc. The next development series following v5.6.0
will be numbered v5.7.x, beginning with v5.7.0, and the
next major production release following v5.6.0 will be
v5.8.0.
The English module now sets $PERL_VERSION to $^V (a string
value) rather than $] (a numeric value). (This is a
potential incompatibility. Send us a report via perlbug
if you are affected by this.)
The v1.2.3 syntax is also now legal in Perl. See "Support
for strings represented as a vector of ordinals" for more
on that.
To cope with the new versioning system's use of at least
three significant digits for each version component, the
method used for incrementing the subversion number has
also changed slightly. We assume that versions older than
v5.6.0 have been incrementing the subversion component in
multiples of 10. Versions after v5.6.0 will increment
them by 1. Thus, using the new notation, 5.005_03 is the
"same" as v5.5.30, and the first maintenance version following
v5.6.0 will be v5.6.1 (which should be read as
being equivalent to a floating point value of 5.006_001 in
the older format, stored in $]).
New syntax for declaring subroutine attributes [Toc] [Back]
Formerly, if you wanted to mark a subroutine as being a
method call or as requiring an automatic lock() when it is
entered, you had to declare that with a "use attrs" pragma
in the body of the subroutine. That can now be accomplished
with declaration syntax, like this:
sub mymethod : locked method ;
...
sub mymethod : locked method {
...
}
sub othermethod :locked :method ;
...
sub othermethod :locked :method {
...
}
(Note how only the first ":" is mandatory, and whitespace
surrounding the ":" is optional.)
AutoSplit.pm and SelfLoader.pm have been updated to keep
the attributes with the stubs they provide. See
attributes.
File and directory handles can be autovivified [Toc] [Back]
Similar to how constructs such as "$x->[0]" autovivify a
reference, handle constructors (open(), opendir(), pipe(),
socketpair(), sysopen(), socket(), and accept()) now autovivify
a file or directory handle if the handle passed to
them is an uninitialized scalar variable. This allows the
constructs such as "open(my $fh, ...)" and "open(local
$fh,...)" to be used to create filehandles that will conveniently
be closed automatically when the scope ends,
provided there are no other references to them. This
largely eliminates the need for typeglobs when opening
filehandles that must be passed around, as in the following
example:
sub myopen {
open my $fh, "@_"
or die "Can't open '@_': $!";
return $fh;
}
{
my $f = myopen("</etc/motd");
print <$f>;
# $f implicitly closed here
}
open() with more than two arguments
If open() is passed three arguments instead of two, the
second argument is used as the mode and the third argument
is taken to be the file name. This is primarily useful
for protecting against unintended magic behavior of the
traditional two-argument form. See "open" in perlfunc.
64-bit support
Any platform that has 64-bit integers either
(1) natively as longs or ints
(2) via special compiler flags
(3) using long long or int64_t
is able to use "quads" (64-bit integers) as follows:
o constants (decimal, hexadecimal, octal, binary) in the
code
o arguments to oct() and hex()
o arguments to print(), printf() and sprintf() (flag
prefixes ll, L, q)
o printed as such
o pack() and unpack() "q" and "Q" formats
o in basic arithmetics: + - * / % (NOTE: operating close
to the limits of the integer values may produce surprising
results)
o in bit arithmetics: & | ^ ~ << >> (NOTE: these used to
be forced to be 32 bits wide but now operate on the
full native width.)
o vec()
Note that unless you have the case (a) you will have to
configure and compile Perl using the -Duse64bitint Configure
flag.
NOTE: The Configure flags -Duselonglong and
-Duse64bits have been
deprecated. Use -Duse64bitint instead.
There are actually two modes of 64-bitness: the first one
is achieved using Configure -Duse64bitint and the second
one using Configure -Duse64bitall. The difference is that
the first one is minimal and the second one maximal. The
first works in more places than the second.
The "use64bitint" does only as much as is required to get
64-bit integers into Perl (this may mean, for example,
using "long longs") while your memory may still be limited
to 2 gigabytes (because your pointers could still be
32-bit). Note that the name "64bitint" does not imply
that your C compiler will be using 64-bit "int"s (it
might, but it doesn't have to): the "use64bitint" means
that you will be able to have 64 bits wide scalar values.
The "use64bitall" goes all the way by attempting to switch
also integers (if it can), longs (and pointers) to being
64-bit. This may create an even more binary incompatible
Perl than -Duse64bitint: the resulting executable may not
run at all in a 32-bit box, or you may have to
reboot/reconfigure/rebuild your operating system to be
64-bit aware.
Natively 64-bit systems like Alpha and Cray need neither
-Duse64bitint nor -Duse64bitall.
Last but not least: note that due to Perl's habit of
always using floating point numbers, the quads are still
not true integers. When quads overflow their limits
(0...18_446_744_073_709_551_615 unsigned,
-9_223_372_036_854_775_808...9_223_372_036_854_775_807
signed), they are silently promoted to floating point numbers,
after which they will start losing precision (in
their lower digits).
NOTE: 64-bit support is still experimental on most
platforms.
Existing support only covers the LP64 data model. In
particular, the
LLP64 data model is not yet supported. 64-bit libraries and system
APIs on many platforms have not stabilized--your
mileage may vary.
Large file support [Toc] [Back]
If you have filesystems that support "large files" (files
larger than 2 gigabytes), you may now also be able to create
and access them from Perl.
NOTE: The default action is to enable large file support, if
available on the platform.
If the large file support is on, and you have a Fcntl constant
O_LARGEFILE, the O_LARGEFILE is automatically added
to the flags of sysopen().
Beware that unless your filesystem also supports "sparse
files" seeking to umpteen petabytes may be inadvisable.
Note that in addition to requiring a proper file system to
do large files you may also need to adjust your per-process
(or your per-system, or per-process-group, or
per-user-group) maximum filesize limits before running
Perl scripts that try to handle large files, especially if
you intend to write such files.
Finally, in addition to your process/process group maximum
filesize limits, you may have quota limits on your
filesystems that stop you (your user id or your user group
id) from using large files.
Adjusting your process/user/group/file system/operating
system limits is outside the scope of Perl core language.
For process limits, you may try increasing the limits
using your shell's limits/limit/ulimit command before running
Perl. The BSD::Resource extension (not included with
the standard Perl distribution) may also be of use, it
offers the getrlimit/setrlimit interface that can be used
to adjust process resource usage limits, including the
maximum filesize limit.
Long doubles [Toc] [Back]
In some systems you may be able to use long doubles to
enhance the range and precision of your double precision
floating point numbers (that is, Perl's numbers). Use
Configure -Duselongdouble to enable this support (if it is
available).
"more bits"
You can "Configure -Dusemorebits" to turn on both the
64-bit support and the long double support.
Enhanced support for sort() subroutines
Perl subroutines with a prototype of "($$)", and XSUBs in
general, can now be used as sort subroutines. In either
case, the two elements to be compared are passed as normal
parameters in @_. See "sort" in perlfunc.
For unprototyped sort subroutines, the historical behavior
of passing the elements to be compared as the global
variables $a and $b remains unchanged.
"sort $coderef @foo" allowed
sort() did not accept a subroutine reference as the comparison
function in earlier versions. This is now permitted.
File globbing implemented internally [Toc] [Back]
Perl now uses the File::Glob implementation of the glob()
operator automatically. This avoids using an external csh
process and the problems associated with it.
NOTE: This is currently an experimental feature. Interfaces and
implementation are subject to change.
Support for CHECK blocks [Toc] [Back]
In addition to "BEGIN", "INIT", "END", "DESTROY" and
"AUTOLOAD", subroutines named "CHECK" are now special.
These are queued up during compilation and behave similar
to END blocks, except they are called at the end of compilation
rather than at the end of execution. They cannot
be called directly.
POSIX character class syntax [: :] supported
For example to match alphabetic characters use
/[[:alpha:]]/. See perlre for details.
Better pseudo-random number generator [Toc] [Back]
In 5.005_0x and earlier, perl's rand() function used the C
library rand(3) function. As of 5.005_52, Configure tests
for drand48(), random(), and rand() (in that order) and
picks the first one it finds.
These changes should result in better random numbers from
rand().
Improved "qw//" operator
The "qw//" operator is now evaluated at compile time into
a true list instead of being replaced with a run time call
to "split()". This removes the confusing misbehaviour of
"qw//" in scalar context, which had inherited that
behaviour from split().
Thus:
$foo = ($bar) = qw(a b c); print "$foo|$bar0;
now correctly prints "3|a", instead of "2|a".
Better worst-case behavior of hashes
Small changes in the hashing algorithm have been implemented
in order to improve the distribution of lower order
bits in the hashed value. This is expected to yield better
performance on keys that are repeated sequences.
pack() format 'Z' supported
The new format type 'Z' is useful for packing and unpacking
null-terminated strings. See "pack" in perlfunc.
pack() format modifier '!' supported
The new format type modifier '!' is useful for packing and
unpacking native shorts, ints, and longs. See "pack" in
perlfunc.
pack() and unpack() support counted strings
The template character '/' can be used to specify a
counted string type to be packed or unpacked. See "pack"
in perlfunc.
Comments in pack() templates
The '#' character in a template introduces a comment up to
end of the line. This facilitates documentation of pack()
templates.
Weak references [Toc] [Back]
In previous versions of Perl, you couldn't cache objects
so as to allow them to be deleted if the last reference
from outside the cache is deleted. The reference in the
cache would hold a reference count on the object and the
objects would never be destroyed.
Another familiar problem is with circular references.
When an object references itself, its reference count
would never go down to zero, and it would not get
destroyed until the program is about to exit.
Weak references solve this by allowing you to "weaken" any
reference, that is, make it not count towards the reference
count. When the last non-weak reference to an object
is deleted, the object is destroyed and all the weak references
to the object are automatically undef-ed.
To use this feature, you need the Devel::WeakRef package
from CPAN, which contains additional documentation.
NOTE: This is an experimental feature. Details are
subject to change.
Binary numbers supported
Binary numbers are now supported as literals, in s?printf
formats, and "oct()":
$answer = 0b101010;
printf "The answer is: %b0, oct("0b101010");
Lvalue subroutines [Toc] [Back]
Subroutines can now return modifiable lvalues. See
"Lvalue subroutines" in perlsub.
NOTE: This is an experimental feature. Details are
subject to change.
Some arrows may be omitted in calls through references [Toc] [Back]
Perl now allows the arrow to be omitted in many constructs
involving subroutine calls through references. For example,
"$foo[10]->('foo')" may now be written
"$foo[10]('foo')". This is rather similar to how the
arrow may be omitted from "$foo[10]->{'foo'}". Note however,
that the arrow is still required for
"foo(10)->('bar')".
Boolean assignment operators are legal lvalues [Toc] [Back]
Constructs such as "($a ||= 2) += 1" are now allowed.
exists() is supported on subroutine names
The exists() builtin now works on subroutine names. A
subroutine is considered to exist if it has been declared
(even if implicitly). See "exists" in perlfunc for examples.
exists() and delete() are supported on array elements
The exists() and delete() builtins now work on simple
arrays as well. The behavior is similar to that on hash
elements.
exists() can be used to check whether an array element has
been initialized. This avoids autovivifying array elements
that don't exist. If the array is tied, the
EXISTS() method in the corresponding tied package will be
invoked.
delete() may be used to remove an element from the array
and return it. The array element at that position returns
to its uninitialized state, so that testing for the same
element with exists() will return false. If the element
happens to be the one at the end, the size of the array
also shrinks up to the highest element that tests true for
exists(), or 0 if none such is found. If the array is
tied, the DELETE() method in the corresponding tied package
will be invoked.
See "exists" in perlfunc and "delete" in perlfunc for
examples.
Pseudo-hashes work better [Toc] [Back]
Dereferencing some types of reference values in a
pseudo-hash, such as "$ph->{foo}[1]", was accidentally
disallowed. This has been corrected.
When applied to a pseudo-hash element, exists() now
reports whether the specified value exists, not merely if
the key is valid.
delete() now works on pseudo-hashes. When given a pseudohash
element or slice it deletes the values corresponding
to the keys (but not the keys themselves). See
"Pseudo-hashes: Using an array as a hash" in perlref.
Pseudo-hash slices with constant keys are now optimized to
array lookups at compile-time.
List assignments to pseudo-hash slices are now supported.
The "fields" pragma now provides ways to create
pseudo-hashes, via fields::new() and fields::phash(). See
fields.
NOTE: The pseudo-hash data type continues to be experimental.
Limiting oneself to the interface elements provided by
the
fields pragma will provide protection from any future
changes.
Automatic flushing of output buffers [Toc] [Back]
fork(), exec(), system(), qx//, and pipe open()s now flush
buffers of all files opened for output when the operation
was attempted. This mostly eliminates confusing buffering
mishaps suffered by users unaware of how Perl internally
handles I/O.
This is not supported on some platforms like Solaris where
a suitably correct implementation of fflush(NULL) isn't
available.
Better diagnostics on meaningless filehandle operations [Toc] [Back]
Constructs such as "open(<FH>)" and "close(<FH>)" are compile
time errors. Attempting to read from filehandles
that were opened only for writing will now produce warnings
(just as writing to read-only filehandles does).
Where possible, buffered data discarded from duped input
filehandle
"open(NEW, "<&OLD")" now attempts to discard any data that
was previously read and buffered in "OLD" before duping
the handle. On platforms where doing this is allowed, the
next read operation on "NEW" will return the same data as
the corresponding operation on "OLD". Formerly, it would
have returned the data from the start of the following
disk block instead.
eof() has the same old magic as <>
"eof()" would return true if no attempt to read from "<>"
had yet been made. "eof()" has been changed to have a
little magic of its own, it now opens the "<>" files.
binmode() can be used to set :crlf and :raw modes
binmode() now accepts a second argument that specifies a
discipline for the handle in question. The two pseudodisciplines
":raw" and ":crlf" are currently supported on
DOS-derivative platforms. See "binmode" in perlfunc and
open.
"-T" filetest recognizes UTF-8 encoded files as "text"
The algorithm used for the "-T" filetest has been enhanced
to correctly identify UTF-8 content as "text".
system(), backticks and pipe open now reflect exec() fail-
ure
On Unix and similar platforms, system(), qx() and
open(FOO, "cmd |") etc., are implemented via fork() and
exec(). When the underlying exec() fails, earlier versions
did not report the error properly, since the exec()
happened to be in a different process.
The child process now communicates with the parent about
the error in launching the external command, which allows
these constructs to return with their usual error value
and set $!.
Improved diagnostics [Toc] [Back]
Line numbers are no longer suppressed (under most likely
circumstances) during the global destruction phase.
Diagnostics emitted from code running in threads other
than the main thread are now accompanied by the thread ID.
Embedded null characters in diagnostics now actually show
up. They used to truncate the message in prior versions.
$foo::a and $foo::b are now exempt from "possible typo"
warnings only if sort() is encountered in package "foo".
Unrecognized alphabetic escapes encountered when parsing
quote constructs now generate a warning, since they may
take on new semantics in later versions of Perl.
Many diagnostics now report the internal operation in
which the warning was provoked, like so:
Use of uninitialized value in concatenation (.) at
(eval 1) line 1.
Use of uninitialized value in print at (eval 1) line
1.
Diagnostics that occur within eval may also report the
file and line number where the eval is located, in addition
to the eval sequence number and the line number
within the evaluated text itself. For example:
Not enough arguments for scalar at (eval
4)[newlib/perl5db.pl:1411] line 2, at EOF
Diagnostics follow STDERR [Toc] [Back]
Diagnostic output now goes to whichever file the "STDERR"
handle is pointing at, instead of always going to the
underlying C runtime library's "stderr".
More consistent close-on-exec behavior [Toc] [Back]
On systems that support a close-on-exec flag on filehandles,
the flag is now set for any handles created by
pipe(), socketpair(), socket(), and accept(), if that is
warranted by the value of $^F that may be in effect. Earlier
versions neglected to set the flag for handles created
with these operators. See "pipe" in perlfunc, "socketpair"
in perlfunc, "socket" in perlfunc, "accept" in
perlfunc, and "$^F" in perlvar.
syswrite() ease-of-use
The length argument of "syswrite()" has become optional.
Better syntax checks on parenthesized unary operators [Toc] [Back]
Expressions such as:
print defined(&foo,&bar,&baz);
print uc("foo","bar","baz");
undef($foo,&bar);
used to be accidentally allowed in earlier versions, and
produced unpredictable behaviour. Some produced ancillary
warnings when used in this way; others silently did the
wrong thing.
The parenthesized forms of most unary operators that
expect a single argument now ensure that they are not
called with more than one argument, making the cases shown
above syntax errors. The usual behaviour of:
print defined &foo, &bar, &baz;
print uc "foo", "bar", "baz";
undef $foo, &bar;
remains unchanged. See perlop.
Bit operators support full native integer width [Toc] [Back]
The bit operators (& | ^ ~ << >>) now operate on the full
native integral width (the exact size of which is available
in $Config{ivsize}). For example, if your platform
is either natively 64-bit or if Perl has been configured
to use 64-bit integers, these operations apply to 8 bytes
(as opposed to 4 bytes on 32-bit platforms). For portability,
be sure to mask off the excess bits in the result
of unary "~", e.g., "~$x & 0xffffffff".
Improved security features [Toc] [Back]
More potentially unsafe operations taint their results for
improved security.
The "passwd" and "shell" fields returned by the getp-
went(), getpwnam(), and getpwuid() 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 ${" syntax error.
Now variable names that begin with a control
character may be arbitrarily long. However, for compatibility
reasons, these variables must be written with
explicit braces, as "${^XY}" for example. "${^XYZ}" is
synonymous with ${" one control character, such as
"${^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
$^V contains the Perl version number as a string composed
of characters whose ordinals match the version numbers,
i.e. v5.6.0. This may be used in string comparisons.
See "Support for strings represented as a vector of ordinals"
for an example.
Optional Y2K warnings [Toc] [Back]
If Perl is built with the cpp macro "PERL_Y2KWARN"
defined, it emits optional warnings when concatenating the
number 19 with another number.
This behavior must be specifically enabled when running
Configure. See INSTALL and README.Y2K.
Arrays now always interpolate into double-quoted strings [Toc] [Back]
In double-quoted strings, arrays now interpolate, no matter
what. The behavior in earlier versions of perl 5 was
that arrays would interpolate into strings if the array
had been mentioned before the string was compiled, and
otherwise Perl would raise a fatal compile-time error. In
versions 5.000 through 5.003, the error was
Literal @example now requires backslash
In versions 5.004_01 through 5.6.0, the error was
In string, @example now must be written as @example
The idea here was to get people into the habit of writing
"[email protected]" when they wanted a literal "@" sign,
just as they have always written "Give me back my "
when they wanted a literal "$" 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 "[email protected]" is going to turn
into "fred.com" if you don't backslash the "@". See
http://www.plover.com/~mjd/perl/at-error.html for more
details about the history here.
Modules
attributes
While used internally by Perl as a pragma, this module
also provides a way to fetch subroutine and variable
attributes. See attributes.
B The Perl Compiler suite has been extensively reworked
for this release. More of the standard Perl testsuite
passes when run under the Compiler, but there is still
a significant way to go to achieve production quality
compiled 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 "tring 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|?' => elp, man => an) 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-peo[email protected] 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 usag
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