perl56delta.pod

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C<^_>, which may be used by user programs and are guaranteed not to
acquire special meaning in any future version of Perl.

=head2 New variable $^C reflects C<-c> switch

C<$^C> has a boolean value that reflects whether perl is being run
in compile-only mode (i.e. via the C<-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 L<perlvar>.

=head2 New variable $^V contains Perl version as a string

C<$^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 C<Support for strings represented as a vector of ordinals> for an
example.

=head2 Optional Y2K warnings

If Perl is built with the cpp macro C<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 F<INSTALL> and F<README.Y2K>.

=head2 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
C<"fred\@example.com"> when they wanted a literal C<@> sign, just as
they have always written C<"Give me back my \$5"> when they wanted a
literal C<$> sign.

Starting with 5.6.1, when Perl now sees an C<@> sign in a
double-quoted string, it I<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 C<"[e-mail]"> is going to turn into
C<fred.com> if you don't backslash the C<@>.
See http://www.plover.com/~mjd/perl/at-error.html for more details
about the history here.

=head2 @- 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 L<perlvar> for
details.

=head1 Modules and Pragmata

=head2 Modules

=over 4

=item attributes

While used internally by Perl as a pragma, this module also
provides a way to fetch subroutine and variable attributes.
See L<attributes>.

=item 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.

=item Benchmark

Overall, Benchmark results exhibit lower average error and better timing
accuracy.  

You can now run tests for I<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 L<Benchmark>.

=item ByteLoader

The ByteLoader is a dedicated extension to generate and run
Perl bytecode.  See L<ByteLoader>.

=item 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 L<constant>.

=item charnames

This pragma implements the C<\N> string escape.  See L<charnames>.

=item Data::Dumper

A C<Maxdepth> setting can be specified to avoid venturing
too deeply into deep data structures.  See L<Data::Dumper>.

The XSUB implementation of Dump() is now automatically called if the
C<Useqq> setting is not in use.

Dumping C<qr//> objects works correctly.

=item DB

C<DB> is an experimental module that exposes a clean abstraction
to Perl's debugging API.

=item DB_File

DB_File can now be built with Berkeley DB versions 1, 2 or 3.
See C<ext/DB_File/Changes>.

=item Devel::DProf

Devel::DProf, a Perl source code profiler has been added.  See
L<Devel::DProf> and L<dprofpp>.

=item 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.

=item Dumpvalue

The Dumpvalue module provides screen dumps of Perl data.

=item 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
C<-Accflags=-DDL_UNLOAD_ALL_AT_EXIT>.  (This maybe useful if you are
using Apache with mod_perl.)

=item English

$PERL_VERSION now stands for C<$^V> (a string value) rather than for C<$]>
(a numeric value).

=item Env

Env now supports accessing environment variables like PATH as array
variables.

=item 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
C<:seek> tag.  The chmod()/stat() S_IF* constants and S_IS* functions
are available via the C<:mode> tag.

=item File::Compare

A compare_text() function has been added, which allows custom
comparison functions.  See L<File::Compare>.

=item 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 C<follow> option is
specified.  Enabling the C<no_chdir> option will make File::Find skip
changing the current directory when walking directories.  The C<untaint>
flag can be useful when running with taint checks enabled.

See L<File::Find>.

=item 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 L<File::Glob>.

=item 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.

=item 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);

=item 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 L<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. 

=item 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.

=item JPL

Java Perl Lingo is now distributed with Perl.  See jpl/README
for more information.

=item lib

C<use lib> now weeds out any trailing duplicate entries.
C<no lib> removes all named entries.

=item Math::BigInt

The bitwise operations C<<< << >>>, C<<< >> >>>, C<&>, C<|>,
and C<~> are now supported on bigints.

=item 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)).