slurping an empty file should return '' rather than undef, with

[p5sagit/p5-mst-13.2.git] / pod / perldelta.pod

=head1 NAME

perldelta - what's new for perl5.006 (as of 5.005_54)

=head1 DESCRIPTION

This document describes differences between the 5.005 release and this one.

=head1 Incompatible Changes

=head2 Perl Source Incompatibilities

None known at this time.

=head2 C Source Incompatibilities

=over 4

=item C<PERL_POLLUTE>

Release 5.005 grandfathered old global symbol names by providing preprocessor
macros for extension source compatibility.  As of release 5.006, these
preprocessor definitions are not available by default.  You need to explicitly
compile perl with C<-DPERL_POLLUTE> in order to get these definitions.

=item C<PERL_POLLUTE_MALLOC>

Enabling the use of Perl's malloc in release 5.005 and earlier caused
the namespace of system versions of the malloc family of functions to
be usurped by the Perl versions of these functions, since they used the
same names by default.

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 behavior to be suppressed with the HIDEMYMALLOC and
EMBEDMYMALLOC preprocessor definitions.

As of release 5.006, Perl's malloc family of functions have default names
distinct from the system versions.  You need to explicitly compile perl with
C<-DPERL_POLLUTE_MALLOC> in order to get the older behavior.  HIDEMYMALLOC
and EMBEDMYMALLOC have no effect, since the behavior they enabled is now
the default.

Note that these functions do B<not> constitute Perl's memory allocation API.
See L<perlguts/"Memory Allocation"> for further information about that.

=item C<PL_na> and C<dTHR> Issues

The C<PL_na> global is now thread local, so a C<dTHR> declaration is needed
in the scope in which it appears.  XSUBs should handle this automatically,
but if you have used C<PL_na> in support functions, you either need to
change the C<PL_na> to a local variable (which is recommended), or put in
a C<dTHR>.

=back

=head2 Binary Incompatibilities

This release is not binary compatible with the 5.005 release and its
maintenance versions.

=head1 Core Changes

=head2 Binary numbers supported

Binary numbers are now supported as literals, in s?printf formats, and
C<oct()>:

	$answer = 0b101010;
	printf "The answer is: %b\n", oct("0b101010");

=head2 syswrite() ease-of-use

The length argument of C<syswrite()> is now optional.

=head2 64-bit support

Better 64-bit support -- but full support still a distant goal.  One
must Configure with -Duse64bits to get Configure to probe for the
extent of 64-bit support.  Depending on the platform (hints file) more
or less 64-awareness becomes available.  As of 5.005_54 at least
somewhat 64-bit aware platforms are HP-UX 11 or better, Solaris 2.6 or
better, IRIX 6.2 or better.  Naturally 64-bit platforms like Digital
UNIX and UNICOS also have 64-bit support.

=head2 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 behavior.  Some of them produced ancillary warnings
when used in this way, while others silently did the wrong thing.

The parenthesized forms of most unary operators that expect a single
argument will now ensure that they are not called with more than one
argument, making the above cases syntax errors.  Note that the usual
behavior of:

	print defined &foo, &bar, &baz;
	print uc "foo", "bar", "baz";
	undef $foo, &bar;

remains unchanged.  See L<perlop>.

=head2 Improved C<qw//> operator

The C<qw//> operator is now evaluated at compile time into a true list
instead of being replaced with a run time call to C<split()>.  This
removes the confusing behavior of C<qw//> in scalar context stemming from
the older implementation, which inherited the behavior from split().  

Thus:

    $foo = ($bar) = qw(a b c); print "$foo|$bar\n";

now correctly prints "3|a", instead of "2|a".

=head2 pack() format 'Z' supported

The new format type 'Z' is useful for packing and unpacking null-terminated
strings.  See L<perlfunc/"pack">.

=head1 Significant bug fixes

=head2 E<lt>HANDLEE<gt> on empty files

With C<$/> set to C<undef>, slurping an empty file returns a string of
zero length (instead of C<undef>, as it used to) for the first time the
HANDLE is read.  Subsequent reads yield C<undef>.

This means that the following will append "foo" to an empty file (it used
to not do anything before):

    perl -0777 -pi -e 's/^/foo/' empty_file

Note that the behavior of:

    perl -pi -e 's/^/foo/' empty_file

is unchanged (it continues to leave the file empty).

=head1 Supported Platforms

=over 4

=item *

VM/ESA is now supported.

=item *

Siemens BS200 is now supported.

=item *

The Mach CThreads (NeXTstep) are now supported by the Thread extension.

=back

=head1 New tests

=over 4

=item	op/io_const

IO constants (SEEK_*, _IO*).
	
=item	op/io_dir

Directory-related IO methods (new, read, close, rewind, tied delete).

=item	op/io_multihomed

INET sockets with multi-homed hosts.

=item	op/io_poll

IO poll().

=item	op/io_unix

UNIX sockets.

=item	op/filetest

File test operators.

=item	op/lex_assign

Verify operations that access pad objects (lexicals and temporaries).

=back

=head1 Modules and Pragmata

=head2 Modules

=over 4

=item Dumpvalue

Added Dumpvalue module provides screen dumps of Perl data.

=item Benchmark

You can now run tests for I<x> seconds instead of guessing the right
number of tests to run.

=item Fcntl

More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
large (more than 4G) file access (the 64-bit support is not yet
working, though, so no need to get overly excited), Free/Net/OpenBSD
locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and
O_ACCMODE: the mask of O_RDONLY, O_WRONLY, and O_RDWR.

=item Math::Complex
 
The accessors methods Re, Im, arg, abs, rho, theta, methods can
($z->Re()) now also act as mutators ($z->Re(3)).

=item Math::Trig

A little bit of radial trigonometry (cylindrical and spherical) added,
for example the great circle distance.

=back

=head2 Pragmata

Lexical warnings pragma, "use warning;", to control optional warnings.

Filetest pragma, to control the behaviour of filetests (C<-r> C<-w> ...).
Currently only one subpragma implemented, "use filetest 'access';",
that enables the use of access(2) or equivalent to check the
permissions instead of using stat(2) as usual.  This matters
in filesystems where there are ACLs (access control lists), the
stat(2) might lie, while access(2) knows better.

=head1 Utility Changes

=head2 New Modules

=over

Todo.

=back

=head2 Changes in existing modules

=over

=item Exporter

Exporter::expand() takes an import list and returns the expanded
list of names.

=back

=head1 Documentation Changes

=over 4

=item perlopentut.pod

A tutorial on using open() effectively.

=item perlreftut.pod

A tutorial that introduces the essentials of references.

=back

=head1 New Diagnostics

=item /%s/: Unrecognized escape \\%c passed through

(W) You used a backslash-character combination which is not recognized
by Perl.  This combination appears in an interpolated variable or a 
C<'>-delimited regular expression.

=item Unrecognized escape \\%c passed through

(W) You used a backslash-character combination which is not recognized
by Perl.

=item Missing command in piped open

(W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
construction, but the command was missing or blank.

=head1 Obsolete Diagnostics

Todo.

=head1 Configuration Changes

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.

=head1 BUGS

If you find what you think is a bug, you might check the headers of
recently posted articles in 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 B<perlbug>
program included with your release.  Make sure you trim your bug down
to a tiny but sufficient test case.  Your bug report, along with the
output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
analysed by the Perl porting team.

=head1 SEE ALSO

The F<Changes> file for exhaustive details on what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=head1 HISTORY

Written by Gurusamy Sarathy <F<gsar@umich.edu>>, with many contributions
from The Perl Porters.

Send omissions or corrections to <F<perlbug@perl.com>>.

=cut