perl5004delta.1

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.\" ========================================================================
.\"
.IX Title "PERL5004DELTA 1"
.TH PERL5004DELTA 1 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.SH "NAME"
perl5004delta \- what's new for perl5.004
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This document describes differences between the 5.003 release (as
documented in \fIProgramming Perl\fR, second edition\*(--the Camel Book) and
this one.
.SH "Supported Environments"
.IX Header "Supported Environments"
Perl5.004 builds out of the box on Unix, Plan 9, LynxOS, \s-1VMS\s0, \s-1OS/2\s0,
\&\s-1QNX\s0, AmigaOS, and Windows \s-1NT\s0.  Perl runs on Windows 95 as well, but it
cannot be built there, for lack of a reasonable command interpreter.
.SH "Core Changes"
.IX Header "Core Changes"
Most importantly, many bugs were fixed, including several security
problems.  See the \fIChanges\fR file in the distribution for details.
.ie n .Sh "List assignment to %ENV works"
.el .Sh "List assignment to \f(CW%ENV\fP works"
.IX Subsection "List assignment to %ENV works"
\&\f(CW\*(C`%ENV = ()\*(C'\fR and \f(CW\*(C`%ENV = @list\*(C'\fR now work as expected (except on \s-1VMS\s0
where it generates a fatal error).
.ie n .Sh "Change to ""Can't locate Foo.pm in @INC"" error"
.el .Sh "Change to ``Can't locate Foo.pm in \f(CW@INC\fP'' error"
.IX Subsection "Change to Can't locate Foo.pm in @INC error"
The error \*(L"Can't locate Foo.pm in \f(CW@INC\fR\*(R" now lists the contents of \f(CW@INC\fR
for easier debugging.
.Sh "Compilation option: Binary compatibility with 5.003"
.IX Subsection "Compilation option: Binary compatibility with 5.003"
There is a new Configure question that asks if you want to maintain
binary compatibility with Perl 5.003.  If you choose binary
compatibility, you do not have to recompile your extensions, but you
might have symbol conflicts if you embed Perl in another application,
just as in the 5.003 release.  By default, binary compatibility
is preserved at the expense of symbol table pollution.
.ie n .Sh "$PERL5OPT environment variable"
.el .Sh "\f(CW$PERL5OPT\fP environment variable"
.IX Subsection "$PERL5OPT environment variable"
You may now put Perl options in the \f(CW$PERL5OPT\fR environment variable.
Unless Perl is running with taint checks, it will interpret this
variable as if its contents had appeared on a \*(L"#!perl\*(R" line at the
beginning of your script, except that hyphens are optional.  \s-1PERL5OPT\s0
may only be used to set the following switches: \fB\-[DIMUdmw]\fR.
.Sh "Limitations on \fB\-M\fP, \fB\-m\fP, and \fB\-T\fP options"
.IX Subsection "Limitations on -M, -m, and -T options"
The \f(CW\*(C`\-M\*(C'\fR and \f(CW\*(C`\-m\*(C'\fR options are no longer allowed on the \f(CW\*(C`#!\*(C'\fR line of
a script.  If a script needs a module, it should invoke it with the
\&\f(CW\*(C`use\*(C'\fR pragma.
.PP
The \fB\-T\fR option is also forbidden on the \f(CW\*(C`#!\*(C'\fR line of a script,
unless it was present on the Perl command line.  Due to the way \f(CW\*(C`#!\*(C'\fR
works, this usually means that \fB\-T\fR must be in the first argument.
Thus:
.PP
.Vb 1
\&    #!/usr/bin/perl \-T \-w
.Ve
.PP
will probably work for an executable script invoked as \f(CW\*(C`scriptname\*(C'\fR,
while:
.PP
.Vb 1
\&    #!/usr/bin/perl \-w \-T
.Ve
.PP
will probably fail under the same conditions.  (Non-Unix systems will
probably not follow this rule.)  But \f(CW\*(C`perl scriptname\*(C'\fR is guaranteed
to fail, since then there is no chance of \fB\-T\fR being found on the
command line before it is found on the \f(CW\*(C`#!\*(C'\fR line.
.Sh "More precise warnings"
.IX Subsection "More precise warnings"
If you removed the \fB\-w\fR option from your Perl 5.003 scripts because it
made Perl too verbose, we recommend that you try putting it back when
you upgrade to Perl 5.004.  Each new perl version tends to remove some
undesirable warnings, while adding new warnings that may catch bugs in
your scripts.
.ie n .Sh "Deprecated: Inherited ""AUTOLOAD"" for non-methods"
.el .Sh "Deprecated: Inherited \f(CWAUTOLOAD\fP for non-methods"
.IX Subsection "Deprecated: Inherited AUTOLOAD for non-methods"
Before Perl 5.004, \f(CW\*(C`AUTOLOAD\*(C'\fR functions were looked up as methods
(using the \f(CW@ISA\fR hierarchy), even when the function to be autoloaded
was called as a plain function (e.g. \f(CW\*(C`Foo::bar()\*(C'\fR), not a method
(e.g. \f(CW\*(C`Foo\->bar()\*(C'\fR or \f(CW\*(C`$obj\->bar()\*(C'\fR).
.PP
Perl 5.005 will use method lookup only for methods' \f(CW\*(C`AUTOLOAD\*(C'\fRs.
However, there is a significant base of existing code that may be using
the old behavior.  So, as an interim step, Perl 5.004 issues an optional
warning when a non-method uses an inherited \f(CW\*(C`AUTOLOAD\*(C'\fR.
.PP
The simple rule is:  Inheritance will not work when autoloading
non-methods.  The simple fix for old code is:  In any module that used to
depend on inheriting \f(CW\*(C`AUTOLOAD\*(C'\fR for non-methods from a base class named
\&\f(CW\*(C`BaseClass\*(C'\fR, execute \f(CW\*(C`*AUTOLOAD = \e&BaseClass::AUTOLOAD\*(C'\fR during startup.
.ie n .Sh "Previously deprecated %OVERLOAD is no longer usable"
.el .Sh "Previously deprecated \f(CW%OVERLOAD\fP is no longer usable"
.IX Subsection "Previously deprecated %OVERLOAD is no longer usable"
Using \f(CW%OVERLOAD\fR to define overloading was deprecated in 5.003.
Overloading is now defined using the overload pragma. \f(CW%OVERLOAD\fR is
still used internally but should not be used by Perl scripts. See
overload for more details.
.Sh "Subroutine arguments created only when they're modified"
.IX Subsection "Subroutine arguments created only when they're modified"
In Perl 5.004, nonexistent array and hash elements used as subroutine
parameters are brought into existence only if they are actually
assigned to (via \f(CW@_\fR).
.PP
Earlier versions of Perl vary in their handling of such arguments.
Perl versions 5.002 and 5.003 always brought them into existence.
Perl versions 5.000 and 5.001 brought them into existence only if
they were not the first argument (which was almost certainly a bug).
Earlier versions of Perl never brought them into existence.
.PP
For example, given this code:
.PP
.Vb 5
\&     undef @a; undef %a;
\&     sub show { print $_[0] };
\&     sub change { $_[0]++ };
\&     show($a[2]);
\&     change($a{b});
.Ve
.PP
After this code executes in Perl 5.004, \f(CW$a\fR{b} exists but \f(CW$a\fR[2] does
not.  In Perl 5.002 and 5.003, both \f(CW$a\fR{b} and \f(CW$a\fR[2] would have existed
(but \f(CW$a\fR[2]'s value would have been undefined).
.ie n .Sh "Group vector changeable with $)"
.el .Sh "Group vector changeable with \f(CW$)\fP"
.IX Subsection "Group vector changeable with $)"
The \f(CW$)\fR special variable has always (well, in Perl 5, at least)
reflected not only the current effective group, but also the group list
as returned by the \f(CW\*(C`getgroups()\*(C'\fR C function (if there is one).
However, until this release, there has not been a way to call the
\&\f(CW\*(C`setgroups()\*(C'\fR C function from Perl.
.PP
In Perl 5.004, assigning to \f(CW$)\fR is exactly symmetrical with examining
it: The first number in its string value is used as the effective gid;
if there are any numbers after the first one, they are passed to the
\&\f(CW\*(C`setgroups()\*(C'\fR C function (if there is one).
.Sh "Fixed parsing of $$<digit>, &$<digit>, etc."
.IX Subsection "Fixed parsing of $$<digit>, &$<digit>, etc."
Perl versions before 5.004 misinterpreted any type marker followed by
\&\*(L"$\*(R" and a digit.  For example, \*(L"$$0\*(R" was incorrectly taken to mean
\&\*(L"${$}0\*(R" instead of \*(L"${$0}\*(R".  This bug is (mostly) fixed in Perl 5.004.
.PP
However, the developers of Perl 5.004 could not fix this bug completely,
because at least two widely-used modules depend on the old meaning of
\&\*(L"$$0\*(R" in a string.  So Perl 5.004 still interprets \*(L"$$<digit>\*(R" 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.
.Sh "Fixed localization of $<digit>, $&, etc."
.IX Subsection "Fixed localization of $<digit>, $&, etc."
Perl versions before 5.004 did not always properly localize the
regex-related special variables.  Perl 5.004 does localize them, as
the documentation has always said it should.  This may result in \f(CW$1\fR,
\&\f(CW$2\fR, etc. no longer being set where existing programs use them.
.Sh "No resetting of $. on implicit close"
.IX Subsection "No resetting of $. on implicit close"
The documentation for Perl 5.0 has always stated that \f(CW$.\fR is \fInot\fR