consider this variable read-only, although it will be altered
across fork() calls. (Mnemonic: same as shells.)
+Note for Linux users: on Linux, the C functions C<getpid()> and
+C<getppid()> return different values from different threads. In order to
+be portable, this behavior is not reflected by C<$$>, whose value remains
+consistent across threads. If you want to call the underlying C<getpid()>,
+you may use the CPAN module C<Linux::Pid>.
+
=item $REAL_USER_ID
=item $UID
one, because C<$ARGV[0]> is the first argument, I<not> the program's
command name itself. See C<$0> for the command name.
+=item ARGVOUT
+
+The special filehandle that points to the currently open output file
+when doing edit-in-place processing with B<-i>. Useful when you have
+to do a lot of inserting and don't want to keep modifying $_. See
+L<perlrun> for the B<-i> switch.
+
=item @F
The array @F contains the fields of each line read in when autosplit
Perl identifiers that begin with digits, control characters, or
punctuation characters are exempt from the effects of the C<package>
-declaration and are always forced to be in package C<main>. A few
-other names are also exempt:
+declaration and are always forced to be in package C<main>; they are
+also exempt from C<strict 'vars'> errors. A few other names are also
+exempt in these ways:
ENV STDIN
INC STDOUT
In particular, the new special C<${^_XYZ}> variables are always taken
to be in package C<main>, regardless of any C<package> declarations
-presently in scope.
+presently in scope.
=head1 BUGS