Perl provides a mechanism for alternative namespaces to protect
packages from stomping on each other's variables. In fact, there's
-really no such thing as a global variable in Perl . The package
+really no such thing as a global variable in Perl. The package
statement declares the compilation unit as being in the given
namespace. The scope of the package declaration is from the
declaration itself through the end of the enclosing block, C<eval>,
local *main::foo = *main::bar;
local $main::{foo} = $main::{bar};
+(Be sure to note the B<vast> difference between the second line above
+and C<local $main::foo = $main::bar>. The former is accessing the hash
+C<%main::>, which is the symbol table of package C<main>. The latter is
+simply assigning scalar C<$bar> in package C<main> to scalar C<$foo> of
+the same package.)
+
You can use this to print out all the variables in a package, for
instance. The standard but antiquated F<dumpvar.pl> library and
the CPAN module Devel::Symdump make use of this.
*PI = \3.14159265358979;
-Now you cannot alter $PI, which is probably a good thing all in all.
+Now you cannot alter C<$PI>, which is probably a good thing all in all.
This isn't the same as a constant subroutine, which is subject to
optimization at compile-time. A constant subroutine is one prototyped
to take no arguments and to return a constant expression. See
(if you can).) You may have multiple C<END> blocks within a file--they
will execute in reverse order of definition; that is: last in, first
out (LIFO). C<END> blocks are not executed when you run perl with the
-C<-c> switch.
+C<-c> switch, or if compilation fails.
Inside an C<END> subroutine, C<$?> contains the value that the program is
going to pass to C<exit()>. You can modify C<$?> to change the exit