The Switch module mistakenly escaped into Perl 5.8.
Do not use it.
The Switch module was deprecated in Perl 5.10 and removed in Perl 5.14.
Notice that in Categorized Damian Modules, the Switch module is categorized
by its author as
"Damian modules you shouldn't use in production because
their purpose is to explore and prototype future core language features".
You can switch to the built-in given/when if using Perl 5.10+.
If stuck with Perl 5.8, I'd just use an if/elsif block instead.
See also: stackoverflow question on why the Switch module is deprecated.