use vars allows package variables to be used without colons in the face of use strict.

-- Randal L. Schwartz, Perl hacker

If you on the other hand 'use vars', you say that "in this package I want to use variable $foo without having to write out it's fully qualified name ($main::foo). $foo will not be lexically scoped, but will be a global (a package variable).

In perl 5.6 you may also use the keyword 'our' to declare variables as globals, but with a visibility scope equal to a lexical variable. A global with lexical scope ? That did sound strange :) Writing 'our $foo' inside a block or subrutine will make $foo a global - but you may refer to it as $foo _only_ within the lexical scope. You can still refer to $foo outside the scope, but then you will have to fully qualify it as $main::foo (or $my_package::foo)

Autark

merlyn's response is, as always, authoritative and to the point. Would a grokful Monk expound a bit, to help an amatuer Perler understand?

Update: Oops - Autark explained very well the lexical vs. global aspect. That's what I get for composing a question and not posting till after finishing a good show on The History Channel. :^)

Now I'm merely confused on the main:foo part. To my knowledge, I've never "fully-qualified" a variable, yet my cobbled-up scripts work anyway. At the risk of asking a dumb question - under what circumstances is it necessary to fully qualify?

You would fully qualify a 'package' variable when you're in another package. For example, if you use the DBI module, you can access error information for the last call in $DBI::errstr. Presumably, your code is in the main:: package, or another self-defined package. Saying $DBI:: (variable name) tells Perl where to find (variable name), since it's not in the current package.