First my variables aka lexical variable are not global, their access is limited to their scope, which is at most the surrounding file.

Declarations with my and our are evaluated at compile time, but an if condition only at run-time.

All ways to execute the if at compile-time (like with BEGIN ) will introduce a surrounding block-scope again.

You could create a workaround with PadWalker, but still...

... the whole question is dubious, there is no point to conditionally declare a lexical variable, because you need to access it somewhere in your compiled code.

BUT the code won't compile if you access a lexical which wasn't declared before (at least under strict)

Maybe you should tell us what you really want to achieve... smells a lot like a XY Problem.