Bob

This is because the unary minus operator is weird. If it's applied to a string that starts with a plus or minus, which isn't a number, it reverses that sign; if it doesn't start with a plus or minus, it adds a minus. It even does this in a strict-safe way with barewords, which is how the popular "use Foo -bar" syntax works in strict mode, and also how this more interesting code is strict safe: "say - -foo". The full details are listed in perldoc perlop "Symbolic Unary Operators".

Personally, I think 1 (obviously) makes sense; the rest are weird Perl unary-minus behaviors. Remember that Perl (unlike shell or C) does not let you concatenate strings by putting them next to each other; instead you have to use . (dot): say "-"."x". (Indeed, say a"x" produces no output — confusing unless you turn on warnings).

And something like say 1+"x" prints 1; Perl turns the string to a 0 (and prints a warning if enabled) — in every math operator but unary +/-. Perl doesn't do algebra.

So I find it weird (but documented, and useful) that 2, 3, and 4 don't all print 0.