I'd say the truthness values come from C.

As C language does not have a bool type, thruthness is expressed with anything different from 0, and 0 is false.

The shell, (and certainly most programs in most OS's) return 0 when everything went OK, and an error code when not...

Notice there'll be a my $rc = 0 is true;, which basically says the result of your sub is a 'zero' and that it's true (not an error, for example...). Only available in Perl6 properties (I wish it arrives soon :-)

laters, david

sub foo { return join '~', @_ }