The only reason anyone would want to say "$($echo $0)", echoing the variable through a subshell and substituting it with itself, is to rely on the subshell para

The only reason anyone would want to say "$($echo $0)", echoing the variable through a subshell and substituting it with itself, is to rely on the subshell parameter splitting to remove duplicate field separators from the variable. That is likely not the case there, and any such file names are unlikely to exist. Just say: which "$0"