> If the shell was executed otherwise, then 'which $0' will tell you where it came from, because it must have come from $PATH. Not true: you can be in a shell

> If the shell was executed otherwise, then 'which $0' will tell you where it came from, because it must have come from $PATH. Not true: you can be in a shell not in $PATH, and if you executed it from a relative path, which $0 will not find it if you cd to a different location.