Reviewed. It seems to be a good. Thanks!

is the external command also run in subshell?

Yes, This is just slow and meaningless, but because I do not distinguish between functions and external commands, external commands are also executed in a subshell. There seems to be room for optimization, but it would be difficult to implement a portable way to distinguish between functions and external commands (e.g. posh: type: not found), and the execution of external commands is inherently slow, so I don't think it makes much sense.

The difference between run and call is simple, but the difference in behavior due to it is difficult to explain...😩