As I’ve learned in response to this thread, apparently some (but not all) Unixy OSes will run a file marked as executable using /bin/sh if no shebang is supplied.
Oh right, I think that's part of how APE[1] works. But I thought the Thompson shell was old and weird, and that it might not support what people use when they write ‘POSIX’ shell scripts nowadays.
Anyway it sounds like in that case the OS _doesn't_ know how to run the script, it just assumes `/bin/sh` will do.
I always assumed that scripts without an interpreter line were like snippets to be invoked via `source`, from some shell script with knowledge of the context in which it should be used.
Anyway, if that's the way it works, the behavior actually isn't a problem for users of Nushell or Elvish or Fish or anything else, since their executables are never installed to `/bin/sh` anyway. Nushell probably gets installed to `/usr/bin/nu`, Fish to `/usr/bin/fish`, and `elvish` can be installed anywhere. So it's still not clear that there's a real problem with un-shebanged scripts when it comes to using a boutique shell for login.
