It seems shlex has quite weird behaviour for escaped characters.
If you enter:

>>> command "a\tb"

The argument you get will be atb. Typing an actual literal tab character is ignored by the shell, so it's also not possible to enter a tab that way.

I don't see a very easy way to fix this, especially since shlex is not maintained anymore. Would you be okay with a PR that removes the dependency on shlex and uses strconv.Unquote() to handle escaping and quoting?