Fix error from basename when directly source in interactive shell

The part for example will result the following error:

```
$ echo $0
-bash
$ source shml.sh
basename: invalid option -- 'b'
Try 'basename --help' for more information.
```

Although, the main code of shml still is sourced correct and useable, even `basename` spits an error, but it might be better for newcomer like me to try it out directly in interactive shell instead of making a script to test out.