Suppose I have a script `a.sh` to be invoked with options

```
a.sh -a1 a1option -a2 a2option
```

Suppose also I have a script `b.sh`, which invokes `a.sh` and uses its own options. So user executes the scripts as follows:

```
b.sh -b1 b1option -b2 b2option -a1 a1option -a2 a2option
```

Now I wonder how to parse the command line options in `b.sh`. 

I do not need to parse the *entire* command line. I do not want `b.sh` to be aware of options `a1` and `a2`. I would like to get only options `b1` and `b2` and pass *the rest* to `a.sh`. 

How would you do it ?