Question: I'd like to know how could I find all files whose extension can be `.xml` and `.py` that contain the string "Jason" under a path "./" recursively?

Or how could I exclude `.po` from the search?

Answer: 
Try the following command. It will search only in the `.xml` and `.py` files for your name:

```
find . -type f \( -iname \*.xml -o -iname \*.py \) | xargs grep "Jason"

```

Hope this helps!
You could do this:

```
grep -r "Jason" ./ | grep .xml; grep -r "Jason" ./ | grep .py

```

That will display the output of any files containing `Jason` and limit it to filenames containing `.xml` or `.py`.

If you want to just exclude `.po`, then try this:

```
grep -r "Jason" | grep -v .po

```