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: 
You can do it with grep only (without using find):

```
grep --include=\*.{xml,py} -Rl ./ -e "Jason"

```

And to exclude .po:

```
grep --exclude=*.po --include=\*.{xml,py} -Rl ./ -e "Jason"

```
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!