pub fn list(output: String) -> Option<Vec<String>> {
    let mut list = Vec::new();
    for line in output.lines() {
        let name = line.split_whitespace().next();
        if let Some(snap_name) = name {
            list.push(snap_name.to_string());
        }
    }
    Some(list.into_iter().filter(|x| x != "NAME").collect())
}

fn main() {
    let output = "NAME                         USED  AVAIL  REFER  MOUNTPOINT
                  rpool@gitlab                    0      -   128K  -
                  rpool/ROOT/ubuntu@version1  6,20M      -   643M  -
                  rpool/ROOT/ubuntu@gitlab1    211M      -   898M  -"
        .to_string();

    let s = list(output);

    assert_eq!(Some([
        "rpool@gitlab",
        "rpool/ROOT/ubuntu@version1",
        "rpool/ROOT/ubuntu@gitlab1"
    ].iter().map(|s| s.to_string()).collect()), s);

    println!("{:?}", s);
}