hosts=(usa1 london2)
for i in ${hosts[@]}; do
    echo ---${i}---
    ssh ttoleung@${i} ls /apps | awk '{ printf("%s:%sn", "hostname", $0) }'
done

---usa01---
hostname:E2.gui
hostname:E1.server
---london2---
hostname:E1.gui

---usa01---
usa01:E2.gui
usa01:E1.server
---london2---
london2:E1.gui