Optimal solution to extract value from line using Grep

Could you please tell me what is the optimal way to extract idle 开发者_运维技巧value from this line using grep?

CPU states:   0.1% user,   0.1% system,   0.0% nice,  99.8% idle

---

awk should do the trick:

top -n 1 | grep "idle" | awk '{ print $9 }'

Since the idle-percentage is the ninth value, it's $9.

---

You can use grep alone:

grep -Po '[0-9.%]+(?= idle)'