如臂使指

rúbìshǐzhǐ
  1. as the arm moves the finger (idiom)
  2. freely and effortlessly
  3. to have perfect command of

CEDICT

to control or handle someone or something effectively and easily; to be in perfect command of

Wiktionary

像胳臂指使手指。语本《汉书．卷四八．贾谊传》：「令海内之势如身之使臂，臂之使指，莫不制从。」比喻指挥如意，得心应手。唐．独孤及〈故江陵尹兼御史大夫吕諲谥议〉：「且训其三军，如臂使指。」

重編國語辭典

指挥如意，得心应手

維基詞典

Entry Composition

1 如 rú
  1. as
  2. as if
  3. such as
2 臂 bì arm
3 使 shǐ
  1. to make
  2. to cause
  3. to enable
  4. to use
  5. to employ
  6. to send
  7. to instruct sb to do sth
  8. envoy
  9. messenger
4 指 zhǐ
  1. finger
  2. to point at or to
  3. to indicate or refer to
  4. to depend on
  5. to count on
  6. (of hair) to stand on end