赶忙 (gǎn máng) is an adverb meaning 'hastily, in a hurry,' used for an action done urgently in response to a situation. It is very similar to 赶紧 and 赶快, but 赶忙 has a stronger sense of last-minute haste triggered by an external event; it is less used in commands than 赶快. 急忙 emphasizes being flustered, while 匆匆 is an adjective describing a hurried appearance.