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Which of the following symbols are used for accessing previous commands by event numbers?

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Which of the following symbols are used for accessing previous commands by event numbers?

(a) !

(b) r

(c) $

(d) ! and r

This question was addressed to me in an online quiz.

This interesting question is from Shell Variables in portion Customizing the Environment & More File Attributes of Unix

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Correct answer is (d) ! and r

The explanation: The ! symbol (r in Korn) is used to repeat previous commands. For repeating the last command we have to use !! in bash and r in Korn. We can repeat other commands also, but with the event number as an argument. For example, following commands will repeat the command with event number 38,

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