I have some string (read from a file) ,such as "Fri Dec 16 16:12:24 CST 2016", and How to convert this string to timestamp, by shell?

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> I need timestamp,such as `Fri Dec 16 16:27:28 CST 2016` -> `1481876854`
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> 
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shell cmd `date` print `Fri Dec 16 16:12:24 CST 2016`,so I think `date` have some method to do it.

but I can't find a solution,Can someone help me?

macos 10.12.2

[![enter image description here](https://i.stack.imgur.com/4c5dL.png)](https://i.stack.imgur.com/4c5dL.png)