ssh to amazon aws instance from virtual machine ubuntu 19.10

It's because of the white space in your path, in that case you have to use quotes.

Try this way:

#!/bin/bash

AWS_KEY="/home/debian/cs605 data management/assignment6/mumbai instance keys"

ssh -v -i "$AWS_KEY"/mumbai-instance-1.pem
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Just remove extra slashes in variable $AWS_KEY and use "" when you use it.