using different database at redis command prompt

Just use the -n argument to choose DB number. It available since Redis 2.4.2.

echo -n "testing" | redis-cli -n 4 -x set my_pass

or

redis-cli -n 4 set my_pass testing

Launch the CLI by issuing command:

redis-cli

Then use the following command:

select <db number>

For example:

select 4