Currently, there are three functions put, get, and keys in the script.

Each of them ends up mutating global state, which probably isn't a good idea in the long term. You can make your functions more "pure" by using command substitution:

function myfunc()
{
    local  myresult='some value'
    echo "$myresult"
}

result=$(myfunc)   # or result=`myfunc`
echo $result

The function keys is probably the most problematic as you're creating a function and a global variable with the same name.