Warning: this command was renamed to GETRANGE, it is called SUBSTR in
Redis versions <= 2.0.
Returns the substring of the string value stored at key, determined by the
offsets start and end (both are inclusive).
Negative offsets can be used in order to provide an offset starting from the end
of the string.
So -1 means the last character, -2 the penultimate and so forth.
The function handles out of range requests by limiting the resulting range to the actual length of the string.
@return
@bulk-string-reply
@examples
SET mykey "This is a string"
GETRANGE mykey 0 3
GETRANGE mykey -3 -1
GETRANGE mykey 0 -1
GETRANGE mykey 10 100