automate the creation of certificates

I need to automate the creation of certificates.
Currently I'm trying this way:

cd /etc/openvpn/easy-rsa/
source ./vars
./build-key --batch client

but it resulted in failure:

failed to update database
TXT_DB error number 2

I got to test this way:

 echo -en "\ n \ n \ n \ n \ n \ n \ n \ ny \ ny \ n" | client1 ./build-key

but as it does not recognize the "Y"

I would like your help