How to download an RPM package and install it in one line?

RPM has native support to download a package from a URL. You can do:

sudo rpm -i <URL>

There is no need to download the RPM manually. If this support didn't exist, you could use bash's process substitution.

sudo bash -c 'rpm -i <(wget -O - <URL>)'

Better to do yum install -y <URL> as this does alto take care of dependencies, as opposed to direct rpm tool use.