I believe there are options to use a command-line interface for the installation, but of course, the default is the graphical "step-through" interface for doing the installation. Is there a reason why you don't want to use the GUI installer?
Ubuntu only seems to provide command-line installation for its alternate installations, that is, the server version or the minimal version (no graphics by default). This is probably because, for a "normal" desktop installation, there is really no point in avoiding the GUI installer. And if the installer's GUI doesn't work (the graphics driver has a problem), then you should verify that your graphics card is supported and all that before attempting to carry out the installation (this is because if the GUI installer doesn't work, it's unlikely that graphics will work out of the box once you install it, and you will have to do some work (in command-line only) to get it to work, and it might never work, so, do that research ahead of time).
The command-line (CLI) package installation tools for Debian-based distributions (which Ubuntu is one of) are the aptitude tools, such as apt-get. Read the Ubuntu documentation on their site. They go into this stuff in great detail.
Oh... I assumed the OP meant "install process" as in the process of installing Ubuntu itself. If the OP is talking about a CLI solution to install software onto a Ubuntu system, then, yeah, like rubberman said, you use apt-get for that, as in $ sudo apt-get install some-software-package.