Install Google Drive Client In Ubuntu 13.04, 12.04

The Google Drive client isn't yet available for Linux and the old Google Docs FS doesn't work too well with Google Drive, so besides the web interface, the best solution to get Google Drive on Linux right now is using Grive, an unofficial, open source, command line Linux client for Google Drive.
For now, the application is considered experimental and it lacks full sync, but it can upload and download new or changed files already (so you can access your files offline). What it can't do yet is: wait for changes and automatically sync the files or delete files (when a file is deleted locally, it's ignored and when it's deleted remotely, it's reuploaded if it exists locally).
Initially, Grive didn't support uploading new files and it could only upload changed files but the latest version from GIT (available in the WebUpd8 PPA) supports uploading new files too. However, in test, this only works for one file at a time. Hopefully, this will be fixed soon.

Update: the issues above have been fixed (except for watching for changes and automatically syncing them) in the latest Grive.

Install Grive in Ubuntu

sudo add-apt-repository ppa:nilarimogard/webupd8
sudo apt-get update
sudo apt-get install grive

Using Grive

Step 1:

Grive will download / upload new or changed files from the directory, run it so firstly, create a new folder, let's call it "grive", in your home directory:

mkdir -p ~/grive

Step 2:

Next, navigate using the terminal into the newly created "grive" folder:

cd ~/grive

Step 3:

The first time you run Grive, you must use the "-a" argument to grant it permission to access your Google Drive:

grive -a

After running the command above, an URL will displayed in the terminal - copy this URL and paste it in a web browser. In the newly loaded page, you'll be asked to give Grive permission to access your Google Drive and after clicking "Allow access", an authentication code will be displayed - copy this code and paste it in the terminal where you ran Grive.