Accessing gitub can be difficult at work;  ssh tunneling is often blocked by firewalls and proxies make it difficult to use http.

The solution is to set the http_proxy environment variable;

export http_proxy=[PROXY_SETTING]

You can now clone a public git repository over http.

However, this is only half the solution as private repositories use https so this setting doesn't work.

The solution is the similar https_proxy environment variable.  Set this with the below command;

export https_proxy=[PROXY_SETTING]

You can now clone public and private repositories with http and https through your companies proxy.