Here is a website that makes it easy to get the proj4 coordinate reference system descriptions that DIVA-GIS now uses.
First find the projection you want by browsing or searching in any of the lists (EPSG, ESRI, ...). If you have selected one, click on the "Proj4" link in the gray box.
For example, click the ESRI references link. Search for "Robinson", select "World Robinson", and click on the Proj4 link to get: