shapefile - ogr2ogr srs options: where is the well known definition determined?

In the ogr2ogr documentation it says that when using -a_srs srs_def:

Srs_def can be a full WKT definition (hard to escape properly), or a well known definition (ie. EPSG:4326) or a file with a WKT definition.

Where are the default well-known definitions listed? Do they include ESRI as well as EPSG? If not, why not, and can I add all the ESRI definitions listed at spatialreference.org? Is there an easy way to load an srs definition using an SRID from a PostGIS spatial_ref_sys table, aside from just running some sql to get the text?

Thanks!

Answer

Well known definitions are in the gdal/data directory. You can browse the current directory source online: http://trac.osgeo.org/gdal/browser/trunk/gdal/data. Look at the gcs.csv and pcs.csv files.