An Input File with Extension by No Language Switch

From InterBase

If a language switch is not specified, but the input file includes a file-name extension, gpre looks for the specified file and assumes the language is indicated by the extension.

For example, suppose the following command is processed:

gpre census.e

gpre looks for a file called census.e. If gpre finds this file, it processes it as a C program and generates an output file called census.c. If gpre does not find this file, it returns the following error:

gpre: can’t open census.e