The e response to Metafont's error-recovery mode invokes the system default editor at the erroneous line of the source file. Chapter 23 of The Metafontbook describes what you can do. This implementation of Metafont uses environment variables to determine which display device you want to use. If it can't find either, you get no online output. This version of Metafont understands the following command line options.
Print help message and exit.
The mode can be one of batchmode , nonstopmode , scrollmode , and errorstopmode . The meaning of these modes is the same as that of the corresponding commands. See the Kpathsea manual for details. Enable mktex fmt , where fmt must be mf . This affects both the for- mat used and the search paths.