ref: 930eae1c242daabda3668532e0638f5d19c65ed8
dir: /man/environ.man/
.TP \fBDOOMWADDIR\fR, \fBDOOMWADPATH\fR These environment variables provide paths to search for Doom .WAD files when looking for a game IWAD file or a PWAD file specified with the `-file' option. \fBDOOMWADDIR\fR specifies a single path in which to look for WAD files, while \fBDOOMWWADPATH\fR specifies a colon-separated list of paths to search. .TP \fBPCSOUND_DRIVER\fR When running in PC speaker sound effect mode, this environment variable specifies a PC speaker driver to use for sound effect playback. Valid options are "Linux" for the Linux console mode driver, "BSD" for the NetBSD/OpenBSD PC speaker driver, and "SDL" for SDL-based emulated PC speaker playback (using the digital output). .TP \fBOPL_DRIVER\fR When using OPL MIDI playback, this environment variable specifies an OPL backend driver to use. Valid options are "SDL" for an SDL-based software emulated OPL chip, "Linux" for the Linux hardware OPL driver, and "OpenBSD" for the OpenBSD/NetBSD hardware OPL driver. Generally speaking, a real hardware OPL chip sounds better than software emulation; however, modern machines do not often include one. If present, it may still require extra work to set up and elevated security privileges to access.