Environment Variable

DISPLAY: specifies where to draw the windows.
BRLCAD_ROOT: specifies where to find the root directory of the installed BRL-CAD package.
EDITOR: specifies which external editor to use when one is required.
FB_FILE: specifies the framebuffer to use when using applications that require a framebuffer.
TCL_LIBRARY: specifies where to look for Tcl files.
TK_LIBRARY: specifies where to look for Tk files.