No subject

    if (NULL != (p = getenv ("GRASS_WIDTH")))
...
    if (NULL != (p = getenv ("GRASS_HEIGHT")))

In this context, GRASS_WIDTH and GRASS_HEIGHT are environment
variables. Whether these variables appear in $GISRC or what values
they have there is irrelevant to the CELL driver. All that matters is
whether they are defined in the environment, and with what values.

The potential for confusion arises because $GISBASE/etc/Init.sh
executes "eval `g.gisenv`" under some circumstances (if GRASS_GUI is
"text", or if it falls back to "text"), which will cause the settings
in $GISRC to be reflected into the environment.

However, if the contents of $GISRC and/or the environment are
subsequently modified so, that the two differ, the version which is
used depends upon whether the program uses getenv() or G__getenv().

-- 
Glynn Clements <glynn.clements at virgin.net>