FlightGear's Nasal doesn't support running external commands. Partly because it's too dangerous, but also because Nasal's "unix" module isn't fully cross-platform (read: Windows isn't good enough for it ;-)
On Unices (Linux, OSX) it's fairly trivial to implement this
feature and to keep it sufficiently secure. Let's implement
a key binding that opens Google Maps in FireFox for the
current location:
1) Make a FIFO:
$ mkdir -p ~/.fgfs/Export && mkfifo ~/.fgfs/Export/cmdfifo
2) Write a script that scans the FIFO (attached). Always start
it together with fgfs. Add it to your fgfs start script (if
you have one) or make an alias:
$ alias fgfs="fgfs.fifo.runner & fgfs;
kill $(/sbin/pidof -x fgfs.fifo.runner) &>/dev/null"
3) Add a Nasal exec() function somewhere, for example in
~/.fgfs/Nasal/local.nas, which writes to the FIFO:
globals.exec = func {
var f = io.open(getprop("/sim/fg-home") ~ "/Export/cmdfifo", "w");
io.write(f, call(sprintf, arg) ~ "\n");
io.close(f);
}
The "globals." prefix makes the function globally available without
prefix. The function can be used with printf()-like formats:
exec("some-command --in %s --out %s", arg1, arg2);
4) And to a key definition of your choice add this binding:
<binding>
<command>nasal</command>
<script>
var lat = getprop("/position/latitude-deg");
var lon = getprop("/position/longitude-deg");
exec("openurl
http://maps.google.com/maps?ll=%.10f,%.10f&z=12&t=h";, lat, lon);
</script>
</binding>
To prevent abuse, the fgfs.fifo.runner script only runs a hard-coded
set of commands and doesn't hand anything over to eval or a subshell.
If you like, make the fifo harder to find by putting it somewhere else
and giving it a non-guessable name. Just make sure to add a WRITE rule
for it to $FG_ROOT/Nasal/IOrules then. (The ~/.fgfs/Export/ directory
is write-enabled by default.)
m.
fgfs.fifo.runner
Description: application/shellscript
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