Is there a way for Lua to check IF Mach4 has a gcode file loaded? 

Thanks, Nick

might try
filename = mc.mcCntrlGcodeFile(inst)
or
linecount = mc.mcCntrlGcodeLineCount(inst)

then see if filename = nil
or linecount > 1

Good thinking, Craig.
Thanks,
Nick

 inst = mc.mcGetInstance()
local linecount = mc.mcCntlGetGcodeLineCount(inst)
if linecount > 0 then
    wx.wxMessageBox ("File loaded")--file is loaded
else
    wx.wxMessageBox ("No file loaded")--no file loaded
end


Not sure I'd use zero (0) as the default seems to be 1
think that needs to be addressed at some point before release.

But your welcome

The Dro says "1" but the var says "0" (since I'm checking the var, then the script works).  Like you say, that should probably be addressed.