start a LTSpice simulation using code in MacOS
I'm maybe a little too late for the party, but after reading the above, and having a similar problem I found that the package content of the LTspice app has an executable file found at:

/Applications/LTspice.app/Contents/MacOS/


I am not sure how to properly work with the command line help specified in laptop2d's answer, as it seems that LTspice saves as .asc on macOS, not .cir. When using the above executable, specifying the .asc file it fails. It appears to be having issues with the params and simulation commands in a given schematic - they are apparently not properly interpreted. 

I circumvented this by generating the netlist manually (It seems that the macOS executable aren't capable of doing this, either). I then run the following command in terminal:

/Applications/LTspice.app/Contents/MacOS/LTspice -b myNetlist.net


I hope this helps others.