[1] Install wine
[2] Install LTSpice v3 (v4 has different format of output file :( )
to it's default path
[3] In Electric menu File->Preferences->Tools->SpiceCDL
setup following command line
~/.wine/drive_c/LTC/LTspiceIV/scad3.sh -i NMOS_IV.spi -r NMOS_IV.raw -o NMOS_IV.outIV/scad3.exe
For NGSpice use command line in [3]
ngspice -b -r ${FILENAME_NO_EXT}.raw ${FILENAME}
Examples using NGSpice syntax in testbenches may be found here:
Note: NGSpice is also available for windows and worked fine for me