Creating Subcircuits
Let's use a basic discrete Class A operational amplifier for our subcircuit:

The filename is sirius-purple-a-mk-2.sch
, so the terminal command is:
gnetlist -g spice-sdb -o sirius-purple-a-mk-2.cir sirius-purple-a-mk-2.sch
Then open the .cir
file in a text editor:

Change the last line from ".end
" to ".ends
".
Then add the .SUBCKT
directive, the subcircuit name (I used sirius-purple-a
for my subcircuit) and the connections (vpos
is pin 1, vneg
is pin 2, vcc
is pin 3, vee
is pin 4 and output
is pin 5):

To include the subcircuit in your schematics, see the Using Subcircuits tutorial.