Using sed to extract the netlist of a specific subcircuit

sed -n "/^\.SUBCKT ZLSABIAS_M\b/,/^\.ENDS/p" zl64k4at.cir > netlist.ZLSABIAS_M

-n tells sed to suppress the automatic printing of the pattern space.

This above sed script dumps the lines between the patterns 
   ".SUBCKT ZLSABIAS_M" at the begging of lines (using \b to match a word boundary), and 
   ".ENDS" at the beginning of lines 
of the netlist file zl64k4at.cir to file
netlist.ZLSABIAS_M.