What's the software you're using? To get the output I think you want
you don't need a regular expression in awk, since the number of fields
is four when there's a letter and three when it's missing.
awk '{if (NF!=4) print "= N"; else print "= " $3}' < /tmp/data | nl
| sed 's! *!line !'
--
Ed Cashin <ecashin at noserose.net>