lopping off signatures

Era Eriksson suggested to Dan Hersam,

| Here's an alternative approach, if you have tac(1) and a tail(1) that
| understands the +n argument -- strip the last four lines from +all+
| mail (-:
| 
|     :0fwb
|     | tac | tail +5 | tac

Youch.

       BOTTOMLINES=4

       :0Bbfwi
       * 1^1 ^.*$
       * $ -$BOTTOMLINES^0
# The following condition might be needed for adjustment; I haven't tested:
#      * -1^0
       | head -$=  # if you don't have head(1), sed "$="q

| Any script that has to do something to the +last+ n lines of a message
| is tricky to write with standard line-oriented tools because they
| usually are based on the assumption that you want to do everything in
| one pass, from start to end. The tac(1) trick can obviously be useful
| for simplifying your sed scripts, too:
| 
|     :0fwb
|     | tac | sed '1,/^-- $/d' | tac

Again, though the anything-but-a-sig-separator-regexp is messy,

      :0B
      * ^()\/-- $((.|..|[^-].*|.[^-].*|..[^ ].*)?$)*^^
      {
        SIGBLOCK=$MATCH

        :0Bbfwi
        * 1^1 ^.*$
        * -1^1 SIGBLOCK ?? ^.*$
        | head -$= # or sed "$="q
      }

Ideally there should not be more than one signature separator, because the
whole idea of a separator is to say, "Everything below here is my
.signature."  For mail like that,

     :0Bbfwi
     * ^-- $
     * ! ^-- $(.*$)*-- $
     | sed -ne '/^-- $/q' -e p

and if a message has more than one signature separator, shame on the sender.