#!/bin/bash
# trimmailbox - A simple script to ensure that only the four most recent
#    messages remain in the user's mailbox. Works with Berkeley Mail
#    (aka Mailx or mail): will need modifications for other mailers!

setglobal keep = '4'  # by default, let's just keep around the four most recent messages

setglobal totalmsgs = $[echo 'x' | mail | sed -n '2p' | awk '{print $2}]

if test $totalmsgs -lt $keep  {
  exit 0          # nothing to do
}

setglobal topmsg = "$shExpr(' $totalmsgs - $keep ')"

mail > /dev/null << """
d1-$topmsg
q
"""

exit 0