#!/bin/sh

# abiff 2.41
# by Adam M. Costello
# <amc@cs.wustl.edu>
#
# Usage (in a .forward file):
#
# "| HOME=/path/to/home/dir /path/to/abiff [-c] user@host ..."
#
# The quote marks are literal, and necessary.  Any number of user@host
# arguments may be supplied.  Be sure to forward your mail somewhere
# else as well, such as \username (the backslash prevents an infinite
# alias loop).
#
# abiff looks for elligible terminals in use by each user on the
# corresponding host.  To each terminal it finds, it writes a message
# including the first few lines of the arriving mail.  The remote
# accounts must have .rhost files set up so that abiff can rsh to each
# host using the corresponding user name.
#
# Without the -c option, eligible terminals are ones with group-execute
# permission that are writable.  With the -c option, eligible terminals
# are ones with owner-execute permission that are writable.  The latter
# criterion is the same one used by normal biff (comsat).
#
# If -c is supplied, and any of the hosts in the argument list are the
# same host on which abiff is running (i.e., the host to which the mail
# was sent), then abiff will skip that host, because it assumes that
# regular biff will take care of it.  For performance reasons, the test
# for equality of the hosts does not use the name service.  See the
# seekout() function below for the actual test.
#
# When -c is supplied in the .forward file, the biff command may
# be used to to turn on and off both biff and abiff notification.
# Otherwise, the commands "abiff y" and "abiff n" turn on and off abiff
# notification.  The command "abiff" outputs "is y" or "is n", depending
# on the group-execute bit of the tty.
#
# I have tried to make abiff secure, but I make no guarantees.  If you
# find a security hole, please tell me!
#
# abiff depends on awk, cat, chmod, ls, mkdir, rsh, sort, tty, and
# either /bin/hostname or uname.

umask 077

if [ $# -eq 0 ]; then
  tty=`tty` || exit $?
  perm=`ls -lL $tty` || exit $?
  case $perm in
    ??????x*) echo "is y" ;;
           *) echo "is n" ;;
  esac
  exit 0
fi

if [ $# -eq 1 ]; then
  if [ "$1" = y ]; then
    tty=`tty` || exit $?
    chmod g+x $tty
    exit $?
  fi
  if [ "$1" = n ]; then
    tty=`tty` || exit $?
    chmod g-x $tty
    exit $?
  fi
fi

if [ "$1" = -c ]; then
  compat=yes
  shift
else
  compat=no
fi
export compat

seekout () {
  oldIFS=$IFS
  IFS=@$oldIFS
  set -- $1
  IFS=$oldIFS
  if [ $compat = yes ]; then
    [ "$2" != "$host" ] || return 0
    case "$2" in
      "$host".*) return 0 ;;
    esac
    case "$host" in
      "$2".*) return 0 ;;
    esac
  fi
  cat $scriptfile | rsh -l "$1" "$2" /bin/sh -s "$1"
}

[ "$HOME" != "" ] || {
  echo "abiff error: HOME is not set"
  exit 1
}

[ -d "$HOME"/.abiff ] || mkdir "$HOME"/.abiff

tmpbase="$HOME"/.abiff/$$
scriptfile="$tmpbase"-s
export scriptfile

[ $compat = no ] || {
  if [ -x /bin/hostname ]; then
    host=`/bin/hostname`
  else
    host=`uname -n`
  fi
  export host
}

cat > $scriptfile << 'endcat'
devs=`
  who |
    while read user tty junk; do
      [ $user != "$1" ] || echo /dev/$tty
    done | sort
`
perms=`
  ls -lL $devs |
    while read perm junk; do
      echo $perm
    done
`
set -- $perms
for dev in $devs; do
  case $1 in
endcat

{ if [ $compat = yes ]; then
    echo '    ???x*)'
  else
    echo '    ??????x*)'
  fi
  echo '      [ ! -w $dev ] || cat > $dev << "EnDcAt"'
  echo ''

  # You probably want to customize this part to your tastes:

  # echo "New mail has just arrived at ${host}:"
  awk 'inbody != "yes" && /^(To:|From:|Subject:)/
       inbody != "yes" && /^$/ { inbody = "yes";  numbody = 0; }
       inbody == "yes" && $0 != "EnDcAt" && ! /^[ \t]*$/ {
         if (++numbody > 5) exit;  print; }'

  echo 'EnDcAt'
  echo '      ;;'
  echo '  esac'
  echo '  shift'
  echo 'done'
} >> $scriptfile

for arg do
  case "$arg" in
    *@*) seekout "$arg" &
         ;;
      *) echo "abiff error: unexpected argument $arg"
         exit 1;
         ;;
  esac
done

wait
rm $scriptfile