/usr/lib/courier/filterctl is in courier-mta 0.68.2-1ubuntu7.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 | #! /bin/bash
#
# Copyright 1998 - 2004 Double Precision, Inc.
# See COPYING for distribution information.
#
prefix="/usr"
exec_prefix="/usr"
libexecdir="/usr/lib/courier"
sysconfdir="/etc/courier"
localstatedir="/var/lib/courier"
piddir="/var/run/courier"
filterbindir="${libexecdir}/filters"
filteractivedir="${sysconfdir}/filters/active"
pidfile="${piddir}/courierfilter.pid"
cmd="$1"
filter="$2"
case "$cmd" in
start)
	;;
stop)
	;;
*)
	filter=""
	;;
esac
if test "$filter" = ""
then
	echo "Usage: $0 (start | stop) [ filter ]" >&2
	exit 1
fi
case "$filter" in
*/*)
	filter=""
	;;
*)
	if test ! -x $filterbindir/$filter
	then
		filter=""
	fi
	;;
esac
if test "$filter" = ""
then
	echo "This filter is not installed in $filterbindir" >&2
	echo >&2
	exit 1
fi
case "$cmd" in
start)
	test ! -x $filterbindir/$filter \
		|| ln -s $filterbindir/$filter $filteractivedir/$filter \
		|| exit 1
	;;
stop)
	rm -f $filteractivedir/$filter || exit 1
	;;
esac
test -f "$pidfile" && kill -HUP "`cat $pidfile`" 2>/dev/null
exit 0
 |