prerm is in postfix 3.1.0-3.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
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  | #!/bin/sh -e
# Debian Postfix prerm
# LaMont Jones <lamont@debian.org>
case "$1" in
    upgrade)
	new=$2			# get new version
	[ -x /usr/sbin/invoke-rc.d ] && \
		INIT="invoke-rc.d postfix" || \
		INIT="/etc/init.d/postfix"
	${INIT} stop
	if dpkg --compare-versions $new lt 0.0.20020113.SNAPSHOT-1; then
	    # Need to handle some changes in services.
	    MASTER=/etc/postfix/master.cf
	    if grep -qE '^cleanup[[:space:]]+unix[[:space:]]+n' ${MASTER}; then
		echo "in master.cf:"
		echo "  forcing pickup=privileged, cleanup=private, flush=private"
		sed 's/^\(cleanup[[:space:]]*unix[[:space:]]*\)n/\1-/
		     s/^\(flush[[:space:]]*unix[[:space:]]*\)n/\1-/
		     s/^\(pickup[[:space:]]*fifo[[:space:]]*.[[:space:]]*\)-/\1n/
		' ${MASTER} > ${MASTER}.$$
		mv ${MASTER}.$$ ${MASTER}
	    fi
	fi
	;;
    deconfigure)
	;;
    remove)
	[ -x /usr/sbin/invoke-rc.d ] && \
		INIT="invoke-rc.d postfix" || \
		INIT="/etc/init.d/postfix"
	${INIT} stop
	rm -rf /var/spool/postfix/lib
	rm -rf /var/spool/postfix/etc
    	;;
    failed-upgrade)
	;;
    *)
	echo "prerm called with unknown argument \`$1'" >&2
	exit 1
	;;
esac
exit 0
 |