preinst is in wpasupplicant 2.1-0ubuntu1.
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 50 51 52 53 54 55 56 57 58 59 | #!/bin/sh
# This script can be called in the following ways:
#
# Before the package is installed:
#       <new-preinst> install
#
# Before removed package is upgraded:
#       <new-preinst> install <old-version>
#
# Before the package is upgraded:
#       <new-preinst> upgrade <old-version>
#
#
# If postrm fails during upgrade or fails on failed upgrade:
#       <old-preinst> abort-upgrade <new-version>
set -e
rm_conffile() {
	local PKGNAME="$1"
	local CONFFILE="$2"
	[ -e "$CONFFILE" ] || return 0
	local md5sum="$(md5sum $CONFFILE | sed -e 's/ .*//')"
	local old_md5sum="$(dpkg-query -W -f='${Conffiles}' $PKGNAME | \
		sed -n -e "\' $CONFFILE ' { s/ obsolete$//; s/.* //; p }")"
	if [ "$md5sum" != "$old_md5sum" ]; then
		echo "Obsolete conffile $CONFFILE has been modified by you."
		echo "Saving as $CONFFILE.dpkg-bak ..."
		mv -f "$CONFFILE" "$CONFFILE".dpkg-bak
	else
		echo "Removing obsolete conffile $CONFFILE ..."
		rm -f "$CONFFILE"
	fi
}
case "$1" in
	install|upgrade)
		if dpkg --compare-versions "$2" lt "0.6.9-4"; then
			rm_conffile wpasupplicant /etc/logrotate.d/wpa_supplicant
			rm_conffile wpasupplicant /etc/logrotate.d/wpa_action
		fi
		if dpkg --compare-versions "$2" lt "0.6.10-1"; then
			rm_conffile wpasupplicant /etc/init.d/wpa-ifupdown
			update-rc.d -f wpa-ifupdown remove >/dev/null
		fi
		;;
	abort-upgrade)
		;;
	*)
		echo "$0 called with unknown argument \`$1'" 1>&2
		exit 1
		;;
esac
exit 0
 |