postinst is in shorewall6-lite 5.0.4-1.
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 | #!/bin/sh -e
case "$1" in
    configure)
        # if we are upgrading from version < 3.4 then we have to rename the
        # configuration file
        if [ "$2" ] && dpkg --compare-versions "$2" lt "3.4"
        then
            if [ -f /etc/shorewall6-lite/shorewall.conf ]
            then
                rm /etc/shorewall6-lite/shorewall.conf
            fi
        fi
        ;;
    abort-upgrade|abort-remove|abort-deconfigure)
        ;;
        
    *)
        echo "postinst called with unknown argument \`$1'" >&2
        exit 0
        ;;
esac
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