prerm is in wmaker 0.95.0+20111028-4.
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 | #!/bin/sh
set -e
case "$1" in
    failed-upgrade|abort-upgrade|deconfigure)
        update-alternatives --remove x-window-manager /usr/bin/wmaker
    ;;
    remove)
        update-alternatives --remove x-window-manager /usr/bin/wmaker
    ;;
    upgrade)
    ;;
    *)
        echo "postrm called with unknown argument \`$1'" >&2
        exit 1
    ;;
esac
exit 0
 |