preinst is in glabels 3.4.0-2.
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  | #!/bin/sh
set -e
if [ "$1" = "upgrade" ] && dpkg --compare-versions "$2" lt-nl "2.2.7-2"
then
    # Remove fucking symlink
    if [ -L /usr/share/doc/glabels ]
    then
        rm /usr/share/doc/glabels
    fi
fi
exit 0
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