preinst is in icinga2-common 2.8.1-0ubuntu2.
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 | #!/bin/sh
set -e
dpkg-maintscript-helper rm_conffile \
"/etc/bash_completion.d/icinga2" "2.4.1-2~" -- "$@"
exit 0
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