preinst is in libtiff4-dev 4.0.3-7ubuntu0.11.
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 | #!/bin/sh
set -e
if [ -h /usr/share/doc/libtiff4-dev ]; then
rm -f /usr/share/doc/libtiff4-dev
fi
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