preinst is in libpango1.0-0 1.38.1-1.
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 | #!/bin/sh
set -e
if [ "$1" = "upgrade" ] && dpkg --compare-versions "$2" lt-nl 1.28.3-4; then
if [ -L /usr/share/doc/libpango1.0-0 ]; then
rm -f /usr/share/doc/libpango1.0-0
fi
fi
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