postinst is in libunwind-setjmp0 1.1-4.1.
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 9 | #!/bin/sh
set -e
if [ configure = "$1" ]; then
# cleanup diversions from wheezy
if dpkg --compare-versions "$2" lt "1.1-3" ; then
dpkg-divert --package libunwind-setjmp0 --remove --rename --divert /usr/lib/libunwind-setjmp.so.0.0.0.old /usr/lib/libunwind-setjmp.so.0.0.0
dpkg-divert --package libunwind-setjmp0 --remove --rename --divert /usr/lib/libunwind-setjmp.so.0.old /usr/lib/libunwind-setjmp.so.0
fi
fi
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