This file is indexed.

postinst is in postgresql-contrib-9.5 9.5.2-1.

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.

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#!/bin/sh

set -e

VERSION=${DPKG_MAINTSCRIPT_PACKAGE##*-}

. /usr/share/postgresql-common/maintscripts-functions

if [ "$1" = configure ]; then
    configure_contrib_version $VERSION "$2"
fi