postinst is in icedtea-7-plugin 1.5-1ubuntu1.
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 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54  | #!/bin/sh -e
PATH=/sbin:/bin:/usr/sbin:/usr/bin
multiarch=x86_64-linux-gnu
priority=1071
browser_dirs="mozilla"
PLUGIN=IcedTeaPlugin.so
basedir=/usr/lib/jvm/java-7-openjdk-amd64
old_basedir=/usr/lib/jvm/java-7/openjdk
PLUGINPTH=$basedir/jre/lib/amd64/$PLUGIN
OLD_PLUGINPTH=$old_basedir/jre/lib/amd64/$PLUGIN
case "$1" in
    configure)
	for browser_dir in $browser_dirs; do
	    if [ $browser_dir = xulrunner-addons ]; then
		browser=xulrunner-1.9
	    else
		browser=$browser_dir
	    fi
	    if [ -n "$multiarch" ] && [ "$DPKG_MAINTSCRIPT_ARCH" != $(dpkg --print-architecture) ]; then
		priority=$(expr $priority - 1)
	    fi
            if [ -n "$multiarch" ] && [ -n "$2" ]; then
                if [ -n "$(update-alternatives --list $browser-javaplugin.so 2>/dev/null | grep ^$old_basedir/)" ]; then
		    update-alternatives --remove $browser-javaplugin.so $OLD_PLUGINPTH || true
                fi
	    fi
            if [ -z "$(update-alternatives --list $browser-javaplugin.so 2>/dev/null | grep ^$basedir/)" ]; then
		update-alternatives --quiet --install \
		    /usr/lib/$browser_dir/plugins/libjavaplugin.so \
		    $browser-javaplugin.so \
		    $PLUGINPTH \
		    $priority
	    elif [ $priority -gt 1060 ]; then
		oldp=$(update-alternatives --query $browser-javaplugin.so | awk -v b=$basedir '/^Alternative:/ && $2~b {p=1} /^Priority:/ && p {print $2; exit}')
		if [ -n "$oldp" ] && [ "$oldp" -le 1060 ]; then
		  update-alternatives --quiet --install \
		    /usr/lib/$browser_dir/plugins/libjavaplugin.so \
		    $browser-javaplugin.so \
		    $PLUGINPTH \
		    $priority
		fi
	    fi
	done
esac
exit 0
 |