postinst is in libphp7.0-embed 7.0.4-7ubuntu2.
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 | #!/bin/sh
set -e
if [ "$1" = "configure" ]; then
    update-alternatives \
	--install /usr/lib/libphp7.so libphp7 /usr/lib/libphp7.0.so 70
fi
[ "$1" = "configure" ] && ldconfig
CONFDIR=/etc/php/7.0/embed/conf.d
if [ "$1" = "configure" ]; then
    phpini="/etc/php/7.0/embed/php.ini"
    if [ "embed" = "cli" ]; then
	ucf /usr/lib/php/7.0/php.ini-production.embed $phpini
    else
	ucf /usr/lib/php/7.0/php.ini-production $phpini
    fi
    ucfr libphp7.0-embed $phpini
    if [ -e /usr/lib/php/php-maintscript-helper ]; then
	. /usr/lib/php/php-maintscript-helper
	
	mods=$(phpquery -M -v 7.0)
	for mod in $mods; do
	    php_invoke enmod 7.0 embed $mod
	done
    fi
    if [ -n "$2" ] && dpkg --compare-versions "$2" lt "7.0.3-2~"; then
	rm -f /etc/php/7.0/embed/conf.d/20-opcache.ini;
    fi	    
fi
exit 0
 |