postinst is in php-crypt-gpg 1.1.1-1.
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
# Deactivated until draft PHP policy is fixed
# http://webapps-common.alioth.debian.org/draft-php/html/ch-php-libs.html
#
# pear install -r package.xml
|