postinst is in scim-pinyin 0.5.91-2ubuntu3.
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 | #!/bin/sh
set -e
update-alternatives \
        --install /etc/X11/xinit/xinput.d/zh_CN xinput-zh_CN \
        /etc/X11/xinit/xinput.d/scim-pinyin 50
 |