postinst is in bison++ 1.21.11-4.
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 | #!/bin/sh
set -e 0
update-alternatives --install /usr/bin/yacc yacc /usr/bin/bison++.yacc 100
|