postinst is in toilet 0.2-1ubuntu1.
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  | #!/bin/sh
set -e
if [ "$1" = configure ]; then
  # Add an alternative for figlet
  update-alternatives --install /usr/bin/figlet figlet \
        /usr/bin/figlet-toilet 20
fi
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