postinst is in maven 3.5.2-2.
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  | #!/bin/sh
set -e
basedir=/usr/share/maven
priority=300
case "$1" in
configure)
    update-alternatives \
    --install /usr/bin/mvn mvn $basedir/bin/mvn $priority \
    --slave \
        /usr/bin/mvnDebug \
        mvnDebug \
        $basedir/bin/mvnDebug \
    --slave \
        /usr/share/man/man1/mvn.1.gz \
        mvn.1.gz \
        $basedir/man/mvn.1.gz \
    --slave \
        /usr/share/man/man1/mvnDebug.1.gz \
        mvnDebug.1.gz \
        $basedir/man/mvnDebug.1.gz
    
    ;;
esac
exit 0
 |