how to write a supervisord compatible shell script for pgbouncer (which can restart gracefully)

pgbouncer_run.sh

#!/bin/bash

# inspired by http://veithen.github.io/2014/11/16/sigterm-propagation.html

if [ -z "$DBNAME" ]; then
    echo "Environment variable DBNAME is not set!!!"
    exit 1
else
    sed -i 's|DBNAME|'"$DBNAME"'|' /etc/pgbouncer/pgbouncer.ini
fi

if [ -z "$USER" ]; then
    echo "Environment variable USER is not set!!!"
    exit 1
else
    sed -i 's|USER|'"$USER"'|' /etc/pgbouncer/pgbouncer.ini
fi

if [ -z "$PASSWORD" ]; then
    echo "Environment variable PASSWORD is not set!!!"
    exit 1
else
    sed -i 's|PASSWORD|'"$PASSWORD"'|' /etc/pgbouncer/pgbouncer.ini
fi


trap 'kill -TERM $PID' TERM INT
pgbouncer -u pgbouncer /etc/pgbouncer/pgbouncer.ini&
PID=$!
wait $PID
trap - TERM INT
wait $PID
EXIT_STATUS=$?