Supervisor'ed dynamic pid

#!/usr/bin/env bash
# Signals from the supervisor are not propagated to the child processes

set -eu

if [[ $# -eq 0 ]] ; then
    echo "Usage $0 <pid_file> <command> [with arguments]"
    exit 0
fi

pidfile=$1
command="${@:2}"

# Proxy signals
function trap_sigterm(){
    kill -SIGTERM $(cat $pidfile)
    sleep_while_process_is_alive 0.1
    exit 0
}
trap trap_sigterm SIGTERM SIGINT

function trap_sigusr2() {
    kill -SIGUSR2 $(cat $pidfile)
}
trap trap_sigusr2 SIGUSR2

function sleep_while_process_is_alive() {
    while [ -f $pidfile ] ; do
        PID=$(cat $pidfile)
        if [ -n "$PID" -a -e /proc/$PID ]; then
            sleep $1
        else
            return
        fi
    done
}

# Run command in background
$command &

# Wait until pid is created
sleep 2

# Loop while the pidfile and the process exist
sleep_while_process_is_alive 0.5

# Exit unexpected
exit 1000