kill recent process of specific user

killover.sh

#!/bin/bash 
# Usage: killover.sh nginx john 3
# Which means john can have maximum 3 nginx processes, the newest ones must be killed.

cmd=$1
user=$2
max_pids=$3

pids="$(ps --sort=start_time --user "$user" --format pid,cmd | grep "$cmd" | awk '{print $1}')"
pids_count=$(echo "$pids" | wc -l)
forbidden="$(echo "$pids" | tail -n "+$max_pids")"

echo "user: $user"
echo "pids: $pids_count / $max_pids"

for i in $forbidden
do
  echo "killing $i..."
  kill -9 "$i"
done