#!/bin/bash
# spawn.sh
PIDS=$(pidof sh $0)  # Process IDs of the various instances of this script.
P_array=( $PIDS )    # Put them in an array (why?).
echo $PIDS           # Show process IDs of parent and child processes.
let "instances = ${#P_array[*]} - 1"  # Count elements, less 1.   Why subtract 1?
echo "$instances instance(s) of this script running."
echo "[Hit Ctl-C to exit.]"; echo
sleep 10              # Wait.
sh $0                # Play it again, Sam.
exit 0               # Not necessary; script will never get to here.  Why not?
几个要点：
1.pidof的用法
以前结束一个进程:ps -ef | grep xxx 返回一个pid,然后,kill pid.
也可以还有一个命令:pidof xxx
pidof xxx 返回一个pid, 那么用pidof xxx | xargs kill  是一个更有效率的方法!
2.shell 数组的语法
注意用法，已学习备忘.