shell 实现并发操作

下面我们来模拟使用shell实现并发操作，有2个工作如下脚本所示：

work1.sh：

#!/bin/sh
echo "work1 start ......."
sleep 5
echo "work1 end .......

work2.sh

#!/bin/sh
echo "work2 start ......."
sleep 2
echo "work2 end .......

使用并发运行这2个work,concurrent_test.sh 

#/bin/sh
time=`date +%s`
#work1 sleep 5s
./work1.sh &
#$!是得到最后一个进程的id
i=$!
#work2 sleep 2s
./work2.sh &
j=$!
#wait是等待线程/进程结束,  用法 wait [id]   不带id代表等待所有子线程结束
wait
echo "work1 pid $i"
echo "work2 pid $j"
time=$((`date +%s` - $time))
echo "cost time: $time s"

运行结果：./concurrent_test.sh 

work1 start .......
work2 start .......
work2 end .......
work1 end .......
work1 pid 5663
work2 pid 5665
cost time: 5 s

两个work同时运行，花费时间5s。