shell创建子进程及并行延时执行命令方法

command &

command1 | command2

(cmd1;cmd2;cmd3)

bash ./test.sh

[root@imx6sabresd ~]# cat test.sh 
#!/bin/bash
# 功能描述：子Shell演示示例
# 父Shell
#set -x
hi="parent shell"
echo "+++++++++++++"
echo -e "\033[31m+ 父Shell +\033[0m"
echo "+++++++++++++"
echo "PWD=$PWD"
echo "PID=$$"
echo "bash_subshell=$BASH_SUBSHELL"
# 通过()开启子Shell
(
sub_hi="subshell"
echo -e "\t+++++++++++++"
echo -e "\t\033[33m+ 子Shell +\033[0m"
echo -e "\t+++++++++++++"
echo -e "\tPWD=$PWD"
echo -e "\tPID=$$"
echo -e "\tbash_subshell=$BASH_SUBSHELL"
echo -e "\thi=$hi"
echo -e "\tsubhi=$sub_hi"
cd /opt;echo -e "\tPWD=$PWD"
)
# 返回父Shell
echo "+++++++++++++++++"
echo "+ 返回父Shell +"
echo "+++++++++++++++++"
echo "PWD=$PWD"
echo "hi=$hi"
echo "sub_hi=$sub_hi"
echo "bash_subshell=$BASH_SUBSHELL"

echo "start"
(sleep 5
echo "hello world") &
echo "1"
sleep 1
echo "2"
sleep 1
echo "3"
sleep 1
echo "4"
sleep 0.5
echo "4.5"