Advice for when you can use shell scripts

The caveat/mistake here is if you treat it / think that it is equivalent to if a then b else c. That is not the case if b has any chance of failing.

Analogue of shift built-in. Too bad there isn't just a pop built-in.

this doesn't run on my system. However ps -f seems to list processes started in the terminal and ps -ef lists all (?) processes

#!/bin/bash  
IP_LIST="192.168.18.1 192.168.1.1 192.168.18.2"
for IP in $IP_LIST; do
    NUM=1
    while [ $NUM -le 3 ]; do
        if ping -c 1 $IP > /dev/null; then
            echo "$IP Ping is successful."
            break
        else
            # echo "$IP Ping is failure $NUM"
            FAIL_COUNT[$NUM]=$IP
            let NUM++
        fi
    done
    if [ ${#FAIL_COUNT[*]} -eq 3 ];then
        echo "${FAIL_COUNT[1]} Ping is failure!"
        unset FAIL_COUNT[*]
    fi
done

方法1：
# echo $RANDOM |md5sum |cut -c 1-8
471b94f2
方法2：
# openssl rand -base64 4
vg3BEg==
方法3：
# cat /proc/sys/kernel/random/uuid |cut -c 1-8
ed9e032c

方法1：

# echo $RANDOM |cksum |cut -c 1-8
23648321
方法2：
# openssl rand -base64 4 |cksum |cut -c 1-8
38571131
方法3：
# date +%N |cut -c 1-8
69024815

1）开头加解释器：#!/bin/bash

2）语法缩进，使用四个空格；多加注释说明。

3）命名建议规则：变量名大写、局部变量小写，函数名小写，名字体现出实际作用。

4）默认变量是全局的，在函数中变量local指定为局部变量，避免污染其他作用域。

5）有两个命令能帮助我调试脚本：set -e 遇到执行非0时退出脚本，set-x 打印执行过程。

6）写脚本一定先测试再到生产上。

This semicolon character is key for the whole thing to work.

The power of BASH!