第十三章、学习 Shell Scripts 条件判断式

if [ 条件判断式 ]; then
	当条件判断式成立时，可以进行的命令工作内容；
fi   <==将 if 反过来写，就成为 fi ！结束 if 之意！

[root@www scripts]# cp sh06.sh sh06-2.sh  <==用改的比较快！
[root@www scripts]# vi sh06-2.sh
#!/bin/bash
# Program:
#       This program shows the user‘s choice
# History:
# 2005/08/25    VBird   First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

read -p "Please input (Y/N): " yn

if [ "$yn" == "Y" ] || [ "$yn" == "y" ]; then
	echo "OK, continue"
	exit 0
fi
if [ "$yn" == "N" ] || [ "$yn" == "n" ]; then
	echo "Oh, interrupt!"
	exit 0
fi
echo "I don‘t know what your choice is" && exit 0

# 一个条件判断，分成功进行与失败进行 (else)
if [ 条件判断式 ]; then
	当条件判断式成立时，可以进行的命令工作内容；
else
	当条件判断式不成立时，可以进行的命令工作内容；
fi

# 多个条件判断 (if ... elif ... elif ... else) 分多种不同情况运行
if [ 条件判断式一 ]; then
	当条件判断式一成立时，可以进行的命令工作内容；
elif [ 条件判断式二 ]; then
	当条件判断式二成立时，可以进行的命令工作内容；
else
	当条件判断式一与二均不成立时，可以进行的命令工作内容；
fi

[root@www scripts]# cp sh06-2.sh sh06-3.sh
[root@www scripts]# vi sh06-3.sh
#!/bin/bash
# Program:
#       This program shows the user‘s choice
# History:
# 2005/08/25    VBird   First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

read -p "Please input (Y/N): " yn

if [ "$yn" == "Y" ] || [ "$yn" == "y" ]; then
	echo "OK, continue"
elif [ "$yn" == "N" ] || [ "$yn" == "n" ]; then
	echo "Oh, interrupt!"
else
	echo "I don‘t know what your choice is"
fi

[root@www scripts]# vi sh09.sh
#!/bin/bash
# Program:
#	Check $1 is equal to "hello"
# History:
# 2005/08/28	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

if [ "$1" == "hello" ]; then
	echo "Hello, how are you ?"
elif [ "$1" == "" ]; then
	echo "You MUST input parameters, ex> {$0 someword}"
else
	echo "The only parameter is ‘hello‘, ex> {$0 hello}"
fi

[root@www ~]# netstat -tuln
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address     Foreign Address   State
tcp        0      0 0.0.0.0:111       0.0.0.0:*         LISTEN
tcp        0      0 127.0.0.1:631     0.0.0.0:*         LISTEN
tcp        0      0 127.0.0.1:25      0.0.0.0:*         LISTEN
tcp        0      0 :::22             :::*              LISTEN
udp        0      0 0.0.0.0:111       0.0.0.0:*
udp        0      0 0.0.0.0:631       0.0.0.0:*
#封包格式           本地IP:端口       远程IP:端口       是否监听

[root@www scripts]# vi sh10.sh
#!/bin/bash
# Program:
# 	Using netstat and grep to detect WWW,SSH,FTP and Mail services.
# History:
# 2005/08/28	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

# 1. 先作一些告知的动作而已～
echo "Now, I will detect your Linux server‘s services!"
echo -e "The www, ftp, ssh, and mail will be detect! \n"

# 2. 开始进行一些测试的工作，并且也输出一些资讯罗！
testing=$(netstat -tuln | grep ":80 ")   # 侦测看 port 80 在否？
if [ "$testing" != "" ]; then
	echo "WWW is running in your system."
fi
testing=$(netstat -tuln | grep ":22 ")   # 侦测看 port 22 在否？
if [ "$testing" != "" ]; then
	echo "SSH is running in your system."
fi
testing=$(netstat -tuln | grep ":21 ")   # 侦测看 port 21 在否？
if [ "$testing" != "" ]; then
	echo "FTP is running in your system."
fi
testing=$(netstat -tuln | grep ":25 ")   # 侦测看 port 25 在否？
if [ "$testing" != "" ]; then
	echo "Mail is running in your system."
fi

[root@www scripts]# vi sh11.sh
#!/bin/bash
# Program:
#	You input your demobilization date, I calculate how many days
#	before you demobilize.
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

# 1. 告知使用者这支程序的用途，并且告知应该如何输入日期格式？
echo "This program will try to calculate :"
echo "How many days before your demobilization date..."
read -p "Please input your demobilization date (YYYYMMDD ex>20090401): " date2

# 2. 测试一下，这个输入的内容是否正确？利用正规表示法
date_d=$(echo $date2 |grep ‘[0-9]\{8\}‘)   # 看看是否有八个数字
if [ "$date_d" == "" ]; then
	echo "You input the wrong date format...."
	exit 1
fi

# 3. 开始计算日期
declare -i date_dem=`date --date="$date2" +%s`    # 退伍日期秒数
declare -i date_now=`date +%s`                    # 现在日期秒数
declare -i date_total_s=$(($date_dem-$date_now))  # 剩余秒数统计
declare -i date_d=$(($date_total_s/60/60/24))     # 转为日数
if [ "$date_total_s" -lt "0" ]; then              # 判断是否已退伍
	echo "You had been demobilization before: " $((-1*$date_d)) " ago"
else
	declare -i date_h=$(($(($date_total_s-$date_d*60*60*24))/60/60))
	echo "You will demobilize after $date_d days and $date_h hours."
fi

case  $变量名称 in   <==关键字为 case ，还有变量前有钱字号
  "第一个变量内容")   <==每个变量内容建议用双引号括起来，关键字则为小括号 )
	程序段
	;;            <==每个类别结尾使用两个连续的分号来处理！
  "第二个变量内容")
	程序段
	;;
  *)                  <==最后一个变量内容都会用 * 来代表所有其他值
	不包含第一个变量内容与第二个变量内容的其他程序运行段
	exit 1
	;;
esac                  <==最终的 case 结尾！『反过来写』！

[root@www scripts]# vi sh09-2.sh
#!/bin/bash
# Program:
# 	Show "Hello" from $1.... by using case .... esac
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

case $1 in
  "hello")
	echo "Hello, how are you ?"
	;;
  "")
	echo "You MUST input parameters, ex> {$0 someword}"
	;;
  *)   # 其实就相当於万用字节，0~无穷多个任意字节之意！
	echo "Usage $0 {hello}"
	;;
esac

[root@www scripts]# vi sh12.sh
#!/bin/bash
# Program:
#	This script only accepts the flowing parameter: one, two or three.
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

echo "This program will print your selection !"
# read -p "Input your choice: " choice # 暂时取消，可以替换！
# case $choice in                      # 暂时取消，可以替换！
case $1 in                             # 现在使用，可以用上面两行替换！
  "one")
	echo "Your choice is ONE"
	;;
  "two")
	echo "Your choice is TWO"
	;;
  "three")
	echo "Your choice is THREE"
	;;
  *)
	echo "Usage $0 {one|two|three}"
	;;
esac

function fname() {
	程序段
}

[root@www scripts]# vi sh12-2.sh
#!/bin/bash
# Program:
#	Use function to repeat information.
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

function printit(){
	echo -n "Your choice is "     # 加上 -n 可以不断行继续在同一行显示
}

echo "This program will print your selection !"
case $1 in
  "one")
	printit; echo $1 | tr ‘a-z‘ ‘A-Z‘  # 将参数做大小写转换！
	;;
  "two")
	printit; echo $1 | tr ‘a-z‘ ‘A-Z‘
	;;
  "three")
	printit; echo $1 | tr ‘a-z‘ ‘A-Z‘
	;;
  *)
	echo "Usage $0 {one|two|three}"
	;;
esac

[root@www scripts]# vi sh12-3.sh
#!/bin/bash
# Program:
#	Use function to repeat information.
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

function printit(){
	echo "Your choice is $1"   # 这个 $1 必须要参考底下命令的下达
}

echo "This program will print your selection !"
case $1 in
  "one")
	printit 1  # 请注意， printit 命令后面还有接参数！
	;;
  "two")
	printit 2
	;;
  "three")
	printit 3
	;;
  *)
	echo "Usage $0 {one|two|three}"
	;;
esac