第十三章、学习 Shell Scripts 循环 (loop)

while [ condition ]  <==中括号内的状态就是判断式
do            <==do 是回圈的开始！
	程序段落
done          <==done 是回圈的结束

until [ condition ]
do
	程序段落
done

[root@www scripts]# vi sh13.sh
#!/bin/bash
# Program:
#	Repeat question until user input correct answer.
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

while [ "$yn" != "yes" -a "$yn" != "YES" ]
do
	read -p "Please input yes/YES to stop this program: " yn
done
echo "OK! you input the correct answer."

[root@www scripts]# vi sh13-2.sh
#!/bin/bash
# Program:
#	Repeat question until user input correct answer.
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

until [ "$yn" == "yes" -o "$yn" == "YES" ]
do
	read -p "Please input yes/YES to stop this program: " yn
done
echo "OK! you input the correct answer."

[root@www scripts]# vi sh14.sh
#!/bin/bash
# Program:
#	Use loop to calculate "1+2+3+...+100" result.
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

s=0  # 这是加总的数值变量
i=0  # 这是累计的数值，亦即是 1, 2, 3....
while [ "$i" != "100" ]
do
	i=$(($i+1))   # 每次 i 都会添加 1 
	s=$(($s+$i))  # 每次都会加总一次！
done
echo "The result of ‘1+2+3+...+100‘ is ==> $s"

for var in con1 con2 con3 ...
do
	程序段
done

[root@www scripts]# vi sh15.sh
#!/bin/bash
# Program:
# 	Using for .... loop to print 3 animals
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

for animal in dog cat elephant
do
	echo "There are ${animal}s.... "
done

[root@www scripts]# vi sh16.sh
#!/bin/bash
# Program
#       Use id, finger command to check system account‘s information.
# History
# 2009/02/18    VBird   first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
users=$(cut -d ‘:‘ -f1 /etc/passwd)  # 撷取帐号名称
for username in $users               # 开始回圈进行！
do
        id $username
        finger $username
done

[root@www scripts]# vi sh17.sh
#!/bin/bash
# Program
#       Use ping command to check the network‘s PC state.
# History
# 2009/02/18    VBird   first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
network="192.168.1"              # 先定义一个网域的前面部分！
for sitenu in $(seq 1 100)       # seq 为 sequence(连续) 的缩写之意
do
	# 底下的程序在取得 ping 的回传值是正确的还是失败的！
        ping -c 1 -w 1 ${network}.${sitenu} &> /dev/null && result=0 || result=1
	# 开始显示结果是正确的启动 (UP) 还是错误的没有连通 (DOWN)
        if [ "$result" == 0 ]; then
                echo "Server ${network}.${sitenu} is UP."
        else
                echo "Server ${network}.${sitenu} is DOWN."
        fi
done

[root@www scripts]# vi sh18.sh
#!/bin/bash
# Program:
#	User input dir name, I find the permission of files.
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

# 1. 先看看这个目录是否存在啊？
read -p "Please input a directory: " dir
if [ "$dir" == "" -o ! -d "$dir" ]; then
	echo "The $dir is NOT exist in your system."
	exit 1
fi

# 2. 开始测试文件罗～
filelist=$(ls $dir)        # 列出所有在该目录下的文件名称
for filename in $filelist
do
	perm=""
	test -r "$dir/$filename" && perm="$perm readable"
	test -w "$dir/$filename" && perm="$perm writable"
	test -x "$dir/$filename" && perm="$perm executable"
	echo "The file $dir/$filename‘s permission is $perm "
done

for (( 初始值; 限制值; 运行步阶 ))
do
	程序段
done

[root@www scripts]# vi sh19.sh
#!/bin/bash
# Program:
# 	Try do calculate 1+2+....+${your_input}
# History:
# 2005/08/29	VBird	First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

read -p "Please input a number, I will count for 1+2+...+your_input: " nu

s=0
for (( i=1; i<=$nu; i=i+1 ))
do
	s=$(($s+$i))
done
echo "The result of ‘1+2+3+...+$nu‘ is ==> $s"