1、while do done ，until do done（不定循环）
while [ condition ] #中间括号内的状态就是判断式
do #循环的开始
程序段落
done #循环的结束
当condition条件成立时，就终止循环，否则就持续进行循环的程序段
[hadoop1@hadoop1 temp]$ sh yes_to_stop.sh un
please input yes/YES to stop this program;un
please input yes/YES to stop this program;yes
ok you input right
#!/bin/bash
#program
# repeat question until user input correct answer
#history
# 20181011 lile first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:usr/local/bin:/usr/local/sbin:~/temp
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 right" 如果将while变成until
[hadoop1@hadoop1 temp]$ sh yes_to_stop_until.sh yes
ok you input right
[hadoop1@hadoop1 temp]$ sh yes_to_stop_until.sh no
ok you input right
#!/bin/bash
#program
# repeat question until user input correct answer
#history
# 20181011 lile first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:usr/local/bin:/usr/local/sbin:~/temp
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 right" 我们可以看出，不管输入什么，until都跳出循环
例：设计计算1+2+3+4+5+6……+100
#!/bin/bash
#program
# use loop to calculate "1 to 100' result
#history
# 20181011 lile first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/temp
export PATH
s=0 #加总的数值变数 sum
i=0 #累加数值
while [ ${i} != "100" ]
do
i=$(($i+2))
s=$(($s+$i))
done
echo "total is $s"
2、for …in…do……done （固定循环）
相对于while与until的循环方式必须要符合某个条件的状态，for语法则需要知道循环的次数，其语法结构如下:
for var in con1 con2 con3…… #var变量在循环时第一次的循环内容是con1，第二次循环内容是com2，以此类推
do
程序段
done
[hadoop1@hadoop1 temp]$ vi for_animal.sh
#!/bin/bash
#program
# usring for ... loop to print 3 animals
#hisroty
# 20181012 lile first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/temp
export=PATH
for animal in dog cat pig xiaolei
do
echo -e "there are ${animal} "
done
[hadoop1@hadoop1 temp]$ sh for_animal.sh
there are dog
there are cat
there are pig
there are xiaolei 由于系统上面的各种账号都是写在/etc/passwd内的第一个字段，，我们需要透过管线命令cut捉出单纯的账号名称后，以id分别检查使用者的标识符和特殊参数。代码如下
如果我想利用 ping来判断网络状态，来进行网络状态的实际侦测中，我要侦测的网域是本机所在的192.168.122.1~192.168.122
.100，指令如下：
#!/bin/bash
#program
# use ping command to check the network's pc state
#history
# 20181011 lile first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/temp
export PATH
network="192.168.122" #定义网域的前一部分
for sitenu in $(seq 1 100) #seq为sequence（连续）的缩写
do
ping -c 1 -w 1 ${network}.${sitenu} &> /dev/null && result=0 || result=1
#以下是进行循环判断显示正确的启动(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
除了使用$(seq 1 100) 以外，还可以直接使用bash的内建机制{1..100}来取代连续输入的意思，中间以两个小数点来表示连续出现的意思
例：用户输入某个目录文件名，找出某目录内的文件名的权限。
#!/bin/bash
#program
# try do calculate 1+...+$(your input)
#history
# 20181012 lile first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
read -p "please input a number ,it will count fot 1+...+" num
s=0 i=0
for((i=0;i<=${num};i++))
do
s=$((${s}+${i}))
done
echo -e "1+...+${num}=${s}"3、for……do……done的数值处理
for（（初始值；限制值；执行步阶））
do
程序段
done
初始值：某个变量在循环当中的起始值，直接以类似i=1设定好
限制值：当变量的值在这个范围内，就执行循环，例如i<=100
执行步阶：每做一次循环时，变量的变化量。例如i=i+1，也可以使用i++
#!/bin/bash
#program
# try do calculate 1+...+$(your input)
#history
# 20181012 lile first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
read -p "please input a number ,it will count fot 1+...+" num
s=0 i=0
for((i=0;i<=${num};i++))
do
s=$((${s}+${i}))
done
echo -e "1+...+${num}=${s}"
4、搭配随机数与数组的实验
例 ：假设你所在的团队，经常为吃午饭的选择问题搞昏，，我们是否可以使用脚本搭配随机数来确定午餐。要达成这个任务，首先我们需要将全部的店家输入到一组数组当中，在透过随机数的处理，去取得可能得数值，在将搭配到该数值的店家显示出来。
#!/bin/bash
#/program
# try to chioce what us may eat
#history
# 20181012 LILE first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/temp
export PATH
eat[0]="humburger"
eat[1]="fried chicken"
eat[2]="handy"
eat[3]="freid bread stick"
eat[4]="instant noodles"
eatnum=5 #需要输入可选择餐厅数
check=$((${RANDOM}*${eatnum}/32767+1))
echo -e "we will eat ${eat[${check}]}"
每次显示三个选择
#!/bin/bash
#/program
# try to chioce what us may eat
#history
# 20181012 LILE first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/temp
export PATH
eat[0]="humburger"
eat[1]="fried chicken"
eat[2]="handy"
eat[3]="freid bread stick"
eat[4]="instant noodles"
eatnum=5
eated=0
while [ "${eated}" -lt 3 ];do
check=$((${RANDOM}*${eatnum}/32767+1)) #产生随机选择
mycheck=0
if [ "${eated}" -ge 1 ];then #如果eated>1,执行以下程序
for i in $(seq 1 ${eated}) #i从1增加到eated
do
if [ ${eatedcon[${i}]} == ${check} ];then #如果已经产生了的选择
mycheck=1
mycheck=1
fi
done
fi
if [ ${mycheck} == 0 ];then #如果mycheck=0，显示随机选择的结果
echo "your may eat ${eat[${check}]}"
eated=$((${eated}+1))
eatedcon[${eated}]=${check} #为了避免产生相同的选择
fi
done