(1)for循环使用方法(for/do/done)
1.for … in 语句——语法结构

for 变量 in seq字符串       # seq字符串 只要用空格字符分割，每次for…in读取时候，就                                                              会按顺序将读到值，给前面的变量。
do
action
done

实例(testfor.sh)：

#!/bin/sh
for i in $(seq 10); do     #seq 10 产生 1 2 3 …… 10空格分隔字符串
echo $i;
done;

2.for((赋值；条件；运算语句))

for((赋值；条件；运算语句))
do
action
done;

实例(testfor2.sh)：

#!/bin/sh
for((i=1;i<=10;i++));do
echo $i;
done;

(2)while循环使用（while/do/done)

while 条件语句
do
action
done;

实例1:

#!/bin/sh
i=10;
while [[ $i -gt 5 ]];do
echo $i;
((i--));
done;

运行结果：

sh testwhile1.sh
10
9
8
7
6

实例2：(循环读取文件内容：)

#!/bin/sh
while read line;do
echo $line;
done < /etc/hosts;

运行结果：

sh testwhile2.sh
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 centos5 localhost.localdomain localhost

(3)until循环语句——语法结构

until 条件              #直到满足条件，就退出。否则执行action.
do
action
done

实例(testuntil.sh)：

#!/bin/sh
a=10;
until [[ $a -lt 0 ]];do
echo $a;
((a—));
done;

结果：

sh testuntil.sh
10
9
8
7
6
5
4
3
2
1
0

case $arg in
pattern | sample) # arg in pattern or sample
;;
pattern1) # arg in pattern1
;;
*) #default
;;
esac

#!/bin/sh
case $1 in
start | begin)
echo "start something"
;;
stop | end)
echo "stop something"
;;
*)
echo "Ignorant"
;;
esac

testcase.sh start
start something

select 变量name in seq变量
do
action
done

#!/bin/sh
select ch in "begin" "end" "exit"
do
case $ch in
"begin")
echo "start something"
;;
"end")
echo "stop something"
;;
"exit")
echo "exit"
break;
;;
*)
echo "Ignorant"
;;
esac
done;