shell中的循环主要有for、while、until、select几种
一、for循环
二、while循环
三、until循环
四、select循环
五、嵌套循环
六、循环控制
一、for循环
1.列表for循环
for VARIABLE in (list)
do
command
done
执行一定次数的循环（循环次数等于列表元素个数）
1 # cat fruit01.sh
2 #!/bin/bash
3 for FRUIT in apple arange banana pear
4 do
5 echo "$FRUIT is John's favorite"
6 done
7 echo "No more fruits"
8 # sh ./fruit01.sh
9 apple is John's favorite
10 arange is John's favorite
11 banana is John's favorite
12 pear is John's favorite
13 No more fruits1 root@kali:~/Shell# vim fruit02.sh
2 root@kali:~/Shell# cat fruit02.sh
3 #!/bin/bash
4 fruits="apple oragne banana pear" #将列表定义到一个变量中，以后有任何修改只需要修改变量即可
5 for FRUIT in ${fruits}
6 do
7 echo "$FRUIT is John's favorite"
8 done
9 echo "No more fruits"
10 root@kali:~/Shell# sh ./fruit02.sh
11 apple is John's favorite
12 oragne is John's favorite
13 banana is John's favorite
14 pear is John's favorite
15 No more fruits如果列表是数字：
1 root@kali:~/Shell# vim for_list01.sh
2 root@kali:~/Shell# cat for_list01.sh
3 #!/bin/bash
4 for VAR in 1 2 3 4 5
5 do
6 echo "Loop $VAR times"
7 done
8 #执行结果
9 root@kali:~/Shell# sh ./for_list01.sh
10 Loop 1 times
11 Loop 2 times
12 Loop 3 times
13 Loop 4 times
14 Loop 5 times使用{}表示,需相应的shell环境支持
1 root@kali:~/Shell# vim for_list02.sh
2 root@kali:~/Shell# cat for_list02.sh
3 #!/bin/bash
4 for VAR in {1..5}
5 do
6 echo "Loop $VAR times"
7 done
8 root@kali:~/Shell# sh ./for_list02.sh
9 Loop 1 times
10 Loop 2 times
11 Loop 3 times
12 Loop 4 times
13 Loop 5 times使用seq替换
1 root@kali:~/Shell# cat for_list03.sh
2 #!/bin/bash
3 sum=0
4 for VAR in `seq 1 100`
5 #for VAR in $(seq 1 100) #也用$替换
6 do
7 sum=$(($sum+$VAR))
8 done
9 #执行结果
10 echo "Total:$sum"
11 root@kali:~/Shell# sh ./for_list03.sh
12 Total:5050利用seq步长计算1到100内的奇数和
1 root@kali:~/Shell# vim for_list04.sh
2 root@kali:~/Shell# cat for_list04.sh
3 #!/bin/bash
4 sum=0
5 for VAR in $(seq 1 2 100)
6 do
7 sum=$(($sum+$VAR))
8 done
9 echo "Total $sum"
10
11 root@kali:~/Shell# sh ./for_list04.sh
12 Total 2500利用ls的输出作为in的列表：
1 root@kali:~/Shell# vim for_list05.sh
2 root@kali:~/Shell# cat for_list05.sh
3 #!/bin/bash
4 for VAR in $(ls)
5 do
6 ls -l $VAR
7 done
8 root@kali:~/Shell# sh ./for_list05.sh
9 -rwxr-xr-x 1 root root 136 9月 24 18:10 chk_file.sh
10 -rwxr-xr-x 1 root root 241 9月 24 18:41 detect_input.sh
11 -rw-r--r-- 1 root root 67 9月 26 11:40 for_list01.sh
12 -rw-r--r-- 1 root root 63 9月 26 11:48 for_list02.sh
13 -rw-r--r-- 1 root root 112 9月 26 12:06 for_list03.sh
14 -rw-r--r-- 1 root root 92 9月 26 12:11 for_list04.sh
15 -rw-r--r-- 1 root root 49 9月 26 12:13 for_list05.sh
16 -rw-r--r-- 1 root root 114 9月 26 11:33 fruit01.sh
17 -rw-r--r-- 1 root root 133 9月 26 11:37 fruit02.sh
18 -rwxr-xr-x 1 root root 318 9月 22 21:46 rwx.sh
19 -rwxr-xr-x 1 root root 197 9月 24 18:04 score01.sh
20 -rwxr-xr-x 1 root root 172 9月 24 18:23 score03.sh
21 -rw-r--r-- 1 root root 0 9月 22 21:46 test2、不带列表的for循环
for VARIABLE
do
command
done
需要在运行脚本时通过参数的方式给for循环传递变量值
1 root@kali:~/Shell# vim for_list06.sh
2 root@kali:~/Shell# cat ./for_list06.sh
3 #!/bin/bash
4 for VARIABLE
5 do
6 echo -n "$VARIABLE "
7 done
8 echo
9 #执行结果
10 root@kali:~/Shell# sh ./for_list06.sh 1 2 3 4 5 99
11 1 2 3 4 5 99或通过$@,上面的可读性很差
1 root@kali:~/Shell# vim for_list07.sh
2 root@kali:~/Shell# cat for_list07.sh
3 #!/bin/bash
4 for VARIABLE in $@
5 do
6 echo -n "$VARIABLE "
7 done
8 #运行时传入参数
9 root@kali:~/Shell# sh ./for_list07.sh 1 8 9 s df
10 1 8 9 s df3、类C的for循环
需要熟悉C语言，语法：
for ((expressoin1;expression2;expression3))
do
command
done
eg:
1 [rhat@localhost shell]$ vim c_for01.sh
2 [rhat@localhost shell]$ cat c_for01.sh
3 #!/bin/bash
4 for ((i=1;i<=10;i++))
5 do
6 echo -n "$i "
7 done
8 echo
9 [rhat@localhost shell]$ sh ./c_for01.sh
10 1 2 3 4 5 6 7 8 9 10循环多个变量
[rhat@localhost shell]$ vim c_for02.sh
[rhat@localhost shell]$ cat c_for02.sh
#!/bin/bash
for ((i=1,j=100;i<=10;i++,j--))
do
echo "i=$i j=$j"
done
echo
#执行结果
[rhat@localhost shell]$ sh ./c_for02.sh
i=1 j=100
i=2 j=99
i=3 j=98
i=4 j=97
i=5 j=96
i=6 j=95
i=7 j=94
i=8 j=93
i=9 j=92
i=10 j=91计算1到100以及1到100的奇数和
1 [rhat@localhost shell]$ vim c_for03.sh
2 [rhat@localhost shell]$ cat c_for03.sh
3 #!/bin/bash
4 sum01=0
5 sum02=0
6 for ((i=1,j=1;i<=100;i++,j+=2))
7 do
8 let "sum01+=i"
9 if [ $j -lt 100 ];then
10 let "sum02+=j"
11 fi
12 done
13 echo "sum01=$sum01"
14 echo "sum02=$sum02"
15 [rhat@localhost shell]$ sh ./c_for03.sh
16 sum01=5050
17 sum02=25004、for的无限循环
无限循环特别消耗资源，测试时注意退出条件.
1 [rhat@localhost shell]$ vim c_for04.sh
2 [rhat@localhost shell]$ cat c_for04.sh
3 #!/bin/bash
4 for ((i=0;i<1;i+=0))
5 do
6 echo "infinite loop"
7 done1 [rhat@localhost shell]$ vim c_for05.sh
2 [rhat@localhost shell]$ cat c_for05.sh
3 #!/bin/bash
4 for(;1;)
5 do
6 ehco "infinite loop"
7 done以上代码会一直打印字符，需手动Ctrl+C停止.
二、While循环
语法:
while expression
do
command
done
首先测试expression的返回值，如果返回值为真则执行循环体，否则不执行循环。
1 [rhat@localhost shell]$ vim while01.sh
2 [rhat@localhost shell]$ cat while01.sh
3 #!/bin/bash
4 CONTER=5
5 while [[ $CONTER -gt 0 ]]
6 do
7 echo -n "$CONTER "
8 let "CONTER-=1" #每次循环减少一次CONTER的值
9 done
10 echo
11 [rhat@localhost shell]$ sh ./while01.sh
12 5 4 3 2 1while：计算1到100的和以及1到100的奇数和
1 [rhat@localhost shell]$ vim while02.sh
2 [rhat@localhost shell]$ cat while02.sh
3 #!/bin/bash
4 sum01=0
5 sum02=0
6 j=1
7 i=1
8 while [[ "$i" -le "100" ]]
9 do
10 let "sum01+=i"
11 let "j=i%2" #变量j用来确定变量i的奇偶性，如果为奇数则j为1
12 if [[ $j -ne 0 ]];then
13 let "sum02+=i"
14 fi
15 let "i+=1"
16 done
17 echo "sum01=$sum01"
18 echo "sum02=$sum02"
19 #执行结果
20 [rhat@localhost shell]$ sh ./while02.sh
21 sum01=5050
22 sum02=2500while:猜数游戏
1 [rhat@localhost shell]$ vim while03.sh
2 #!/bin/bash
3 PRE_SET_NUM=8
4 echo "Input a number between 1 and 10"
5 while read GUESS
6 do
7 if [[ $GUESS -eq $PRE_SET_NUM ]];then
8 echo "You get the right number"
9 exit
10 else
11 echo "Wrong,try again"
12 fi
13 done
14 echo
15 #执行结果
16 [rhat@localhost shell]$ sh ./while03.sh
17 Input a number between 1 and 10
18 i
19 Wrong,try again
20 1
21 Wrong,try again
22 8
23 You get the right numberwhile：按行读取文件
例如文件为：
1 [rhat@localhost shell]$ cat student_info.txt
2 John 30 Boy
3 Sue 28 Girl
4 Wang 25 Boy
5 Xu 23 Birlshell文件：
1 [rhat@localhost shell]$ vim while04.sh
2 #!/bin/bash
3 FNAME=student_info.txt
4 while read LINE #这会产生1个shell，此为重定向
5 #cat $FNAME | while read LINE #或者this，这会产生3个shell，第一个shell为cat，第二个sehll为管道，第三个shell为while
6 do
7 NAME=`echo $LINE | awk '{print $1}'`
8 AGE=`echo $LINE | awk '{print $2}'`
9 Sex=`echo $LINE | awk '{print $3}'`
10 echo "My name is $NAME I'm $AGE years old, I'm a $Sex"
11 done < $FNAME
12 #执行结果
13 [rhat@localhost shell]$ sh ./while04.sh
14 My name is John I'm 30 years old, I'm a Boy
15 My name is Sue I'm 28 years old, I'm a Girl
16 My name is Wang I'm 25 years old, I'm a Boy
17 My name is Xu I'm 23 years old, I'm a Birlwhile的无限循环：
语法：3种
while ((1))
do
command
done
----------------------
while true
do
command
done
----------------------
while :
do
command
done
1 [rhat@localhost shell]$ vim while05.sh
2 #!/bin/bash
3 while true
4 do
5 HTTPD_STATUS=`service httpd status | grep runing`
6 if [ -z "$HTTP_STATUS" ]; then
7 echo "HTTPD is stoped,try to restart"
8 service httpd restart
9 else
10 echo "HTTPD is running,wait 5 secuntil next check"
11 fi
12 sleep 5
13 done
14 #执行结果,需要有相应执行权限，否则会报错，Permission deniedLED]
15 [rhat@localhost shell]$ sh ./while05.sh
16 HTTPD is stoped,try to restart
17 ....三、until循环
until循环也是运行前测试，但是until采用的是测试假值得方式，当测试结果为假时才执行循环体，直到测试为真时才停止循环.语法：
until exprssion
do
command
done
eg:
1 [rhat@localhost shell]$ vim until01.sh
2 #!/bin/bash
3 sum01=0
4 sum02=0
5 i=1
6 until [[ $i -gt 100 ]]
7 do
8 let "sum01+=i"
9 let "j=i%2"
10 if [[ $j -ne 0 ]];then
11 let "sum02+=i"
12 fi
13 let "i+=1"
14 done
15 echo $sum01
16 echo $sum02
17 [rhat@localhost shell]$ sh ./until01.sh
18 5050
19 2500until无限循环
语法：
until ((0))
do
command
done
------------------------------------------------
until false
do
command
done
四、select循环
select 是一种菜单扩展循环方式，其语法和带列表的for循环类似，语法如下：
select MENU in (list)
do
command
done
1 [rhat@localhost shell]$ vim select01.sh
2 #!/bin/bash
3 echo "Which car do you prefer?"
4 select CAR in Benz Audi VolksWagen
5 do
6 break
7 done
8 echo "You chose $CAR"
9 #执行结果
10 [rhat@localhost shell]$ sh ./select01.sh
11 Which car do you prefer?
12 1) Benz
13 2) Audi
14 3) VolksWagen
15 #? 2
16 You chose Audi其中带有|的
1 [rhat@localhost shell]$ vim select02.sh
2 #!/bin/bash
3 select DAY in Mon Tue Wed Thu Fri Sat Sun
4 do
5 case $DAY in
6 Mon) echo "Today is Monday";;
7 Tue) echo "Today is Tuesday";;
8 Wed) echo "Today is Wednesday";;
9 Thu) echo "Today is Thursday";;
10 Fri) echo "Today is Friday";;
11 Sat|Sun) echo "You can have a rest today";;
12 *) echo "Unkown input,exit now" && break;;
13 esac
14 done
15 #执行结果
16 [rhat@localhost shell]$ sh ./select02.sh
17 1) Mon
18 2) Tue
19 3) Wed
20 4) Thu
21 5) Fri
22 6) Sat
23 7) Sun
24 #? 1
25 Today is Monday
26 #? 8
27 Unkown input,exit now五、嵌套循环
for、while、until、select循环语句都可以使用嵌套循环.不建议三层以上的嵌套，否则程序会晦涩难懂.
1 [rhat@localhost shell]$ vim nesting01.sh
2 #!/bin/bash
3 for ((i=1;i<=9;i++))
4 do
5 for ((j=1;j<=9;j++))
6 do
7 let "multi=$i*$j"
8 echo -n "$i*$j=$multi "
9 done
10 echo
11 done
12 #执行结果
13 [rhat@localhost shell]$ sh ./nesting01.sh
14 1*1=1 1*2=2 1*3=3 1*4=4 1*5=5 1*6=6 1*7=7 1*8=8 1*9=9
15 2*1=2 2*2=4 2*3=6 2*4=8 2*5=10 2*6=12 2*7=14 2*8=16 2*9=18
16 3*1=3 3*2=6 3*3=9 3*4=12 3*5=15 3*6=18 3*7=21 3*8=24 3*9=27
17 4*1=4 4*2=8 4*3=12 4*4=16 4*5=20 4*6=24 4*7=28 4*8=32 4*9=36
18 5*1=5 5*2=10 5*3=15 5*4=20 5*5=25 5*6=30 5*7=35 5*8=40 5*9=45
19 6*1=6 6*2=12 6*3=18 6*4=24 6*5=30 6*6=36 6*7=42 6*8=48 6*9=54
20 7*1=7 7*2=14 7*3=21 7*4=28 7*5=35 7*6=42 7*7=49 7*8=56 7*9=63
21 8*1=8 8*2=16 8*3=24 8*4=32 8*5=40 8*6=48 8*7=56 8*8=64 8*9=72
22 9*1=9 9*2=18 9*3=27 9*4=36 9*5=45 9*6=54 9*7=63 9*8=72 9*9=81or
1 [rhat@localhost shell]$ vim nesting02.sh
2 #!/bin/bash
3 i=1
4 while [[ "$i" -le "9" ]]
5 do
6 j=1
7 while [[ "$j" -le "9" ]]
8 do
9 let "multi=$i*$j"
10 if [[ "$j" -gt "$i" ]];then
11 break
12 else
13 echo -n "$i*$j=$multi "
14 let "j+=1"
15 fi
16 done
17 echo
18 let "i+=1"
19 done
20 #执行结果
21 [rhat@localhost shell]$ sh ./nesting02.sh
22 1*1=1
23 2*1=2 2*2=4
24 3*1=3 3*2=6 3*3=9
25 4*1=4 4*2=8 4*3=12 4*4=16
26 5*1=5 5*2=10 5*3=15 5*4=20 5*5=25
27 6*1=6 6*2=12 6*3=18 6*4=24 6*5=30 6*6=36
28 7*1=7 7*2=14 7*3=21 7*4=28 7*5=35 7*6=42 7*7=49
29 8*1=8 8*2=16 8*3=24 8*4=32 8*5=40 8*6=48 8*7=56 8*8=64
30 9*1=9 9*2=18 9*3=27 9*4=36 9*5=45 9*6=54 9*7=63 9*8=72 9*9=81六、循环控制
1.break语句
break用于终止当前循环体。一般情况下，break都是和if判断语句一起使用的.
eg：上面改造的99乘法表
2.continue语句
continue语句用于结束当前循环转而进入下一次循环，这和break不同，break是直接终止当前循环，continue是继续下次循环.
eg：打印1到100之间的素数
1 [rhat@localhost shell]$ vim continue02.sh
2 #!/bin/bash
3 for (( i=1;i<=100;i++ ))
4 do
5 for ((j=2;j<i;j++))
6 do
7 if !(($i%$j));then
8 continue 2 #2代表跳出循环的嵌套数.
9 fi
10 done
11 echo -n "$i "
12 done
13 echo
14 #执行结果
15 [rhat@localhost shell]$ sh ./continue02.sh
16 1 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97回到顶部
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