循环
文章目录
- 循环
-
- 1. while
-
- 1.1 大小判断
- 1.2 100相加
- 1.3 无限循环
- 1.4 多列输出
- 1.5 读行
- 2. for
- 3. break
- 4. continue
1. while
示例
#!/bin/bash
#基础
i=1
while [ $i -le 5 ]
do
echo $i
let i++
done
输出:
$ sh while.sh
1
2
3
4
5
1.1 大小判断
i=10
while [ $i -ne 0 ]
do
i=`expr $i - 1`
echo $i
# sleep 1
done
输出:
sh while2.sh
9
8
7
6
5
4
3
2
1
0
1.2 100相加
#!/bin/bash
#计算1+2+...+100的值
i=1
sum=0
while (( i<101 ))
do
(( sum=sum+i ))
(( i++ ))
done
echo "The total value is $sum"
输出:
$ bash while.sh
The total value is 5050
1.3 无限循环
while true
do
uptime
sleep 1
done
输出:
sh while.sh
10:20:54 up 4 min, 1 user, load average: 0.05, 0.19, 0.12
10:20:56 up 4 min, 1 user, load average: 0.05, 0.19, 0.12
10:20:57 up 4 min, 1 user, load average: 0.05, 0.19, 0.12
10:20:58 up 4 min, 1 user, load average: 0.05, 0.19, 0.12
参考:
- Shell中while循环的陷阱, 变量实效,无法赋值变量
1.4 多列输出
$ cat test.txt
xiaoming 122458930 山西
dali 343536546232 新疆
lihua 35354646565 广东
$ cat while2.sh
#!/bin/bash
while read name phone origin
do
echo "$name : $phone : $origin"
done < test.txt
执行:
$ bash while2.sh
xiaoming : 122458930 : 山西
dali : 343536546232 : 新疆
lihua : 35354646565 : 广东
1.5 读行
$ cat test
1
22
33 3
while-read.sh
#!/bin/bash
# while-read: read lines from a file
count=0
while read; do
printf "%d %s\n" $REPLY
count=$(expr $count + 1)
done <$1
执行:
$ bash wile_read.sh test
1
22
33 3
count:3
2. for
格式:
for var in item1 item2 ... itemN
do
command1
command2
...
commandN
done
写成一行:
for var in item1 item2 ... itemN; do command1; command2… done;
- in列表可以包含替换、字符串和文件名。
- in列表是可选的,如果不用它,for循环使用命令行的位置参数。
例如,顺序输出当前列表中的数字:
#!/bin/bash
for varible1 in {1..5}
#for varible1 in 1 2 3 4 5
do
echo "Hello, Welcome $varible1 times "
done
计算1~100内所有的奇数之和
#!/bin/bash
sum=0
for i in {1..100..2}
do
let "sum+=i"
done
echo "sum=$sum"
执行:
$ bash while1.sh
sum=2500
通过i的按步数2不断递增,计算sum值为2500。同样可以使用seq命令实现按2递增来计算1~100内的所有奇数之和,for i in $(seq 1 2 100),seq表示起始数为1,跳跃的步数为2,结束条件值为100。
#!/bin/bash
sum=0
for i in $(seq 1 2 100)
do
let "sum+=i"
done
echo "sum=$sum"
[root@localhost control]# bash while2.sh
sum=2500
查看当前目录下文件以及文件夹
#!/bin/bash
for file in $( ls )
#for file in *
do
echo "file: $file"
done
for循环列表参数
#!/bin/bash
echo "number of arguments is $#"
echo "What you input is: "
for argument
do
echo "$argument"
done
#!/bin/bash
for((integer = 1; integer <= 5; integer++))
do
echo "$integer"
done
3. break
break 跳出整个循环
$ cat break1.sh
#!/bin/bash
for ((a=1; a<=3; a++))
do
echo "outer loop: $a"
for ((b=1; b<=4; b++))
do
if [ $b -eq 3 ]
then
break
fi
echo "inter loop: $b"
done
done
执行:
$ bash break1.sh
outer loop: 1
inter loop: 1
inter loop: 2
outer loop: 2
inter loop: 1
inter loop: 2
outer loop: 3
inter loop: 1
inter loop: 2
4. continue
continue跳出本次循环
$ cat continue1.sh
#!/bin/bash
for ((a=1; a<=3; a++))
do
echo "outer loop: $a"
for ((b=1; b<=4; b++))
do
if [ $b -eq 3 ]
then
continue
fi
echo "inter loop: $b"
done
done
执行:
$ bash continue1.sh
outer loop: 1
inter loop: 1
inter loop: 2
inter loop: 4
outer loop: 2
inter loop: 1
inter loop: 2
inter loop: 4
outer loop: 3
inter loop: 1
inter loop: 2
inter loop: 4
参考:
- Looping Statements | Shell Script
- Bash 脚本教程:循环