1. 循环
shell循环，不断执行某段程序，直到符合条件。
循环分为4种， while循环，until循环，for固定处理， for数值处理。
2. while循环
while循环是一直执行，直到条件不符合，才停止。
语法：
while [ condition ]
do
//do something
done
例： 循环直到用户输入正确
#!/bin/bash
# desc : while loop
while [ "$yn" != "yes" -a "$yn" != "YES" ]
do
read -p "Please input yes/YES to stop : " yn
done
echo "OK"
执行结果：
[[email protected] sh]$ sh while.sh Please input yes/YES to stop : no Please input yes/YES to stop : yes OK [[email protected] sh]$
例：从1加到100
#!/bin/bash
# desc : while loop
sum=0
i=0
while [ $i -lt 100 ]
do
i=$(($i+1));
sum=$(($sum+$i))
done
echo "From 1 to 100, sum is : " $sum
3. until循环
until循环和while相反，当条件condition成立时，终止循环。
语法：
until [ condition ]
do
//do something
done
例：
#!/bin/bash
# desc : while loop
until [ "$yn" == "yes" -o "$yn" == "YES" ]
do
read -p "Please input yes/YES to stop : " yn
done
echo "OK"
执行：
[[email protected] sh]$ sh while.sh Please input yes/YES to stop : hi Please input yes/YES to stop : yes OK [[email protected] sh]$
4. for固定循环
for为已知次数的循环。
语法：
for var in con1 con2 ..
do
//do something
done
例：
#!/bin/bash
# desc : for loop
for animal in dog cat pig
do
echo "HI, ${animal}"
done
执行：
[[email protected] sh]$ sh for.sh HI, dog HI, cat HI, pig [[email protected] sh]$
例：当前目录文件
#!/bin/bash
# desc : for loop
filelist=$(ls)
for filename in $filelist
do
echo $filename
done
5. for数值循环
for数值循环，适用于循环数值计算。
语法
for (( 初始值; 限制值; 步长))
do
// do something
done
例：
#!/bin/bash
# desc : for loop
sum=0
for (( i=0; i<=100; i++ ))
do
sum=$(($sum+$i))
done
echo "sum is : " $sum
地址：http://blog.csdn.net/yonggang7/article/details/40679701
时间： 2024-10-11 08:40:58