shell循环，判断介绍，以及实例

shell的循环主要有3种，for，while，until

shell的分支判断主要有2种，if，case

 

一，for循环

#!/bin/bash

for file in $(ls /tmp/test/mytest |grep sh) //for in格式是shell for的基本格式，根js的for in类似
do //循环开始你就把它当成{
echo $file
done //循环结束你就把它当成}

for ((i=0;i<10;i++)) //注意是双小括号，由于受其他语言的影响，很容易搞错
do
echo -n $i
done

echo \ //输出换行

for i in 0 1 2 3 4 5 6 7 8 9
do
echo -n $i
done

echo \

for i in "0 1 2 3 4 5 6 7 8 9" //这个根上面是有区别的，这个循环只循环了一次，双引号里面只是一个变量
do
echo -n $i
done

exit 0

#!/bin/bash for file in $(ls /tmp/test/mytest |grep sh) //for in格式是shell for的基本格式，根js的for in类似 do //循环开始你就把它当成{ echo $file done //循环结束你就把它当成} for ((i=0;i<10;i++)) //注意是双小括号，由于受其他语言的影响，很容易搞错 do echo -n $i done echo \ //输出换行 for i in 0 1 2 3 4 5 6 7 8 9 do echo -n $i done echo \ for i in "0 1 2 3 4 5 6 7 8 9" //这个根上面是有区别的，这个循环只循环了一次，双引号里面只是一个变量 do echo -n $i done exit 0

 

二，while循环

#!/bin/bash
i=0
while ((i<10))
do
echo $i
((i += 1))
done

i=0
while [ $i -lt 10 ] //注意括号内侧二边的空格
do
echo $i
let "i+=1" //加1
done
exit 0

#!/bin/bash i=0 while ((i<10)) do echo $i ((i += 1)) done i=0 while [ $i -lt 10 ] //注意括号内侧二边的空格 do echo $i let "i+=1" //加1 done exit 0

三，until循环

#!/bin/bash

END_CONDITION=end
until [ "$var1" = "$END_CONDITION" ] //读取的变量根设定的变量相等时退出循环，不然永远循环
do
echo "Input variable #1 "
echo "($END_CONDITION to exit)"
read var1
echo "variable #1 = $var1"
echo
done
exit 0

#!/bin/bash END_CONDITION=end until [ "$var1" = "$END_CONDITION" ] //读取的变量根设定的变量相等时退出循环，不然永远循环 do echo "Input variable #1 " echo "($END_CONDITION to exit)" read var1 echo "variable #1 = $var1" echo done exit 0

四，if语句

#!/bin/bash

echo "Input a number #1 "
read num
echo "variable #1 = $num"

if [ $num -lt 60 ] //注意lt前面的-，很容易忘的
then
echo "you are not pass"
elif [ $num -lt 70 ] && [ $num -ge 60 ] //多个条件的判断
then
echo "pass"
elif [[ $num -lt 85 && $num -ge 70 ]] //如果放在一起，要注意是双方括号，不要写成[ $num -lt 85 && $num -ge 70 ]
then
echo "good"
elif (( $num <= 100 )) && (( $num >= 85 )) //对于有语言基础的人来说，这种写法让人觉得很舒服，不要忘了是双小括号
then
echo "very good"
else
echo "num is wrong"
fi //if要有结束标签的，根XML很像,不闭合，就报错

exit 0

#!/bin/bash echo "Input a number #1 " read num echo "variable #1 = $num" if [ $num -lt 60 ] //注意lt前面的-，很容易忘的 then echo "you are not pass" elif [ $num -lt 70 ] && [ $num -ge 60 ] //多个条件的判断 then echo "pass" elif [[ $num -lt 85 && $num -ge 70 ]] //如果放在一起，要注意是双方括号，不要写成[ $num -lt 85 && $num -ge 70 ] then echo "good" elif (( $num <= 100 )) && (( $num >= 85 )) //对于有语言基础的人来说，这种写法让人觉得很舒服，不要忘了是双小括号 then echo "very good" else echo "num is wrong" fi //if要有结束标签的，根XML很像,不闭合，就报错 exit 0

 

五，case语句

#!/bin/sh
case $1 in
start)
echo "start ok"
;; //注意一点，要注意是双分号
stop)
echo "stop ok"
;;
restart)
echo "restart ok"
;;
*)
echo "no param"
;;
esac //注意闭合标签
exit 0

[root@krlcgcms01 forif]# sh c1.sh stop
stop ok