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

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

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

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

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

作者:海底苍鹰
地址:http://blog.51yip.com/shell/1132.html

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