shell scripts学习(四)

循环(loop)

1. while......do.....done循环

语法格式:

while [ condition ]#continue为真的时候开始循环,假的时候停止循环

do

程序段

done

ex

[root@linux ~]# vim sh12.sh

#!/bin/bash

PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin

export PATH

while [ "$yn" != "yes" ] && [ "$yn" != "YES" ]

do

read -p "Please input yes/YES to stop this program:" yn

done

2. until [ continue ] #--------------->continue为假的时候开始循环,真的时候停止循环

do

程序段落

done

ex:

#!/bin/bash

PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin

export PATH

until [ "$yn" == "yes" ] && [ "$yn" == "YES" ]

do

read -p "Please input yes/YES to stop this program:" yn

done

3. for......do......done循环

数值方面循环语法格式:

for (( 初始值; 限制值; 执行步阶))

do

程序段

done

ex: ----------->执行从1累加到100

主要程序段:

s=0

for (( i=1; i<=100; i=i+1 ))

do

s=$(($s+$i))

done

echo "The result of '1+2+3+...+100' is==>$s"

非数值方面的循环语法格式

for variable in content1 content2 content3

do

程序段

done

说明:

第一次循环时,$variable的内容是content1

第二次循环时,$variable的内容是content2

第三次循环时,$variable的内容是content3

ex:

for animal in dog cat elephant

do

echo "There are ""$animal""s..."

done