流程控制_for循环与select

一，语法

1，shell风格的for循环

fou循环 又叫取值循环
语法：
for x in 参数值1 参数值2 参数值3
do
...
done

例1）：
[root@m01~]# vim /script/for1.sh
#!/bin/bash
for i in 111 222 "abx"
do
    echo "hello"
done

执行：
[root@m01~]# chmod +x /script/for1.sh
[root@m01~]# /script/for1.sh
hello
hello
hello


例2）：加上了参数
[root@m01~]# vim /script/for1.sh
#!/bin/bash
for i in 111 222 "abx"
do
    echo "hello $i" 
done


[root@m01~]# /script/for1.sh
hello 111
hello 222
hello abx



例3）：
[root@m01~]# vim /script/for1.sh
#!/bin/bash
for i in `ls /root`
do
    echo "hello $i"
done



[root@m01~]# /script/for1.sh
hello 2
hello 3
hello 4
hello 8
hello ab



例4）：
[root@m01~]# vim /script/for1.sh
#!/bin/bash
for i in {1..4}
do
    echo "hello $i"
done
echo =====
for i in {a,c,z}
do
    echo "hello $i"
done




[root@m01~]# /script/for1.sh
hello 1
hello 2
hello 3
hello 4
=====
hello a
hello c
hello z

2，C风格的for循环

[root@m01~]# vim /script/for2.sh
#!/bin/bash
for ((i=1;i<4;i++))
do
    echo $i
done



[root@m01~]# chmod +x /script/for2.sh
[root@m01~]# /script/for2.sh
1
2
3


##  i=1是初始值，i<4是条件，i++是语法无实际意义

3，continue和break

1) continue
[root@m01~]# vim /script/for3.sh
#!/bin/bash
for i in {1..5}
do
    if [ $i -eq 3 ];then
        continue
    fi
    echo $i
done



[root@m01~]# chmod +x /script/for3.sh
[root@m01~]# /script/for3.sh
1
2
4
5


2) break
[root@m01~]# vim /script/for3.sh
#!/bin/bash
for i in {1..5}
do
    if [ $i -eq 3 ];then
        break
    fi
    echo $i
done



[root@m01~]# /script/for3.sh
1
2

二，案例

1, ping 网通

[root@m01~]# vim /script/for4.sh
#!/bin/bash
for i in {1..100}
do
    (ping -c 10.0.0.$i &> /dev/null
    if [ $? -eq 0 ];then
        echo "10.0.0.$i is up"
    else
        echo "10.0.0.$i is down"
    fi) &
done


[root@m01~]# 10.0.0.7 is down
10.0.0.10 is down
10.0.0.5 is down
10.0.0.6 is down
10.0.0.1 is down
10.0.0.2 is down
10.0.0.3 is down
10.0.0.8 is down
10.0.0.9 is down
10.0.0.4 is down

2,计算文件夹里各类文件数量

[root@m01~]# vim /script/for5.sh
#!/bin/bash
dir="/etc"
file=0
link=0
directory=0
others=0
for i in `ls $dir`
do
    if [ -f "$dir/$i" ];then
        let file++
    elif [ -L "$dir/$i" ];then
        let link++
    elif [ -d "$dir/$i" ];then
        let directory++
    else
        let others++
    fi
done

echo "普通文件数量为：$file"
echo "软连接文件数量为：$link"
echo "目录文件数量为：$directory"
echo "其他文件数量为：$others"


[root@m01~]# /script/for5.sh
普通文件数量为：109
软连接文件数量为：8
目录文件数量为：83
其他文件数量为：0


##注意，字符一定要加上双引号

三，select

用于交互式环境
1）
[root@m01~]# vim /script/select.sh
#!/bin/bash
PS3="输入编号："
select cho in {"退出","取款","转账","查询余额"}
do
    case $cho in
    "退出")
        break
        ;;
    "取款")
        echo "取款中"
        ;;
    "转账")
        echo "转账中"
        ;;
    "查询余额")
        echo "查询余额中"
        ;;
    esac
done



[root@m01~]# /script/select.sh
1) 退出
2) 取款
3) 转账
4) 查询余额
输入编号：2
取款中
输入编号：1






2）
[root@m01~]# vim /script/select.sh
#!/bin/bash
PS3="输入编号："
select cho in
do
    case $cho in
    "退出")
        break
        ;;
    "取款")
        echo "取款中"
        ;;
    "转账")
        echo "转账中"
        ;;
    "查询余额")
        echo "查询余额中"
        ;;
    esac
done



[root@m01~]# /script/select.sh 退出 取款 转账 查询余额
1) 退出
2) 取款
3) 转账
4) 查询余额
输入编号：3
转账中
输入编号：1