Linux Shell脚本编程while语句案例

1，每隔3秒，打印一次系统负载

#!/bin/bash

while true
do
    uptime
    sleep
done

2，把监控结果保存到文件，在后台执行，然后用tail -f监控文件变化

ghostwu@dev:~/linux/shell/flow_control$ sh while.sh &
[] 

#!/bin/bash

while true
do
    uptime >> log.txt
    sleep
done

ghostwu@dev:~/linux/shell/flow_control$ tail -f log.txt
 :: up  min,   user,  load average: 0.33, 0.35, 0.32
 :: up  min,   user,  load average: 0.33, 0.35, 0.32
 :: up  min,   user,  load average: 0.31, 0.34,
...

3，进程调度相关命令

fg: 把当前脚本或者任务放到前台执行。如果指定某个任务：fg 任务编号。 任务编号通过jobs查询

bg: 把任务放到后台执行

jobs:查看当前执行的脚本或者任务

ctrl+z:暂停执行当前的脚本

sh while1.sh & : 加上&，表示后台执行脚本

ghostwu@dev:~/linux/shell/flow_control$ fg
sh while.sh
^Z
[]+  Stopped                 sh while.sh
ghostwu@dev:~/linux/shell/flow_control$ jobs
[]+  Stopped                 sh while.sh
ghostwu@dev:~/linux/shell/flow_control$ bg
[]+ sh while.sh &
ghostwu@dev:~/linux/shell/flow_control$ jobs
[]+  Running                 sh while.sh &
ghostwu@dev:~/linux/shell/flow_control$ sh while.sh &
[]
ghostwu@dev:~/linux/shell/flow_control$ jobs
[]-  Running                 sh while.sh &
[]+  Running                 sh while.sh &
ghostwu@dev:~/linux/shell/flow_control$ fg
sh while.sh
^Z
[]+  Stopped                 sh while.sh
ghostwu@dev:~/linux/shell/flow_control$ bg
[]+ sh while.sh &
ghostwu@dev:~/linux/shell/flow_control$ jobs
[]-  Running                 sh while.sh &
[]+  Running                 sh while.sh &

4，用while循环打印0, 1, 2, 3, 4

#!/bin/bash
i=
while [ $i -lt  ]
do
    echo $i
    (( i++ ))
done

两个中括号也可以

#!/bin/bash
i=
while [[ $i -lt  ]]
do
    echo $i
    (( i++ ))
done

还可以用计算表达式

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

5，计算1....100的和

ghostwu@dev:~/linux/shell/flow_control$ sh sum.sh
++..+=
ghostwu@dev:~/linux/shell/flow_control$ cat sum.sh
#!/bin/bash

i=
sum=
while (( i <=  ))
do
    (( sum = sum + i ))
    (( i++ ))
done
echo "1+2+3..+100="${sum}

6，猜数字

#!/usr/bin/bash

sum=$((RANDOM%))

echo "需要你猜的数是:"$sum

sleep 

echo "请输入1-50之间的数,开始猜吧!"

count=

function type_num(){
    read -p "请输入一个数吧:" n
    expr $n +  &>/dev/null
    if [ $? -ne  ]; then
        echo "请输入一个数字"
        type_num
    fi
}

function guess(){
    (( count++ ))
    if [ $n -eq $sum ]; then
        echo "你猜中了,你的次数是:"${count}
        if [ $count -lt  ]; then
            echo "你太厉害了"
        elif [ $count -ge  -a $count -lt  ]; then
            echo "还是不错的,加油"
        else
            echo "你有点水啊"
        fi
        exit
    elif [ $n -gt $sum ]; then
        echo "猜大了"
        type_num
    else
        echo "猜小了"
        type_num
    fi
}

function main(){
    type_num
    while true
    do
        guess
    done
}

main