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  • Linux Shell脚本编程while语句

    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 3
    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 &
    [1] 12867
    #!/bin/bash
    while true
    do
        uptime >> log.txt
        sleep 3
    done
    ghostwu@dev:~/linux/shell/flow_control$ tail -f log.txt
     06:14:32 up 33 min,  1 user,  load average: 0.33, 0.35, 0.32
     06:14:35 up 33 min,  1 user,  load average: 0.33, 0.35, 0.32
     06:14:38 up 33 min,  1 user,  load average: 0.31, 0.34, 0
    ...
    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
    [1]+  Stopped                 sh while.sh
    ghostwu@dev:~/linux/shell/flow_control$ jobs
    [1]+  Stopped                 sh while.sh
    ghostwu@dev:~/linux/shell/flow_control$ bg
    [1]+ sh while.sh &
    ghostwu@dev:~/linux/shell/flow_control$ jobs
    [1]+  Running                 sh while.sh &
    ghostwu@dev:~/linux/shell/flow_control$ sh while.sh &
    [2] 13411
    ghostwu@dev:~/linux/shell/flow_control$ jobs
    [1]-  Running                 sh while.sh &
    [2]+  Running                 sh while.sh &
    ghostwu@dev:~/linux/shell/flow_control$ fg
    sh while.sh
    ^Z
    [2]+  Stopped                 sh while.sh
    ghostwu@dev:~/linux/shell/flow_control$ bg
    [2]+ sh while.sh &
    ghostwu@dev:~/linux/shell/flow_control$ jobs
    [1]-  Running                 sh while.sh &
    [2]+  Running                 sh while.sh &
     4,用while循环打印0, 1, 2, 3, 4
    #!/bin/bash
    i=0
    while [ $i -lt 5 ]
    do
        echo $i
        (( i++ ))
    done
    两个中括号也可以
    #!/bin/bash
    i=0
    while [[ $i -lt 5 ]]
    do
        echo $i
        (( i++ ))
    done
    还可以用计算表达式
    #!/bin/bash
    i=0
    while (( i < 5 ))
    do
        echo $i
        (( i++ ))
    done
    5,计算1....100的和
    ghostwu@dev:~/linux/shell/flow_control$ sh sum.sh
    1+2+3..+100=5050
    ghostwu@dev:~/linux/shell/flow_control$ cat sum.sh
    #!/bin/bash
    i=1
    while (( i <= 100 ))
    do
        (( sum = sum + i ))
        (( i++ ))
    done
    echo "1+2+3..+100="${sum}
     6,猜数字
    #!/usr/bin/bash
    sum=$((RANDOM%51))
    echo "需要你猜的数是:"$sum
    sleep 1
    echo "请输入1-50之间的数,开始猜吧!"
    count=0
    function type_num(){
        read -p "请输入一个数吧:" n
        expr $n + 1 &>/dev/null
        if [ $? -ne 0 ]; 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 3 ]; then
                echo "你太厉害了"
            elif [ $count -ge 3 -a $count -lt 6 ]; then
                echo "还是不错的,加油"
            else
                echo "你有点水啊"
            fi
            exit 0
        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
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  • 原文地址:https://www.cnblogs.com/ect123/p/11798387.html
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