zoukankan      html  css  js  c++  java
  • Linux 基础教程 45-read命令

    基本用法

        read命令主要用于从标准输入读取内容或从文件中读取内容,并把信息保存到变量中。其常用用法如下所示:

    read [选项] [文件]
    
    选项 解释
    -a array 将内容读取到数值中,变量默认为数组且以空格做为分割符
    -d delimiter 遇到指定的字符即停止读取
    -n nchars 指定最多可以读入的字符数,即定义输入文本的长度
    -r 屏蔽转义符
    -p prompt 显示提示信息
    -s 静默模式,在输入字符时不在终端中显示,常用于密码输入等
    -t timeout 指定超时时间
    -u FD 从文件描述符中读入,该FD可以由exec开启

    用法示例

    1、从标准输入读入

    [root@localhost test]# cat read.sh
    #!/bin/bash
    echo -n "Please input your name:"
    read name
    echo "Hello $name"
    [root@localhost test]# bash read.sh
    Please input your name:Jack
    Hello Jack
    

    2、指定显示信息从标准输入读入

    [root@localhost test]# cat read.sh
    #!/bin/bash
    # echo -n "Please input your name:"
    read -p "Please input your name:" name
    # read name
    echo "Hello $name"
    [root@localhost test]# bash read.sh
    Please input your name:Jack
    Hello Jack
    

    在以上示例中,read是一次可以接受多个参数的,如下所示:

    read -p "Please input your name:" firstName secondName lastName
    

    但需要注意的事项如下:

    • 如果输入的数据少于变量个数,则多余的变量不会获取到数据,即变量值为空
    • 如果输入的数据多于变量个数,则超出的数据将全部赋给最后一个变量
    • 如果在read命令后面没有定义任何变量,脚本在执行时,如果用户输入数据,此时数据则保存到环境变量$REPLY

    3、指定超时时间

    [root@localhost test]# cat read.sh
    #!/bin/bash
    if read -t 3 -p "Please input your name:" firstName secondName lastName
    then
      echo "variable is $firstName - $secondName - $lastName"
    else
       echo -e  "
    timeout
    "
    fi
    [root@localhost test]# bash read.sh
    Please input your name:
    timeout
    

    4、从指定文件中读取内容

    [root@localhost test]# cat -n test.txt
         1	this is test text.
         2	this is second line.
         3	Hello world
         4	C# Main
         5	Python
    # 使用-u选项
    [root@localhost test]# cat readtest.sh
    #!/bin/bash
    exec 5< ~/test/test.txt
    count=0
    while read -u 5 var
    do
     let count=$count+1
     echo "Line $count is $var"
    done
    echo "Total line count is $count"
    exec 5<&-
    [root@localhost test]# bash readtest.sh
    Line 1 is this is test text.
    Line 2 is this is second line.
    Line 3 is Hello world
    Line 4 is C# Main
    Line 5 is Python
    Total line count is 5
    # 使用管道
    [root@localhost test]# cat readtest.sh
    #!/bin/bash
    count=1
    cat ~/test/test.txt |  while read line
    do
     echo "Current line $count - $line "
     let count=$count+1
    done
    echo "Total line count is $count"
    [root@localhost test]# bash readtest.sh
    Current line 1 - this is test text.
    Current line 2 - this is second line.
    Current line 3 - Hello world
    Current line 4 - C# Main
    Current line 5 - Python
    Total line count is 1
    # 使用重定向
    [root@localhost test]# cat readtest.sh
    #!/bin/bash
    count=0
    while read line
    do
     let count=$count+1
     echo "Current line $count - $line "
    done < ~/test/test.txt
    echo "Total line count is $count"
    [root@localhost test]# bash readtest.sh
    Current line 1 - this is test text.
    Current line 2 - this is second line.
    Current line 3 - Hello world
    Current line 4 - C# Main
    Current line 5 - Python
    Total line count is 5
    

    本文同步在微信订阅号上发布,如各位小伙伴们喜欢我的文章,也可以关注我的微信订阅号:woaitest,或扫描下面的二维码添加关注:
    MyQRCode.jpg

  • 相关阅读:
    字符串替换
    字符串查找
    字符串比较
    字节与字符串相互转换
    1365. How Many Numbers Are Smaller Than the Current Number
    1486. XOR Operation in an Array
    1431. Kids With the Greatest Number of Candies
    1470. Shuffle the Array
    1480. Running Sum of 1d Array
    【STM32H7教程】第56章 STM32H7的DMA2D应用之刷色块,位图和Alpha混合
  • 原文地址:https://www.cnblogs.com/surpassme/p/9576464.html
Copyright © 2011-2022 走看看