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中

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  "\ntimeout\n"
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
     1this is test text.
     2this is second line.
     3Hello world
     4C# Main
     5Python
# 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