基本用法

? ? read命令主要用於從標準輸入讀取內容或從文件中讀取內容，並把信息保存到變量中。其常用用法如下所示：

read [選項] [文件]

用法示例

1、從標準輸入讀入

[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、指定顯示信息從標準輸入讀入

[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是一次可以接受多個參數的，如下所示：

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

但需要註意的事項如下：

• 如果輸入的數據少於變量個數，則多余的變量不會獲取到數據，即變量值為空
• 如果輸入的數據多於變量個數，則超出的數據將全部賦給最後一個變量
• 如果在read命令後面沒有定義任何變量，腳本在執行時，如果用戶輸入數據，此時數據則保存到環境變量$REPLY中

3、指定超時時間

[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、從指定文件中讀取內容

[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選項
[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

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Linux 基礎教程 45-read命令