Getting Started with Shell Scripting-7

Shell echo command

Shell's echo command is similar to PHP's echo command, both of which are used for string output . Command format: echo string

You can use echo for more sophisticated output format control.

1. Display a normal string:  echo "It is a test" , the double quotes here can be completely omitted,

The following command has the same effect as the above example: echo It is a test

2. Display escape characters : echo "\"It is a test\"" , the result will be: "It is a test" , also, double quotes can be omitted.

 Remarks: \" \": Transfer a pair of "" symbols.

3. Display variables: The read command reads a line from standard input and assigns the value of each field of the input line to a shell variable

#!/bin/sh
read name 
echo "$name It is a test"

以上代码保存为 test.sh，name 接收标准输入的变量，结果将是:
[root@www ~]# sh test.sh
OK                     #标准输入
OK It is a test        #输出

4. Display newline: Note: echo -e

echo -e "OK! \n" # -e 开启转义
echo "It it a test"

输出结果：
OK!
               -- 备注:(有一空行)
It it a test

5. Display does not wrap: Note: echo -e

#!/bin/sh
echo -e "OK! \c" # -e 开启转义 \c 不换行
echo "It is a test"

输出结果：
OK! It is a test

6. The display result is directed to the file:  echo "It is a test" > myfile; (the first contact with this operation)

7. Output the string as it is, without escaping or taking variables (with single quotes):

echo '$name\"'
输出结果：
$name\"

8. Display the command execution result:

echo `date`

注意： 这里使用的是反引号 `, 而不是单引号 '。
结果将显示当前日期
2018年 3月11日 星期日 11时57分18秒 CST

Remark 1: String summary of echo output:

===================================================== ================
             Can reference variables | Can reference transfer characters | Can reference text format characters (such as line breaks, tabs)

single quote | no | no | no

double quotes | can | can | can

no quotes | can | can | no                          
=========================================== ===========================

Remarks 2. The read command is related:

The read command receives the input parameters one by one, and each phrase needs to be separated by a space; if the number of input phrases is greater than the required number of parameters, the extra phrases will be received as the last parameter as a whole.

The test file test.sh code is as follows:

read firstStr secondStr
echo "第一个参数:$firstStr; 第二个参数:$secondStr"

执行测试：
$ sh test.sh 
一 二 三 四
第一个参数:一; 第二个参数:二 三 四

Example, file test.sh:

read -p "请输入一段文字:" -n 6 -t 5 -s password
echo "\npassword is $password"

Parameter Description:

•  -p  enter prompt text
•  -n  input character length limit (up to 6 digits, automatic end)
•  -t  input time limit
•  -s  hide input

$ sh test.sh 
请输入一段文字:
password is asdfgh