Shulou(Shulou.com)06/01 Report--

This article introduces the "Linux shell script string variable splicing and assignment method" related knowledge, in the actual case operation process, many people will encounter such a dilemma, then let the editor lead you to learn how to deal with these situations! I hope you can read it carefully and be able to achieve something!

1. String stitching shell script can concatenate strings and assign the stitched value to another variable. The following figure shows several examples of string stitching for your reference.

#! / bin/bash a = "123" # define a variable as "123" b = "456" # define b variable as "456" first=$a$b # the first way to concatenate strings: directly take 2 values Concatenate the variable value echo $first second= "$aqb" # the second way to concatenate the string: add the string echo $second third= "${a} ${b}" # to the outermost of the two variable values: the third way is to concatenate the string: similar to the second, add ${} to the variable value. When echo $third 123456789101112 executes the above script, you can see the execution result of the script. The results of the three methods are the same. The above three kinds of strings can be concatenated:

123456 123456 123456 1232. We know that single quotation marks and double quotation marks have a special meaning in shell, but how to define a string so that the value of the string itself contains double quotation marks or single quotation marks? the following code gives an example:

#! / bin/bash a = "\"\ "b =" 'centering' "" 'dwindling' echo $an echo $b echo $c echo $d 123456789 execute the above script, and we can see the execution result of the script:

The value of variable an is 2 double quotation marks, the value of variable b is 3 single quotation marks, the value of variable c is 2 single quotation marks, and the value of variable d is empty 1234. We also have a rough understanding of how to define a string with a value of double quotation marks or single quotation marks. Let's share my summary of technical knowledge:

There are two ways to define a string whose value is double quotation marks: 1.1 when defining a variable, use double quotation marks in the outermost layer, and use * * inside the double quotation marks to escape the double quotation marks, similar to the definition of the variable a. 1.2 when defining variables, use single quotation marks * * at the outermost layer and write double quotation marks directly inside the single quotation marks to define them, similar to the way variable c is defined.

The string method that defines the value as single quotation marks: use double quotation marks at the outermost layer and write single quotation marks directly inside the double quotation marks to define them, similar to the way the variable b is defined.

The above are just some of the knowledge points I have summarized. There must be some omissions or other methods. You are welcome to add. In fact, as to why this happens, I think the fundamental reason is that single quotation marks and double quotation marks play a different role in shell scripts. People who are interested can do Baidu on their own, and it is the difference between the two that leads to the above situation.

3. The difference between using single quotation marks and double quotation marks in variable values shell in single quotation marks and double quotation marks leads to the difference in values between single quotation marks and double quotation mark variables. let's first look at an example to explain the difference between the two:

#! / bin/bash name= "test" axiom'{"name": $name, "age": "45"}'b = "{" name ": $name," age ":" 45 "}" echo $an echo $b 123456789101112 execute the above shell script, and you can see the output:

{"name": $name, "age": "45"} # this is the value of a {name:test, age:45} # this is the value of b 12 through the above execution results, we can see the following problems:

The only difference between the definition of variable an and that of variable b is that an is single quotation mark and b is double quotation mark.

The value of variable a does not take out the value of the name variable, and variable b takes out the value of name.

The attribute names defined in variable an are all in double quotation marks (for example: "name"), and the attribute names defined by the value of variable b are not in double quotation marks (for example: name)

So how to solve the second and third problems mentioned above? first of all, let's look at the second problem. Here is one of my solutions:

In the string defined by single quotation marks, if you want to get the value of the variable, you need to add another layer of single quotation marks to the value of the variable.

Let's modify the definition of the previous variable an and give an example to illustrate the results.

#! / bin/bash name= "test" axiom'{"name":'$name',-- > here adds an extra layer of single quotation marks "age": "45"}'b = "{" name ": $name," age ":" 45 "}" echo $an echo $b 123456789101112 to execute the above result again, and we can see the execution result:

{"name": test, "age": "45"} {name:test, age:45} 12 you can see the result of the execution. In the variable a, the value of the variable name is indeed taken out and assigned.

Next, let's look at the third question, which is how to put double quotation marks on the attribute name of variable B. the solution to this problem is similar to how to define a string whose value is double quotation marks or single quotation marks in the second section. Here is my solution: using escaped characters. Here is my example:

Name= "test" axiom'{"name":'$name',-- > here adds an extra layer of single quotation marks to the definition of a: "age": "45"}'b = "{"\ "name\": $name,-> the double quotation marks of each attribute value are appended with the escape character "\" age\ ":"\ "45\"} "echo $an echo $b 1234567891011 to execute the above results We can see that the implementation result is:

{"name": test, "age": "45"} {"name": test, "age": "45"} 12 you can see that the values of the two are consistent, and we can draw the following conclusions:

Although the two achieve the same function, it is found that the definition of double quotation marks is more tedious, and the way of using single quotation marks is relatively simple.

When using single quotation marks, it is important to note that if you want to take the value of a variable, add single quotation marks to the value of the variable to get the value of the variable.

When using single quotation mark definition, if you want to display double quotation marks properly, you need to use escape characters to define double quotation marks.

This is the end of the content of "the method of concatenation and assignment of shell script string variables under Linux". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.