Definition of common linux commands (Day 5) -- shell variable learning

Due to limited time, I can write this blog for up to 30 minutes. It is only used for study notes, and the content will be as clear as possible. If you are not clear about it, you can beat me!

Due to limited time, I can write this blog for up to 30 minutes. It is only used for study notes, and the content will be as clear as possible. If you are not clear about it, you can beat me!

Joke: Today's study is officially started.

Some commands in linux are in/bin, which can be used by general users. Some others can be used by Super users. This command is placed under/sbin.

However, some commands are directly built into bash and read directly into memory as the system starts. This can minimize the file index time and improve the system efficiency.

You can use the type command to view details. Type indicates the type. You can interpret the image as a demon mirror to see what the source of your nature is.

Let's take a look at the type command

In command execution, if a command is super long. . You can use \ (backslash) to wrap a line. Let's take a look at how to use it.

 

Variable functions in shell

What is the variable in the shell variable part? laruence is very careful, but he is also very embarrassed. Maybe some of the groups that laruence faces do not have the foundation for programming, so they are so detailed that they can be understood in this way.

The variables in shell are no different from those in PHP. It also requires fame. for example, if roverliang = 'roverliang is a good guy, 'the right half of the equal sign is assigned to the left as a value assignment statement. The call variables are surprisingly consistent with those in PHP. The $ operator is used to print the variables with echo. Echo $ roverliang; the result shows that roverliang is a good guy. Come on, everybody, verb. let's look at the figure.

Others are more like PHP. for example, the variable name cannot start with a number. Variables are not parsed in single quotes. variables are parsed in single quotes. Run the command with the command operator (the key on the left of the number 1. Use unset to delete famous variables.

In addition, variables also have variable scopes. For example, if we open the shell, the system will allocate a process to it. The variables we set in this process cannot enter the next process (you need to set them later ). Three processes display three variable scopes.

It took 50 minutes to write a blog within half an hour. I say that I only learn linux for one hour every day, but it is actually two hours. In the future, it will take some time to strictly control the time and I will not be able to learn mysql.

 

If the summary in this article is incorrect, please correct me.