I met a shell script

Foreword: Now more and more individuals and enterprises are using the linux operating system, so some basic commands are understood.So if you want to reduce manual input, can you?The answer is yes.What method to use? The answer is to write a script. The most convenient is the shell script that comes with Linux.Next, follow me, recognize, learn and use the shell to achieve basic operations, let's get started!

Since it is a script, there must be an interpreter.There are many shell interpreters, we can view it with the following command

cat /etc/shells

The result is shown below

We can use one of them. How to use it will be mentioned later

Begin editing the script below and specify the interpreter

Using commands

vi test1.sh

Enter inside to edit

#!/bin/bashecho "hello world"

Where #!/bin/bash is the role of the specified interpreter

You can execute it, but you must give this file an execute permission before executing it

chmod +x test1.sh

Next execution

./test1.sh

This is the simplest shell script, just output hello world

In the future, you may come into contact more with $, so I will list some common combinations and meanings of it here, and I will use them when I encounter them in the future

• $0: The shell's command itself

• $1 to 9: the first parameter of Shell

• $? : show the execution of the last command

• $#: the number of arguments passed to the script

• $$: The current process ID number of the script running

• $*: Displays all parameters passed to the script as a single string

• $!: ID number of the last process running in the background

• $-: Displays the current options used by the shell

You can try to tap these commands to output, I will show you here first

echo $0

Some questions and answers

Q: Can I not specify an interpreter

Answer: Yes, if you don't specify it, then the default interpreter will be executed, that is, /bin/bash

Q: What is the default interpreter

Answer: You can use the following command

echo $SHEL

Q: Is there any other implementation method

Answer: Yes, there are two other ways, everyone can follow their own habits

The first is to execute the interpreter, and the file name is used as a parameter

/bin/bash test1.sh

In this way, there is no need to specify the interpreter in the file, because the interpreter is mainly executed

The second is the source command

source test1.sh

The above two execution methods do not need to assign an execution permission to the script, because the execution is not the file itself

Q: Is there any difference between these execution methods?

Answer: There is a difference. The source word can be understood as a sequential execution command. Now the final result is displayed. At the same time, the directory is the directory where the final execution is located. The other two words can be understood in this way. A new process is started.The current and execution environment is independent and has no effect on the current. You can take an example to see it

Create a new test2.sh file, and then the content is

cd /cd ~

Direct interpreter execution

sh test2.sh

Then pwd, you will find that the path has not changed

What about the source

source test2.sh

At this time, you will find that the path has changed, and the difference is already very clear

Q: Does my suffix have to be .sh?

Answer: No, in linux, all files do not have the concept of suffix name, they can have any name, the reason why we do this is to facilitate viewing and understanding

The above is about the basic content of shell scripting, and it will be updated continuously~