Shell operation principle

One The architecture of the computer

understand shell Before operating the principle , Let's first understand the computer architecture

Bottom up ： Hardware -> Hardware drivers （ After the hardware is connected Relevant driver required Can be used ）-> operating system （ In essence, it is to better manage software and hardware Provide users with a good experience environment ）-> Software （ Graphical interface or instruction operation ）

In everyday life , We are linux Next or windows Next , Access the operating system through instructions or graphical interfaces , No direct access to operating system . But through the shell program .

Two Shell

shell Is one of the shell programs

Basic concepts ： A related concept based on operating system

in real life , There are many very professional things , We can't operate , Shell program is needed .
For example, go to the bank to deposit money , We only need simple operation , But bank staff need to do more background operations .

For example, drivers can only drive , But you don't need to understand the principle of cars and car repair

-> No one is required to participate in the relevant details

in other words , In everyday life , We go through shell Operating system , In essence, it is not a direct operation of the operating system . Instead, it interacts with the operating system through the shell program .

1 Why is there a shell

The most fundamental reason is that people cannot directly access the operating system .

Why can't people directly access the operating system ？

If you want to operate the operating system directly , What is the monitor , Where in the operating system , If you want to write data ,…… And other operation details , Care about these details is called direct access to the operating system . Very professional .

If you directly access the operating system , One side , High threshold for users , High operating cost , On the other hand , If the user makes a mistake , It will bring unsafe factors .

So we need to use outsourcing procedures

summary ：

1 ‘ people ‘ Not good at using the operating system

2 If you let people directly access the operating system , It can lead to problems

2 How do we access the operating system in our daily life

So how do we access the operating system ？ What is the graphical interface and instruction operation ？

Graphical interface and instruction operation are shell programs provided by the operating system . Mainly for command line parsing . It's a command line interpreter . Translate the user's commands to the core processing , At the same time, the results of the core processing will be returned to the user .

The meaning of shell program ：

1 Intermediate software layer for user and operating system interaction

 2 It can protect the operating system to a certain extent ： The operating system can reject the user's request , The shell will also deny users

How to query shell programs through commands ？

 

The shell program is carried out through subroutines .

Bash It's a dead circle front [] The hint is bash Tips for cycling Prompt the user to keep typing

Bash shell What is the difference between different shell programs ？

Shell bash All have certain functions shell Is a general term for all shell programs .