What are linux commands and dos commands

Linux commands are commands for managing Linux systems. There are two types of them in the system: 1. Built-in Shell commands, which are recognized by the shell program and run inside the shell program. They are executed when the system starts. Transferred into the memory, it is resident in the memory; 2. External commands (file system commands) are programs outside the bash shell. DOS command refers to the command of DOS operating system, which is a kind of disk-oriented operation command, mainly including directory operation commands, disk operation commands, file operation commands and other commands.

The operating environment of this tutorial: linux7.3&&windows10 system, Dell G3 computer.

What is the linux command?

The linux command is a command for managing the Linux system. For the Linux system, whether it is the central processor, memory, disk drive, keyboard, mouse, or user, they are all files. The commands for Linux system management are the core of its normal operation, similar to the previous DOS commands.

There are two types of Linux commands in the system: built-in Shell commands (built-in commands) and Linux commands (external commands).

• The built-in commands are transferred into the memory when the system starts. They are resident in the memory, so the execution efficiency is high.

• External commands are software functions of the system, which are read from the hard disk into the memory when the user needs them.

1. External commands

External commands are also called file system commands. They are programs other than the bash shell. They are not part of the shell. part. External commands are typically located in /bin, /usr/bin, /sbin, or /usr/sbin. External commands are the utility part of the Linux system. Because the functions of utility programs are usually relatively powerful, the amount of programs they contain will also be large. When the system is loaded, they are not loaded into the memory together with the system, but when needed. Only then will it be called into memory.

Usually the entity of the external command is not included in the shell, but its command execution process is controlled by the shell program. The shell program manages the path search, loading and storage of external command execution, and controls the execution of commands. External commands are installed additionally outside of bash, usually placed in /bin, /usr/bin, /sbin, /usr/sbin... etc. You can use the "echo

$PATH" command to view the storage path of external commands, such as: ls, vi, etc.

2. Built-in commands

The internal commands are actually part of the shell program, which contain some relatively simple Linux system commands, which are recognized by the shell program. And complete the operation inside the shell program. Usually when the Linux system is loaded and run, the shell is loaded and resides in the system memory.

Internal commands are written in the bash source code, and their execution speed is faster than external commands, because parsing the internal command shell does not require the creation of a child process. For example: exit, history, cd, echo, etc.

Explanation

The pwd command is a special command with two versions, one is a built-in command and the other is an external command.

3. Distinguish between built-in commands and external commands

Syntax

type command

Case

We use the type command to check the cd command is Internal command or external command, the specific command is as follows:

type cd

After running, the terminal output is as follows:

We see that the output cd is a built-in command , Now, we use the type command again to check whether the ps command is a built-in command or an external command. The specific command is as follows:

type ps

After running, the terminal output is as follows:

We see that the location of the ps command is output, that is, it indicates that the ps command is an external command.

#What is the dos command?

DOS command, a computer term, refers to the command of the DOS operating system, which is a disk-oriented operation command. , mainly including directory operation commands, disk operation commands, file operation commands and other commands.

Commonly used operating systems include windows 10, windows 7, etc., all of which have graphical interfaces. The operating system people used before these systems was DOS.

The dos command is actually similar to the function we usually use the mouse to click. The earliest computers did not have a mouse and a graphical interface, and they were all executed by entering commands. The graphical interface is used because the operation is more intuitive and concise, and it is popularized quickly.

1. How to use dos command

In the window system, press windows R and enter cmd to enter dos, as follows:

Among them, C:\User\***\ represents the current directory location (that is, the folder), and you can enter the command later.

2. Introduction to basic dos commands

Switch directory

cd Space the directory address to go to the folder you want to go to ( Absolute address)

# If you want to go to the folder under the current folder, you can use cd space folder name

If you want to change the drive letter, from drive C to drive D, you can directly enter D: to

View the folder contents

dir Space folder address, you can view the contents of the specified folder. If you do not add the folder address later, the content contained in the current folder will be viewed by default.

md command and rd command

are the abbreviations of make dictionary and remove dictionary, which are to create folders and delete folders. The syntax is the same.

##If you directly md the folder name, just By default, a new folder is created in the current directory. It is worth mentioning that md D:\Study\123, there is no "Study" folder in the D drive. This command will create a new "Study" folder on the D drive, and then create a new "123" file under the "Study folder" folder. And the rd D:\learning\123 command will only delete the "123" folder.

ping command

ping space target ip (or url) that is You can check the network status between the local machine and the target.

It is worth mentioning that ping url will resolve the target’s IP address. As shown above, after pinging the Toutiao URL, the IP address is parsed. This is a very important part of information collection during hacker penetration testing (of course, there are also techniques to fake this IP, and there are also techniques to bypass the fake IP. These are all (More details later).

Dos commands are very rich. It can be said that if you can operate dos skillfully, you can completely abandon the mouse. There is a lot of information on the Internet for more commands. It is recommended here to prepare a complete collection of dos commands and consult them at any time. When you need to simply operate the computer, check the usage at any time and use dos commands instead of mouse operations. Use dos commands more often, and you will gradually become proficient in using them.

3. Batch file

If we need to execute multiple commands at once, we can write multiple commands in a text file, change the file suffix name to .bat, save it, and then execute the file, the computer will execute them one by one according to the order. Complete the command execution. For example:

Execute this file, the computer will create a new "123" under the "Learning" folder folder, and then delete it. This is actually equivalent to using the dos command to write a script. The more dos commands you know, the richer the scripts you can write will be. You can also write some spoof viruses, for example :

shutdown -s -t 7200; in this command, shutdown -s represents the shutdown command, -t represents the time, and the unit of 7200 is seconds. It means automatic shutdown after 2 hours. As shown in the figure:

After entering this command, the computer reminded me that the computer is about to shut down.

Enter This command is cancelled.

Then if we write this command to the batch file, the time will be changed to 2 minutes. And put this file into the self-starting folder of a friend's computer (friends who can afford to joke, be careful not to get beaten up, hahaha). What will happen? As soon as the other party turns on the computer, the file will be automatically executed, and the computer will prompt that the computer will automatically shut down in 2 minutes. If he doesn't know the dos command, I don't know how to cancel it. Then his computer is useless? Another friendly reminder: be careful of getting beaten!

Related recommendations: "Linux Video Tutorial"

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