Linux Command Line notes (1), commandline

Linux Command Line notes (1), commandline
Yunduan CUI

Graphical user interfaces make easy tasks easy, while command line interfaces make difficult tasks possible

Part 1 learning Shell1. what is Shell?

Shell is a program for users to communicate with the operating system. It reads users' keyboard input and submits it to the operating system to execute corresponding commands. All linux systems support a shell called bash. Its full name is "Bourne Again SHell", and bash's predecessor is sh written by Steve Bourne.

When we use Shell, we actually need another program named terminal emulator to interact with shell, which is a common program called terminal. (You can select different shells for the terminal)

2. Cruise

Cruise linux file system, common commands:
* Ls: displays the files in the current working directory.
* Cd: change the working directory
* Pwd: displays the name of the current working directory.

Linux uses a shuide-based file system. Unlike windows, which regards every disk as an independent file system, linux always maintains a file system.

When using the cd command, cd directly returns the default directory, cd ~ User_name returns the user's default directory, and cd-returns the previous directory. In addition, it indicates the current directory and... indicates the parent directory.

By default, hidden files are not displayed when the ls command is used.

3. Explore files

With more tips of ls, ls supports displaying the content of a specified folder, and also supports displaying the content of two folders. Use ls-l to display the long format of the file. -T can sort files according to the change time. Other useful options:
*-F special note/after the folder name-r reverse display in the alphabet-S sort by file size-t sort by change time

About the long format of a file

The first column is the first letter of the file access permission: -represents regular file d represents folder l represents the permissions of the file owner for the next three letters of the connected file, and the next three letters for the same group members, the last three permissions are for everyone. r indicates reading w indicates writing x indicates executing the second column to indicate the number of files (for folders, the file is naturally 1) the third column indicates the owner. The fourth column indicates the group. The fifth column indicates the file size (bytes). The sixth column is the creation date. The seventh column is the file name.

Determine the file type

Use the file command to determine the file type

Read File Content

Use the less command to read the file content. The operation after entering the content is as follows:
Page Up/B roll back one Page
Page Down/space to roll back one Page
Roll up/down arrows forward/back a row
G move to the end of the file
1 G/g move to the file header
/[Characters] Forward to [characters]
N find the next search Target
H Show Help
Q exit

The predecessor of less is more. The reason why the opposite name is used is becauseLess is more

Introduction to file systems

Directory Name	Introduction
/	Root directory
/Bin	Contains binaries program for storing the system
/Boot	Startup information, initialized RAM and hard disk images, and Linux Kernel
/Dev	Store drivers
/Etc	Stores system, program configuration files, and shell scripts.
/Home	The folder used by the user. Generally, the user only needs to work in this file.
/Lib	The library files used by all programs (a bit like windows DLL files) are here
/Lost + found	This folder is only available in the formatted linux file system and can be used to restore partial files. Unless something bad happens, it is generally empty.
/Mnt	It only appears on the old linux and is used to store the drive of the mobile device.
/Opt	The optional programs are stored here, which generally stores the programs installed later by the user.
/Proc	This is a special folder. It is a virtual folder, which is equivalent to a peep hole to the Linux kernel. You can see from the files in it how the kernel looks at the current PC's
/Root	Root Account directory
/Sbin	Used by super users, including core system programs
/Tmp	Temporary File Storage
/Usr	Generally, the folder is the largest and contains all programs and files used by common users.
/Usr/bin	Stores installed linux executable files
/Usr/lib	Library files used by the user's installation files
/Usr/local	The programs installed by the user are usually installed here from the files compiled by the source code.
/Usr/sbin	Store the installed administrator Program
/Usr/share	Store files shared by programs in/usr/share
/Usr/share/doc	Generally, some packages that are installed contain documents. Put them here.
/Var	It is also used to store frequently changed files, such as user emails.
/Var/log	Store log files

Symbolic Links

A unique file form in Linux that can be connected to other files. It is also called soft link. It allows us to update the version of some components, because link can be used as a variable name.

4. Operation files and directories