2. Linux directory structure
Before talking about the Linux directory structure, you must first be clear that the difference between the Linux directory and the Windows directory may not be much different from the general operation experience, but it is completely different from their implementation mechanism. .
A difference is reflected in the relationship between directories and storage media (disk, memory, DVD, etc.). In the past, Windows has always been based on storage media, mainly drive letters (C drive, D drive...) and partitions. To achieve file management, and then the directory is below, the directory is not so important, and user files other than system files are placed anywhere in any directory. It doesn't matter much. Therefore, usually after Windows has been used for a period of time, the file directory on the disk will appear disorganized (except for a few users who are good at organizing). However, UNIX/Linux is just the opposite. UNIX is mainly based on directories, and Linux also inherits this excellent feature. Linux builds the entire system in the form of a tree-shaped directory structure, which can be understood as the skeleton of a user-operable operating system. Although essentially both the directory structure and the operating system kernel are stored on the disk, logically speaking, the Linux disk is "mounted" (mounted) on the directory, and each directory can not only use local disk partitions file system, you can also use a file system on the network. For example, a network file system (Network File System, NFS) server can be used to load a specific directory, etc.
1. FHS Standards
The directory structure of Linux is complex and complicated, and simple and simple. The complication is that because the normal operation of the system is based on the directory structure, for beginners, most of the directories in it do not know their function, whether it is important or not, especially for those who used to be heavy Windows users, they will struggle for a long time. , about where the software I installed is located. It's simple because most of the directory structure is prescriptive (FHS standard), dead, and when you get the hang of it, everything you do in it becomes orderly.
FHS (English: Filesystem Hierarchy Standard Chinese: Filesystem Hierarchy Standard), most Linux versions use this file organization form, FHS defines the purpose of each area in the system, the minimum required files and directories, and also gives Exception handling and conflict handling.
FHS defines two layers of specifications. The first layer is, / what file data should be placed in the following directories, such as /etc setting files should be placed, /bin and /sbin executable files should be placed, and so on.
The second level is defined for the subdirectories of these two directories /usr . /varFor example /var/log put system log files, /usr/share put shared data and so on.
If you don't understand this, you can try the most realistic and intuitive way, and execute the following command:
$ tree /
Regarding the FHS mentioned above, there is another very important content that you must understand. FHS is based on the experience of countless Linux users and developers in the past, and will be maintained and updated. FHS is based on the frequent use of the file system. And whether to allow users to change at will (note that it is not impossible, don't be afraid of these during the learning process), define the catalog as four interactive forms, as shown in the following table:
2. Directory path
path
Some people may not understand what this path refers to and what it is for. As the name suggests, a path is a route to where you are going. If you want to enter a specific directory or want to get a file in a directory (the directory itself is also a file), you have to use the path to find it.
You can use cd commands to switch directories. In Linux, it . means the current directory and ..the upper-level directory (note that . the files that start with are all hidden files, so these two directories must also be hidden, you You can use the ls -a command to view hidden files), - indicating the last directory, ～ usually the current user's home directory. Use the pwd command to get the current path (absolute path).
Enter the previous directory:
$ cd ..
into your home directory:
$ cd ~
# 或者 cd /home/<你的用户名> Use pwd to get the current path:
$ pwd
absolute path
Regarding the absolute path, simply put, it is the complete path starting from the root "/" directory and ending with the directory you want /usr/local/binto go usr to .localbin
relative path
The relative path is the path relative to your current directory. The relative path starts from the current directory . and ends with the directory you want to go to usr/local/bin. You may have noticed that the relative path we indicated does not actually add the one that represents the current directory . , but directly starts with the directory name, because this usr directory is / a subdirectory under the directory, you can omit this . (we will talk about a similar If it is the upper-level directory of the current directory, it needs to be used .. . For example, if your current directory is a home directory, the root directory should be expressed as ../../ , indicating the upper-level directory ( home directory) of the upper-level directory ( / directory). .
Below we take your homedirectory as the starting point, and enter the directory in the form of an absolute path and a relative path /usr/local/bin :
# absolute path $ cd /usr/local/bin # relative path $ cd ../../usr/local/bin
To enter a directory, you can use an absolute path or a relative path, so when should we choose the correct way to enter a directory? It's just a matter of intuition. You can use whichever one is convenient for you, instead of using only one. For example, suppose I am currently in a /usr/local/bin directory, and I want to enter the local directory of the previous level. Do you think it is cd .. convenient or cd /usr/local convenient to use? And if you want to enter the usr directory, then cd /usr it is more cd ../.. convenient.
Tip: During the process of directory switching, please use the Tab key to complete automatically to avoid input errors. Press twice in a row to Tab display all candidate results.
Third, the basic operation of Linux files
Create a new blank file
Use the touch command to create a blank file. Regarding the touch command, its main function is to change the timestamp of the existing file (for example, the last access time, the last modification time), but it only specifies a file name without adding any parameters. , you can create a blank file with the specified file name (will not overwrite the existing file with the same name). Of course, you can also specify the timestamp of the file at the same time. More about touch the usage of the command will be covered in the next lecture on file search.
Create a blank file named test, because there is no permission in other directories, so you need to cd ~ switch back to the user's /home/shiyanlou directory first:
$ cd ~
$ touch test new directory
Use the mkdir(make directories) command to create an empty directory, or to specify the permission attribute to create the directory at the same time.
Create an empty directory named "mydir":
$ mkdir mydir
Using the -p parameters, create the parent directory at the same time (if the parent directory does not exist), as follows, we create a multi-level directory at the same time (this is very useful when installing software and configuring the installation path):
$ mkdir -p father/son/grandson
The following directory path can also be expressed as an absolute path.
copy file
Use the cp(copy) command to copy a file to the specified directory.
Copy the "test" file created earlier into the "/home/shiyanlou/father/son/grandson" directory:
$ cp test father/son/grandson
Isn't it very convenient? If you are in the graphical interface, you need to copy the file in the source directory first, and then go to the destination directory to paste the file, and the command line operation steps are in place in one step.
copy directory
If you use the cp command to copy a directory directly, the following error will occur:
To successfully copy a directory, you need to add -r or -R parameters, which means recursive copying, which means that it is a bit "connected with nine families":
$ cp -r father family
Delete Files
Use the rm(remove files or directories) command to remove a file:
$ rm test
Sometimes you will encounter a file that you want to delete with read-only permissions. Using rm delete directly will display a prompt, as follows:
If you want to ignore this prompt and delete the file directly, you can use the -f parameter to force deletion:
$ rm -f test
delete directory
Like copying a directory, to delete a directory, you also need to add the -r or -R parameter:
$ rm -r family
move files
Use the mv(move or rename files) command to move files (cut). Move the file "file1" to the Documents directory:
mv 源目录文件 目的目录：
$ mkdir Documents
$ mv file1 Documents
rename file
Rename the file " file1 " to " myfile ":
mv 旧的文件名 新的文件名：
$ mv file1 myfile
Bulk rename
To achieve batch renaming, the mv command is a bit weak, we can use a more professional-looking command rename to achieve. However, it uses perl regular expressions as parameters. We will introduce regular expressions later. This is just a demonstration. You just need to remember that this rename command can be renamed in batches, and you will not learn it again later. Any problem, after all you have mastered a more commonly used mv command.
# 使用通配符批量创建 5 个文件:
$ touch file{1..5}.txt
# 批量将这 5 个后缀为 .txt 的文本文件重命名为以 .c 为后缀的文件: $ rename 's/\.txt/\.c/' *.txt # 批量将这 5 个文件，文件名改为大写: $ rename 'y/a-z/A-Z/' *.c A brief explanation of the above command rename is to first use the wildcard of the second parameter to match all .txt files with a suffix of , and then use the regular expression provided by the first parameter to .txt replace the suffixes of the matched files with .c, which we will learn later. After the sedcommand, I believe you will understand better.
Use catthe , tac and nl commands to view files
The first two commands are used to print the contents of the file to the standard output (terminal), which cat is displayed in positive order and displayed in tac reverse order.
Standard input and output: When we execute a shell command line, three standard files are usually opened automatically, namely the standard input file (stdin), which corresponds to the keyboard of the terminal by default, the standard output file (stdout) and the standard error output file (stderr), The last two files correspond to the screen that is redirected to the terminal so that we can see the output directly. The process will get input data from the standard input file, output normal output data to the standard output file, and send error messages to the standard error file.
For example, we want to view the files /etc copied from the directory before passwd :
$ cat passwd
You can add a -n parameter to display the line number:
$ cat -n passwd
nl command, add line number and print, this is a cat -n more professional line number printing command.
Here is a brief list of its commonly used parameters:
-b : 指定添加行号的方式，主要有两种：
-b a:表示无论是否为空行，同样列出行号("cat -n"就是这种方式)
-b t:只列出非空行的编号并列出（默认为这种方式） -n : 设置行号的样式，主要有三种： -n ln:在行号字段最左端显示 -n rn:在行号字段最右边显示，且不加 0 -n rz:在行号字段最右边显示，且加 0 -w : 行号字段占用的位数(默认为 6 位) 
You will find that using these commands, the default terminal window size, the content of the text can not be displayed on one screen, you have to use the mouse to drag the scroll bar or slide the wheel to continue to page down, if you can directly use the keyboard to turn the page Well, then you can use the commands to be introduced below.
Use more and less commands to view files in pagination
If the above cat is used to quickly view the content of a file, then this more sum less is naturally used to "read" the content of a file, for example, the man manual is used internally less to display the content. Among them, the more commands are relatively simple, and can only scroll in one direction, while less the development based on more and vi (a powerful editor, we have a separate course for you to learn) is more powerful. less The use of the command is basically and more consistent. Please refer to the man manual for the specific use. Only more the use of the command is introduced here.
more Open the passwd file with the command:
$ more passwd
After opening, only one screen of content is displayed by default, and the current reading progress is displayed at the bottom of the terminal. You can use the Enter key to scroll down one line, use the Space key to scroll down one screen, press h to display help, and q exit.
Use head and tail commands to view files
Those who are more impatient should like these two commands, because one of them is to view only the first few lines of the file (the default is 10 lines, and if it is less than 10 lines, it will display all) and the last few lines. Let's take the passwd file as an example. For example, when we want to view the newly added users, we can view this /etc/passwd file, but as we have seen earlier, there are a lot of messy things in this file, which looks really troublesome. Because a new user is added to the system, the user's information will be added to the end of the passwd file, so we can use tail the command at this time:
$ tail /etc/passwd
Or even more straightforward to just look at one line, add the -n parameter, followed by the line number:
$ tail -n 1 /etc/passwd
Regarding the tail command, I have to mention that it has a very good parameter -f, which can continuously read the content of a file and display it. This allows us to dynamically view logs for real-time monitoring purposes. However, I will not introduce more details of it in this basic course, and interested users can find out for themselves.
As I mentioned earlier, the type of file in Linux is not judged by the file suffix. We usually use the file command to view the type of the file:
$ file /bin/ls
Description This is an executable file that runs on a 64-bit platform and uses dynamically linked files (shared libraries).
To edit files under Linux, we usually directly use special command line editors such as (emacs, vim, nano). Since there are many editors on Linux, and they are very important, we have a separate basic course to introduce One of these editors is vim. It is strongly hoped that if you are learning this Linux basics course, you will pause here to learn the use of the vim editor (at least master the basic operations), and then continue with the content of the later part of this course, because the latter content will assume that you have already learned it. Use of vim editor. If you want to get started more quickly, you can directly use the vim inside Linux to learn the tutorial, and enter the following command to start:
$ vimtutor
relax for a while
Do you find it easy and stress-free to study in our environment, so it’s okay to be lazy every now and then? If this is the case, it is not very good. You have to learn to put a little pressure on yourself and be strict with yourself. You might think it would be nice if someone could supervise it, so that you can learn faster. Well, today I will teach you how to summon a pair of eyes to supervise you:
$ xeyes
You can run it in the background with the following command:
$ nohup xeyes &
