linux common commands 2

Posted by buzz on Sun, 13 Feb 2022 17:43:49 +0100

preparation

# Switch the directory to / export / and empty the contents
cd /export/ && rm -rf /export/* && tree

# Add a directory and switch directories and add files
mkdir -p /export/aaa/bbb/ccc/ddd/eee/ 
touch /export/aaa/bbb/ccc/ddd/eee/abc.txt
touch /export/aaa/123.txt
touch /export/aaa/312.txt

# View the contents of the / export directory
tree /export

1, Search command

1.find search

1.1 objectives

Use the find command to search for qualified files in a specific directory (including its descendant directory)

1.2 path

Step 1: search the specified directory. The file is ABC Txt file
Step 2: search the file with 1 in the file name under the specified directory
Step 3: search the specified directory, and all the files will be displayed in txt file with extension
Step 4: search for files starting with the number 1 in the specified directory

1.3 implementation: search by name in the specified directory

select * from table name

[where condition]

Command format

Serial number	Command format	effect
01	find [path] - name '* txt’	Find the extension under the specified path is txt files, including subdirectories

If the path is omitted, it means to find it under the current folder
The wildcards learned earlier are also available when using the find command

Step 1: search the specified directory. The file is ABC Txt file

# ===================Achieve goals============================
# Method 1: specify the full directory
find /export/ -name 'abc.txt'
# Method 2: current directory
find . -name 'abc.txt'
# Method 3: the current directory can be omitted
find -name 'abc.txt'

Step 2: search the file with 1 in the file name under the specified directory

# =================Implementation directory===============
find /export/ -name "*1*"

Step 3: search the specified directory, and all the files will be displayed in txt file with extension

find /export/ -name "*.txt"

Step 4: search for files starting with the number 1 in the specified directory

find /export -name "1*"

1.3 summary

Search for files by name through find [path] -name "*1 *"

Decompression command

preparation

# Empty the contents of the specified directory
cd /export/ && rm -rf *

# Create test file
touch 1.txt 2.txt 3.txt

# Create a test directory with content
mkdir -p /export/aaa/
touch /export/aaa/4.txt /export/aaa/5.txt

# View results
tree /export

1. Objectives

Compress backup files by packaging

Jar: compressed package of Java rar java project

War: compressed package of Web rar web project

Path 2

2.1 step 1: packaging and unpacking
**2.2 step 2: package compression and unpack decompression**

3. Realization

3.1 step 1: packaging and unpacking

3.1.1 packaging

Similar to putting winter clothes in bags
The packaged large file needs to be packaged in End. tar

tar packaging command format

# Package a series of files into a large file
tar -cvf Package name.tar Packaged directory
tar -cvf Package name.tar Packaged file 1 packaged file 2 packaged file 3

tar option description

command	english	meaning
c	create	Generate archive file and create package file
v	Verbosely	Report progress like "Tang Monk"
f	file	Specify the file name of the file, which must be followed by f tar file, so it must be put in the back left

Exercise 1: Will 1.txt,2.txt,3.txt Package into 123.tar file

Exercise 2: There will be content aaa Catalog packaged as aaa.tar file

[root@node01 export]# tar -cvf 123.tar 1.txt 2.txt 3.txt 
1.txt
2.txt
3.txt
[root@node01 export]# ll
total 16
-rw-r--r--. 1 root root 10240 Jul 31 06:04 123.tar
-rw-r--r--. 1 root root     0 Jul 31 06:03 1.txt
-rw-r--r--. 1 root root     0 Jul 31 06:03 2.txt
-rw-r--r--. 1 root root     0 Jul 31 06:03 3.txt
drwxr-xr-x. 2 root root  4096 Jul 31 06:03 aaa
[root@node01 export]# tar -cvf aaa.tar aaa/
aaa/
aaa/4.txt
aaa/5.txt
[root@node01 export]# ll
total 28
-rw-r--r--. 1 root root 10240 Jul 31 06:04 123.tar
-rw-r--r--. 1 root root     0 Jul 31 06:03 1.txt
-rw-r--r--. 1 root root     0 Jul 31 06:03 2.txt
-rw-r--r--. 1 root root     0 Jul 31 06:03 3.txt
drwxr-xr-x. 2 root root  4096 Jul 31 06:03 aaa
-rw-r--r--. 1 root root 10240 Jul 31 06:04 aaa.tar
[root@node01 export]# rm -rf *.txt aaa
[root@node01 export]# ll
total 24
-rw-r--r--. 1 root root 10240 Jul 31 06:04 123.tar
-rw-r--r--. 1 root root 10240 Jul 31 06:04 aaa.tar
[root@node01 export]# 
[root@node01 export]# tree
.
├── 123.tar
└── aaa.tar

3.1.2 unpacking

Similar to taking winter clothes out of the bag

tar unpacking command format

# Decompose a packaged into a series of small files in the current directory
tar -xvf Package name.tar

# Decompose a packaged into a series of small files in the specified directory
tar -xvf Package name.tar -C Unpacking path location

command	english	meaning
x	extract	Unpack
C (capital C)	directory	Save to the current directory by default. Change the decompression directory through - C. note: the decompression directory must exist

Exercise 1: Will 123.tar Extract to the current directory

Exercise 2: take aaa.tar Unpack to /export/test/a1/b1/c1/ In the directory

[root@node01 export]# ll
total 24
-rw-r--r--. 1 root root 10240 Jul 31 06:04 123.tar
-rw-r--r--. 1 root root 10240 Jul 31 06:04 aaa.tar
[root@node01 export]# tar -xvf 123.tar 
1.txt
2.txt
3.txt
[root@node01 export]# ll
total 24
-rw-r--r--. 1 root root 10240 Jul 31 06:04 123.tar
-rw-r--r--. 1 root root     0 Jul 31 06:03 1.txt
-rw-r--r--. 1 root root     0 Jul 31 06:03 2.txt
-rw-r--r--. 1 root root     0 Jul 31 06:03 3.txt
-rw-r--r--. 1 root root 10240 Jul 31 06:04 aaa.tar
[root@node01 export]# mkdir -p /export/test/a1/b1/c1
[root@node01 export]# tree
.
├── 123.tar
├── 1.txt
├── 2.txt
├── 3.txt
├── aaa.tar
└── test
    └── a1
        └── b1
            └── c1

4 directories, 5 files
[root@node01 export]# tar -xvf aaa.tar -C /export/test/a1/b1/c1
aaa/
aaa/4.txt
aaa/5.txt
[root@node01 export]# tree
.
├── 123.tar
├── 1.txt
├── 2.txt
├── 3.txt
├── aaa.tar
└── test
    └── a1
        └── b1
            └── c1
                └── aaa
                    ├── 4.txt
                    └── 5.txt

Summary

pack: tar -cvf Packaged file name.tar   Packaged directory or file name
	
Unpack: tar -xvf Packaged file name.tar  [ -C  Specify unpacking location ]

preparation

# Empty the contents of the specified directory
cd /export/ && rm -rf *

# Create test file
touch 1.txt 2.txt 3.txt

# Create a test directory with content
mkdir -p /export/aaa/
touch /export/aaa/4.txt /export/aaa/5.txt

# View results
tree /export

3.2 step 2: compress and decompress using gzip format

Packaging and compression are two things
It is similar to putting winter clothes into compressed bags first, and then extracting the air from them
In Linux, the most commonly used compressed file format is XXX tar. gz
There is an option - z in the tar command, which can call gzip, so it is convenient to realize the functions of compression and decompression

The command format is as follows

# Compressed file
tar -zcvf Packed compressed file name.tar.gz Compressed file/catalogue

# Decompress the file (memory knocking: Zhixiao Weifang)
tar -zxvf Packed File .tar.gz

# Extract to the specified path
tar -zxvf Packed File .tar.gz -C Directory path

Description of tar options

command	english	meaning
z	gzip	Compress and decompress using gzip
j	bzip2	Compress and decompress using bzip2

Demand 1: Will 1.txt,2.txt,3.txt Pack and compress into 123.tar.gz file(gzip Compression format)

Demand 2: There will be content aaa Catalog packaged as aaa.tar.gz file(gzip Compression format)

Demand 3: Will 123.tar.gz Extract to the current directory(gzip Compression format)

Demand 4: take aaa.tar.gz Unpack to /export/bbb In the directory(gzip Compression format)

Answers to requirements 1 and 2

[root@node01 export]# tree
.
├── 1.txt
├── 2.txt
├── 3.txt
└── aaa
    ├── 4.txt
    └── 5.txt

1 directory, 5 files
[root@node01 export]# tar -zcvf 123.tar.gz 1.txt 2.txt 3.txt 
1.txt
2.txt
3.txt
[root@node01 export]# tar -zcvf aaa.tar.gz aaa/
aaa/
aaa/4.txt
aaa/5.txt
[root@node01 export]# ll
total 12
-rw-r--r--. 1 root root  122 Jul 31 06:11 123.tar.gz
-rw-r--r--. 1 root root    0 Jul 31 06:10 1.txt
-rw-r--r--. 1 root root    0 Jul 31 06:10 2.txt
-rw-r--r--. 1 root root    0 Jul 31 06:10 3.txt
drwxr-xr-x. 2 root root 4096 Jul 31 06:10 aaa
-rw-r--r--. 1 root root  142 Jul 31 06:11 aaa.tar.gz

Empty useless content

[root@node01 export]# tree
.
├── 123.tar.gz
├── 1.txt
├── 2.txt
├── 3.txt
├── aaa
│   ├── 4.txt
│   └── 5.txt
└── aaa.tar.gz

1 directory, 7 files
[root@node01 export]# rm -rf *.txt aaa/
[root@node01 export]# tree
.
├── 123.tar.gz
└── aaa.tar.gz

Answers to requirements 3 and 4

[root@node01 export]# tree
.
├── 123.tar.gz
├── 1.txt
├── 2.txt
├── 3.txt
└── aaa.tar.gz

0 directories, 5 files
[root@node01 export]# mkdir -p /export/bbb
[root@node01 export]# tar -zxvf aaa.tar.gz -C /export/bbb/
aaa/
aaa/4.txt
aaa/5.txt
[root@node01 export]# tree
.
├── 123.tar.gz
├── 1.txt
├── 2.txt
├── 3.txt
├── aaa.tar.gz
└── bbb
    └── aaa
        ├── 4.txt
        └── 5.txt

Summary

Packing compression: tar -zcvf Packaged file name.tar.gz   The directory or file name that is packaged and compressed
	
Unpack and decompress: tar -zxvf Packaged file name.tar.gz  [ -C  Specify unpacking location ]

preparation

# Empty the contents of the specified directory
cd /export/ && rm -rf *

# Create test file
touch 1.txt 2.txt 3.txt

# Create a test directory with content
mkdir -p /export/aaa/
touch /export/aaa/4.txt /export/aaa/5.txt

# View results
tree /export

3.3 step 3: compress and decompress using bzip2 format

bzip is the second way of compression
It is similar to putting winter clothes into compressed bags first, and then extracting the air from them
In Linux, the bzip2 compressed file format is XXX tar. bz2
In the tar command, there is an option - j to call bzip2, which can easily realize the functions of compression and decompression

The command format is as follows

# Compressed file
tar -jcvf Packed compressed file name.tar.bz2 Compressed file/catalogue

# Unzip file (Weifang)
tar -jxvf Packed File .tar.bz2

# Extract to the specified path
tar -jxvf Packed File .tar.bz2 -C Directory path

Description of tar options

command	english	meaning
z	gzip	Compress and decompress using gzip
j	bzip2	Compress and decompress using bzip2

Exercise 1: Will 1.txt,2.txt,3.txt Pack and compress into 123.tar.bz2 file(bzip2 Compression format)

Exercise 2: There will be content aaa Catalog packaged as aaa.tar.bz2 file(bzip2 Compression format)

Exercise 3: Will 123.tar.bz2 Extract to the current directory(bzip2 Compression format)

Exercise 4: take aaa.tar.bz2 Unzip to /export/bbb In the directory(bzip2 Compression format)

Answers to requirements 1 and 2

[root@node01 export]# tar -jcvf 123.tar.bz2 1.txt 2.txt 3.txt 
1.txt
2.txt
3.txt
[root@node01 export]# tar -jcvf aaa.tar.bz2 aaa/
aaa/
aaa/4.txt
aaa/5.txt
[root@node01 export]# tree
.
├── 123.tar.bz2
├── 1.txt
├── 2.txt
├── 3.txt
├── aaa
│   ├── 4.txt
│   └── 5.txt
└── aaa.tar.bz2

Empty content

[root@node01 export]# rm -rf *.txt
[root@node01 export]# rm -rf aaa/
[root@node01 export]# tree
.
├── 123.tar.bz2
└── aaa.tar.bz2

Answers to requirements 3 and 4

[root@node01 export]# tar -jxvf 123.tar.bz2 
1.txt
2.txt
3.txt
[root@node01 export]# mkdir -p /export/bbb
[root@node01 export]# tar -jxvf aaa.tar.bz2 -C /export/bbb/
aaa/
aaa/4.txt
aaa/5.txt
[root@node01 export]# tree
.
├── 123.tar.bz2
├── 1.txt
├── 2.txt
├── 3.txt
├── aaa.tar.bz2
└── bbb
    └── aaa
        ├── 4.txt
        └── 5.txt

Summary

Packing compression: tar -jcvf Packaged file name.tar.bz2   The directory or file name that is packaged and compressed
	
Unpack and decompress: tar -jxvf Packaged file name.tar.bz2  [ -C  Specify unpacking location ]

Shut down

halt

restart

reboot

VI editor_ Terminal editor (key)

target

vi introduction
Open and new files
Three working modes
Common command query

1 Introduction

1.1 purpose of learning vi

In work, to make simple modifications to the files on the server, you can use ssh to log in to the remote server and use vi editor for simple editing
Documents to be modified include
- source code
- configuration file
  - For example: configuration file of tomcat server
  - For example: configuration file of network card information
In the environment without graphical interface, vi is the best choice to edit files
Every programmer using linux should learn some common commands of vi more or less

1.2 vi and vim

In many linux distributions, vi is directly made into the soft connection of vim

1.2.1 VI

vi is the abbreviation of visual interface and the most classic text editor in linux
vi's core design idea
- By keeping the programmer's fingers in the core area of the keyboard, all editing operations can be completed
Characteristics of vi
- Only the text content can be edited, and the font paragraph cannot be typeset
- Mouse operation is not supported
- No menu
- Only command
When vi editor manages and edits files in the system management server, its function is never comparable to that of the graphical interface editor

1.2.2 VIM

vim = vi improved
viM is a text editor developed from vi. it supports code completion, compilation, error jump and other convenient programming functions. It is widely used by programmers and is called the God of editor

2 opening and creating new files

Enter vim in the terminal, followed by the file name

vim file name

If the file already exists, it will be opened directly
If the file does not exist, a new file will be created when saving and exiting

1 vim No file name
2 Edit content
	2.1 Write class
	2.2 Output one line statement
	2.3 Copy and paste 2.2 Content 19 times
	2.4 Save and exit
3 see

Note: this section focuses on opening and creating files. Other commands will be explained later

[root@node01 export]# cd /export/ && rm -rf *
[root@node01 export]# vim Hello.java

public class Hello {

        public static void main(String[] args) {
                System.out.println("Hello World!");
                // 1 move the cursor to the previous line and press yy
                // 2 press ESC to exit the editing mode
                // 3 press 19p
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                System.out.println("Hello World!");
                // 1 press ESC to exit the editing mode
                // 2 press: enter the silent mode
                // 3. Enter wq(write quit) to save and exit. Press enter to execute 
        }
}

2.1 open the file and locate the line

In daily work, you may encounter the situation of opening a file and locating to the specified line
For example, in development, if you know that there is an error in a line of code, you can quickly locate the location of the error code
At this time, you can open the file with the following command

vim file name +Number of rows

[root@node01 export]# vim Hello.java +10

2.2 exception handling

If vi exits abnormally, swap files may be saved on disk
The next time you use vi to edit a file, you will see the following screen information. Press the letter d to delete the exchange file

Tip: when pressing the keyboard, pay attention to turn off the input method

How to produce
- Edit the file without exiting. Close the reply window

2.3 three working modes of VI

VI has three working modes

Command mode
- When opening a file, you first enter the command mode, which is the entry to use vi
- Perform routine editing operations on files through commands, such as positioning, turning pages, copying, pasting, deleting
- In other graphic editors, the operations realized by shortcut keys or mouse are realized in command mode
Last line mode – perform operations such as saving and exiting
- To exit vi and return to the console, you need to enter a command in silent mode
- The last line mode is the exit of vi
Edit mode – normal text editing

Working mode switching

2.4 last line mode command

command	english	function
w	write	preservation
q	quit	Exit. If not saved, exit is not allowed
q!	quit	Forcibly exit without saving
wq	write & quit	Save and exit (Mo line mode)
x		Save and exit (Mo line mode)
ZZ		Save and exit (command mode)

4 common commands

Command wiring diagram

Number of repetitions

In the command mode, first enter a number and then add a command, which can be repeated n times, such as 19p

Move and select (practice more)
The key to the speed of vi is that it can quickly locate the line of code to be edited
The move command can be used in combination with the edit operation
Edit operation
- Delete copy paste replace indent
Undo and repeat
Replacement found
edit

Learning tips

There are many vi commands. Don't expect to remember them all at once. Forgetting individual commands will only affect the editing speed
. when using the vi command, pay attention to turn off the Chinese input method

4.1 movement

To be proficient in vi, you should first learn how to move the cursor quickly in command mode
The edit operation command can be used with the move command

1) Up, down, left and right

command	function	finger
h	towards the left	index finger
j	down	index finger
k	Upward	middle finger
l	towards the right	ring finger

2) Intra line movement

command	english	function
w	word	Move one word backward
b	back	Move one word forward
0		Line beginning
^		At the beginning of a line, the first position that is not a blank character
$		End of line

3) Row number movement

command	english	function
gg	go	Top file
G	go	end of file
Digital gg	go	Move to the number of rows corresponding to the number
Digital G	go	Move to the number of rows corresponding to the number
: number		Move to the number of rows corresponding to the number

4) Screen movement

command	english	function
Ctrl + b	back	Page up
Ctrl + f	forward	Page down
H	Head	Top of screen
M	Middle	Middle of screen
L	Low	bottom of screen

4.2 mobile (program)

1) Paragraph movement

Empty lines are used in vim to distinguish paragraphs
During program development, a piece of function related code is usually written together - there is no blank line between them

command function
{ the preceding paragraph
} Next paragraph

command	function
{	the preceding paragraph
}	Next paragraph

2) Bracket switching

In the program world, * * (), [], {} * * are highly used, and they all appear in pairs

command function
% Bracket matching and switching

command	function
%	Bracket matching and switching

3) Mark

During development, a piece of code may need to be processed later, such as editing and viewing
At this time, try m to add a mark first, so that you can quickly jump back or perform other editing operations when necessary
The tag name can be a ~ Z or any letter between a ~ Z
If the marked line is deleted, the mark will be deleted at the same time
If a tag with the same name is added to another row, the tag added earlier will also be replaced

command	english	function
mx	mark	Add or edit x, where x is any letter of A~Z or A~Z
'x		Navigate directly to the location of the mark x

4.3 selected text (visual mode)

Before learning the copy command, you should first learn how to select the code to copy
To select text in vi, you need to display the visual command to switch to visual mode
vi provides three visual modes, which can facilitate programmers to choose the way to select text
Press ESC to discard the selection and return to command mode

command	pattern	function
v	Visual Modes	Select the text in normal mode starting from the cursor position
V	Visualization mode	Select the complete line that the cursor passes through
Ctrl + v	But block mode	Select text vertically

In visual mode, it can be used in conjunction with mobile commands. For example, ggVG can select all contents

4.4 revocation and recovery (life saving instruction)

Before learning editing commands, you should know how to undo the previous wrong editing operation

command	english	function
u	undo	Undo the last command (ctrl + z)
Ctrl + r	uredo	10dd resume undone command

4.5 delete text

command	english	function
x	cut	Delete the character where the cursor is located or the selected text
D (move command)	delete	Delete corresponding content
dd	delete	Delete the line where the cursor is located. You can ndd delete multiple lines
D	delete	Delete to end of line

Tip: if you have selected a piece of text in visual mode, you can delete the selected text whether you use d or x

The delete command can be used in conjunction with the move command. The following are common combined commands (extensions):

command	effect
dw	Delete from cursor position to end of word
d0	Delete from cursor position to the beginning of a line
d}	Delete from cursor position to end of paragraph
ndd	Delete n rows consecutively from the cursor position
d'a	Delete all codes from the line where the cursor is located to the mark a

4.6 copying and cutting

vi provides a buffer for copied text
- The copy command saves the selected text in a buffer
- Delete command the deleted text will be saved in the buffer
- Use the paste command to insert the text of the buffer pair into the position of the cursor at the desired position

command	english	function
Y (copy command)	copy	copy
yy	copy	Copy one line, you can nyy copy multiple lines
D (cut command)	delete	shear
DD (shear)	delete	Cut one line, you can ndd cut n lines
p	paste	paste

Tips:

The commands d and x are similar to the cutting operation of the graphical interface – ctrl + x
The command y is similar to the copy operation of the graphical interface – Ctrl+
The command p is similar to the paste operation of the graphical interface – Ctrl + v
If there is only one content in the. vi buffer that has been cut and copied, it will be replaced

be careful

The text buffer in vi is not the same as the system clipboard
Therefore, the content copied by Ctrl + C in other software can no longer be pasted by p command in vi
You can paste with the right mouse button in edit mode

4.7 replacement

command	english	function	Working mode
r	replace	Replace current character	Command mode
R	replace	Replace the character after the current line cursor	Replacement mode

The R command can enter the replacement mode. After the replacement is completed, press ESC, and press ESC to return to the command mode
The function of the replace command is to make lightweight modifications to the file without entering the edit mode

4.8 indent and repeat

command	function
>>	Increase Indent right
<<	Indent left
.	Repeat last command

Indent command when developing programs, it is more useful to uniformly increase the indent of code!
- Adding four spaces in front of the selected code at one time is called adding indentation
- Deleting four spaces before the selected code at one time is called less indentation
In visual mode, the indent command needs to use a > or<

In programs, indentation is often used to indicate the ownership of code

The less space in front, the higher the level of code
The more spaces in the front, the lower the level of code

4.9 search

General search

command	function
/str	Find str

After finding the specified content, use Next to find the Next location
- n: find next
- N: find previous
If you don't want to see the highlight, you can just look for something that doesn't exist in a file
Fast word matching

command	function
*	Find the word of the current cursor backward
#	Look forward to the word where the current cursor is located

In development, through word quick matching, you can quickly see that the word has been used in other places

4.10 find and replace

Find and replace commands in vi need to be executed in last line mode
Memory command format

:%s///g

Global replacement

Replace all the old text that appears in the file at once
The command format is as follows
```
:%s/Old text/new text/g
```

Visual area replacement

First select the range of text to replace
The command format is as follows

:s/Old text/new text/g

Confirm replacement:

c confirm

If you change the g at the end to gc, you will be prompted when replacing it! Recommended use
The command format is as follows
```
:%s/Old text/new text/gc
```

y - yes substitution
n - no replace
a - all replace all
q -quit quit replace
l - last and move the cursor to the beginning of the line
^E scroll down
^Y scroll up

4.11 insert command (key)

In vi, in addition to the common i to enter the editing mode, the following commands are also provided to enter the editing mode

command	english	function	Commonly used
i	insert	Insert text before current character	Commonly used
I	insert	Insert text at the beginning of the line	More commonly used
a	append	Add text after current character
A	append	Add text at the end of the line	More commonly used
o		Insert an empty line after the current line	Commonly used
O		Inserts an empty line before the current line	Commonly used

Insert picture description here

4.12 practice

Exercise 1 – editing commands with numbers

In development, you may encounter continuous input of N same characters
For example: ********** 10 consecutive asterisks

To achieve this effect, in command mode:

Enter 10 to repeat 10 times
Enter i to enter editing mode
Enter * that is, duplicate text
Press ESC to return to the command mode. After returning, vi will repeat steps 2 and 3 for 10 times

Tip: during normal development, do not press the number before entering the editing mode

Walkthrough 2 – using visual blocks to annotate multiple lines of code

If you encounter more than one line of comment in the development, you may add one line to the code

In java, to add comments to the code, you can

Add one before//

This effect can be achieved in command mode

Move to the first line of code where you want to add comments, and press ^ to get to the beginning of the line
Press Ctrl + v to enter visualization mode
Use j to continuously select the lines of code to be added
Enter I to enter editing mode and insert at the beginning of the line. Note: be sure to use I
Enter / / which is the comment symbol
Press ESC to return to the command:: mode. After returning, vi will be inserted in front of each line of code previously selected//

Exercise 3: tank battle case (save as backup)

The last command you have learned

command	english	function
: w file		Save as
:w	write	Save (ctrl + s)
:q	quit	Exit. If not saved, exit is not allowed
:q!	quit	Forcibly exit without saving
:wq	write & quit	Save and exit
:x		Save and exit

In actual development, you can use the w command to backup the code periodically

User authority related commands

target

Understand the basic concepts of users and permissions
User management terminal command
Group management terminal command
Modify authority terminal command

01. Basic concepts of users and permissions

1.1 basic concepts

User is an important part of Linux system. User management includes user and group management
In Linux system, whether it is logged in by the same level or remotely, each system must have an account and have different permissions for different system resources
Permissions for files / directories include:

Serial number	jurisdiction	english	abbreviation	Digital serial number
01	read	read	r	4
02	write	write	w	2
03	implement	execute	x	1
04	No permission		-	0

In Linux, you can specify different permissions for different files or directories for each user

1.2 group

In order to facilitate user management, the concept of group is proposed, as shown in the figure below

1.3 ls -l extension

ls -l you can view the details of the files under the folder, from left to right:
- Permission. If the first character is d, it indicates the directory
- The number of hard links, in popular terms, is the number of ways to access the current directory and files
- Owner: the owner of the file / Mulan road under the home directory is usually the current user
- Group. In linux, the group name and user name are often the same. I'll talk about it later
- size
- time
- name

02. Group management terminal command

Essence: assign permissions to users of the same type

Serial number	command	effect
01	groupadd group name	add group
02	groupdel group name	delete group
03	cat /etc/group	Confirm group information
04	chgrp group name file / directory name	Modify the group to which the file / directory belongs

Tips:

The group information is saved in the / etc/group file
/The etc directory is a directory dedicated to storing system configuration information

In practical application, you can set permissions for groups in advance, and then add different users to the corresponding groups, so you don't have to set permissions for each user in turn

chgrp : change group

Drill objectives

Create aaa directory under the specified directory
New dev group
Change the group of aaa directory to dev

[root@node01 export]# mkdir -p aaa/
[root@node01 export]# ll
total 4
drwxr-xr-x. 2 root root 4096 Jul 31 06:48 aaa
[root@node01 export]# chgrp dev aaa/
[root@node01 export]# ll
total 4
drwxr-xr-x. 2 root dev 4096 Jul 31 06:48 aaa

03. User management terminal command

3.1 create user / set password / delete user

command	effect	explain
useradd -m -g group new user name	Add new user	-m automatically create user home directory -g specify the group where the user belongs, otherwise a group with the same name will be established
passwd user name	Set user password	If you are an ordinary user, You can change your account and password directly with passwd
userdel -r username	delete user	-The r option will automatically delete the user's home directory
cat /etc/passwd \| grep user name	Confirm user information	After creating a new user, the user information will be saved in the / etc/passwd folder

Tips:

If you forget to add the - m option to specify the new user's home directory when creating a new user - the easiest way is to delete the user and recreate it
When creating a user, a group name with the same name as the user name will be created by default
The user information is saved in the / etc/passwd file

/The etc/passwd file stores the user's information, which is composed of seven pieces of information divided into six parts, namely

user name
Password (x for encrypted password)
UID (user ID)
GID (group flag)
Full user name or local account
Home directory
The Shell used for login is the terminal command used after login

demand

1 Create user zhangsan, Assigned to dev group
2 Set user zhangsan Password for
3 Check whether users are added in the configuration file zhangsan observation zhangsan Create your home directory
4 delete zhangsan user

[root@node01 export]# useradd -m -g dev zhangsan
[root@node01 export]# passwd zhangsan
Changing password for user zhangsan.
New password: 
BAD PASSWORD: it is too simplistic/systematic
BAD PASSWORD: is too simple
Retype new password: 
passwd: all authentication tokens updated successfully.

[root@node01 export]# cat /etc/passwd | grep zhangsan
zhangsan:x:500:500::/home/zhangsan:/bin/bash
[root@node01 export]# tree /home
/home
└── zhangsan

[root@node01 export]# userdel -r zhangsan
[root@node01 export]# cat /etc/passwd | grep zhangsan
[root@node01 export]# tree /home
/home

3.2 viewing user information

Serial number	command	effect
01	id [user name]	View user UID and GID information
02	who	View the list of all currently logged in users
03	whoami	View the account name of the currently logged in user

[root@node01 ~]# useradd -m -g dev lisi
[root@node01 ~]# passwd lisi
Changing password for user lisi.
New password: 
BAD PASSWORD: it is too simplistic/systematic
BAD PASSWORD: is too simple
Retype new password: 
passwd: all authentication tokens updated successfully.
[root@node01 ~]# id lisi
uid=500(lisi) gid=500(dev) groups=500(dev)
[root@node01 ~]# who
root     pts/0        2019-07-31 07:02 (192.168.100.2)
[root@node01 ~]# whoami
root

3.3 su switching users

Because ordinary users cannot use certain permissions, they need to switch users

Serial number	command	effect	explain
01	su - user name	Switch users and plan directories	-You can switch to the user's home directory, otherwise the location remains unchanged
02	exit	Exit the currently logged in user

su can switch to root without receiving the user name, but it is not recommended because it is unsafe
The schematic diagram of exit is as follows:

[lisi@node01 ~]$ whoami
lisi
[lisi@node01 ~]$ su - root
Password: 
[root@node01 ~]# whoami
root
[root@node01 ~]# exit
logout
[lisi@node01 ~]$ whoami
lisi

3.4 sudo

Although you can switch to the root user through su -u root, there are serious security risks

The root account in linux system is usually used for system maintenance and management, and has access to all resources of the operating system
If you accidentally use rm -rf, It could paralyze the system
In most versions of linux, it is not recommended to log in to the system directly with only the root account
The sudo command is used to execute commands in other identities. The default identity is root
When using sudo, the user must first enter the password, and then the validity period of 5 minutes. If the expiration period is exceeded, the user must re-enter the password

Tip: if its unauthorized user attempts to use sudo, a warning email will be sent to the administrator

3.4.1 grant permissions to designated users

Essence: notify the server to assign temporary administrator privileges to specific users

vim /etc/sudoers

# Default: the root user has all permissions
root    ALL=(ALL)       ALL

# Grant all permissions to lisi users
lisi    ALL=(ALL)       ALL

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3.4.2 log in with user lisi and operate administrator commands

Temporary access: essential

# You can also complete the function of adding users without switching the root user 
sudo useradd -m -g dev zhaoliu

[lisi@node01 ~]$ sudo useradd -m -g dev zhaoliu

We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:

    #1) Respect the privacy of others.
    #2) Think before you type.
    #3) With great power comes great responsibility.

[sudo] password for lisi: 
[lisi@node01 ~]$ sudo cat /etc/passwd | grep zhaoliu
zhaoliu:x:501:500::/home/zhaoliu:/bin/bash

Preparation: use root user operation

# Empty contents of directory
rm -rf /export/*

# Create test directory
mkdir -p /export/aaa/

# Create test file
touch /export/aaa/01.txt /export/aaa/02.txt

# View the contents of the specified directory
tree /export

04. Modify user permissions

Serial number	command	effect
01	chmod	Modify permissions

4.1 method 1: modify user permissions

chmod can modify the permissions of users / groups on files / directories
The command format is as follows:
```
chmod +/- rwx file name|Directory name
```
Tip: the previous method will modify the owner / group permission to the user once

Target drill:

# 1. Use root to delete the readable, writable and executable permissions of the directory

# 2. Other users such as lisi cannot switch to this directory

# 3. Use root to increase the execution permission of the directory, and then use lisi to switch to the directory again

Answer: # 1 Use root to remove the read, write, and executable permissions of the directory

[root@node01 export]# ll
total 4
drwxr-xr-x. 2 root root 4096 Jul 31 07:10 aaa
[root@node01 export]# chmod -rwx aaa/
[root@node01 export]# ll
total 4
d---------. 2 root root 4096 Jul 31 07:10 aaa

Answer to requirement 2: other users such as lisi cannot switch to this directory

[lisi@node01 ~]$ cd /export/
[lisi@node01 export]$ ll
total 4
d---------. 2 root root 4096 Jul 31 07:10 aaa
[lisi@node01 export]$ cd aaa/
-bash: cd: aaa/: Permission denied

Answer to requirement 3: use root to increase the execution permission of the directory, and then use lisi to switch to the directory again

[root@node01 export]# chmod +x aaa/
[root@node01 export]# ll
total 4
d--x--x--x. 2 root root 4096 Jul 31 07:10 aaa

[lisi@node01 export]$ cd aaa/
[lisi@node01 aaa]$ pwd
/export/aaa

4.2 mode II

Although the method is always used to modify the read, write and execute permissions of files and directories, it cannot be accurate to the owner, group and other permissions
The command format is as follows: (u indicates the user / g indicates the group / o indicates other)

chmod -R u=rwx,g=rx,o=rwx file|catalogue

Serial number	jurisdiction	english	abbreviation	Digital serial number
01	read	read	r	4
02	write	write	w	2
03	implement	execute	x	1
04	No permission		-	0

Target drill:

# 1. Use the root user to assign readable, writable and executable permissions to its users, 
    The group to which you belong is assigned readable and executable permissions, 
    Assign readable and executable permissions to others

[root@node01 export]# chmod u=rwx,g=rx,o=rx aaa/
[root@node01 export]# ll
total 4
drwxr-xr-x. 2 root root 4096 Jul 31 07:10 aaa

4.3 mode 3: simplified mode 2

The command format is as follows:

chmod -R 755 file|catalogue

Description: the first number is owner permission, the second number is group permission, and the third number is other user permission

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Common combinations of numbers are (u for user / g for group / o for others)

777 ===> u=rwx, g=rwx, o=rwx
755 ===> u=rwx, g=rx, o=rx
644 ===> u=rw, g=r, o=r

Target drill:

# 1. Use the root user to assign readable, writable and executable permissions to its users, 
    The group to which you belong is assigned readable and executable permissions, 
    Assign readable and executable permissions to others

[root@node01 export]# chmod 755 bbb/
[root@node01 export]# ll
total 8
drwxr-xr-x. 2 root root 4096 Jul 31 07:10 aaa
drwxr-xr-x. 3 root root 4096 Jul 31 07:19 bbb

System information related commands

The purpose of this section is to check the current system date and time / disk space occupation / program execution on the server when maintaining the server through the remote terminal
In this summary, the learning terminal commands are query commands, through which we can have an understanding of the use of system resources

target

Time and date
- date
- cal
Disk and directory space
- df
- du
Process information
- ps
- top
- kill

1. Time and date

1.1 date time

command	effect
date	View system time (default)
date +"%Y-%m-%d %H:%M:%S"	View system time (specify format)
date -s "time string"	Set system time

Step 1: display the current time

# Display time
date

# Displays the time in the specified format
date +"%Y-%m-%d %H:%M:%S"

Step 2: set the system time

date -s "Time string"

[root@node01 export]# date
Wed Jul 31 07:20:31 CST 2019
[root@node01 export]# date +"%Y-%m-%d %H:%M:%S"
2019-07-31 07:20:49
[root@node01 export]# date -s '2019-07-31 20:21:49'
Wed Jul 31 20:21:49 CST 2019
[root@node01 export]# date +"%Y-%m-%d %H:%M:%S"    
2019-07-31 20:21:52

1.2 cal calendar

Serial number	command	effect
01	cal	View the calendar of the current month
02	cal -y	View the calendar of the current year
03	cal 2020	View calendar for 2020
04	cal 10 2020	View the calendar for October 2020

02. Disk information

Serial number	command	effect
01	df -h	disk free displays the remaining disk space
02	du -h [directory name]	disk usage displays the size of the directory under the directory
03	free -h	View memory usage

Option description

parameter	meaning
-h	Displays the size of the file in a user-friendly manner

03. Process information

The so-called process, popularly speaking, is a process currently being implemented

Serial number	command	effect
01	ps aux	View process status details
02	top	Dynamic display of running processes and sorting
03	kill [-9] process code	Terminate the process with the specified code - 9 indicates forced termination

ps by default, only the applications launched by the current user through the terminal will be displayed

ps option description function

Topics: Linux Big Data

Programmer Think

linux common commands 2

preparation

1, Search command

1.find search

1.1 objectives

1.2 path

1.3 implementation: search by name in the specified directory

Command format

Step 1: search the specified directory. The file is ABC Txt file

Step 2: search the file with 1 in the file name under the specified directory

Step 3: search the specified directory, and all the files will be displayed in txt file with extension

Step 4: search for files starting with the number 1 in the specified directory

1.3 summary

Decompression command

1. Objectives

Path 2

3. Realization

3.1 step 1: packaging and unpacking

3.1.1 packaging

3.1.2 unpacking

Summary

3.2 step 2: compress and decompress using gzip format

Summary

3.3 step 3: compress and decompress using bzip2 format

Summary

VI editor_ Terminal editor (key)

target

1 Introduction

1.1 purpose of learning vi

1.2 vi and vim

1.2.1 VI

1.2.2 VIM

2 opening and creating new files

2.1 open the file and locate the line

2.2 exception handling

2.3 three working modes of VI

2.4 last line mode command

4 common commands

Command wiring diagram

Learning tips

4.1 movement

1) Up, down, left and right

2) Intra line movement

3) Row number movement

4) Screen movement

4.2 mobile (program)

1) Paragraph movement

2) Bracket switching

3) Mark

4.3 selected text (visual mode)

4.4 revocation and recovery (life saving instruction)

4.5 delete text

4.6 copying and cutting

4.7 replacement

4.8 indent and repeat

4.9 search

4.10 find and replace

4.11 insert command (key)

4.12 practice

Exercise 1 – editing commands with numbers

Walkthrough 2 – using visual blocks to annotate multiple lines of code

Exercise 3: tank battle case (save as backup)

User authority related commands

target

01. Basic concepts of users and permissions

1.1 basic concepts

1.2 group

1.3 ls -l extension

02. Group management terminal command

03. User management terminal command

3.1 create user / set password / delete user

3.2 viewing user information

3.3 su switching users

3.4 sudo

3.4.1 grant permissions to designated users

3.4.2 log in with user lisi and operate administrator commands

04. Modify user permissions

4.1 method 1: modify user permissions

Target drill: