Linux (Practical Part 1)

Linux (Practical Part 1)

1. Commonly used basic commands

Shell can be regarded as a command interpreter, providing us with an interactive text console interface. We can enter commands through the terminal console, which are interpreted by the shell and finally handed over to the kernel for execution.

1.1 Help commands

1.1.1 man to get help information

• basic grammar

  man [command or configuration file]Function description: Get help information

• show description

  • NAME: Name and one-line description of the command
  • SYNOPSIS: How to use commands
  • DESCRIPTION: In-depth discussion of command functionality
  • EXAMPLES: Examples of how to use the command
  • SEE ALSO: Related topics (usually man pages)

• Practical examples

  man ls View help information for the ls command

1.1.2 help Get help information for shell built-in commands

Some system commands with basic functions are directly embedded in the shell., it will be loaded together with the shell after the system is loaded and started, and will reside in the system memory. These commands are called "built-in commands"; the corresponding other commands are called "external commands".

Availabletype commandTo determine whether the command is an embedded command

[guozihan@hadoop100 ~]$ type cd
cd is shell embedded

• basic grammar

  help commandFunction description: Get help information for shell built-in commands

• Practical examples

  help cd View help information for the cd command

1.1.3 Commonly used shortcut keys

ctrl + c Stop process

ctrl+l Clearing the screen is equivalent to clear; completely clearing the screen is: reset

Good at using the tab keyTips (more importantly, it can prevent typos)

Up and down keysFind executed commands

1.2 File directory class

1.2.1 pwd displays the absolute path of the current working directory

pwd:print working directory print working directory

• basic grammar

  pwd (Function description: Display the absolute path of the current working directory)

• Practical examples

  Display the absolute path of the current working directory

  [guozihan@hadoop100 ~]$ pwd
  /home/guozihan

1.2.2 ls lists the contents of a directory

ls:list lists directory contents

• basic grammar

  ls [options] [directory or file]

• Option description

  • -a: List all files, together with hidden files (files starting with .) (commonly used)
  • -l: Long data string list, including file attributes and permissions, etc.; (commonly used) is equivalent to "ll"

• show description

  The information listed on each line is:File type and permission link number File owner File group File size Use bytes to represent the time of creation or last modification Name

• Practical examples

  View all content information of the current directory

  

1.2.3 cd to switch directories

cd:Change Directory switch path

• basic grammar

  cd [parameter]

• Parameter Description

  cd absolute pathswitch path

  cd relative pathswitch path

  cd ~ or cdReturn to your home directory

  cd - Return to the last directory

  cd … Return to the directory one level above the current directory

  cd -P Jump to actual physical path, not shortcut path

1.2.4 mkdir creates a new directory

mkdir:Make directory Create directory

• basic grammar

  mkdir [options] Directory to create

• Option description

  -p Create multi-level directories

• Practical examples

  Create a directory

  [root@hadoop101 ~]# mkdir xiyou

  [root@hadoop101 ~]# mkdir xiyou/mingji

  Create a multi-level directory

  [root@hadoop101 ~]# mkdir -p xiyou/dssz/meihouwang

1.2.5 rmdir deletes an empty directory

rmdir:Remove directory remove directory

• basic grammar

  rmdir The empty directory to be deleted

• Case practice

  Delete an empty folder

  [root@hadoop101 ~]# rmdir xiyou/dssz/meihouwang

  If you want to delete a multi-level directory, delete it layer by layer from the inside out!

1.2.6 touch creates empty file

• basic grammar

  touch file name

• Practical examples

  [guozihan@hadoop100 desktop]$ touch a.txt

1.2.7 cp copy files or directories

• basic grammar

  cp [option] source destFunction description: Copy source files to dest

• Option description

  -r Copy entire folder recursively

• Parameter Description

  • source source file
  • dest object file

• Practical examples

  Copy files

  [root@hadoop100 desktop]# cp a.txt /home/

  Copy entire folder recursively

  [guozihan@hadoop100 desktop]$ mkdir a/b/c.txt

  [guozihan@hadoop100 桡面]$ cp -ra /home/guozihan

1.2.8 rm deletes files or directories

• basic grammar

  rm [options] deleteFileFunction description: Recursively delete all contents in the directory

• Option description

  • -r: Recursively delete all contents in the directory
  • -f: Force the deletion without prompting for confirmation
  • -v: Display the detailed execution process of the command

• Case practice

  Delete the contents of a directory

  [guozihan@hadoop100 desktop]$ rm test

  Recursively delete all contents in a directory

  [guozihan@hadoop100 desktop]$ rm -rf a

1.2.9 mv moves or renames files and directories

• basic grammar

  mv oldNameFile newNameFile Function description: Rename

  mv /temp/movefile /targetFolder Function description: Move files

• Case practice

  double naming

  [guozihan@hadoop100 desktop]$ touch test.txt

  [guozihan@hadoop100 desktop]$ mv test.txt a.txt

  Move files

  [guozihan@hadoop100 desktop]$ mv a.txt /home/guozihan

1.2.10 cat to view file content

View the file contents, starting from the first line

• basic grammar

  cat [options] file to view

• Option description

  -n Display line numbers for all lines, including blank lines

• Practical examples

  View file contents and display line numbers

  [guozihan@hadoop100 桌面]$ cat -n a.txt
  1 test
  2 test
  3 test
  4 test
  5 test
  6 test
  7 test
  8 test
  9 test

1.2.11 more file content split screen viewer

The more command is a VI editor-basedtext filter, which displays the contents of a text file page by page in full screen mode. There are several shortcut keys built into the more command. Please refer to the operating instructions for details.

• basic grammar

  more files to view

• Instructions

  • space keyRepresents turning down one page
  • Enter Represents scrolling down "one line"
  • q The representative leaves more immediately and no longer displays the contents of the file.
  • Ctrl+F Scroll down one screen
  • Ctrl+B Return to previous screen
  • = Output the line number of the current line
  • :f Output file name and line number of current line

• Case practice

  Use more to view files

  [guozihan@hadoop100 desktop]$ more a.txt

1.2.12 less displays file contents in split screen

The less command is used to view file contents in split screen. Its function is similar to the more command, but it is more powerful and supports various display terminals.When the less command displays the content of a file, it does not load the entire file at once, but loads the content according to the display needs, which is more efficient for displaying large files.

• basic grammar

  less file to view

• Instructions

  • space keyScroll down a page
  • [pagedown] Scroll down a page
  • [shut up]Scroll up a page
  • /stringThe function of searching "string" downwards; n: search downwards; N: search upwards
  • ?StringFunction to search "string" upward; n: search upward; N: search downward
  • qleave less

• Case practice

  Use less to view files

  [guozihan@hadoop100 desktop]$ less a.txt

1.2.13 echo

echo outputs content to the console

• basic grammar

  echo [options] [output content]

  Options:

  -e: Supports character conversion controlled by backslash

• Special characters

  • \\ output\self
  • \n newline character
  • \t Tab character, also known as Tab key

• Case practice

  [guozihan@hadoop100 desktop]$ echo “hello\tworld”
  hello\tworld

  [guozihan@hadoop100 desktop]$ echo -e “hello\tworld”
  hello world

1.2.14 head displays the file header content

head is used to display the beginning of the file,By default, the head command displays the first 10 lines of the file.

• Basic usage

  head fileFunction description: View the first 10 lines of the file

  head -n 5 filesFunction description: View the first 5 lines of the file, 5 can be any number of lines

• Option description

  -n<number of lines>Specify the number of lines to display header content

• Practical examples

  View the first 2 lines of the file

  [guozihan@hadoop100 desktop]$ head -n2 a.txt
  test
  test

1.2.15 tail outputs the content at the end of the file

tail is used to output the content at the end of the file,By default, the tail command displays the last 10 lines of the file.

• Basic usage

  tail fileFunction description: View the content of the last 10 lines of the file

  tail -n 5 filesFunction description: View the 5 lines at the end of the file, 5 can be any number of lines

  tail -f fileFunction description: Track all updates to this document in real time

• Option description

  • -n<number of lines>Output n lines at the end of the file
  • -f Display the latest added content of the file and monitor file changes

• Practical examples

  View the content of the last line of the file

  [guozihan@hadoop100 desktop]$ tail -n 1 a.txt
  test

  Track all updates to this file in real time

  [guozihan@hadoop100 desktop]$ tail -f a.txt

1.2.16 > Output Redirection and >> Append

• basic grammar

  ls -l > fileFunction description: Write the contents of the list to a file (overwrite)

  ls -al >> fileFunction description: Append the contents of the list to the end of the file

  cat file 1 > file 2Function description: Overwrite the contents of file 1 to file 2

  echo "content" >> fileFunction description: Append content to the end of the file

• Case practice

  Write ls view information to file

  [guozihan@hadoop100 desktop]$ ls -l>a.txt

  Append ls view information to file

  [guozihan@hadoop100 desktop]$ ls -l>>a.txt

  Use echo to append the hello word to the file

  [guozihan@hadoop100 desktop]$ echo hello>>a.txt

1.2.17 ln soft link

Soft links are also called symbolic links, similar to shortcuts in Windows.Has its own data block, mainly stores the paths linking to other files

• basic grammar

  ln -s [original file or directory] [soft link name]Function description: Create a soft link to the original file

• Practical examples

  Create a soft link

  [root@hadoop101 ~]# ln -s xiyou/dssz/houge.txt ./houzi

  Delete the soft link (be careful not to write the last /)

  [root@hadoop101 ~]# rm -rf houzi

  Enter the actual physical path of the soft connection

  [root@hadoop101 ~]# ln -s xiyou/dssz/ ./dssz

  [root@hadoop101 ~]# cd -P dssz/

1.2.18 history View historical commands that have been executed

• basic grammar

  history Function description: View historical commands that have been executed

• Case practice

  View historical commands that have been executed

  [guozihan@hadoop100 desktop]$ history