1. What is a terminal
- In short, it is something that can accept input and display (output) results. Terminal is the most important man-machine interface of computer system.
- Corresponding program file of desktop terminal (pseudo terminal) of CentOS / usr / bin / Gnome terminal
2. console and Terminal
- In the early days, the physical I / O device directly connected to the computer was called the console
- The input and output devices remotely connected to the computer through the network cable are called terminals
3. Virtual terminal (TTY: teletypewriter)
- In the Linux operating system, multiple users can log in to the system for operation, or the same user can open multiple windows to perform multiple tasks. The Linux operating system sets up multiple virtual terminal devices, corresponding to / dev/tty1~/dev/tty6 respectively.
- By default, only 6 of them are enabled for users in CentOS, namely tty1~tty6, which can be switched through the shortcut key: Ctrl + Alt + < F1 ~ F6 >.
4. What is a shell (command line)
- Simply put, a shell is a shell program that receives commands entered by users and then submits them to the Linux kernel for processing.
- When the terminal is opened, the shell program will be started automatically. There are many kinds of shell programs, and Linux mostly makes bash(GNU) by default
Bourne again shell), which is a superset of Bourne shell(bsh), that is, an extension. - bash corresponding program file: / usr/bin/bash
5. Reasons for using shell
1. High efficiency
2. Stability
3. Development saves worry and money
4. It is indispensable in software testing, deployment and operation and maintenance
5. It is indispensable in software testing, deployment and operation and maintenance
6. command prompt
Generally speaking, after opening the terminal window, the character displayed in front of the cursor is the so-called command prompt. The command prompt of root user is' # ', and that of other users is' $'.
7. Execute orders
Start to input the command at the cursor behind the command prompt. After completing the command input, press enter to start executing the command.
8. Basic format of command
command [option] [target] #Command: command name #Options: command options #target: operable objects such as files, devices and users
9. Options
Different options can be used to instruct commands to complete specific operations. Generally, options are divided into short format (-) and long format (–). Short format options are usually represented by a single character, and multiple short format options can be used together.
# Example: ls -l -d /home/zc # Equivalent to ls -l --directory /home/zc # Equivalent to ls -ld /home/zc
10. Standard input (stdin)
The simple understanding is the keyboard. In Linux, the standard input is connected to the device file / dev/stdin. The standard input file descriptor is 0.
11. Standard output (stdout)
The simple understanding is the screen. In Linux, the standard output is connected to the device file / dev/stdout. The file descriptor for standard output is 1.
12. Standard error output (stderr)
The standard error output is the output location when the command executes an error. It is also the screen by default and is connected to the device file / dev/stderr. The file descriptor for standard error output is 2.
12. I / O redirection
Redirection is to change the original input or output position to another place.
13. Output redirection (> or > >)
#The content originally output to the screen is redirected and overwritten to the file file command 1> file #The content originally output to the screen is redirected and appended to the file file command 1>> file #File descriptor 1 can be omitted command > file command >> file
13. Error output redirection
#When the command is wrong, the error message is output to the screen #Output the error to the black hole device, that is, discard all error messages command 2> /dev/null
14. Standard input redirection
#Note that not all commands can receive data from standard input #Redirect the file to the standard input of the command command 0< file #File descriptor 0 can be omitted command < file
15. Pipeline (|)
Pipes are used to connect the standard output of one command to the standard input of another command. What is actually done is that the output of the previous command is redirected, and the standard input of the latter command is redirected.
# Basic syntax: command1 | command2 | ...
16. Command multiline input
By default, when you enter a command, the shell will execute the command automatically after you press enter. If the command to be input is too long and you want to input in multiple lines, you can't press enter directly. You need to press a backslash '' first, and then press enter. The special meaning of the sample enter will be escaped to the ordinary line feed meaning.
17. Order completion
When entering a command on the command line, you can complete the command, file name, directory name, etc. by pressing tab. If you press the tab key twice in a row, all possible complements will be output according to the currently entered characters.
18. Historical orders
bash has the function of recording commands executed in the past. You can view all commands entered by the current user through the history command.
[zc@localhost /]$ history 1 df 2 man fdisk 3 fdisk /dev/sda 4 sudo fdisk /dev/sda 5 man gdisk ...
Use exclamation marks! Add the historical command number to execute the historical command again
[zc@localhost /]$ !1 df Filesystem 1K-blocks Used Available Use% Mounted on devtmpfs 885628 0 885628 0% /dev tmpfs 916220 0 916220 0% /dev/shm ...
You can also press the ↑ direction key in the terminal window to view the previous historical commands in turn. When you turn to the command to be re executed, press the enter key.
19. Command line help
19.1 -- help option of command
If you only want to view the usage and common options of the command, you can use the -- help option. Most Linux commands provide this option.
ls --help [zc@localhost /]$ ls --help Usage: ls [OPTION]... [FILE]... List information about the FILEs (the current directory by default). Sort entries alphabetically if none of -cftuvSUX nor --sort is specified. Mandatory arguments to long options are mandatory for short options too. -a, --all do not ignore entries starting with . -A, --almost-all do not list implied . and .. --author with -l, print the author of each file -b, --escape print C-style escapes for nongraphic characters --block-size=SIZE with -l, scale sizes by SIZE when printing them; ...
19.2 man page
The full name of man page is Manual page, which is the help document for commands and functions in linux /unix environment.
# man page use the man command to view # Command format: man [option] [Command name]
19.3 contents of the manual
- name: function brief description
- SYNOPSIS: Syntax
- DESCRIPTION: precautions
- OPTIONS: description of OPTIONS
- SEE ALSO: relevant contents
Section 19.4 man
| chapter | explain |
|---|---|
| man1 | Provides a description of commands used by ordinary users |
| man2 | Description of system call and kernel function |
| man3 | Description of subroutines and library functions |
| man4 | /Device file description in dev directory |
| man5 | /Format description of configuration file in etc directory |
| man6 | Game manual |
| man7 | Protocol conversion manual |
| man8 | System management manuals available to root |
| man9 | Linux system routine manual |
19.5 see which sections of the command help
whereis
# The where is command displays the path of the command, its source code, and all help files # Command format: whereis Command name # Example: whereis read read: /usr/bin/read /usr/share/man/man1/read.1.gz /usr/share/man/man1p/read.1p.gz /usr/share/man/man2/read.2.gz /usr/share/man/man3p/read.3p.gz
19.6 whatis
# The whatis command is used to view the database. The database needs to be created by the root user through the mandb command in advance # Command format: whatis Command name # Example: mandb whatis read read (1) - bash built-in commands, see bash(1) read (1p) - read a line from standard input read (2) - read from a file descriptor read (3p) - read from a file
19.7 man page operation command
| Shortcut key | function |
|---|---|
| Space bar | Turn down one page |
| ctrl+f | Turn down one page |
| ctrl+b | Turn up one page |
| G | Go to page 1 |
| g | To the last page |
| /string | Search down the string |
| ?string | Search up for string |
| n | Search next |
| N | Search previous |
| q | sign out |
20. info page
It is a proprietary help system for Linux system and has stronger interactivity.
# The info page can be viewed using the info command # Command format: info [option] [Command name]
20.1 info page operation command
| Shortcut key | function |
|---|---|
| Space bar | Turn down one page |
| tab | Move between nodes, and nodes are displayed with asterisks |
| enter | When the cursor is on the node, it will enter the node |
| b | Move to the first node of the current page |
| e | Move to the last node of the current page |
| n | Go to the next node |
| p | Go to the previous node |
| u | Return to the previous level |
| s string | Keyword search |
| ? | List of commands |
| q | sign out |