Linux basic-01-linux basic command


1. Linux command format

1) syntax format of Linux command:
Command options parameters
2) specific meaning of command, option and parameter in command format
A) command: tell the Linux (Unix) operating system what to do (execute).
B) option: describes the way the command is run (the function of the command can be changed). The options section starts with the “-” character.
C) parameters: describe what the command affects (operation) (such as a file, a directory or a paragraph of text)

2. WhoamI command

1) function of whoamI command: list the user name (account) currently used to log in to Linux system.

3. who command

1) function of who command: list which users are currently working on the system.
2) output results of who command: display all currently logged in users, as well as the current date and time.

4. Date, Cal, and clear commands and commands with parameters

1) function of date command: display the current date and time of the system.
2) the date command sets the format of time and time: date, month, day, hour, year.
For example: set the time to 10:18 a.m. on December 24, 2013:
Extension (date 122410182013
Hwlock – s synchronization hardware – w synchronization system)
3) cal command function: display the calendar of a month.
4) apply cal command to list the calendar of a certain month in a certain year:
For example, the command to display the calendar of August 2008 is cal 8 2008
5) function of clear command: clear screen
6) clear screen shortcut key: Ctrl + L

5. Su and passwd commands

1) Su command function: switch from the current user to another specified user.
2) Su command to switch users:
For example: switch to the command of root user: Su – root
3) passwd command function: modify the password of the user (either ordinary user or root user), check the password status of the user, etc. Useradd
4) use the passwd command to change the user password:
For example: command to change the password of the dog user: passwd dog

6. Get command help information

1) use man command
For example: the command to view the instructions for using the Su command is: man Su
2) use — help
For example: the command to view LS command help is: LS — help
Note: the content displayed by man command is the manual page (man is the abbreviation of manual). Generally, the help information displayed by man command is richer. It has more command usage examples, command descriptions and other contents than the help option of command. Another difference is that the man command is displayed from the man man man page file on the disk. If a man man page file is deleted, it cannot be displayed. The help option of the command is a built-in function of most commands. As long as the command is available on the system, the help option can be displayed.