Linux system commands can be divided into internal commands and external commands. Internal command, also known as built-in command (builtin). How to distinguish between internal commands and external commands? Enter the command man bash, you can see all the internal commands.
How to use the command View
Internal command
method one
#help COMMAND, directly help, followed by the command to query, for example:
help cd
Second way
#man help, execute this command, you get a list of all the built-in commands and how to use
Man Cd
External command
method one
Use COMMAND --help, for example:
bash --help
Second way
Manual (manual), format: man COMMAND, for example,
man bash
Three ways
Use information pages info COMMAND, for instance:
info bash