Linux help command : help,--help,man,info

type command : View command type(Internal Command,External Command)

eg.:
[root@levi ~]# type -a cd 
cd is a shell builtin (Internal Command)

[root@levi ~]# type -a grep 
 grep is /bin/grep    ( External Command)

1.Internal Command (Help view)

help COMMAND

2.External Command (help view)

COMMAND --help

3.Command Manual(man)

man    COMMAND
whatis COMMAND : The query where the section.

Sub sections:

1. The user command (/bin, /usr/bin, /usr/local/bin)

2. System Calls

3. The library calls

4. The special file (device file)

5. File Format (syntax of the configuration file)

6. Games

7. Miscellaneous (Miscellaneoous)

8. Management Command (/sbin, /user /sbin, /usr/local/sbin)

MAN Help symbol meaning:

[] : Optional

<> : Must be given

...: Can appear multiple times

|  : A multiple-choice

{} : Grouping

Scroll screen:

Turned back one screen: SPACE

Backward one screen: b

Backward row: k

Backward line: ENTER

Find:

/ KEYWORD: back
? KEYWORD: Forward
n: next
N: Previous
q: Quit

Online Documentation

info COMMAND