Man/ls/clock/date/echo notes

Login
User name: User ID

Authentication mechanism: Authentication
Authorization: Authorization
Audit: Audition (log)

Prompt, command prompt:
Command:
Magic Number: Magic Numbers
Shebang

#!/bin/bash

# Command Options ... arguments ...

Options:
Short options
Long options
Parameters:

List:ls
Lists, lists

Directories: Files, path mappings

Path: The location from the specified starting point to the destination

FileSystem: File System

List files under the specified path


Catalog: Working directory, current directory

Pwd:printing working Directory

Ls
-L: Long format
File type: the
-: Normal file (f)
D: Catalog file
B: Block device files (blocks)
C: Character device file (character)
L: Symbolic Link files (symbolic link file)
P: Command pipe file (pipe)
S: Socket file (socket)
File permissions: 9-bit, every 3-bit group, each group: rwx (Read, write, execute), r--
Number of hard links to files
Owner of the file
Genus Group of files
File size (size), in bytes
Timestamp (timestamp): Last Modified Time
Access: Access
Modified: Modify, the file content has changed
Change: change,metadata, meta data
-H: Do unit conversions
-A: Show hidden files starting with.
. Represents the current directory
.. Represents the parent directory
-A
-D: Display the directory's own properties
-i:index node, inode
-R: Reverse Display
-R: Recursive (Recursive) display

Cd:change Directory
Home directories, home directories, home directory
CD ~username: Enter the home directory of the specified user
CD-: Switch back and forth between the current directory and the previous directory

Command type:
Built-in command (shell built-in), internal, built-in
External command: There is an executable file corresponding to the command name in a path on the file system

Environment variables: named memory space
Assigning values to variables
Name=jerry

Path: Paths separated by colons
O (1)

Type: display specifies which type to belong to

Date: Time Management
Linux:rtc

Hardware clock
System clock


Get help with the use of commands:
Internal command:
Help COMMAND
External command:
COMMAND--help

Command manual: Manual
Mans COMMAND

Whatis command View commands are described in those chapters

Sub-chapters:
1: User command (/bin,/usr/bin,/usr/local/bin)
2: System call
3: Library User
4: Special files (device files)
5: File Format (configuration file syntax)
6: Game
7: Miscellaneous (Miscellaneous)
8: Management Command (/sbin,/usr/sbin,/usr/local/sbin)

<>: Required
[]: Optional
... : multiple times can occur
|: Choose one More
{}: Grouping

Mans:
Name: command names and features brief description
Synopsis: Usage notes, including available options
DESCRIPTION: A detailed description of the command function, which may include the meaning of each option
Options: Explaining the meaning of each option
Files: The configuration file associated with this command
BUGS:
EXAMPLES: Using the example
See ALSO: Another reference

Flip Screen:
Turn back one screen: SPACE
Turn One screen forward: b
Turn back one line: ENTER
Turn One line forward: K

Find:
/keyword: Backwards
N: Next
N: Previous

? KEYWORD: Forward
N: Next
N: Previous

Q: Exit


Online Documentation:
Info COMMAND

Document:/usr/share/doc

Google

Apache, Hadoop

Practice:
Use date to get the system's current year, month, day, hour, minute, second separately

Hwclock
-W: Writes the system time to the hardware clock
-S: Write hardware clock to system


Cal:calendar

Practice:
1. is echo an internal command or an external command?
2, its role?
3, how to display "The year is 2013." Today is 26. " For two lines?

Escaping, escaping

Practice:
1. is printf an internal command or an external command?
2, its role?
3, how to display "The year is 2013." Today is 26. " For two lines?

The file command and its usage.

Man/ls/clock/date/echo notes