Linux Self-Study notes (5): Linux basic commands

Basic command:
Date:date--help
Usage: date [options] ... [+ format]
Or: Date [-u|--utc|--universal] [MMDDHHMM[[CC]YY][-SS]]
Date [MMDDHHMM[[CC]YY][-SS]]: Set
MM: Month
DD: Day
HH: When
MM: Min
YY: two-digit year
CCYY: four-bit year
-ss: Seconds

Two types of clocks for Linux
System clock: The timing of the CPU's operating frequency by the Linux kernel;
Hardware clock:
Huclock: Display Hardware clock
-s,--hctosys
-w,--systohc

        cal：日历            cal 2018 年历

Directory-related commands:
Working directory for current directory
Home directory: Family directory: Home
Root:/root
Normal User:/home/username

    ~用户主目录

Cd:
CD or CD ~: Back to the current user's home directory
CD ~ USERNAME: Switch to the home directory of the specified directory
CD ~: Switch back and forth between the previous directory and the current directory

相关的环境变量    PWD：保存了当前目录路径    OLDPWD：上一次所在的目录路径

PWD: Show current directory

Ls:list
Displays a list of files under the path path

Usage: LS [option] ... [File] ...
-A,--all does not hide anything. Start of Project
-L: Long format
-H: Unit conversion
-D: View the directory's own related properties to use with-l
Dr-xr-xr-x. 5 root root 4096 January 16:01 boot
First bit: File type
Second to Nineth bit: access rights
Number: The number of times a file has been hard-linked;
First Root: The owner of a file
Second Root: The genus Group of a file
4096: Size of the file
January 16:01 Boot: The time the file was last modified

stat /PARHTO/SOMEFILE：获取指定文件的元数据

File View command:
Cat, TRC
Usage: cat [options] ... [File] ...
-E,--show-ends displays "$" at the end of each line
File content view command: Files
File/

Echoing command: Echo
[email protected] ~]# help Echo
Echo:echo [-nee] [parameters ...]
Writes the parameters to standard output.

在标准输出上显示 ARG 参数后跟一个换行。选项：  -n    不要追加换行  -e    启用下列反斜杠转义的解释  -E    显式地抑制对于反斜杠转义的解释

• ' Echo ' escapes the following backslash characters:
  \a Warning (Bell)
  \b Backspace
  \c suppresses more output
  \e Escape character
  \f Format provides
  \ nthe line break
  \ r Enter
  \ t Transverse tab
  \v Portrait tab

echo "$VAR _name": variable is substituted, double-cited indicates weak reference
Echo ' $VAR _name ': variable does not replace, strong reference

[Email protected] ~]# Whatis--help
Usage:whatis [OPTION ...] keywords ...

-D,--debug output debug information
-V,--verbose output verbose warning message
-R,--regex each keyword as a regular expression
-W,--wildcard keyword contains wildcard characters
-L,--long do not truncate the output by the end width
-C, the--config-file= file uses the user settings file
-L,--locale= region defines the locale used for this search
-M,--systems= system use manual pages from other systems
-M,--manpath= path Setting the path to the Search man page is "path"
-S,--sections= list,--section= list
Search only these sections (colon-separated)
-?,--help give this help list
--usage give a short usage message
-V,--version print program version

Whatis
Oh, yes, that whatis. command to create a database of all the help manuals for the current system and the corresponding keywords;

Linux Self-Study notes (5): Linux basic commands