Four, Linux common commands

A few basic commands (pwd, cd, ls, echo, date, clock, cal, hwclock, cat, tac, file, type, tty, halt, poweroff, shutdown, reboot):

• tty: View the current terminal equipment;

• ifconfig or ip addr list: View active interface ip address;

• echo: echo

• ping: the communication between the detection target host with the current host network;

• Ctrl + c: termination command;

• Shutdown command:
  CentOS 7:
  ~] # systemctl poweroff
  ~] # systemctl reboot

• *：
  ~]# poweroff
  ~]# halt
  ~]# reboot

Linux Basics

• The general format of the command syntax:
  1. The COMMAND the OPTIONS ARGUMENTS #
     - the COMMAND:
     initiating a command: ask the kernel will run a binary program is a process;
     Programs -> Process
     Static -> Dynamic (life cycle)
     - the OPTIONS:
     operating characteristics specified command;
     Option Two kinds of forms:
     short options: -C, e.g. -l, -d
     Note: some commands are not options -;
     if the same command simultaneously using a plurality of short options, the majority can be combined: -l -d = -ld
     long options: - word, such as -help, --human-readable
     NOTE: long options can not be combined;
     Note: some options can take parameters, this option is called a parameter;
     - aRGUMENTS:
     role of the object command; command what to take effect;
     Note: different commands parameter; some commands can be simultaneously with a plurality of parameters, separated by whitespace between the plurality;
     example: ls -ld / var / etc
  2. Command itself is an executable program file: binary file format, there may be calls shared library files;
     most system files are stored in: / bin, / sbin, / usr / bin, / usr / sbin, / usr / local / bin, / usr / local / sbin
     - Normal command: / bin, / usr / bin, / usr / local / bin
     - management commands: / sbin, / usr / sbin , / usr / local / sbin
     shared libraries: / lib, / lib64, / usr / lib, / usr / lib64, / usr / local / lib, / usr / local / lib64
     32bits libraries: / lib, / usr / lib, / usr / local / lib
     64bits libraries: / lib64, / usr / lib64, / usr / local / lib64
     Note : not all of the command has a corresponding executable program files in a directory
  3. Commands are divided into two categories:
     a built-in command shell program: built-in command (builtin)
     stand-alone executable program file, the file name is the command name: external command
  4. shell program is a unique program that is responsible for parsing command provided by the user;
     environment variables :
     the PATH: Find command file the user types the command string corresponding to the path from which;
     ~] # echo $ the PATH
     /usr/lib64/qt-3.3 / bin: / usr / local / sbin: / usr / local / bin: / usr / sbin: / usr / bin: / root / bin
     lookup order: from left to right ;
  5. View command types: type COMMAND

Get help using the command:

Internal commands: Help the COMMAND
external command:

1. Command comes with brief format using the Help
   # COMMAND --help

2. Manual : manual
   location: / usr / report this content share / man
   # man the COMMAND

   • The SECTION:
     NAME: Functional Description
     SYNOPSIS: syntax
     DESCRIPTION: Description
     OPTIONS: Option
     EXAMPLES: Example of use
     AUTHOR: Author
     BUGS: bug reporting procedures manner
     SEE ALSO: reference
     ...
   • The SYNOPSIS:
     []: optional content;
     <>: content must be provided;
     A | B | C: a multiple-choice;
     ...: a plurality of similar content may occur;

   Manual :
   compression format, there are sub-sections of;
   / usr / Share / man
   man1, man2, ...
   . 1: user command;
   2: system call;
   . 3: C library calls;
   4: device files and special files;
   5: file formats; (configuration file format)
   6: The game uses the help;
   7: miscellaneous;
   8: management tools and be the guardian;

   • ~] # Man CHAPTER COMMAND
     Note: Not every COMMAND in all chapters have manuals;
   • View:
     ~] # whatis the COMMAND
     Note: its execution is to query the database;
     manually update the database:
     ~] # makewhatis

3. After the man command to open the manual method of operation:

• Scroll:
  spacebar: turning a screen to the end of the file;
  B: turning a screen to the header file;
  the Ctrl + D: Total half screen to the end of the file;
  the Ctrl + U: Total half screen to the header file;
  ENTER: the file turn tail line;
  K: a line to turn the file header;
  G: jump to last line;
  #G: Jump to the specified line;
  . 1G: jumping to a file header;
• Text Search:
  / keyword: Find the file header to the end of the file sequentially; not case sensitive characters;
  keyword:? In order to find the end of the file to the file header;
  the n-: the same as the Find command direction;
  N: Contrary to the Find command direction;
• Quit:
  q: quit

3. info COMMAND
   obtain online documentation command;

4. The application comes with a lot of help documentation: / usr / report this content share / DOC / APP-VERSION
   the README: information related to the program;
   the INSTALL: installation help;
   the CHANGES: change information when the iterative version;

5. Mainstream release official documents
   http://www.redhat.com/doc

6. The official program documents:
   "the Document" on the official site

7. Search engine
   Google
   keyword filetype: pdf
   keyword Site: domain.tld
   ...

Linux file system

1. File names are case-sensitive strict
2. File names can be used in addition to / unexpected characters
3. File name can not exceed 255 characters
4. With files beginning for hidden files
5. .: Indicates the current directory
6. ...: Indicates the current directory of the parent directory

Linux common commands

1. pwd: print working directory (Display the working directory)
2. cd: change directory (change directory) with no home directory for the parameter (Home)

 cd [-L|[-P [-e]]] [dir]

• cd ~ hyf: indicates the home directory to the user hyf
• cd -: Switch to the last visited directory (related environmental variables)
  - $ PWD: current working directory
  - OLDPWD: once the working directory

[hyf@pc001 ~]$ type cd
cd 是 shell 内嵌
使用help cd
-L      force symbolic links to be followed(强制遵循符号链接)
-P      use the physical directory structure without following symbolic
        links(使用物理目录结构而不使用以下符号链接)
-e      if the -P option is supplied, and the current working directory
        cannot be determined successfully, exit with a non-zero status
        (如果提供了-p选项，以及当前工作目录无法成功确定，以非零状态退出)

3. ls: list, list the contents of the specified directory
   LS [the OPTION] ... [the FILE] ...
   -a: show all files, including hidden files;
   -A: Show ... and all files except the;.
   -l: - long, long list of formats, displays detailed file attribute information;
   -h, --human-readable: file size unit conversion; the conversion results may be inexact value;
   -d: view the directory itself, rather than its internal documents list;
   -R & lt: Reverse, reverse display;
   -R & lt: recursive This, recursively display;

-rw-r--r--. 1 root   root     8957 10月 14 19:34 boot.log
-：文件类型，-, d, b, c, l, s, p
rw-r--r--
rw-：文件属主的权限；
r--：文件属组的权限；
r--：其它用户（非属主、属组）的权限；
1：数字表示文件被硬链接的次数；
oot：文件的属主；
root：文件的属组；
8957：数字表示文件的大小，单位是字节；
10月 14 19:34 ：文件最近一次被修改的时间；
boot.log：文件名

4. cat: concatenate
   file text viewer;
   CAT / etc / fstab
   CAT / etc / passwd

• CAT [the OPTION] ... [the FILE] ...
  -n: to display the text line number;
  -E: display linefeed $;

5. tac:
   File text viewer;
   tac / etc / fstab
   tac / etc / passwd
   tac [OPTION] ... [FILE] ...
   -n: to display the number of lines of text;
   -E: display linefeed $;
6. file: Check file content type;
   File [FILE] ...
7. echo: echo
   echo [SHORT-the OPTION] ... [STRING] ...
   -n: not wrap;
   -e: Let tropes take effect;
   \ n-: newline
   \ t: tab
   STRING
   can use quotation marks, apostrophes and bis quotes are available;
   single quotes: strong references, variable reference replacement is not carried;
   ~] # echo ' Katex the parse error: the Expected' the EOF ', GOT' # 'AT position 28: ... reference variable reference will be replaced; ~] # echo " SHELL"

Date related commands:

Linux: read the system startup date and time information from the hardware; after reading is completed, it is no longer associated with the hardware;
the system clock
hardware clock

date: The system clock
displays date and time: DATE [the OPTION] ... [+ the FORMAT]
the FORMAT: specifier
% F.
% T
% the Y
% m
% D
% H
% M
% S
% S: 1970 January 1 (unix element years) 0:00:00 to command the moment the number of seconds elapsed;
...

Set the date and time : DATE [MMDDhhmm [[the CC] YY] [SS].]
Hwclock, Clock: hardware clock
display or set the hardware clock
-s, --hctosys: prevail in hardware, the hardware system with the adjusted time same;
-w, --systohc: subject to the system, the time was adjusted to the same hardware with the system clock;
CAL: calendar
cal [[month] year]

filename globbing wildcard

• *: Content matches any string length
• ? : Matches any single character
• []: Matches any single character within the specified range \: that the escape character
  • [[: Upper:]]: matches all capital letters
  • [[: Lower:]]: Match all lowercase letters
  • [[: Alpha:]]: matches all the letters
  • [[: Digit:]]: matches all numbers
  • [[: Alnum:]]: Match all letters and digits
  • [[: Space:]]: matches whitespace characters
  • [[: Punct:]]: Matches all punctuation
• [^]: Antisense

Redirection and piping

• >: Redirect coverage
• >>: append redirection
• set -C prohibited to overwrite a file that already exists in the redirection
• > |: Indicates a mandatory coverage