Rights Management 2 and Bash feature shortcuts, completion functions and types of variables, login types, scripts

Rights Management:

Owner Group Other

Belong to the main group other

Permissions: Read Write Execute

R W X

File:

-R: You can use the File View Class command to display related content

-W: You can use the editor to modify the content

-X: You can launch it into a process

Directory:

-R: You can use the LS command to view file information for directory contents

-W: can create delete file

-X: You can use the Ls-l command to view the file information for the content, and you can use the CD command

The user does not have a certain permission, then the-placeholder

Use a 8-digit number to represent

R W X

4 2 1

Modify the owner and owner of the file, only administrators can perform: Chown chgrp

Modify file Permissions chmod

ACTION Specifies the permissions of the category user: Use U g o A to empower, based on = or +/-

Assign rights to the current file by referencing other files

chmod--reference= Reference file name

Permissions Application Model

The owner of the process is the same as the owner of the file, and if it is the same, the process is accessed with the permissions of the owner of the file;

The genus of the process is the same as the group of files, and if the same, the process is accessed with the permissions of the group of files;

The process accesses the file with the permission of the other user of the file

Bash Introduction:

Shell: human-computer interface

Called the command interpreter

Features of Bash

Shortcut keys:

CTRL + A: Jump to the beginning of the command

Ctrl+e: Jump to the end of the command line

Ctrl+u: Deletes the contents of the command line from the beginning to the current cursor location

Ctrl+k: Deletes the contents of the current cursor at the end of the line

Ctrl+l: Clear Screen

CTRL + C: Terminate or Cancel commands

CTRL + Z: Send the current command to the background (FG recall)

Features of Bash

Complement function

Command completion: Search for completion in path

Shell command: Internal external

External: There is an executable program under a certain path in the system

Path, a colon-delimited set of paths

Use the TAB key to complete

Path completion: Complete under the given heading path, or the current directory if there is no path to the prefix

Programming Languages:
C: A set of specifications defined in advance, converted to assembler by keyword in a specific grammatical structure (selection, order)
Compiler: Language platform
Interpreter: Language platform

Program execution Logic

Sequential execution from top to bottom

Select Execution (condition)

Loop execution

Dynamic Language:
Explanatory language
Perl bash Python
Static language:
Compiled languages
C,c++,
Variable:
Data storage format:
Ascii:
Binary:
According to whether their variables need to be strictly defined by their type to divide
Strongly typed language: C
Weakly typed language: Bash
Define the role of the variable type:
1. Data storage format:
2. Limited storage range of data
3, the comparison mechanism is different,
4. Different types of operations involved
Character type:

Numeric type: positive or negative
Precise numerical type:
Plastic:
Approximate numerical type:
Floating point number:
Single precision:
Double precision:
Time and Date type:
Boolean type: True and False

Features of BASH: providing a programming environment

Support for using variables

Support for environmental control

Any program that needs to be executed has an interpreter

#！ /bin/bash is called Shebang

program = instruction + data
Variable
Weakly typed languages:
1. Do not enforce the type of the variable, regardless of the data stored in the character format
2. No prior declaration: When used, direct use, direct assignment
BASH: A dynamic programming language, a weakly typed language

Rights Management 2 and Bash feature shortcuts, completion functions and types of variables, login types, scripts