2.5-shell Programming Preliminary

Previously review:

File management, user management, rights Management, Bash's basic features

File Management: CP,MV,RM

User management:

Useradd,usermod,userdel,chfn,chsh,chage

Groupadd,groupmod,groupdel

Passwd,gpasswd,pwck

Id,finger,who,whoami,w

Su

Configuration file:/etc/passwd,/etc/shadow,/etc/group,/etc/gshadow

Rights Management:

Perm:mode (RWXRWXRWX), ownership

Chmod,chown,chgrp

-R,---Reference=rfile

File:666-umask

Dir:777-umask

Bash Basic Features:

Command line expansion: ~,{}

Command alias: Alias/unalias

Command history: Historical

Command and path completion: $PATH

glob:*,?, [],[^]

Shortcut key: Ctrl+{a,e,l,c,u,k}

Command hash:

Basic features of Bash (3)

1. Provides a programming environment

Program: Instruction + data

Program Programming Style:

Program: command-centric, data-serving instruction

Object type: Data-centric, instruction serves data

Shell program: Provides programming capabilities to interpret execution

How the program is executed:

Computers: Running binary directives

Programming Languages:

Low Level: Compilation

Senior:

Compiling: High-level language--compiler---Target code

C,c++

Explanation: High-level language--interpreter---Target code

Shell,python,perl

Program Programming:

Sequential execution

Loop execution

Select Execute

Shell programming: Over-Program, interpreting execution

The basic structure of the programming language:

Data storage: variables, arrays

An expression

Statement

Shell script: Text file

Shebang:

#!/bin/bash

#!/usr/bin/python

#!/usr/bin/perl

Magic Number: Magic Numbers

To run the script:

1. Give execution permission to specify file execution through a specific file path:./test.sh

2. Run the interpreter directly and run the script as a parameter of the Interpreter program: Bash test.sh

Variable:

Named memory space:

Data storage mode: ASCII

Characters: 110:24 bit

Value: 110:8 bit

Integral and floating-point types

Variable: Variable type

Role:

1. Data storage format

2. Participate in the operation

3. Range of data represented

Type:

Character

Value: Integer, Float, Boolean

Programming Languages:

Strong type: C

Weak type: Bash

All the data to be stored as characters

Floating-point numbers are not supported

Logical operation:

True,false

1,0

And:

1 && 1 = 1

1 && 0 = 0

0 && 0 = 0

0 && 1 = 0

Or:

1 | | 1 = 1

1 | | 0 = 1

0 | | 0 = 0

0 | | 1 = 1

Non -:

!0 = 1

!1 = 0

Short-circuit Operation:

And:

The first one is 0, and the result must be 0.

The first one is 1, the second must be involved in the operation

Or:

The first one is 1, and the result must be 1.

The first one is 0, the second must be involved in the operation

2.5-shell Programming Preliminary