Shell Basic Features 2

                          Bash of the Base Infrastructure Special Sex2

1. provides a programming environment

Program: Instruction + data

program programming Style:

Process: command-centric, data-serving instruction;

Object type: Data-centric, instruction service to data;

2.Shell Program: Provides programming capability to interpret execution

3. How the program is executed:

3.1 computer: Running binary instructions;

Programming languages:

Low Level: Compilation

Senior:

compiling: Advanced language - > Compilers- à Target Code

C, C + +

Explanation: High-level language-à interpreter-à machine code

SHell, Perl, Python

3.2 Procedural programming Languages:

Sequential execution:

Loop execution:

Select Execute

3.3 S Hell Programming: Process, interpretation and execution

The basic structure of the programming language:

Data storage: variables, arrays

An expression

Statement

4.Shell script: Text file

#!/bin/bash

#!/usr/bin/python

#!/usr/bin/perl

Magic Number: Magic Numbers

4.1 To run the script:

1. give execution permission to make file execution through specific file path;

2. run the interpreter directly and run the script as a parameter of the interpreter program;

5. Variables:

Named memory space:

6. Data storage method:

Characters: 110:24 bits (8 bits in one byte)

Value: 110:8 bits (2^8)

Integral type

Floating point Type

7. variables: Variable type

Role:

1>. Data storage format:

2>. participate in the Operation :

1. the range of data represented :  

Type:

Character

Numerical

Integral type

Floating point type (how to store, how to run??? ）

8. programming Language:

Strong type:

Weak type: Bash

All the data to be stored as characters

Floating-point numbers are not supported:

9. logic operation:

TRue (1), False (0)

And:

1&&1=1

0&&0=0

1&&0=0

0&&1=0

Or:

1 | | 1=1

1 | | 0=1

0 | | 1=1

0 | | 0=0

non- :

! 1=0

！ 0= 1

xor:

Short - circuit operation:

And:

The first one is 0, the result must be 0;

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

or:

The first one is 1, the result must be 1;

the first one is 0, the second must be involved in the Operation

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Shell Basic Features 2