Puff---------Linux Bash Basic features (2)

The philosophical thought of Linux

All documents

Avoid interaction and implement bash programming

Text Programming Command Implementation configuration

Combine small programs to complete complex tasks

Summarize

Program programming

Interpreting execution

The difference between character and value storage

Shebang, CPU, interpreter

Data type

Variable type, which is the type of the internal data

Bash

Program programming, interpreting execution

The type of the variable is: weak type

ONE) Bash programming

Programming Style: procedural programming, Object-type programming

Program Programming: purpose to solve problems

Only consider how the data is organized

Instruction Organization Data

To complete a complex task

Sequential execution: Running tasks individually

Select Execute: There is a standard to execute only some code snippets

Loop execution: Make some code fragments repeat n times

How the program executes

compile execution: C,java after translation: Advanced language ---------------------------

Explanation execution: Shell,python,java side translation Side Execution , in order to avoid the confusion of the context, the first grammar examination of the program, will be translated: interpreted language---interpreter----Target code

Explain the characteristics of execution

Plain Text , magic number is a code that indicates the path of the interpreter

The source program is executed by the interpreter

The interpreter runs on the CPU , and the text is run by the interpreter

magic number : The source code is compiled into binary, the first n bytes of the file, used to determine the format of the executable program

the structure of the programming language :

data storage: variables, arrays

An expression, a statement

programming languages, in order to make programming simple :

Operating system provides libraries

Provide an interpreter

Shell program:

procedural programming, interpreting execution

Shell Programming Features

Calling System programs directly

Stacking of commands

Environments that rely heavily on the operating system

the format of the shell script :

must have a fixed format: first act magic number

Must be able to read the $path value, bash relies heavily on path to find the execution program file

、

To run the script:

1, give permission, specify the file execution through the specific path

2, direct interpretation of execution, the script as the parameters of the Interpreter program execution

12. Variables

variable name : The memory space of the command that can be referenced by name, and the name of the memory space that can be called beforehand.

Variables: memory space for a single command

program = instruction + data

Data can be stored in variables, arrays, lists, files

The type of data stored in the variable

character type : Use bits to represent all changes. For example, 2^16 represents 5000 variations of all Chinese characters, and this stipulation has gbk2313,gb18030 and so on. 127 variations of all numbers, letters, and special characters with 2^8, ASCII code table specified by the United States

So when storing a Chinese character, use 16 bits, and store a number with 8 bits.

Numeric Type

Integer, numeric data such as 1100 binary conversion to binary number:-----1101110 with 7-bit

Floating point Type

* Any data can be included in these two types of

Today: Characters with 16 + 16 bit

Number of days equivalent to Unix

Boolean type

1:true 0 representation of the status result of a command in bash

1-255 representation of the status result of a command in 0:false bash

Logical operation:

With: The circuit is in series, while the true result is true, the others are false.

Or: The circuit is in parallel, a true result is true, the others are false.

Non: Electromagnetic induction of the circuit, the result of the operation is reversed, non-true is false. Non-false is true

Short-circuit Operation:

With: False on the left and false on the left. True, the second must participate in an operation

or: The first is true and the result is true. False on the left, tenth must participate in the operation

Operation:

All character type: 10 + 110 = 10110

All numeric: 10 + 110 = 120

If the data types in the variables are not uniform, the operation will be confusing

2) variables

Types of variables :

the type of the variable is the type of the data store in the variable

The role of variables:

Deciding which operations to participate in

Determine the data range of the variable: integer 4 bytes, 32 bits, 2^32=40 more than billions of digits

Variable type

Character

Numerical

Integral type

Floating point Type

strongly typed and weakly typed

Strongly typed: Must declare that the variable is a character or numeric type

Weak type : No prior declaration of the type of variable, shell

Characteristics of weak types

Unified storage for Character type

Automatic switching is done if the operation is required

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Puff---------Linux Bash Basic features (2)