Shell Programming-Initial

Programming languages are generally divided into static languages and dynamic languages.

Static language: Compiled language strongly typed (variable) pre-compiled

Example: C C + + Java C #

Dynamic language: Interpreted language weak type (default variable type is not distinguished, and the default type is String type)

Example: PHP Shell python perl

Object-oriented : Java python

process oriented : Shell

variables : Memory space, named memory space #能回收

memory : addressable memory space

the types of variables can be divided into: character, value, true and false declaration variable type is the role of predetermined storage format and length

logical Operations : with, or, non-, XOR, or

#非门在现实中使用电磁感应, switch closed circuit.

the variables in bash can be divided into: environment variables , local variables (local variables), positional variables, special variables

Local Variables ; Varname=value acting on the entire bash process

reference variable $ (VARNAME) variable can sometimes be omitted

Locals local Varname=value acting on the current code snippet

Environment Variables acting on the current shell process and its child processes

Export Varname=value "Exporting"

The child shell process is started as the script executes

The command-line startup script inherits the environment variables of the current shell

Scripts that are automatically executed by the system (not command-line startup) require a self-defined environment variable

position Variable $1,$2

Special variable $? Save Last Command execution status return value

Program status return code 0: Execute correctly

1-255: Error 1.2.127 System reservation

Output REDIRECT :>,>>,2>,2>>,&>

Example: ID username &>/dev/null #/dev/null for data black hole bit bucket

Undo Variable unset VARNAME #创建变量为

View variable Set

View the current shell environment variables printenv ENV Export

environment variable Add : String variable can be used, such as export path= $PATH:(add pathname)

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Shell Programming-Initial