Shell Programming Details (i)

Shell programming

The language is divided into:

Compiled languages: first to be translated into executable format

Interpreted language: Side interpretation side Execution

Variables: The shell is a weakly typed programming language, and the variable does not need to indicate the type and initialization, but the context determines the type

Bash Variable type:

Environment variables

Local variables

Positional variables

Special Custom variables

Local variables: scope for the entire bash process

Varname=value

Local variables: Scope current Code

Local Varname=value

Environment variable: scope is the current shell process and child process

Export Varname=value

Conditional judgment

How to achieve conditional judgment in hash?

Condition Test Type:

Integer test

Character test

File test

Expressions for Conditional tests:

[Expression]

[[Expression]]

Test expression

Integer comparison:

-EQ: Tests whether two integers are equal

-ne: Not Equal

-GT: Greater Than

-LT: Less than

-ge: greater than or equal to

-le: Less than or equal to

Logical relationships between commands:

Logic and:&&

Logical OR: | |

Logical non-:!

Condition Judgment: Control structure

if judgment condition; Then

Statements

Elif judgment condition; Then

Statements

Else

Statements

Fi

How to perform arithmetic operations in the shell:

A=3

B=6

Let arithmetic op-expression

Let c= $a + $b

$[arithmetic Operation expression "

c=$[$a + $b]

$ ((arithmetic operation expression))

c==$ (($a + $b))

Expr arithmetic expression, with spaces between operands and operators in an expression, and using command references

C= ' expr $a + $b '

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Shell Programming Details (i)