Linux Learning Record-number comparison-IF statement-arithmetic operations

Integer comparison

-eq: Equals

-NQ: Unequal

-GT: Greater Than

-LT: Less than

-ge: greater than or equal to

-le: Less than or equal to

Usage:

A=3

B=4

[$A-eq $B]

echo $?

Logic and:&&

Logical OR: | |

Variable name:

1. Can only contain letters, numbers, underscores, and cannot begin with a number

2. Should not be the same as the existing environment variables in the system

3. It is best to see the name and the meaning

Single Branch if statement

If judgment condition: Then

Statement1

Statement2

..

Fi

If statements for dual branches

if judgment condition; then

Statement1

Statement2

..

Else

Statement3

Statement4

..

Fi

How to perform arithmetic operations in the shell:

A=3

B=6

1. Let arithmetic op-expression

c= $A + $B

2. $[arithmetic operation expression]

c=$[$A + $B]

3.$ ((arithmetic expression))

c=$ (($A + $B))

4.expr arithmetic expression, in which the various operands and operations in the expression are to be inverted, and to use the command reference

c= ' expr $A + $B '

Linux Learning Record-number comparison-IF statement-arithmetic operations