Shell Programming-operators

1.declare command

Declare declaring variable type: Declare [+/-][option] Variable name

-: Set type attribute to variable

+: Cancels the Type property of a variable

-A: Declaring a variable as an array

-I: Integer

-X: Environment variables

-R: Read-only variable

-P: Displays the declared type of the specified variable

Definition array: movie[0]=zp,movie[1]=tp,declare-d movie[2]=live

View array: ${movie},${movie[2]},${movie[*]}

2. Numerical Operation method

Expr or let numeric arithmetic tool

dd=$ (expr $aa + $bb): Note that there must be spaces between the "+" sign and the left side

dd=$ (($aa + $bb))

dd=$[$aa + $BB]

3. Testing of variables

Shell Programming-operators