Bash variables - numeric operations and operators

1、declare Declare variable type

#declare [+_] [ Options ] Variable name

- ---- Set type properties to variables

+ ----- Remove the type attribute of a variable

-i ------- Declare a variable as an integer (integer)

-x ------ Declare a variable as an environment variable

-p ------ Displays the declared type of the specified variable

2、 Numerical operation --- Method 1

#aa=11

#bb=22

#declare -i cc=$aa+$bb

#echo $cc

Method 2:expr or let Numerical tools

#aa=11

#bb=22

#dd=$(expr $aa + $bb) ---------- Be careful + There must be spaces on the left and right sides

Method 3:$(( Arithmetic expression )) or $[ Arithmetic expression ]

#aa=11

#bb=22

#ff=$(($aa+$bb))

#echo $ff

You can do logical operations && ||.