Shell operator

declare Declare variable type

declare [+/-][ Options ] Variable name
-： Set the type of comfort for the variable
+： 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

Numerical operation

Method 1

Use declare -i

 aa=11
 bb=22
 declare -i cc=$aa+$bb
 echo $cc
33

expr or let Numerical tools

 aa=22
 bb=33
 dd=$(expr $aa + $bb)
 echo $dd
55

$((shipmentcounttype))or$[ Arithmetic expression ]

 aa=33
 bb=44
 cc=$(($aa+$bb))
 echo $cc
77