List of Arithmetic Operators
+ Addition
- Subtraction
/ Division
* Multiplication
% Modulus
++ post-increment
-- post-decrement
** Exponentiation
Using Operators
expr command
In Linux arthmatic operation can be done by the expr command, expr became popular in the days of the Bourne Shell, which did not support math. With Bash and Korn shell, it is generally not needed. expr treats the variable as a string
Example usage
$ z=10
$ z=`expr $z+1` ---- Need spaces around + sign.
$ echo $z
10+1
$ z=`expr $z + 1`
$ echo $z
11
let command
In Bash and Korn shell we have a command called let which is used for mathematical operations. It is also a little picky about spaces and behave opposite of expr. let also relaxes the normal rule of needing a $ in front of variables to be read.
Example
$ let z=10
$ echo $z
10
$ let z=$z+1
$ echo $z
11
$ let z=$z + 1 # --- Spaces around + sign are bad with let
$ let z=z+1 # --- no $ to read a variable.
$ echo $z
12
Alternate Method
An alternate method is use of double parenthesis and similar to let command but more forgiving about spaces.
$ ((e=10))
$ echo $e
10
$ (( e = e + 3 ))
$ echo $e
13
$ (( e=e+4 )) # -- spaces or no spaces, it doesn't matter
$ echo $e
17
