linux-bash-shell-command-line-math

note for fractions/decimals you need "bc"

echo $((1+2))


$((expression))

 id++ id--   variable post-increment and post-decrement
       ++id --id   variable pre-increment and pre-decrement
       - +             unary minus and plus
       ! ~             logical and bitwise negation
       **              exponentiation
       * / %         multiplication, division, remainder
       + -             addition, subtraction
       <>       left and right bitwise shifts
       =
                        comparison
       == !=       equality and inequality
       &               bitwise AND
       ^               bitwise exclusive OR
       |                bitwise OR
       &&             logical AND
       ||              logical OR
       expr?expr:expr
                        conditional operator
       = *= /= %= += -= <>= &= ^= |=
                        assignment
       expr1 , expr2
                        comma