Introduction
BASH was not designed to do anything but the most basic math operations, and does not natively support anything more than integer operations. However, there are a few shell utilities that can overcome this limitation (namely bc).
Arithmetic Evaluation
Description
This command evaluates a given arithmetic expression, <EXPRESSION>.
Arithmetic evaluation implements the standard PEMDAS order of operations (Parentheses, Exponents, Multiplication, Division, Addition, Subtraction).
It does not support arithmetic operations on floating-point numbers (only integer values are supported).
Format
(( <EXPRESSION> ))
Examples
$ echo $(( 5+5 ))
10
$ echo $(( 5*5 ))
25
$ echo $(( 5/5 ))
1
$ echo $(( 5-5 ))
0
$ echo $(( 12 * 13 ))
156
$ echo $(( 5+6/3*2 ))
9
$ echo $(( (5+6)/3*2 ))
6
$ echo $(( 5 % 5 )) # modulus (divides and returns remainder)
0
$ echo $(( 5 % 6 ))
5
$ echo $(( 2**16 ))
65536
$
The let built-in
Description
This command is similar to the arithmetic evaluation command, except that it is specifically designed to set variables to the result of a given expression ( as opposed to direct output of the result).
This command implements the standard PEMDAS order of operations (Parentheses, Exponents, Multiplication, Division, Addition, Subtraction).
It does not support arithmetic operations on floating-point numbers (only integer values are supported).
Format
let x=
Examples
$ let a=5+5
$ echo $a
10
$ let a=5*5
$ echo $a
25
$ let a=5/5
$ echo $a
1
$ let a=5-5
$ echo $a
0
$ let b=5+6/3*2
9
$ let b=(5+6)/3*2
6
$ let a=5%5 # modulus (divides and returns remainder)
$ echo $a
0
$ let a=5%6
$ echo $a
5
$ let a=2**16
$ echo $a
65536
$
bc (basic calculator) - an arbitrary precision calculator language
Description
bc is a built-in shell utility that interprets an “interactive algebraic language with arbitrary precision” by the same name. While there is a lot it can do, it would be outside the scope of this tutorial to explain it all.
The primary advantage to using bc for solving challenges on the site is that it natively handles floating-point operations (not just integers).
We’ll just cover the basics here. For more information, you can read the manual on the GNU website here: bc.
Format
echo <EXPRESSION> | bc
While bc can be used in many more ways than simply piping expressions into it, this is a simple format that is easy to understand for basic calculations.
Examples
$ echo 5.5 + 5.6 | bc
11.1
$ echo 5.5 % 5.5 | bc
0
$ echo 5.5 % 5.6 | bc
5.5
$ echo 2^16 | bc
65536
Exercises
- Submit Simple_Addition (10 point challenge)
- Submit Stupid_Addition (10 point challenge)
- Submit Summation_as_a_service (10 point challenge)
- Submit Strange_Addition (12 point challenge)
- Submit Adding_Horizontally (15 point challenge)
- Submit Quad_Math (15 point challenge)
- Submit Multiplicity (15 point challenge)
- Submit Range_Multiplication (15 point challenge)
- Submit Number_pattern_v1 (15 point challenge)
- Submit Evenly_Divisible (10 point challenge; what is a number?)