A circle is one of the simple shapes of Euclidean geometry. It is the locus of all points in a plane at a constant distance, called the radius, from a fixed point, called the center. Through any three points not on the same line, there passes one and only one circle.

A diameter is a chord passing through the center. The length of a diameter is twice the radius. A diameter is the largest chord in a circle.

Circles are simple closed curves which divide the plane into an interior and an exterior. The circumference of a circle is the perimeter of the circle, and the interior of the circle is called a disk.

## Sample Shell Script To Calculate Area and Circumference of Circle

```
#!/bin/bash
# Shell script to calulate area and Circumference of circle.
# It take radius of a circle as input.
# -------------------------------------------------------------------------
# Copyright (c) 2005 nixCraft project
```
# This script is licensed under GNU GPL version 2.0 or above
# -------------------------------------------------------------------------
# This script is part of nixCraft shell script collection (NSSC)
# Visit http://bash.cyberciti.biz/ for more information.
# ----------------------------------------------------------------------
# Lesson on Circumference of a Circle :
# Visit http://www.mathgoodies.com/lessons/vol2/circumference.html
echo -n "Enter the radius of a circle : "
read r
# use formula to get it
area=$(echo "scale=2;3.14 * ($r * $r)" | bc)
# use formula to get it
d=$(echo "scale=2;2 * $r"|bc)
circumference=$(echo "scale=2;3.14 * $d"| bc)
echo "Area of circle is $area"
echo "Circumference of circle is $circumference"

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