Recipe: Math with shell

let
===
$ no1=4 ; no2=5
$ let result = no1 + no2
$ echo $result
9

Alternatives
============
$ result=$[ no1 + no2 ]
$ echo $result
9

$ result=$(( no1 + 50 ))
$ echo $result 
54

expr
====
$ result=`expr 3 + 4`

$ result=$(expr $no1 + 5)

bc
==

$ echo "4 * 0.56" | bc
2.24

$ no=54
$ result=`echo "$no * 1.5" | bc`
$ echo $result
81.0

Decimal places scaling
=====================
$ echo "scale=2;3/8" | bc
0.37

Square and square root
======================
$ echo "sqrt(100)" | bc
10

$ echo "10^2" | bc
100

Scripts
=======
baseconvert.sh