This just an example of expression evaluation different way. Also equality and even odd checking in a different way.

ExpressionEvaluation.sh

#!/bin/bash


# Do not use space before and after equal sign.

a=1
b=3

sum=`expr $a + $b`
sum=$(( $sum + 5  ))

echo $sum


# If condition, must be closed with fi

a=2
b=2

if [ $a -eq $b ];then
	echo "match"
else
	echo "not match"
fi


# Check if even

read input

two=2

val=$(( $input / $two ))
val=$(( $val * $two ))

#echo $val

if [ $val -eq $input ];then
	echo "Even"
else
	echo "Odd"
fi