• If you want to calculate with an integer it's possible without using other programs.

• For example 34+23=57

COUNT1="34"
COUNT2="23"
echo $[$COUNT1 + $COUNT2]

• If you want to move the decimal point one digit to the left than you will have to use modulo.
• For example 34/10=3.4

COUNT1="34"
COUNT2="10"
echo "$[$COUNT1 / $COUNT2].$[$COUNT1 % $COUNT2]"

• To calculate with float or more complex thing use “bc”

echo "2.5 + 3.2" | bc -l
5.7

• If you want to cut digits after the decimal point you can use scale (It's no rounding like you see in the example)

echo "scale = 4; 2.5 / 1.9 " | bc -l 
1.3157
echo "scale = 2; 2.5 / 1.9 " | bc -l 
1.31

• The remaining Problem is:

echo "scale = 2; 2.5 / 3.1 " | bc -l 
.8064

• The leading zero is lost
• You can search and replace using “sed”

echo "scale = 3; 2.5 / 3.1 " | bc -l | sed -r 's/^\./0./g'
0.806