The short and direct answer is using ‘bc‘ command – “An arbitrary precision calculator language.”
Just run bc and enter some floating point calculation expression, such as “1.2+8.2”, bc will give the result.
In a script, we certainly need a more automatic way. This is a piece of simple script:
$ echo "scale=4; $*" | bc -q
For example, to calculate “1.2+8.2”
$ echo "scale=4; 1.2+8.2" | bc -q
and you will get 9.4 .
“By default bc outputs its result with no digits to the right of the decimal point and without a decimal point. To change this you have to change one of bc‘s builtin variables: scale. This is where the “language” features of bc are relevant, in bc as in C statements are separated by semi-colons.”