How to compare two floating point numbers in Bash?

Question

I am trying hard to compare two floating point numbers within a bash script. I have to variables, e.g.

let num1=3.17648e-22
let num2=1.5

Now, I just want do a simple comparison of these two numbers:

st=`echo "$num1 < $num2" | bc`
if [ $st -eq 1]; then
  echo -e "$num1 < $num2"
else
  echo -e "$num1 >= $num2"
fi

Unfortunately, I have some problems with the right treatment of the num1 which can be of the "e-format".

Answer 1

More conveniently

This can be done more conveniently using Bash's numeric context:

if (( $(echo "$num1 > $num2" |bc -l) )); then
  …
fi

Explanation

Piping through the basic calculator command bc returns either 1 or 0.

The option -l is equivalent to --mathlib; it loads the standard math library.

Enclosing the whole expression between double parenthesis (( )) will translate these values to respectively true or false.

Please, ensure that the bc basic calculator package is installed.

Caveat: Exponential notation should be written as *10^; not E, nor e.

For example:

$ echo '1*10^3==1000" |bc
1

Whereas

$ echo '1E3==1000" |bc
0

Strategies to overcome this bc limitation are discussed here.