арифметичні операції з цифрами з комою в bash

Floating Point Arithmetic in Bash

Using floating point in bash scripts requires an external calculator like GNU bc. Pipe your request to bc and note that escaping is not needed for quoted asterisks.

bash$ echo "3.8 + .4" | bc
4.2
bash$ echo '6 * 1.5' | bc
9.0

If all input values are integers, the bc option scale must be defined if you expect a floating point result.

bash$ echo '2 / 5' | bc
0
bash$ echo 'scale=2; 2 / 5' | bc

.40

You can also use the bash here string <<< to accomplish the same as a pipe of echo to bc:

bash$ echo 'scale=2; 2 / 5' | bc
.40
bash$ bc <<< 'scale=2; 2 / 5'
.40

Or, use bc -l to evoke the standard (but not default!) mathlib and see the result in floating point at max scale:

bash$ bc -l <<< '10.5 / 1'
10.50000000000000000000