bourne shell script

Question

I'm trying to convert this line of C program to bash script: C:

bin = bin+d*10^n-1;

bin,d,n are declared as int. bash:

bin=`exp $bin+$d\*10^n-1`

but it's incorrect

Answer 1

Bash has built-in functionality for arithmetic expressions. The feature is called "Arithmetic Expansion". The bash man page contains more information.

The syntax is $((expression)). In your case the script might contain the following.

#!/bin/bash

set -x

bin=1
d=2
n=3
echo $((${bin} + ${d}*10^${n}-1))

The operator precedence resembles C's but is not exactly the same, as Bash and C support different operators. Here is a useful reference: https://www.gnu.org/software/bash/manual/html_node/Shell-Arithmetic.html#Shell-Arithmetic

The above is appropriate only because the operands are C ints. Arithmetic Expansion does not support floating-point arithmetic.