bash arithmetic expressions with variables

Question

I am having troubles with the arithmetic expressions in a bash file (a unix file .sh).

I have the variable "total", which consists of a few numbers separated by spaces, and I want to calculate the sum of them (in the variable "dollar").

#!/bin/bash
..
dollar=0
for a in $total; do
  $dollar+=$a
done

I know I am missing something with the arithmetic brackets, but I couldn't get it to work with variables.

As you have it in a variable with space between values you can do like this also: $dollar=$(echo $total | tr ' ' '+' | bc) — Azize
– Azize, Commented Jul 18, 2017 at 17:55
Also see Arithmetic expressions in Bash?, How do I do if statement arithmetic in bash?, How to use Shellcheck, How to debug a bash script? (U&L.SE), How to debug a bash script? (SO), etc. — jww
– jww, Commented Sep 29, 2019 at 20:49

janos · Accepted Answer · 2017-07-18 17:48:36Z

9

Wrap arithmetic operations within ((...)):

dollar=0
for a in $total; do
  ((dollar += a))
done

answered Jul 18, 2017 at 17:48

janos

126k31 gold badges242 silver badges253 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Charles Duffy · Accepted Answer · 2024-04-22 20:29:43Z

8

There are a number of ways to perform arithmetic in Bash. Some of them are:

dollar=$((dollar + a))           # modern: in-process, POSIX-defined
((dollar += a))                  # modern: in-process, non-POSIX bash extension
dollar=$(expr "$dollar" + "$a")  # legacy: out-of-process, slow, POSIX-defined
let "dollar += $a"               # legacy: in-process, pre-POSIX ksh syntax

You may see more on the wiki. If you need to handle non-integer values, use a external tool such as bc.

edited Apr 22, 2024 at 20:29

Charles Duffy

299k43 gold badges441 silver badges497 bronze badges

answered Jul 18, 2017 at 17:50

ephemient

207k39 gold badges292 silver badges402 bronze badges

Collectives™ on Stack Overflow

bash arithmetic expressions with variables

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related