How can I do bash arithmetic with variables that are numbers with leading zeroes? [duplicate]

Question

I have the following code in a bash script, where "values" is a variable of newline separated numbers, some of which have leading 0's, and I am trying to iterate through each value in values and add each value to the variable "sum".

sum=0
while read line; do
    sum=$(( sum + line ))
done <<< "$values"

this code segment gives me the error: "value too great for base (error token is "09")", which as I understand, is because the bash arithmetic expression interprets the value "line" to be an octal value because it has a leading zero.

How can I allow for bash to interpret the value of line to be its decimal value? (e.g. 09 -> 9) for the value "line" within this bash arithmetic expression?

Answer 1

You can override the "leading 0 means octal" by explicitly forcing base ten with 10#:

sum=$(( 10#$sum + 10#$line ))

Note that, while you can usually leave the $ off variable references in arithmetic contexts, in this case you need it. Also, if the variable has leading spaces (in front of the first "0"), it won't parse correctly.