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

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?

@Rafael, ...why does that strike you as meaning the assumption is wrong? `02` is still 2, and `3` is decimal because it doesn't have any leading zero. Hence, you get `5` whether the `02` is octal *or* decimal. — Charles Duffy, Oct 31 '18 at 02:00

score 16 · Accepted Answer · answered Oct 31 '18 at 01:42

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.

score 2 · Answer 2 · answered Oct 31 '18 at 01:31

2

To trim a single leading zero:

"${line#0}"

To trim any number of leading zeros:

"${line##+(0)}"

For example:

$ line=009900
$ echo "${line##+(0)}"
9900

answered Oct 31 '18 at 01:31

l0b0

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paxdiablo · Answer 3 · 2018-10-31T01:57:40.280

You can just get rid of the leading zeros, with something like:

shopt extglob on
x="${x##+(0)}"
[[ -z "${x}" ]] && x=0

This will remove all leading zeros and then catch the case where it was all zeros (leading to an empty string), restoring it to a single zero.

The following function (and test code) will show this in action:

#!/bin/bash

stripLeadingZeros() {
    shopt -s extglob
    retVal="${1##+(0)}"
    [[ -z "${retVal}" ]] && retVal=0
    echo -n "${retVal}"
}

for testdata in 1 2 3 4 5 0 09 009 00000009 hello 00hello ; do
    result="$(stripLeadingZeros ${testdata})"
    echo "${testdata} -> ${result}"
done

The output of that is:

1 -> 1
2 -> 2
3 -> 3
4 -> 4
5 -> 5
0 -> 0
09 -> 9
009 -> 9
00000009 -> 9
hello -> hello
00hello -> hello

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

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