How to cut a number into digits and add them to each other in linux

Question

For example 2211 needs to display 6 but I can't find a command that helps me with it. I have already tried with cut but that can only cut one at a time.

Answer 1

Works in Debian. Try this:

#!/bin/bash

number="2211"

result=0
for (( i=0; i<${#number}; i++ )); do
   echo "number[${i}]=${number:$i:1}"
  result=$(( result + ${number:$i:1} ))
done

echo "result = ${result}"

Answer 2

If you have bash version 5.2 (the most recent version to this date):

shopt -s patsub_replacement
n=2211
echo $((${n//?/+&}))

Answer 3

Using a while + read loop.

#!/usr/bin/env bash

str=2211

while IFS= read -rd '' -n1 addend; do
  ((sum+=addend))
done < <(printf '%s' "$str")

declare -p sum

---

If your bash is new enough, instead of declare

echo "${sum@A}"

Answer 4

Math variant probably there are more elegant variants

sum=0
num=2211
n=${#num}

for ((i=n-1; i>=0; i--)); {
    a=$((10**i))
    b=$((num/a))
    sum=$((sum+b))
    num=$((num-(b*a)))
    echo $i $a $b $num $sum
}
3 1000 2 211 2
2 100 2 11 4
1 10 1 1 5
0 1 1 0 6

$ echo $sum
6

Answer 5

Another ( Shellcheck -clean) way to do it with arithmetic instead of string manipulation:

#! /bin/bash -p

declare -i num=2211 sum=0
while (( num > 0 )); do
    sum+=num%10
    num=num/10
done
echo "$sum"