Bash Shell nested for loop on multiple arrays doesn't go though all elements

Question

OUTER_LIST=(1 2)
INNER_LIST=(a b)
for (( i=0; i < ${#OUTER_LIST[@]}; i++ )); do
    echo "outer...${OUTER_LIST[$i]}"

    for (( i=0; i < ${#INNER_LIST[@]}; i++ )); do
        echo "inner...${INNER_LIST[$i]}"
    done
done

Output:

outer...1
inner...a
inner...b

Question: why does it loop OUTER_LIST only 1 time ?

Answer 1

You use the same loop variable, i, in the inner loop so when that is done the first time, i will be 2 which is out of the range of the outer loop.

Fix it by using a different variable:

#!/bin/bash

OUTER_LIST=(1 2)
INNER_LIST=(a b)
for (( i=0; i < ${#OUTER_LIST[@]}; i++ )); do
    echo "outer...${OUTER_LIST[$i]}"

    for (( j=0; j < ${#INNER_LIST[@]}; j++ )); do
        echo "inner...${INNER_LIST[$j]}"
    done
done

Alternatively:

for outer in "${OUTER_LIST[@]}"; do
    echo "outer...$outer"

    for inner in "${INNER_LIST[@]}"; do
        echo "inner...$inner"
    done
done

Output:

outer...1
inner...a
inner...b
outer...2
inner...a
inner...b