How can I join elements of an array in Bash?

Question

If I have an array like this in Bash:

FOO=( a b c )

How do I join the elements with commas? For example, producing a,b,c.

Answer 1

This approach takes care of spaces within the values, but requires a loop:

#!/bin/bash

FOO=( a b c )
BAR=""

for index in ${!FOO[*]}
do
    BAR="$BAR,${FOO[$index]}"
done
echo ${BAR:1}