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

I would echo the array as a string, then transform the spaces into line feeds, and then use paste to join everything in one line like so:

tr " " "\n" <<< "$FOO" | paste -sd , -

Results:

a,b,c

This seems to be the quickest and cleanest to me !