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

With re-use of @doesn't matters' solution, but with a one statement by avoiding the ${:1} substition and need of an intermediary variable.

echo $(printf "%s," "${LIST[@]}" | cut -d "," -f 1-${#LIST[@]} )

printf has 'The format string is reused as often as necessary to satisfy the arguments.' in its man pages, so that the concatenations of the strings is documented. Then the trick is to use the LIST length to chop the last sperator, since cut will retain only the lenght of LIST as fields count.