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

Use perl for multicharacter separators:

function join {
   perl -e '$s = shift @ARGV; print join($s, @ARGV);' "$@"; 
}

join ', ' a b c # a, b, c

Or in one line:

perl -le 'print join(shift, @ARGV);' ', ' 1 2 3
1, 2, 3