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

Perhaps I'm missing something obvious, since I'm a newb to the whole bash/zsh thing, but it looks to me like you don't need to use printf at all. Nor does it get really ugly to do without.

join() {
  separator=$1
  arr=$*
  arr=${arr:2} # throw away separator and following space
  arr=${arr// /$separator}
}

At least, it has worked for me thus far without issue.

For instance, join \| *.sh, which, let's say I'm in my ~ directory, outputs utilities.sh|play.sh|foobar.sh. Good enough for me.

EDIT: This is basically Nil Geisweiller's answer, but generalized into a function.