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

Combine best of all worlds so far with following idea.

# join with separator
join_ws()  { local IFS=; local s="${*/#/$1}"; echo "${s#"$1$1$1"}"; }

This little masterpiece is

• 100% pure bash ( parameter expansion with IFS temporarily unset, no external calls, no printf ... )
• compact, complete and flawless ( works with single- and multi-character limiters, works with limiters containing white space, line breaks and other shell special characters, works with empty delimiter )
• efficient ( no subshell, no array copy )
• simple and stupid and, to a certain degree, beautiful and instructive as well

Examples:

$ join_ws , a b c
a,b,c
$ join_ws '' a b c
abc
$ join_ws $'\n' a b c
a
b
c
$ join_ws ' \/ ' A B C
A \/ B \/ C