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

liststr=""
for item in list
do
    liststr=$item,$liststr
done
LEN=`expr length $liststr`
LEN=`expr $LEN - 1`
liststr=${liststr:0:$LEN}

This takes care of the extra comma at the end also. I am no bash expert. Just my 2c, since this is more elementary and understandable

Answer 2

Here's one that most POSIX compatible shells support:

join_by() {
    # Usage:  join_by "||" a b c d
    local arg arr=() sep="$1"
    shift
    for arg in "$@"; do
        if [ 0 -lt "${#arr[@]}" ]; then
            arr+=("${sep}")
        fi
        arr+=("${arg}") || break
    done
    printf "%s" "${arr[@]}"
}

Answer 3

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 !

Answer 4

Using no external commands:

$ FOO=( a b c )     # initialize the array
$ BAR=${FOO[@]}     # create a space delimited string from array
$ BAZ=${BAR// /,}   # use parameter expansion to substitute spaces with comma
$ echo $BAZ
a,b,c

Warning, it assumes elements don't have whitespaces.

Answer 5

Here's a single liner that is a bit weird but works well for multi-character delimiters and supports any value (including containing spaces or anything):

ar=(abc "foo bar" 456)
delim=" | "
printf "%s\n$delim\n" "${ar[@]}" | head -n-1 | paste -sd ''

This would show in the console as

abc | foo bar | 456

Note: Notice how some solutions use printf with ${ar[*]} and some with ${ar[@]}? The later ones (with @) use the printf feature that support multiple arguments by repeating the format template, while the former ones do not actually need printf and rely on manipulating the field separator and bash's word expansion and would work just as well with echo, cat and others - these solutions likely use printf because the author doesn't really understand what they are doing, and you should not use them.

Answer 6

My attempt.

$ array=(one two "three four" five)
$ echo "${array[0]}$(printf " SEP %s" "${array[@]:1}")"
one SEP two SEP three four SEP five