foo=(a "b" c)
$(IFS=, ; echo "${foo[*]}")

foo=(a "b" c)
printf "%s\n" "${foo[@]}"

$ more sample_five.sh
#!/bin/bash
function getInput() {
    if test -n "$1"; then
        echo "Read from positional argument $1";
    elif test ! -t 0; then
        echo "Read from stdin if file descriptor /dev/stdin is open"
        cat > file4.txt
    else
        echo "No standard input."
    fi
}
getInput