Bash function with an array input and output

Question

If I define an array in bash shell:

a=()
a+=(\"A\")
a+=(\"B\")
a+=(\"C\")

I can interact with it as expected:

echo \"${a[0]}\"
         


        

Answer 1

bash does not have array values. The statement echo "${sorted[@]}" does not "return" an array value, it simply writes each element of the array to standard output, separated by a single space. (More specifically, the array expansion produces a sequence of words, one per element, that are then passed to echo as arguments.)

It is somewhat difficult to simulate in bash. You have to create a global array parameter, something you couldn't do inside a function until bash 4.2. Working with said array was difficult until namerefs were introduced in bash 4.3.

sort_array () {
    declare -n input=$1     # Local reference to input array
    declare -ga "$2"        # Create the output array
    declare -n output="$2"  # Local reference to output array

    # As a simple example, just reverse the array instead
    # of sorting it.
    n=${#input[@]}
    for((i=n-1; i>=0; i--)); do
        echo "*** ${input[i]}"
        output+=( "${input[i]}" )
    done
}

Now, you pass sort_array two arguments, the names of the input and output arrays, respectively.

$ a=("foo 1" "bar 2" "baz 3")
$ sort_array a b
$ echo "${b[0]}"
baz 3