Copy music files, in alphabetical order, to a new directory, converting non-mp3 files along the way

copyto.sh

#!/bin/bash

set -euo pipefail

audio_file_extensions=(mp3 mp4 ogg oga ogv opus 3ga wav mka aiff mpeg mpg m4a wma wmv flac)

act() {
    if [[ "${APPLY:-}" = true ]]; then
        ( set -x
        # We don't want this command consuming the parent stdin
        "$@" </dev/null
        )
    else
        echo "$*"
    fi
}

findfiles() {
    local target extension
    target="$1"; shift

    for extension in "$@"; do
        find "$target" -name "*.$extension"
    done
}

main() {
    dest="$1"; shift

    IFS=$'\n\t'
    songdirs=($(for x in "$@"; do echo "$x"; done|sort))
    IFS=$' \n\t'

    for src in "${songdirs[@]}"; do
        if [[ "${LIST:-}" = true ]]; then
            echo "--> $src"
            continue
        fi

        if [[ "$src" =~ (/\.\./|/\.\.$|^\.\./|^\.\.$) ]]; then
            echo "ERROR --- '$src' cannot have '../' references in it"
            exit 1
        fi

        while read origin_file; do
            mp3dir="$(dirname "$origin_file")"
            [[ -d "$dest/$mp3dir" ]] || act mkdir -p "$dest/$mp3dir"

            if [[ "$origin_file" =~ \.mp3$ ]]; then
                destfile="$dest/$origin_file"
                if [[ -f "$destfile" ]]; then
                    echo "SKIP: $destfile"
                else
                    act cp "$origin_file" "$dest/$origin_file"
                fi
            else
                new_file="${origin_file%%.*}.mp3"
                destfile="$dest/$new_file"
                if [[ -f "$destfile" ]]; then
                    echo "SKIP: $destfile"
                else
                    act ffmpeg -loglevel -8 -nostats -i "$origin_file" "$destfile"
                fi
            fi
        done < <(findfiles "$src" "${audio_file_extensions[@]}" | sort) # this stdin causes issues, hence above `</dev/null`
    done
}

main "$@"