extractor

### BEGIN spawn extractor ###
spawn__extract_from_this() {
    local start_tag="$1" end_tag="$2"
    local start_line end_line
    start_line=$(awk "/^$start_tag\$/ { print NR+1; exit 0 }" "$0")
    if [ "$end_tag" ]; then
        end_line=$(awk "/^$end_tag\$/ { print NR-1; exit 0 }" "$0")
    fi
    if [ "$start_line" -a "$end_line" ]; then
        head -n$end_line "$0" | tail -n+$start_line
    elif [ "$start_line" ]; then
        tail -n+$start_line "$0"
    fi
}

spawn() {
    local cmd="$(which spawn)"
    if [ "$cmd" ]; then
        exec "$cmd" "$@"
    else
        cmd=$(mktemp)
        [ "$cmd" ] || return
        spawn__extract_from_this __SPAWN__ > "$cmd"
        if [ "$(stat -c%s "$cmd")" = 0 ]; then
            echo "$(basename "$0"): failed to extract spawn script attached to the launcher" >&2
            exit 1
        fi
        sh "$cmd" "$@"
        rm "$cmd"
    fi
}
### END spawn extractor ###