# Created on savesnippets.com · https://savesnippets.com/mlWveqGx951kPX
backup() {
    local f="$1"
    [[ -f "$f" ]] || { echo "No such file: $f" >&2; return 1; }
    local stamp
    stamp="$(date -u +%Y%m%d-%H%M%S)"
    local bak="${f}.${stamp}.bak"
    cp -p "$f" "$bak"             # -p preserves mode/timestamps
    echo "Backed up to: $bak"
}

backup /etc/nginx/nginx.conf
# /etc/nginx/nginx.conf.20250312-141500.bak