dynmotd-notify

#!/bin/bash
# dynmotd-notify — manage MOTD notices shown to users at login
set -e

NOTICES_DIR='/var/lib/dynmotd/notices'

usage() {
    cat <<EOF
Usage: dynmotd-notify COMMAND [args]

Commands:
  add [--expires YYYY-MM-DD] MESSAGE...   Add a notice
  list                                    List all notices
  remove ID                               Remove a notice by ID
  clear                                   Remove all notices

Notices appear for every user at login. Storage: ${NOTICES_DIR}/*.notice
Writing requires root (or membership of the directory's group).
EOF
}

require_writable() {
    mkdir -p "${NOTICES_DIR}" 2>/dev/null || true
    if [[ ! -w "${NOTICES_DIR}" ]]; then
        echo "dynmotd-notify: ${NOTICES_DIR} not writable — run as root" >&2
        exit 1
    fi
}

validate_date() {
    if ! [[ "$1" =~ ^[0-9]{4}-[0-9]{2}-[0-9]{2}$ ]]; then
        echo "dynmotd-notify: invalid date '$1' (expected YYYY-MM-DD)" >&2
        exit 2
    fi
}

cmd_add() {
    local expires=''
    while [[ $# -gt 0 ]]; do
        case "$1" in
            --expires) expires="$2"; validate_date "${expires}"; shift 2;;
            --)        shift; break;;
            -*)        echo "dynmotd-notify: unknown option: $1" >&2; exit 2;;
            *)         break;;
        esac
    done
    local message="$*"
    if [[ -z "${message}" ]]; then
        echo "dynmotd-notify: message required" >&2
        exit 2
    fi
    require_writable
    local id
    id="$(date +%Y%m%d-%H%M%S)-$$"
    local path="${NOTICES_DIR}/${id}.notice"
    {
        [[ -n "${expires}" ]] && echo "# expires: ${expires}"
        echo "${message}"
    } > "${path}"
    chmod 644 "${path}"
    echo "added notice ${id}"
}

cmd_list() {
    if [[ ! -d "${NOTICES_DIR}" ]]; then
        echo "no notices"
        return
    fi
    local found=0 f id expires text
    for f in "${NOTICES_DIR}"/*.notice; do
        [[ -f "${f}" ]] || continue
        found=1
        id=$(basename "${f}" .notice)
        expires=$(awk -F': *' '/^# *expires:/ {print $2; exit}' "${f}")
        text=$(grep -v '^#' "${f}" | sed '/^$/d')
        printf '[%s]%s\n' "${id}" "${expires:+ (expires ${expires})}"
        while IFS= read -r line; do
            printf '    %s\n' "${line}"
        done <<< "${text}"
    done
    [[ ${found} -eq 0 ]] && echo "no notices"
}

cmd_remove() {
    local id="${1:-}"
    if [[ -z "${id}" ]]; then
        echo "usage: dynmotd-notify remove ID" >&2
        exit 2
    fi
    local path="${NOTICES_DIR}/${id}.notice"
    if [[ ! -f "${path}" ]]; then
        echo "dynmotd-notify: no such notice: ${id}" >&2
        exit 1
    fi
    require_writable
    rm -f "${path}"
    echo "removed ${id}"
}

cmd_clear() {
    [[ -d "${NOTICES_DIR}" ]] || { echo "no notices"; return; }
    require_writable
    rm -f "${NOTICES_DIR}"/*.notice
    echo "cleared all notices"
}

case "${1:-}" in
    add)               shift; cmd_add "$@";;
    list|ls)           cmd_list;;
    remove|rm|delete)  shift; cmd_remove "$@";;
    clear)             cmd_clear;;
    -h|--help|help|'') usage;;
    *)                 echo "dynmotd-notify: unknown command: $1" >&2; usage >&2; exit 2;;
esac