send-mail-on-failure-or-output

#!/bin/bash

# Run a command and send a mail if the command fails or produces output.  Use
# --ignore_exit_status to only send mail if output is produced.
# Redirects stdout and stderr, so if your command or caller does that it won't
# work properly.

set -e -f -u -o pipefail

usage() {
  printf "%s [OPTIONS] EMAIL_ADDRESS command args\\n" "$0"
  printf "OPTIONS: --ignore_exit_status, --only_on_failure\\n"
  printf "Cannot use --ignore_exit_status and --only_on_failure together\\n"
}

main() {
  local IGNORE_EXIT_STATUS=0 ONLY_ON_FAILURE=0
  while :; do
    case "${1:-}" in
      --ignore_exit_status)
        IGNORE_EXIT_STATUS=1
        shift
        ;;
      --only_on_failure)
        ONLY_ON_FAILURE=1
        shift
        ;;
      --help)
        usage
        return 0
        ;;
      --*)
        printf "Unrecognised option: %s\\n" "$1" >&2
        usage >&2
        return 1
        ;;
      *)
        break
    esac
  done
  readonly IGNORE_EXIT_STATUS ONLY_ON_FAILURE
  if [[ "${IGNORE_EXIT_STATUS}" -eq 1 && "${ONLY_ON_FAILURE}" -eq 1 ]]; then
    printf "Cannot use both --ignore_exit_status and --only_on_failure\\n" >&2
    return 1
  fi

  if [[ "$#" -eq 0 ]]; then
    printf "No email address given!\\n" >&2
    usage >&2
    return 1
  fi
  local DESTINATION="$1"
  shift
  readonly DESTINATION

  if [[ "$#" -eq 0 ]]; then
    printf "No command to run!\\n" >&2
    usage >&2
    return 1
  fi

  local EXIT_STATUS=0
  "$@" > "${OUTPUT_FILE}" 2>&1 || EXIT_STATUS="$?"

  local SEND_MAIL=0
  if [[ "${EXIT_STATUS}" -ne 0 && "${IGNORE_EXIT_STATUS}" -eq 0 ]]; then
    SEND_MAIL=1
  fi
  if [[ -s "${OUTPUT_FILE}" ]]; then
    if [[ "${ONLY_ON_FAILURE}" -eq 1 ]]; then
      if [[ "${EXIT_STATUS}" -ne 0 ]]; then
        SEND_MAIL=1
      fi
    else
      SEND_MAIL=1
    fi
  fi

  # Support overriding the subject prefix to make testing idempotent.
  local SUBJECT="${SUBJECT_PREFIX:-${USER}@${HOSTNAME}}: $*"
  if [[ "${SEND_MAIL}" -eq 1 ]]; then
    (printf "Exit status: %s\\nOutput:\\n" "${EXIT_STATUS}";
      cat "${OUTPUT_FILE}"
    ) | mail -s "${SUBJECT}" "${DESTINATION}"
    printf "%s -- %s\n" "${DESTINATION}" "${SUBJECT}" \
      >> "${HOME}/tmp/logs/send-mail-on-failure-or-output.log"
  fi
  return "${EXIT_STATUS}"
}

# Set this up unconditionally so it is set up once and cleaned up once,
# including during testing.
OUTPUT_FILE="$(mktemp -t send-mail-on-failure-or-output.XXXXXXXXXXXXXXXX)"
trap 'rm -f "${OUTPUT_FILE}"' EXIT

# Only run main if being executed directly; do nothing if sourced for testing.
# Use basename so that it can be run as 'bash -x ./program ...'.
if [[ "$(basename "${BASH_SOURCE[0]}")" == "$(basename "${0}")" ]]; then
  main "$@"
fi