ほぼ bash オンリーで smtp client

sendmail.sh

#!/usr/bin/env bash
PATH=/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/sbin:/usr/sbin
export PATH


# usage
_usage() {
  echo "usage:"
  echo "  echo hogehoge | ${0} -t to@add.re.ss [-f from@add.re.ss] [-s subject] [-m mxhost] [-p mxport]"
  exit 1
}

# getopts
while getopts :t:f:s:m:p: OPT; do
  case ${OPT} in
    t) ENABLE_t="t"; VALUE_t=${OPTARG};;
    f) ENABLE_f="t"; VALUE_f=${OPTARG};;
    s) ENABLE_s="t"; VALUE_s=${OPTARG};;
    m) ENABLE_m="t"; VALUE_m=${OPTARG};;
    p) ENABLE_p="t"; VALUE_p=${OPTARG};;

    :|\?) _usage;;
  esac
done

shift $((OPTIND - 1))


# check
[ "${ENABLE_t}" != "t" ] && _usage


# make params
MAIL_TO=${VALUE_t}
MAIL_FROM=${VALUE_f:-$(whoami)@${HOSTNAME}}
MAIL_SUB=${VALUE_s}
MAIL_BODY=$(cat)

SMTP_HOST=${VALUE_m:-$(dig +short $(echo ${MAIL_TO} | cut -d'@' -f2) mx | head -n 1 | cut -d' ' -f2)}
SMTP_PORT=${VALUE_p:-25}
FD=5


# start
_fd=${FD}
eval "exec ${_fd}<>/dev/tcp/${SMTP_HOST}/${SMTP_PORT}"

RETVAL=255
_cnt_250=1

while read -r -u ${_fd} res; do
  echo ${res} >&2

  case ${res} in
    220\ *)
      _req="EHLO ${HOSTNAME}\r\n"
      echo -ne "${_req}" >&${_fd}
      echo "--- sent: ${_req}" >&2
      ;;

    250\ *)
      if   [ ${_cnt_250} -eq 1 ]; then
        _req="MAIL FROM: <${MAIL_FROM}>\r\n"
      elif [ ${_cnt_250} -eq 2 ]; then
        _req="RCPT TO: <${MAIL_TO}>\r\n"
      elif [ ${_cnt_250} -eq 3 ]; then
        _req="DATA\r\n"
      elif [ ${_cnt_250} -eq 4 ]; then
        _req="quit\r\n"
      fi

      echo -ne "${_req}" >&${_fd}
      echo "--- sent: ${_req}" >&2
      _cnt_250=$((_cnt_250 + 1))
      ;;

    [0-9][0-9][0-9]-*)
      :
      ;;

    354\ *)
      echo -ne "From: ${MAIL_FROM}\r\n" >&${_fd}
      echo -ne "To: ${MAIL_TO}\r\n" >&${_fd}
      echo -ne "Subject: ${MAIL_SUB}\r\n\r\n" >&${_fd}
      echo "${MAIL_BODY}" >&${_fd}
      echo -ne "\r\n.\r\n" >&${_fd}
      echo "--- sent: <MAILDATA>" >&2
      ;;

    221\ *)
      echo "--- closed" >&2
      RETVAL=0
      ;;

    *)
      echo "--- error occured" >&2
      RETVAL=1
      ;;
  esac

  if [ ${RETVAL} -ne 255 ]; then
    exit ${RETVAL}
  fi
done