send_file

#!/bin/ksh

#################################################
#	send_file				#
#################################################
# Sends a file, Base64-encoded, as an attach-	#
# ment by email, using the system sendmail	#
# program.					#
#################################################
# Copyright (c)2023 Sridhar K.N. Ayengar	#
# Available on the MIT License.			#
# Please refer to the file LICENSE.		#
#################################################

base64=/usr/bin/base64
basename=/usr/bin/basename
hostname=/bin/hostname
id=/usr/bin/id
sendmail=/usr/sbin/sendmail

usage() {
	echo "Usage: $0 -f <file_name> -r <recipient_email>" 1>&2
	exit 1
}

HOSTNAME=$($hostname -f)
SEPARATOR=$(echo "${RANDOM}${RANDOM}${RANDOM}" | $base64)
USERID=$($id -urn)
USERNAME=$($id -F)
SENDER="${USERNAME} <${USERID}@${HOSTNAME}>"

if [ $# -ne 4 ] || [ "$1" = "$3" ]
then
	usage
fi

for parameter in 1 3
do
	case $(eval echo \$$parameter) in
		"-f")
			FILE_PATH=$(eval echo "\$$((parameter + 1))")
			;;
		"-r")
			RECIPIENT=$(eval echo "\$$((parameter + 1))")
			;;
		*)
			usage
			;;
	esac
done

if [ ! -f "${FILE_PATH}" ]
then
	echo "Can only send a normal file." 1>&2
	echo 1>&2
	usage
fi

if [ ! -r "${FILE_PATH}" ]
then
	echo "Cannot read file." 1>&2
	echo 1>&2
	usage
fi

FILENAME=$($basename "${FILE_PATH}")

case "${RECIPIENT}" in
	"*@*@*")
		echo "Invalid recipient address." 1>&2
		echo 1>&2
		usage
		;;
	"*@*")
		:
		;;
	"*")
		RECIPIENT="${RECIPIENT}@localhost"
		;;
esac

$sendmail -t <<BLONG
From: ${SENDER}
To: ${RECIPIENT}
Subject: File ${FILENAME} Sent from ${HOSTNAME}
Content-Type: multipart/mixed; boundary=${SEPARATOR}

This is a multipart message in MIME format.

--${SEPARATOR}
Content-Type: text/plain

Hello.  This is a file sent by the user ${USERID} on host ${HOSTNAME}.

Please, do not assume this file is safe.  Plesse check or scan it before
opening.

Thank you.

--${SEPARATOR}

Content-Type: ${MIMETYPE}
Content-Transfer-Encoding: Base64
Content-Disposition: attachment; filename=\"${FILENAME}\"

$($base64 < "${FILE_PATH}")

--${SEPARATOR}--
BLONG