The traditional method of automating telnet sessions meets macOS Keychain

telnet-auto.sh

#!/bin/sh

#### This script enables automated telnet login using macOS Keychain.
#### In addition, automatically entering privilege EXEC mode is available.
####
#### Copyright (c) 2017 Masaki Tagawa
#### Released under the MIT license
#### http://opensource.org/licenses/mit-license.php

set -ef -o pipefail

PROGNAME=$(basename $0)

function usage() {
	echo "Usage: ${PROGNAME} [OPTIONS] [user@]host [port]"
	echo
	echo "Options:"
	echo "  -h, --help"
	echo "  -k, --disable-keychain   Disable Keychain integration"
	echo "  -l user"
	echo "  -u, --update             Update Username and Password on Keychain"
}

function get_passwords() {
	# First, check whether the enable password is stored.
	if security find-generic-password -s ${host}:${port} -a enable 1>/dev/null 2>&1; then
		enablepass=`security find-generic-password -s ${host}:${port} -a enable -w`
	fi

	if [ ! -z ${username} ]; then
		# Check whether the login password is stored for specific user.
		if security find-generic-password -s ${host}:${port} -a ${username} 1>/dev/null 2>&1; then
			loginpass=`security find-generic-password -s ${host}:${port} -a ${username} -w`
		else
			echo "${PROGNAME}: the login password is not stored in Keychain." 1>&2
		fi
	else
		if security find-generic-password -s ${host}:${port} -a login 1>/dev/null 2>&1; then
			loginpass=`security find-generic-password -s ${host}:${port} -a login -w`
		fi
	fi

	return 0
}

function connect_telnet() {
	# We cannot use heredoc.
	# ref. http://stackoverflow.com/questions/33026478/keeping-alive-a-ssh-session-with-a-script-bash-expect
	expect -c "
	set timeout 30

	spawn telnet ${host} ${port}
	expect {
		timeout { send_user \"\nTimeout Exceeded - Check Host\n\"; exit 1 }
		eof { send_user \"\nSSH Connection To ${host} Failed\n\"; exit 1 }
		\"*sername\" {
			if { \"${flag_disable_keychain}\" != \"true\" } {
				if { \"${flag_update}\" == \"true\" || \"${username}\" == \"\" } { 
					expect_user -re \"(.*)\n\"
					set username \$expect_out(1,string)
					send -- \"\$username\r\"
					exp_continue
				} else {
					send -- \"${username}\r\"; exp_continue
				}
			}
		}
		\"*assword\" {
			if { \"${flag_disable_keychain}\" != \"true\" } {
				if { \"${flag_update}\" == \"true\" || \"${loginpass}\" == \"\" } { 
					stty -echo
					expect_user -re \"(.*)\n\"
					set loginpass \$expect_out(1,string)

					if { \$username == \"\" } { set username \"${username}\" }
					if { \$username == \"\" } { set username login }
					catch {exec security delete-generic-password -s ${host}:${port} -a \$username}
					catch {exec security add-generic-password -s ${host}:${port} -a \$username -w \$loginpass}

					send -- \"\$loginpass\r\"
					stty echo
					exp_continue
				} else {
					send -- \"${loginpass}\r\"; exp_continue
				}
			}
		}
		\"*>\" {
			if { \"${flag_disable_keychain}\" != \"true\" } {
				send \"enable\n\"
				expect \"*assword\"

				if { \"${flag_update}\" == \"true\" || \"${enablepass}\" == \"\" } { 
					stty -echo
					expect_user -re \"(.*)\n\"
					set enablepass \$expect_out(1,string)
					catch {exec security delete-generic-password -s ${host}:${port} -a enable}
					catch {exec security add-generic-password -s ${host}:${port} -a enable -w \$enablepass}
					send -- \"\$enablepass\r\"
					stty echo
					exp_continue
				} else {
					send -- \"${enablepass}\r\"
				}
			}
		}
		\"*#\" { }
	}

	interact
	"
}

# Default
flag_disable_keychain=false
flag_update=false

for OPT in "$@"
	do
	case "$OPT" in
		'-h'|'--help' )
			usage
			exit 1
			;;
		'-l' )
			if [[ -z "$2" ]] || [[ "$2" =~ ^-+ ]]; then
				echo "$PROGNAME: option requires an argument -- $1" 1>&2
				exit 1			fi
			username="$2"
			shift 2
			;;
		'-k'|'--disable-keychain' )
			flag_disable_keychain=true
			shift 1
			;;
		'-u'|'--update' )
			flag_update=true
			shift 1
			;;
		'--'|'-' )
			shift 1
			param+=( "$@" )
			break
			;;
		-*)
			echo "${PROGNAME}: illegal option -- '$(echo $1 | sed 's/^-*//')'" 1>&2
			exit 1
			;;
		*)
			if [[ ! -z "$1" ]] && [[ ! "$1" =~ ^-+ ]]; then
				param+=( "$1" )
				host=${param[0]:-}
				port=${param[1]:-}
				
				# Perse "username@host"
				if [[ "${host}" = *"@"* ]]; then
					username=`echo ${host} | cut -d'@' -f1`
					host=`echo ${host} | cut -d'@' -f2`
				fi

				# Default port is 23
				if [ -z ${port} ]; then port=23; fi

				shift 1
			fi
			;;
	esac
done

if [ -z $param ]; then
	echo "${PROGNAME}: too few arguments" 1>&2
	echo "Try '${PROGNAME} --help' for more information." 1>&2
	exit 1
fi

# Keychain Integration
if [ "${flag_disable_keychain}" != "true" ]; then
	get_passwords
fi

# Start telnet with expect
connect_telnet