Version 3:

Now, I can set it as startup script.

alias vpn='~/vpn/runvpn-start.sh'

runvpn-start.sh:

#!/usr/bin/env bash

cd $(dirname "${0}")
nmcli con down id my-vpn
screen -S vpn -X kill
screen -S vpn -d -m ./runvpn-except.sh
nmcli con up id my-vpn
cd -

runvpn-except.sh:

#!/usr/bin/env expect

set pass MySecredPassword

spawn ./runvpn

expect Pass:
send "$pass\r"

interact

expect eof

Version 2:

alias vpn='cd ~/vpn && screen -m -d -S vpn ./runvpn-except.sh && nmcli con up id my-vpn'

runvpn-except.sh:

#!/usr/bin/env expect

set pass MySecredPassword

spawn ./runvpn

expect Pass:
send "$pass\r"

interact

expect eof

Version 1:

Paste password from clipboard when user input; Press CTRL+A and D to detach and continue

alias vpn='cd ~/vpn && xclip -selection c ./pass && screen -S vpn ./runvpn && nmcli con up id my-vpn; xclip -selection c /dev/null'

Manuals:

• https://linux.die.net/man/1/expect
• https://linux.die.net/man/1/nmcli
• https://linux.die.net/man/1/xclip
• https://linux.die.net/man/1/screen