如果bash指令碼中一些命令需要手工輸入進行互動的時候，那麼指令碼的自動化就沒法進行下去。比如：ssh somehost需要輸入使用者名稱和密碼，指令碼執行到這個命令後，便會停止，等待使用者輸入。
如果在簡單情景下，比如只需要使用者輸入一次，即一次性互動時，可以直接這樣：

# ... some directives here

# Remove the machine, confirming "y" when asked by docker-machine
echo 'y' | docker-machine rm default

# ... more directives here

通常情況下需要expect

#timeout is a predefined variable in expect which by default is set to 10 sec
#spawn_id is another default variable in expect.
#It is good practice to close spawn_id handle created by spawn command
set timeout 60
spawn ssh $user@machine
while {1} {
  expect {

    eof                          {break
 
}
    "The authenticity of host"   {send "yes\r"}
    "password:"                  {send "$password\r"}
    "*\]"                        {send "exit\r"}
  }
}
wait
close $spawn_id

另外一個telnet的例子：

# Assume $remote_server, $my_user_id, $my_password, and $my_command were read in earlier
# in the script.
 

# Open a telnet session to a remote server, and wait for a username prompt.
spawn telnet $remote_server
expect "username:"
# Send the username, and then wait for a password prompt.
send "$my_user_id\r"
expect "password:"
# Send the password, and then wait for a shell prompt.
send "$my_password\r"
expect "%"
# Send the prebuilt command, and then wait for another shell prompt.
send "$my_command\r"
expect "%"
# Capture the results of the command into a variable. This can be displayed, or written to disk.
set results $expect_out(buffer)
# Exit the telnet session, and wait for a special end-of-file character.
send "exit\r"
expect eof