Python pexpect - TIMEOUT属于追溯和退出

Question

我是python-pexpect的新手.在Tcl /期望当我达到超时时 - 我会回复消息并退出该函数.我试图使用发布的示例代码尝试类似的响应 http://pexpect.svn.sourceforge.net/viewvc/pexpect/trunk/pexpect/examples/sshls.py?revision=489&view=markup

我基于上面的代码 - 如果我给出一个伪造的密码,我希望这只是暂停,打印"ERROR!",并退出程序.但是当我运行它 - 进入'Traceback输出(见下文)时,有人可以帮助我让程序打印"ERROR"并优雅地退出程序.

test@ubuntu:~/scripts$ ./tmout.py 
Hostname: 192.168.26.84
User: root
Password: 
Timeout exceeded in read_nonblocking().
<pexpect.spawn object at 0xb77309cc>
version: 2.3 ($Revision: 399 $)
command: /usr/bin/ssh
args: ['/usr/bin/ssh', '-l', 'root', '192.168.26.84', '/bin/ls', '-l']
searcher: searcher_re:
    0: EOF
buffer (last 100 chars): 
Permission denied, please try again.
root@192.168.26.84's password: 
before (last 100 chars): 
Permission denied, please try again.
root@192.168.26.84's password: 
after: <class 'pexpect.TIMEOUT'>
match: None
match_index: None
exitstatus: None
flag_eof: False
pid: 14997
child_fd: 3
closed: False
timeout: 30
delimiter: <class 'pexpect.EOF'>
logfile: None
logfile_read: None
logfile_send: None
maxread: 2000
ignorecase: False
searchwindowsize: None
delaybeforesend: 0.05
delayafterclose: 0.1
delayafterterminate: 0.1
Traceback (most recent call last):
  File "./tmout.py", line 54, in <module>
    traceback.print_exc()
NameError: name 'traceback' is not defined
test@ubuntu:~/scripts$ 

源代码:

#!/usr/bin/env python

"""This runs 'ls -l' on a remote host using SSH. At the prompts enter hostname,
user, and password.

$Id$
"""

import pexpect
import getpass, os

def ssh_command (user, host, password, command):

    """This runs a command on the remote host. This could also be done with the
pxssh class, but this demonstrates what that class does at a simpler level.
This returns a pexpect.spawn object. This handles the case when you try to
connect to a new host and ssh asks you if you want to accept the public key
fingerprint and continue connecting. """

    ssh_newkey = 'Are you sure you want to continue connecting'
    child = pexpect.spawn('ssh -l %s %s %s'%(user, host, command))
    i = child.expect([pexpect.TIMEOUT, ssh_newkey, 'password: '])
    if i == 0: # Timeout
        print 'ERROR!'
        print 'SSH could not login. Here is what SSH said:'
        print child.before, child.after
        return None
    if i == 1: # SSH does not have the public key. Just accept it.
        child.sendline ('yes')
        child.expect ('password: ')
        i = child.expect([pexpect.TIMEOUT, 'password: '])
        if i == 0: # Timeout
            print 'ERROR!'
            print 'SSH could not login. Here is what SSH said:'
            print child.before, child.after
            return None       
    child.sendline(password)
    return child

def main ():

    host = raw_input('Hostname: ')
    user = raw_input('User: ')
    password = getpass.getpass('Password: ')
    child = ssh_command (user, host, password, '/bin/ls -l')
    child.expect(pexpect.EOF)
    print child.before

if __name__ == '__main__':
    try:
        main()
    except Exception, e:
        print str(e)
        traceback.print_exc()
        os._exit(1)

Answer 1

关于自动执行ssh登录的注意事项:如果您正在考虑使用(p)期望自动执行ssh登录,请考虑使用ssh密钥.作为奖励,ssh密钥比密码更安全.它们比在文件系统上存储纯文本密码安全得多,许多用户都希望这样做.如果您使用ssh代理,则可以键入一次密码以在本地解锁密钥,然后在多个主机上自动使用该密钥进行多次登录.为方便起见,您可以设置或禁用密码到期的时间限制.

首先,您应该导入回溯,因此如果程序中出现意外错误,则traceback.print_exc()可以正常工作.

import getpass, os, traceback

我还创建了一个die()函数,以便在程序退出时关闭ssh.

def die(child, errstr):
    print errstr
    print child.before, child.after
    child.terminate()
    exit(1)

删除这一行,因为在下一行添加正确的命令后可能会错误地将它留在那里:

        child.expect ('password: ')

正确的行(处理超时)是:

        i = child.expect([pexpect.TIMEOUT, 'password: '])

然后替换这个:

    child.expect(pexpect.EOF)
    print child.before

有了这个:

    i = child.expect([pexpect.TIMEOUT, 'Permission denied', pexpect.EOF])
    if i == 0:
        die(child, 'ERROR!\nSSH timed out. Here is what SSH said:')
    elif i == 1:
        die(child, 'ERROR!\nIncorrect password Here is what SSH said:')
    elif i == 2:
        print child.before

此更改将告诉程序检测到错误的密码,或者如果存在未知输入则优雅地超时,而不是引发异常.请注意,如果您的命令运行时间超过默认超时持续时间,则它将在完成之前中止.你需要设置类似于timeout=60参数的东西expect()才能改变它.

此外,None超时后返回无用.相反,打电话给die()谁exit(1):

        die(child, 'error message')

这是最终的代码:

#!/usr/bin/env python

"""This runs 'ls -l' on a remote host using SSH. At the prompts enter hostname,
user, and password.

$Id$
"""

import pexpect
import getpass, os, traceback

def ssh_command (user, host, password, command):

    """This runs a command on the remote host. This could also be done with the
pxssh class, but this demonstrates what that class does at a simpler level.
This returns a pexpect.spawn object. This handles the case when you try to
connect to a new host and ssh asks you if you want to accept the public key
fingerprint and continue connecting. """

    ssh_newkey = 'Are you sure you want to continue connecting'
    child = pexpect.spawn('ssh -l %s %s %s'%(user, host, command))
    i = child.expect([pexpect.TIMEOUT, ssh_newkey, 'password: '])
    if i == 0: # Timeout
        die(child, 'ERROR!\nSSH could not login. Here is what SSH said:')
    if i == 1: # SSH does not have the public key. Just accept it.
        child.sendline ('yes')
        i = child.expect([pexpect.TIMEOUT, 'password: '])
        if i == 0: # Timeout
            die(child, 'ERROR!\nSSH could not login. Here is what SSH said:')
    child.sendline(password)
    return child

def die(child, errstr):
    print errstr
    print child.before, child.after
    child.terminate()
    exit(1)

def main ():

    host = raw_input('Hostname: ')
    user = raw_input('User: ')
    password = getpass.getpass('Password: ')
    child = ssh_command(user, host, password, '/bin/ls -l')

    i = child.expect([pexpect.TIMEOUT, 'Permission denied', pexpect.EOF])
    if i == 0:
        die(child, 'ERROR!\nSSH timed out. Here is what SSH said:')
    elif i == 1:
        die(child, 'ERROR!\nIncorrect password Here is what SSH said:')
    elif i == 2:
        print child.before

if __name__ == '__main__':
    try:
        main()
    except Exception, e:
        print str(e)
        traceback.print_exc()
        os._exit(1)