Use subprocess to send a password

问题:

I'm attempting to use the python subprocess module to log in to a secure ftp site and then grab a file. However I keep getting hung up on just trying to send the password when it is requested. I so far have the following code:

from subprocess import Popen, PIPE

proc = Popen(['sftp','user@server', 'stop'], stdin=PIPE)
proc.communicate('password')

This still stops at the password prompt. If I enter the password manually it then goes to the ftp site and then enters the password on the command line. I've seen people suggest using pexpect but long story short I need a standard library solution. Is there anyway with subprocess and/or any other stdlib? What am I forgetting above?

回答1:

Perhaps you should use an expect-like library instead?

For instance Pexpect (example). There are other, similar python libraries as well.

回答2:

Try

proc.stdin.write('yourPassword\n')
proc.stdin.flush()

That should work.

What you describe sounds like stdin=None where the child process inherits the stdin of the parent (your Python program).

回答3:

from subprocess import Popen, PIPE

proc = Popen(['sftp','user@server', 'stop'], stdin=PIPE)
proc.communicate(input='password')

Try with input=‘password’ in communicate, that worked for me.

回答4:

I would recommend scrapping the subprocess approach and using the paramiko package for sftp access.

回答5:

Use Paramiko for SFTP. For anything else, this works:

import subprocess

args = ['command-that-requires-password', '-user', 'me']

proc = subprocess.Popen(args, 
                        stdin=subprocess.PIPE, 
                        stdout=subprocess.PIPE, 
                        stderr=subprocess.PIPE)

proc.stdin.write('mypassword\n')
proc.stdin.flush()

stdout, stderr = proc.communicate()
print stdout
print stderr

回答6:

This same problem plagued me for a week. I had to submit a password from user input through subprocess securely because I was trying to avoid introducing a command injection vulnerability. Here is how I solved the problem with a little help from a colleague.

import subprocess

command = ['command', 'option1', '--password']
subprocess.Popen(command, stdin=subprocess.PIPE).wait(timeout=60)

The .wait(timeout=int) was the most important component because it allows the user to feed input to stdin. Otherwise, the timeout is defaulted to 0 and leaves the user no time to enter input, which consequently results in a None or null string. Took me FOREVER to figure this out.

For repeat use-cases where you know you'll have to do this multiple times, you can override the popen function and use it as a private method which I was told by the same programmer is best practice if you anticipate someone else will be interested in maintaining the code later on and you don't want them to mess with it.

def _popen(cmd):
   proc_h = subprocess.Popen(cmd, stdin=subprocess.PIPE)
   proc_h.wait(timeout=60)
   return proc_h.poll() == os.EX_OK

It is important to remove stdout=subprocess.PIPE if the user is going to be prompted for input. Otherwise, the process appears to hang for 60 seconds, and the user doesn't get a prompt, nor do they realize they are expected to give a password. The stdout will naturally go to the shell window and allow the user to pass input to popen().

Also, just to explain why you return proc_h.poll() == os.EX_OK, is that it returns 0 if the command succeeded. This is just c-style best-practice for when you want to return system error codes in the event the function fails, while accounting for the fact that return 0 will be treated as "false" by the interpreter.

回答7:

This is a pure Python solution using expect - not pexpect.

If on Ubuntu you first need to install expect with:

sudo apt install expect

Python 3.6 or later:

def sftp_rename(from_name, to_name):
    sftp_password = 'abigsecret'
    sftp_username = 'foo'
    destination_hostname = 'some_hostname'
    from_name = 'oldfilename.txt'
    to_name = 'newfilename.txt'
    commands = f"""
spawn sftp -o "StrictHostKeyChecking no" 
{sftp_username}@{destination_hostname}
expect "password:"
send "{sftp_password}\r"
expect "sftp>"
send "rename {from_name} {to_name}\r"
expect "sftp>"
send "bye\r"
expect "#"
"""
    sp = subprocess.Popen(['expect', '-c', commands], stdin=subprocess.PIPE, stdout=subprocess.PIPE)