Scripting and interactive terminal client in Python

Question

I need to script/automate an interactive terminal client using Python. The client accepts three arguments and runs as follows:

>./myclient <arg1> <arg2> <arg3>
Welcome...
blah...
blah..
[user input]
some more blah... blah... for the input entered
blah.. 
blah..
[basically it accepts input and puts the output in the console until the user types 'quit']

Now I need to automate this in Python and the console output saved in a file.

• confused1: i tried the Popen but couldn't manage to run the terminal client effectively. I also wasn't able to send more than one input using communicate(). When i used stdin=PIPE and then send the data using stdin.read the client was acting weird

Answer 1

You probably want to use pexpect (which is a pure-python version of the venerable expect).

import pexpect
proc = pexpect.spawn('./myclient <arg1> <arg2> <arg3>')
proc.logfile = the_logfile_you_want_to_use
proc.expect(['the string that tells you that myclient is waiting for input'])
proc.sendline('line you want to send to myclient')
proc.expect(['another line you want to wait for'])
proc.sendline('quit') # for myclient to quit
proc.expect([pexpect.EOF])

Something like this should be enough to solve your case. pexpect is capable of a lot more though, so read up on the documentation for more advanced use-cases.

• confused1: Thanks. This worked like charm. But now i have another issue. I am sending two inputs to the client proc.sendline('input1') time.sleep(60) proc.sendline('input2') but the issue is that it doesn't wait. It seems to send the input irrespective of the thread.sleep(60)..
• dnaq: It's usually better not to try to sleep before sending data, but instead looking for some kind of acknowledgment message from the other process.

Answer 2

You could have a look at http://docs.python.org/library/cmd.html.

Example code:

import cmd
import sys
class Prompt(cmd.Cmd):
 def __init__(self, stufflist=[]):
 cmd.Cmd.__init__(self)
 self.prompt = '>>> '
 self.stufflist = stufflist
 print "Hello, I am your new commandline prompt! 'help' yourself!"
 def do_quit(self, arg):
 sys.exit(0)
 def do_print_stuff(self, arg):
 for s in self.stufflist:
 print s
p = Prompt(sys.argv[1:])
p.cmdloop()

Example test:

$ python cmdtest.py foo bar
Hello, I am your new commandline prompt! 'help' yourself!
>>> help
Undocumented commands:
======================
help print_stuff quit
>>> print_stuff
foo
bar
>>> quit

In order to save the output to a file, you can write what usually goes to stdout also to a file, using for example this class:

class Tee(object):
 def __init__(self, out1, out2):
 self.out1 = out1
 self.out2 = out2
 def write(self, s):
 self.out1.write(s)
 self.out2.write(s)
 def flush(self):
 self.out1.flush()
 self.out2.flush()

You can use it like this:

with open('cmdtest.out', 'w') as f:
 # write stdout to file and stdout
 t = Tee(f, sys.stdout)
 sys.stdout = t

A problem is that the commands read in via stdin do not appear in this output, but I believe that this can be easily solved.

• Samuel Lampa: Very bad by someone to minus-vote. Although it might not be the best solution to this question, it is a highly informative and usable answer, that shows other options to solve this (so, I voted up to zero again).
• SunSparc: @Jan-PhilipGehrcke just because someone asks a question and accepts an answer, does not mean the other answers are incorrect. :) I also found your answer to be quite informative.
• Dr. Jan-Philip Gehrcke: @SunSparc I think this was about a down-vote and not about not being accepted :-)