How to see the output in pexpect?

Question

I have write this program:

[mik@mikypc ~]$ cat ftp.py 
 #!/usr/bin/env python

 # This connects to the rediris ftp site
 # 
 import pexpect
 child = pexpect.spawn('ftp ftp.rediris.es')

 child.expect('Name .*: ')
 child.sendline('anonymous')
 child.expect('ftp> ')
 child.sendline('noah@example.com')
 child.expect('ftp> ')
 child.sendline('lcd /tmp')
 child.expect('ftp> ')
 child.sendline('pwd')
 child.expect('ftp> ')
 child.sendline('bye')

[mik@mikypc ~]$ ./ftp.py 
[mik@mikypc ~]$ 
[mik@mikypc ~]$ 
[mik@mikypc ~]$ 

But I cannot see the output. How could I see it?. I don't see anything when I execute it. How could I see the output?.

Answer 1

According to the pexpect doc:

The logfile_read and logfile_send members can be used to separately log the input from the child and output sent to the child. Sometimes you don’t want to see everything you write to the child. You only want to log what the child sends back. For example:

child = pexpect.spawn('some_command')
child.logfile_read = sys.stdout

You will need to pass an encoding to spawn in the above code if you are using Python 3.

To separately log output sent to the child use logfile_send:

child.logfile_send = fout 

See following example:

# cat foo.py

import pexpect, sys

pat_ps1 = 'bash-[.0-9]+[$#] $'

if sys.version_info[0] < 3:
    # python2
    proc = pexpect.spawn('bash --norc')
else:
    # python3
    proc = pexpect.spawn('bash --norc', encoding='utf8')

if len(sys.argv) != 1:
    proc.logfile_read = sys.stdout

proc.expect(pat_ps1)

proc.sendline("echo hello world")
proc.expect(pat_ps1)

proc.sendline('exit')
proc.expect(pexpect.EOF)
proc.wait()

$ python3 foo.py
$ python3 foo.py 1
bash-5.2$ echo hello world
hello world
bash-5.2$ exit
exit
$

Answer 2

From the pexpect docs:

After each call to expect() the before and after properties will be set to the text printed by child application. The before property will contain all text up to the expected string pattern. The after string will contain the text that was matched by the expected pattern.

So, a print(child.before) in strategic places should fulfill your need.

Answer 3

You can also log the output of pexpect to a log file:

child.logfile = open("/tmp/mylog", "w")

Then every response of sendline will be printed to the log