pexpect suppresses first prompt

[nbeaver]

Minimal working example:

#! /usr/bin/env python
import pexpect
child = pexpect.spawn('bash')
index = child.expect_exact("$ ")
child.interact()

This should show the bash shell prompt, but it does not.

Typing Ctrl-L will repaint the screen and show the prompt, but not all shells support Ctrl-L (e.g. dash does not), so sending that keystroke is not always a possible workaround.

First brought up here:

https://stackoverflow.com/questions/28860660/pexpect-eats-bash-prompt

[jquast]

Not a bug, pexpect does indeed "suppress" up until interact, as this is intended, it doesn't know you would later call interact. If you want to make a PR for adding something about it to the documentation i'll accept it.

Anyway. If you want to see the prompt (and anything else) printed up until the match, just print it:

#! /usr/bin/env python
from __future__ import print_function
import pexpect
child = pexpect.spawn('bash')
index = child.expect_exact("$ ")
print(child.before + child.match, end='')
child.interact()

(Be careful about matching $, not all prompts have them. If you're going to use this for any portability, you should take care to force-set PS1 and so on, an example in the pexpect.replwrap.bash() function: https://github.com/pexpect/pexpect/blob/master/pexpect/replwrap.py#L108-113 )

[jquast]

it has been a very long time since i used the original tcl/expect, but i seem to recall that it implies duplicating all child program output to the parent process: it always duplicates stdout, which is why the tcl/expect version doesn't require printing before interact to "see" what was given up until interact is called

[nbeaver]

Thanks, that's exactly what I needed to know.