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Description of problem:
expect behavior on RHEL-7 is unexpected comparing to RHEL-6

Version-Release number of selected component (if applicable):
expect-5.45-8.el7

How reproducible:
always

Steps to Reproduce:
see below
mind the second expect


Actual results:
[root@rhel7 tmp]# expect << EOF
> spawn -noecho sudo su -
> expect "#" {send "echo a\r"}
> expect "#" {send "exit\r"}
> EOF
[root@rhel7 ~]# echo a
a
[root@rhel7 ~]# [root@rhel7 tmp]# 
[root@rhel7 tmp]# expect << EOF
> spawn -noecho bash
> send "sudo su -\r"
> expect "#" {send "echo a\r"}
> expect "#" {send "exit\rexit\r"}
> EOF
sudo su -
[root@rhel7 tmp]# sudo su -
[root@rhel7 ~]# [root@rhel7 tmp]# 

Expected results:
[root@rhel6 ~]# expect << EOF
> spawn -noecho sudo su -
> expect "#" {send "echo a\r"}
> expect "#" {send "exit\r"}
> EOF
[root@rhel6 ~]# echo a
a
[root@rhel6 ~]# [root@rhel6 ~]# 
[root@rhel6 ~]# expect << EOF
> spawn -noecho bash
> send "sudo su -\r"
> expect "#" {send "echo a\r"}
> expect "#" {send "exit\rexit\r"}
> EOF
sudo su -
[root@rhel6 ~]# sudo su -
echo a
[root@rhel6 ~]# echo a
a
[root@rhel6 ~]# [root@rhel6 ~]# 


Additional info:

In my opinion this is not fault of expect.

Dalibor tested RHEL6 expect version (expect-5.44.1.15-4) built for RHEL7 in RHEL7 and it behaved same like RHEL7 expect version (expect-5.45-8) - wrong. I tested RHEL7 expect version build for RHEL6 in RHEL6 and it worked fine, so something else must be different...

We have also found workaround, the second script works when it's modified like this:

spawn -noecho bash
send "sudo su -\r"
expect "#" {send "echo a\r"}
sleep 1
expect "#" {send "exit\rexit\r"}

('sleep 0.2' should suffice)

Created attachment 751722 [details]
strace output (RHEL7 expect, original script)

Created attachment 751723 [details]
strace output (RHEL7 expect, modified script)

Created attachment 751724 [details]
RHEL6 strace output (RHEL6 expect, original script)

Created attachment 751725 [details]
RHEL6 strace output (RHEL7 expect, original script)

Created attachment 751726 [details]
RHEL6 strace output (RHEL7 expect, modified script)

*** Bug 950070 has been marked as a duplicate of this bug. ***

You are not waiting to bash initialization. You have to do:
expect '#' {send "sudo su -\r"}
instead of:
send "sudo su -\r"