Running multiple expect/TCL code inside same shell script

Question

I have to run multiple chunks of expect script inside the shell script. In between each expect scripts, I have to run shell code. Below is conceptual non-working code where, 1st chunk would SSH into a remote node, and the subsequent chunks will run some other commands on the same remote server.

#!/bin/bash

#first chunk of expect code
/usr/bin/expect - <<EOF
    global spawn_id
    spawn /bin/bash
    expect -re ".*\$"
    spawn -- "ssh   -oStrictHostKeyChecking=no -oCheckHostIP=no admin@localstack1\r"
    expect -re  ".*assword.*"
    send 'admin\r'
    expect -re ".*\$"
    interact
EOF

#running shell commands
ls -lrt


#2nd chunk of expect code

/usr/bin/expect - <<EOF
    expect -re ".*\$"
    send -- "hostname\r"
    expect -re ".*\$"
EOF

This seems to be impossible, However would like to know more from experts. unlike pexepct, here I am unable to find any way to reuse the spawned shell(passing the child object).

why?

from another program I am getting the list of commands,expected_results and timeout , so I cannot hardcode them within the expect script. Sometime there are 1 set of commands,sometimes multiple set of commands.

you are right that's a limitation when using Expect unless you write all your script in Expect/Tcl (just like you do all the things with Python when using pexpect). you can try my sexpect which is specifically designed to be used in shell scripts. — sexpect - Expect for Shells
– sexpect - Expect for Shells, Commented Jan 31, 2023 at 3:46
Expect is using Tcl which is also a general purpose programming language. You can use Tcl's exec to run Linux commands (e.g. your ls -lrt). — pynexj
– pynexj, Commented Jan 31, 2023 at 4:15
If you do it all in tcl you don't need ls at all; you can get and sort filenames directly in it. — Shawn
– Shawn, Commented Jan 31, 2023 at 4:41
In this case I would write the whole program in Tcl, and shell out only for those commands where you want to use bash. — user1934428
– user1934428, Commented Jan 31, 2023 at 7:42
Note that the first spawn of bash appears redundant, it's unrelated to the second spawn which starts ssh. — Colin Macleod
– Colin Macleod, Commented Jan 31, 2023 at 9:06

Colin Macleod · Accepted Answer · 2023-01-31 09:08:27Z

2

Here's an example of writing the whole thing in Expect/Tcl as suggested in the comments:

#!/usr/bin/expect

#spawn /bin/bash
#expect -re ".*\$"
spawn -- "ssh   -oStrictHostKeyChecking=no -oCheckHostIP=no admin@localstack1\r"
expect -re  ".*assword.*"
send 'admin\r'
expect -re ".*\$"
interact

#running shell commands
puts [exec ls -lrt]

expect -re ".*\$"
send -- "hostname\r"
expect -re ".*\$"

I've commented out the spawn of bash because that appears redundant.

edited Jan 31, 2023 at 9:08

answered Jan 31, 2023 at 9:03

Colin Macleod

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8 Comments

pynexj Over a year ago

are you sure spawn -- "ssh -oStrictHostKeyChecking=no -oCheckHostIP=no admin@localstack1\r" would work?

Colin Macleod Over a year ago

Good point, that line should be changed to spawn -- ssh -oStrictHostKeyChecking=no -oCheckHostIP=no admin@localstack1.

pynexj Over a year ago

spawn even does not support --.

Colin Macleod Over a year ago

You're right of course, -- should be omitted also. I suspect this line in the original script was meant to be a send.

pynexj Over a year ago

and usually after interact returns, the spawned process would have exited so you cannot call send/expect any more.

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