Embedding an Expect script inside a Bash script

Question

I have the following script:

#!/bin/bash

if [ `hostname` = 'EXAMPLE' ]
then

/usr/bin/expect << EOD

spawn scp -rp host:~/outfiles/ /home/USERNAME/outfiles/
expect "id_rsa':"
send "PASSWORD\r"
interact

spawn scp -rp host:~/errfiles/ /home/USERNAME/errfiles/
expect "id_rsa':"
send "PASSWORD\r"
interact

expect eof

EOD

echo 'Successful download'
fi

Unfortunately it doesn't seem to work and I get an error message:

spawn scp -rp host:~/outfiles/ /home/USERNAME/outfiles/
Enter passphrase for key '/home/USERNAME/.ssh/id_rsa': interact: spawn id exp0 not open
    while executing
"interact"

I don't know what it means and why it doesn't work. However, when I wrote the above code using a not-embedded Expect script:

#!/usr/bin/expect

spawn scp -rp host:~/outfiles/ /home/USERNAME/outfiles/
expect "id_rsa':"
send "PASSWORD\r"
interact

spawn scp -rp host:~/errfiles/ /home/USERNAME/errfiles/
expect "id_rsa':"
send "PASSWORD\r"
interact

It worked without any problems. So what am I doing wrong?

NOTE: Often when someone posts a question about using Expect to use scp or ssh the answer given is to use RSA keys. I tried, unfortunately on one of my computers there is some crappy bug with the GNOME keyring that means that I can't remove my password from the RSA key, which is exactly why I'm trying to write the above script with an if statement. So please don't tell me to use RSA keys.

If you want expect to execute exactly the text between your delimiter (without variable or special characters expansion before it is interpreted), you'll have to quote your here-doc delimiter, like so : /usr/bin/expect << "EOD" ... EOD. This question is similar, it has the same problem but the other way around. — Aserre
– Aserre, Commented Dec 15, 2016 at 14:07
I just tried it /usr/bin/expect << "EOD" but it still gives the error spawn scp -rp host:~/outfiles/ /home/USERNAME/outfiles/ Enter passphrase for key '/home/USERNAME/.ssh/id_rsa': interact: spawn id exp0 not open while executing "interact" Successful download — Marses
– Marses, Commented Dec 15, 2016 at 14:18

Peter Mortensen · Accepted Answer · 2020-06-12 20:18:54Z

14

Your Bash script is passing the Expect commands on the standard input of expect. That is what the here-document <<EOD does. However, expect... expects its commands to be provided in a file, or as the argument of a -c, per the man page. Three options are below. Caveat emptor; none have been tested.

Process substitution with here-document:
```
expect <(cat <<'EOD'
spawn ... (your script here)
EOD
)
```
The EOD ends the here-document, and then the whole thing is wrapped in a <( ) process substitution block. The result is that expect will see a temporary filename including the contents of your here-document.

As @Aserre noted, the quotes in <<'EOD' mean that everything in your here-document will be treated literally. Leave them off to expand Bash variables and the like inside the script, if that's what you want.
Edit Variable+here-document:
```
IFS= read -r -d '' expect_commands <<'EOD'
spawn ... (your script here)
interact
EOD

expect -c "${expect_commands//
/;}"
```
Yes, that is a real newline after // - it's not obvious to me how to escape it. That turns newlines into semicolons, which the man page says is required.

Thanks to this answer for the read+heredoc combo.
Shell variable
```
expect_commands='
spawn ... (your script here)
interact'
expect -c "${expect_commands//
/;}"
```
Note that any ' in the expect commands (e.g., after id_rsa) will need to be replaced with '\'' to leave the single-quote block, add a literal apostrophe, and then re-enter the single-quote block. The newline after // is the same as in the previous option.

edited Jun 12, 2020 at 20:18

Peter Mortensen

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answered Dec 15, 2016 at 20:45

cxw

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3 Comments

Marses Over a year ago

Thanks for the help, I used example 1. and it worked. I appreciate it.

kvantour Over a year ago

You can also make use of the -f flag in expect which accepts a file with commands. However, the file could be -, resembling /dev/stdin. This could be a heredoc. But if the heredoc contains interact it will fail as interact uses /dev/stdin but the heredoc is finished, hence the script terminates.

trinth Over a year ago

Worked on Mac OS X

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