requested change to the behavior of the podman run --env-merge flag

[lastephey]

Feature request description

Dear Podman developers,

Thank you for providing the podman run --env-merge flag we requested in #15288.

We are working on getting this into production for our podman-hpc modules. We would like to prepend some directories to the user container LD_LIBRARY_PATH settings without overwriting whatever they may already have.

However, we have found that in the situation where an environment variable (ex: LD_LIBRARY_PATH) is not already set in the container, the --env-merge flag returns an empty LD_LIBRARY_PATH.

I've included an example below. In the first command, I am running the test container test:test that contains the setting LD_LIBRARY_PATH=foo. In the second command, I am running the ubuntu:jammy container which does not define LD_LIBRARY_PATH.

(base) DOE-7616476:test stephey$ cat Containerfile 
FROM ubuntu:jammy

ENV LD_LIBRARY_PATH=foo
(base) DOE-7616476:test stephey$ cat print-env-helper.sh 
#!/bin/bash
#
##helper script to print environment variable
#
echo $LD_LIBRARY_PATH
(base) DOE-7616476:test stephey$ podman run --rm -it --volume=$(pwd):/test --workdir=/test test:test ./print-env-helper.sh 
foo
(base) DOE-7616476:test stephey$ 
(base) DOE-7616476:test stephey$ podman run --rm --env-merge LD_LIBRARY_PATH=\${LD_LIBRARY_PATH},bar --volume=$(pwd):/test --workdir=/test test:test ./print-env-helper.sh 
foo,bar
(base) DOE-7616476:test stephey$ podman run --rm -it --volume=$(pwd):/test --workdir=/test ubuntu:jammy ./print-env-helper.sh 

(base) DOE-7616476:test stephey$ 
(base) DOE-7616476:test stephey$ podman run --rm --env-merge LD_LIBRARY_PATH=\${LD_LIBRARY_PATH},bar --volume=$(pwd):/test --workdir=/test ubuntu:jammy ./print-env-helper.sh 

(base) DOE-7616476:test stephey$ 

Suggest potential solution

Feature request: update the behavior of the --env-merge flag to preserve the requested additional variable setting, even if there is no original variable defined.

Desired behavior:

(base) DOE-7616476:test stephey$ podman run --rm --env-merge LD_LIBRARY_PATH=\${LD_LIBRARY_PATH},bar --volume=$(pwd):/test --workdir=/test ubuntu:jammy ./print-env-helper.sh 
bar
(base) DOE-7616476:test stephey$ 

Have you considered any alternatives?

We are open to alternatives.

Additional context

Thank you for considering this change.

[vrothberg]

Thanks for reaching out, @lastephey.

I agree on your desired behavior and personally see it more as a bug fix. @Luap99, WDYT?

[Luap99]

Yeah I think that can be considered a bug fix. I would expect it to follow shell like behaviour and just have a empty string in place of an undefined var.
Although one important thing is that means your command would return ,bar not bar.

[danishprakash]

Mind if I take a look at this?

[vrothberg]

It's all yours, thank you, @danishprakash

[lastephey]

Thanks very much for looking at this @danishprakash. Good point about the leading/trailing character that may be left behind @Luap99. I think this should be okay in our case since we will always be prepending rather than appending. I could see an issue for the case where people want to append and may end up with a leading :, so maybe that's worth noting as a caveat in the docs.

Thanks again and sorry for my late reply- yesterday was a holiday here in the US.