quadlet: environment variable substitution works differently for podman.addf("-w=%s", workdir) and podman.add("--workdir", workdir)

[eriksjolund]

Environment variable substitution in systemd user service works differently
for podman.addf("-w=%s", workdir) and podman.add("--workdir", workdir)

test environment variable substitution in systemd user service

I perfomed these steps:

1. sudo useradd test
2. sudo machinectl shell --uid=test
3. mkdir -p ~/.config/systemd/user
4. Create the file /var/home/test/.config/systemd/user/test.service containing

   [Service]
   Type=oneshot
   ExecStart=/usr/bin/echo foobar -w=$HOME -w=${HOME} --workdir $HOME --workdir ${HOME}
   

5. systemctl --user daemon-reload
6. systemctl --user start test.service
7. Check the journal

   journalctl --user --no-pager -xeu test.service | grep foobar
   

   The command prints the following output

   Sep 29 16:28:08 localhost.localdomain echo[17465]: foobar -w=$HOME -w=/var/home/test --workdir /var/home/test --workdir /var/home/test
   

summary of the result:

input	result after substitution
-w=$HOME	-w=$HOME
-w=${HOME}	-w=/var/home/test
--workdir $HOME	--workdir /var/home/test
--workdir ${HOME}	--workdir /var/home/test

Discussion

Variable substitution thus behaves differently depending on whether quadlet.go implements WorkingDir= with

podman.addf("-w=%s", workdir)

or

podman.add("--workdir", workdir)

Currently the first alternative is used

podman/pkg/systemd/quadlet/quadlet.go

Line 786 in e1496c9

podman.addf("-w=%s", workdir)

(a GitHub permalink as of 29 September 2024)

Because of that, the following example

WorkingDir=$HOME

in

• podman/docs/source/markdown/podman-systemd.unit.5.md

  Line 336 in e1496c9

  | WorkingDir=$HOME | --workdir $HOME |

does not work.

[Luap99]

This looks interesting, I guess it would make the most sense if quadlet behaves consistently for all options as this would effect all options not just workdir.

I would say podman.add("--workdir", workdir) makes more sense as this allows the "normal" $var syntax to work as most would expect.

cc @ygalblum

[ygalblum]

@eriksjolund Thanks for the analysis.
@Luap99, yes, I agree. Quadlet should be consistent. I'll take a look