I don't have this installed, but this might help describe the process to see what's available in a container.
@Corneloues The shell interpreter (bash, sh , zsh, csh) has nothing to do with your package availability (e.g., curl, netstat). I think you aren't getting into the container properly if you don't see `curl` because that exact binary is used within the ubuntu base docker container itself here during the pkg install. The simplest webGUI way is to right click on the soulseek container and select "_> Console". Once that new window pops up, `which curl` should show you the exact path it's installed and available to you. If you want full CLI, here's an example how to go into a specific container environment using the deluge-vpn. To have an operational VPN there (not just installed), you'll need to have non-default username and password setup with a provider - I think all cost money.
# View containers that have case insensitive "vpn" (here you'd want "seek" or something similar)
docker ps -a | grep -i vpn
8c7a8bc6f19b binhex/arch-delugevpn "/usr/bin/dumb-init …" 4 weeks ago Up 2 days 0.0.0.0:8112->8112/tcp, :::8112->8112/tcp, 0.0.0.0:8118->8118/tcp, :::8118->8118/tcp, 0.0.0.0:58846->58846/tcp, :::58846->58846/tcp, 0.0.0.0:58946->58946/tcp, :::58946->58946/tcp, 0.0.0.0:58946->58946/udp, :::58946->58946/udp binhex-delugevpn
ea0fd9c974c6 binhex/arch-rtorrentvpn "/usr/bin/tini -g --…" 14 months ago Exited (0) 4 weeks ago binhex-rtorrentvpn
# Identify the specific container hash ID (deluge-vpn in this case but you'd switch to soulseek) "8c7a8bc6f19b"
docker exec -it 8c7a8bc6f19b bash
# Now you're *IN" the container! Try to see which binaries are pre-installed and available
which curl
which netstat
# The `which` command gives a path if it's available, otherwise it'll print nothing (just a newline). So in deluge-vpn, you'll see:
/usr/sbin/curl
/usr/sbin/netstat
# If there's a weird pkg you need unavailable, we know from the Dockerfile it's using Ubuntu here, which uses the apt package manager, so you can just `sudo apt install NAME` to install something new like "netstat" or "curl".
@realies AFAIK there's no way to see the Dockerfile on dockerhub, right? So my assumption might be incorrect in what you have on GH vs DH?