Stable macOS hostname conditionals, interoperable with Linux

[th0rgall]

I'm managing some config differences in the same files between a specific macOS system and Linux hosts.

I hit the snag where the macOS hostname is not stable or reliable for configuration usage, which is documented in the macOS-specific user guide.

It took me some time however to figure out how to actually use the recommended scutil method in files that are shared across machines, since my Linux hosts would throw errors when applying config files because they don't have the scutil program.

What I landed on after some iterations is a callable shared template:

.chezmoitemplates/computerName:

{{ output "/bin/sh" "-c" (list "command" "-v" "scutil" "&&" "(scutil" "--get" "ComputerName)" "||" "echo" "''" | join " ") | trim }}

This uses the output function with a more complex shell expression that first checks for the presence of the scutil command. Another discussion showed me how to do this with list and join.

Then, in any template where I need to add a conditional:

{{ $computerName := includeTemplate "computerName"}}
{{- if eq $computerName "My Mac Name"}}
...
{{end -}}

This seems to work well, maybe it can help others!

[Lockszmith-GH]

I found stat to be the safest and fastest method - this way a shell isn't spun if you don't need it.

Pros: fast, built-in, will work on any environment (even on windows)
Cons: doesn't search PATH, must have full path.

Example on MacOS:

$ chezmoi execute-template '{{ lookPath "/usr/sbin/scutil" }}' && echo
/usr/sbin/scutil

final template will look something like:

{{- if lookPath "scutil" }}
{{/* {{- if eq .chezmoi.os "darwin" -}} /*}} {{/* alternative test you might be inclined to test, even more performant */}}
{{ output "scutil" "--get" "ComputerName" | trim }}
{{ else }}
{{ .chezmoi.hostname }}
{{ end -}}

However, I'm not sure I would do this in a template at all.
Template evaluation = compute, hostname/computer name isn't something I'm expecting to be evaluated dynamically - but rather once upon init.
Adding the code into chezmoi.toml and storing it in .chezmoi.data seems to me to be the more performant solution - but then again, you're use-case might be different than mine.

[th0rgall]

That looks better, thanks. It's a more general way to get the hostname with a single universal call, and not just on macOS.

I also had not thought to do this on chezmoi init, but I'm fine keeping it "dynamically" if that means that it just re-computes on every chezmoi apply, or config change. Those are pretty infrequent for me. It is also possible that my hostnames may change, and then it's good to not have to remember to keep that piece of chezmoi state up-to-date manually.

[halostatue]

You could also use {{ lookPath "scutil" }}.

[Lockszmith-GH]

lookPath - for some reason I always forget about this, even though I use it - thanks @halostatue. I updated my code above.