How to cache a function's output?

[muuvmuuv]

I would like to cache a function's output, but what I get is "command not found: <function_output_here>". What am I missing?

function ca_pw {
  echo $(docker run --rm -v step:/home/step smallstep/step-ca cat secrets/password)
}
znap eval _ca_pw "ca_pw"

[marlonrichert]

This looks problematic:

  echo $(docker run --rm -v step:/home/step smallstep/step-ca cat secrets/password)

1. Using $( ... ) instead of "$( ... )" turns all whitespace into word separators, which changes the meaning of line breaks.
2. If you use echo instead of print -r -- , then almost anything starting with a \ will be processed as an escape sequence.
3. Using echo $( <command> ) is completely superfluous. You can just use <command> instead (unless you actually want the above).

So, I would rewrite that line like this:

docker run --rm -v step:/home/step smallstep/step-ca cat secrets/password

Is there a particular reason why don't just do this?

znap eval _ca_pw 'docker run --rm -v step:/home/step smallstep/step-ca cat secrets/password'

[muuvmuuv]

I mean the standard output sorry for the wording. Usually, I need to run the docker command each day when certificates need to be updated (the standard output of the command is the password for the CA Server), since the password does not change but is stored in the container I would like to cache it so the command does not always take several seconds to run.

[marlonrichert]

the standard output of the command is the password for the CA Server

A password is not a command, is it? You cannot eval a password. So, don't use znap eval for that. Just redirect the output to a file. Or alternative, change your function to output code that does something with the password, instead of just outputting the password. Then you can use it with znap eval.

[muuvmuuv]

With command, I mean the docker command, not the password. I did expect that znap eval caches the standard output, so I just misunderstood that point, I guess? Redirecting to a file would work for now, just thought I could use znap for it.

[marlonrichert]

I could separate the caching part of znap eval into a separate command, but the problem here is: How would the code know when to invalidate the cache? For this case, I don’t think it can. You would end up having to do it manually anyway.

[muuvmuuv]

That sounds great, but I don't think this is worth your time if its just for my specific case.

Anyway, invalidating manually is fine in my case, I would only need to do that one time per month when I reset my containers (so the password will change).