Thanks, even if that doesn't go into the docs, I'm putting that into a
github gist.
On 21/06/2016 5:44 PM, Bas van Dijk wrote:
Hi Erik,
Do note that I went through the same trouble as you figuring out how
to apply builtins.readFile to a dynamically constructed path. Maybe we
can document this "trick" in the documentation of builtins.readFile so
other people don't have to go through the same trouble.
To understand these things I would recommend using nix-repl:
$ nix-repl
Welcome to Nix version 1.11.2. Type :? for help.
nix-repl> name = "bar"
nix-repl> ./foo + "${name}"
/home/bas.van.dijk/foobar
Note that the previous is equivalent to the simpler:
nix-repl> ./foo + name
/home/bas.van.dijk/foobar
The reason that you get "foobar" is that we didn't include a "/". So
lets try to do that:
nix-repl> ./foo/ + name
error: syntax error, unexpected '+', at (string):1:8
Apparently the Nix path parser doesn't like a slash at the end of a
path literal. So lets try adding the slash dynamically:
nix-repl> ./foo + "/" + name
/home/bas.van.dijk/foobar
What happened here? Well, + is left associative so it is interpreted as:
(./foo + "/") + name
Lets try evaluating that left expression alone:
nix-repl> ./foo + "/"
/home/bas.van.dijk/foo
Apparently Nix performs normalization on paths since the final slash
is not included. So lets put the parenthesis differently:
nix-repl> ./foo + ("/" + name)
/home/bas.van.dijk/foo/bar
That's better! Now we can shorten this using some antiquotation:
nix-repl> ./foo + "/${name}"
/home/bas.van.dijk/foo/bar
I hope this helped.
Cheers,
Bas
On 21 June 2016 at 09:19, 4levels <[email protected]> wrote:
Hi Bas,
Out of curiosity I've been experimenting with different approaches but only
yours works and I have no clue why.. Is there anything I can learn / read /
study to understand why? Without having to study C++ (or python for that
matter as I can't even tell them apart ;-)
Is this basic lambda programming or very specific to Nix?
Works
builtins.readFile (./keys + "/${name}")
Doesn't work
builtins.readFile (./keys/ + "${name}") - unexpected +
builtins.readFile (./keys/ + name) - unexpected +
builtins.readFile (./keys + "/" + name") - no build errors, but doesn't
parse the / in the middle -> ./keysmancloud.amazon.iam.key_id -> not found
Kind regards and thanks again, my key deployment sections have become very
compact and maintainable now..
Erik
On Tue, Jun 21, 2016 at 1:56 AM 4levels <[email protected]> wrote:
Hi Bas,
Thank you so much! Exactly what I was looking for.
It's these basic things that I keep not getting my head around.. You have
no idea how many fruitless Google and GitHub searches I tried on this one
;-)
Finally resolved and another lesson learned, amazing!
Kind regards,
Erik
On Tue, Jun 21, 2016, 01:39 Bas van Dijk <[email protected]> wrote:
On 19 June 2016 at 15:58, 4levels <[email protected]> wrote:
builtins.readFile "./keys/${name}"
Hi Erik, try this:
builtins.readFile (./keys + "/${name}")
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