Low-level derivations: Difference between revisions
Second example |
aaaand done |
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| Line 48: | Line 48: | ||
{{File|example.nix|nix|highlight=1-3,7,11|<nowiki> | {{File|example.nix|nix|highlight=1-3,7,11|<nowiki> | ||
let | let | ||
pkgs = import | pkgs = import </nowiki><<nowiki>nixpkgs</nowiki>><nowiki> { }; | ||
in | in | ||
derivation { | derivation { | ||
| Line 95: | Line 95: | ||
The SHA is the same, because our inputs haven't changed. This is the essence to why derivations are ''pure functions'' of their inputs. | The SHA is the same, because our inputs haven't changed. This is the essence to why derivations are ''pure functions'' of their inputs. | ||
In rewriting our derivation, we need to import <code>chmod</code>, which is part of the <code>coreutils</code> package. We could point to the binary similarly to how we did it before, but for variation, let's modify our <code>PATH</code> variable instead: | |||
{{File|example.nix|nix|highlight=11|<nowiki> | |||
let | |||
pkgs = import </nowiki><<nowiki>nixpkgs</nowiki>><nowiki> { }; | |||
in | |||
derivation { | |||
name = "hello-world"; | |||
system = builtins.currentSystem; | |||
builder = "${pkgs.bash}/bin/bash"; | |||
args = [ | |||
"-c" | |||
'' | |||
export PATH="$PATH:${pkgs.coreutils}/bin" | |||
echo '#!${pkgs.bash}/bin/bash' </nowiki>><nowiki> $out | |||
echo 'echo "Hello, World!"' </nowiki>>><nowiki> $out | |||
chmod +x $out | |||
'' | |||
]; | |||
}</nowiki>}} | |||
Let's rebuild it again, noticing how the SHA will change again, as we changed our derivation's inputs: | |||
{{code|lang=console|line=no|highlight=3| | |||
$ nix-build example.nix | |||
this derivation will be built: | |||
/nix/store/ipjigfvbj371a5g966xbnj790sjvq5hp-hello-world.drv | |||
building '/nix/store/ipjigfvbj371a5g966xbnj790sjvq5hp-hello-world.drv'... | |||
/nix/store/lsm49a32nmc3ihi3f119p17lvwadr5ms-hello-world | |||
}} | |||
This time it built successfully. Finally, let's run our script: | |||
{{code|lang=console|line=no|highlight=3| | |||
$ ./result | |||
Hello, world! | |||
}} | |||
As mentioned above, building derivations this way can be unwieldy. But working through this example should shed some light onto why the community has built the [[standard environment]], providing utility functions to build derivations for the most common use cases. | |||