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diff --git a/nixpkgs/doc/builders/trivial-builders.chapter.md b/nixpkgs/doc/builders/trivial-builders.chapter.md new file mode 100644 index 000000000000..32944567c053 --- /dev/null +++ b/nixpkgs/doc/builders/trivial-builders.chapter.md @@ -0,0 +1,52 @@ +# Trivial builders {#chap-trivial-builders} + +Nixpkgs provides a couple of functions that help with building derivations. The most important one, `stdenv.mkDerivation`, has already been documented above. The following functions wrap `stdenv.mkDerivation`, making it easier to use in certain cases. + +## `runCommand` {#trivial-builder-runCommand} + +This takes three arguments, `name`, `env`, and `buildCommand`. `name` is just the name that Nix will append to the store path in the same way that `stdenv.mkDerivation` uses its `name` attribute. `env` is an attribute set specifying environment variables that will be set for this derivation. These attributes are then passed to the wrapped `stdenv.mkDerivation`. `buildCommand` specifies the commands that will be run to create this derivation. Note that you will need to create `$out` for Nix to register the command as successful. + +An example of using `runCommand` is provided below. + +```nix +(import <nixpkgs> {}).runCommand "my-example" {} '' + echo My example command is running + + mkdir $out + + echo I can write data to the Nix store > $out/message + + echo I can also run basic commands like: + + echo ls + ls + + echo whoami + whoami + + echo date + date +'' +``` + +## `runCommandCC` {#trivial-builder-runCommandCC} + +This works just like `runCommand`. The only difference is that it also provides a C compiler in `buildCommand`'s environment. To minimize your dependencies, you should only use this if you are sure you will need a C compiler as part of running your command. + +## `runCommandLocal` {#trivial-builder-runCommandLocal} + +Variant of `runCommand` that forces the derivation to be built locally, it is not substituted. This is intended for very cheap commands (<1s execution time). It saves on the network roundrip and can speed up a build. + +::: note +This sets [`allowSubstitutes` to `false`](https://nixos.org/nix/manual/#adv-attr-allowSubstitutes), so only use `runCommandLocal` if you are certain the user will always have a builder for the `system` of the derivation. This should be true for most trivial use cases (e.g. just copying some files to a different location or adding symlinks), because there the `system` is usually the same as `builtins.currentSystem`. +::: + +## `writeTextFile`, `writeText`, `writeTextDir`, `writeScript`, `writeScriptBin` {#trivial-builder-writeText} + +These functions write `text` to the Nix store. This is useful for creating scripts from Nix expressions. `writeTextFile` takes an attribute set and expects two arguments, `name` and `text`. `name` corresponds to the name used in the Nix store path. `text` will be the contents of the file. You can also set `executable` to true to make this file have the executable bit set. + +Many more commands wrap `writeTextFile` including `writeText`, `writeTextDir`, `writeScript`, and `writeScriptBin`. These are convenience functions over `writeTextFile`. + +## `symlinkJoin` {#trivial-builder-symlinkJoin} + +This can be used to put many derivations into the same directory structure. It works by creating a new derivation and adding symlinks to each of the paths listed. It expects two arguments, `name`, and `paths`. `name` is the name used in the Nix store path for the created derivation. `paths` is a list of paths that will be symlinked. These paths can be to Nix store derivations or any other subdirectory contained within. |