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diff --git a/doc/builders/trivial-builders.chapter.md b/doc/builders/trivial-builders.chapter.md new file mode 100644 index 00000000000..779a0a801b4 --- /dev/null +++ b/doc/builders/trivial-builders.chapter.md @@ -0,0 +1,223 @@ +# 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`. + +Here are a few examples: +```nix +# Writes my-file to /nix/store/<store path> +writeTextFile { + name = "my-file"; + text = '' + Contents of File + ''; +} +# See also the `writeText` helper function below. + +# Writes executable my-file to /nix/store/<store path>/bin/my-file +writeTextFile { + name = "my-file"; + text = '' + Contents of File + ''; + executable = true; + destination = "/bin/my-file"; +} +# Writes contents of file to /nix/store/<store path> +writeText "my-file" + '' + Contents of File + ''; +# Writes contents of file to /nix/store/<store path>/share/my-file +writeTextDir "share/my-file" + '' + Contents of File + ''; +# Writes my-file to /nix/store/<store path> and makes executable +writeScript "my-file" + '' + Contents of File + ''; +# Writes my-file to /nix/store/<store path>/bin/my-file and makes executable. +writeScriptBin "my-file" + '' + Contents of File + ''; +# Writes my-file to /nix/store/<store path> and makes executable. +writeShellScript "my-file" + '' + Contents of File + ''; +# Writes my-file to /nix/store/<store path>/bin/my-file and makes executable. +writeShellScriptBin "my-file" + '' + Contents of File + ''; + +``` + +## `concatTextFile`, `concatText`, `concatScript` {#trivial-builder-concatText} + +These functions concatenate `files` to the Nix store in a single file. This is useful for configuration files structured in lines of text. `concatTextFile` takes an attribute set and expects two arguments, `name` and `files`. `name` corresponds to the name used in the Nix store path. `files` will be the files to be concatenated. You can also set `executable` to true to make this file have the executable bit set. +`concatText` and`concatScript` are simple wrappers over `concatTextFile`. + +Here are a few examples: +```nix + +# Writes my-file to /nix/store/<store path> +concatTextFile { + name = "my-file"; + files = [ drv1 "${drv2}/path/to/file" ]; +} +# See also the `concatText` helper function below. + +# Writes executable my-file to /nix/store/<store path>/bin/my-file +concatTextFile { + name = "my-file"; + files = [ drv1 "${drv2}/path/to/file" ]; + executable = true; + destination = "/bin/my-file"; +} +# Writes contents of files to /nix/store/<store path> +concatText "my-file" [ file1 file2 ] + +# Writes contents of files to /nix/store/<store path> +concatScript "my-file" [ file1 file2 ] +``` + +## `writeShellApplication` {#trivial-builder-writeShellApplication} + +This can be used to easily produce a shell script that has some dependencies (`runtimeInputs`). It automatically sets the `PATH` of the script to contain all of the listed inputs, sets some sanity shellopts (`errexit`, `nounset`, `pipefail`), and checks the resulting script with [`shellcheck`](https://github.com/koalaman/shellcheck). + +For example, look at the following code: + +```nix +writeShellApplication { + name = "show-nixos-org"; + + runtimeInputs = [ curl w3m ]; + + text = '' + curl -s 'https://nixos.org' | w3m -dump -T text/html + ''; +} +``` + +Unlike with normal `writeShellScriptBin`, there is no need to manually write out `${curl}/bin/curl`, setting the PATH +was handled by `writeShellApplication`. Moreover, the script is being checked with `shellcheck` for more strict +validation. + +## `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. +Here is an example: +```nix +# adds symlinks of hello and stack to current build and prints "links added" +symlinkJoin { name = "myexample"; paths = [ pkgs.hello pkgs.stack ]; postBuild = "echo links added"; } +``` +This creates a derivation with a directory structure like the following: +``` +/nix/store/sglsr5g079a5235hy29da3mq3hv8sjmm-myexample +|-- bin +| |-- hello -> /nix/store/qy93dp4a3rqyn2mz63fbxjg228hffwyw-hello-2.10/bin/hello +| `-- stack -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1/bin/stack +`-- share + |-- bash-completion + | `-- completions + | `-- stack -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1/share/bash-completion/completions/stack + |-- fish + | `-- vendor_completions.d + | `-- stack.fish -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1/share/fish/vendor_completions.d/stack.fish +... +``` + +## `writeReferencesToFile` {#trivial-builder-writeReferencesToFile} + +Writes the closure of transitive dependencies to a file. + +This produces the equivalent of `nix-store -q --requisites`. + +For example, + +```nix +writeReferencesToFile (writeScriptBin "hi" ''${hello}/bin/hello'') +``` + +produces an output path `/nix/store/<hash>-runtime-deps` containing + +```nix +/nix/store/<hash>-hello-2.10 +/nix/store/<hash>-hi +/nix/store/<hash>-libidn2-2.3.0 +/nix/store/<hash>-libunistring-0.9.10 +/nix/store/<hash>-glibc-2.32-40 +``` + +You can see that this includes `hi`, the original input path, +`hello`, which is a direct reference, but also +the other paths that are indirectly required to run `hello`. + +## `writeDirectReferencesToFile` {#trivial-builder-writeDirectReferencesToFile} + +Writes the set of references to the output file, that is, their immediate dependencies. + +This produces the equivalent of `nix-store -q --references`. + +For example, + +```nix +writeDirectReferencesToFile (writeScriptBin "hi" ''${hello}/bin/hello'') +``` + +produces an output path `/nix/store/<hash>-runtime-references` containing + +```nix +/nix/store/<hash>-hello-2.10 +``` + +but none of `hello`'s dependencies, because those are not referenced directly +by `hi`'s output. |