102 lines
2.6 KiB
Markdown
102 lines
2.6 KiB
Markdown
# Build Support {#sec-build-support}
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## `pkgs.substitute` {#pkgs-substitute}
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`pkgs.substitute` is a wrapper around [the `substitute` Bash function](#fun-substitute) in the standard environment.
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It replaces strings in `src` as specified by the `substitutions` argument.
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:::{.example #ex-pkgs-substitute}
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# Usage of `pkgs.substitute`
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In a build script, the line:
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```bash
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substitute $infile $outfile --replace-fail @foo@ ${foopkg}/bin/foo
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```
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is equivalent to:
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```nix
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{ substitute, foopkg }:
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substitute {
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src = ./sourcefile.txt;
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substitutions = [
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"--replace"
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"@foo@"
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"${foopkg}/bin/foo"
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];
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}
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```
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:::
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## `pkgs.substituteAll` {#pkgs-substituteall}
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`pkgs.substituteAll` substitutes all instances of `@varName@` (`@`s included) in file `src` with the value of the corresponding environment variable.
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As this uses the [`substituteAll`] (#fun-substitute) function, its limitations regarding variable names that will or will not be replaced also apply here.
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:::{.example #ex-pkgs-substituteAll}
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# Usage of `pkgs.substituteAll`
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If `say-goodbye.sh` contains the following:
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```bash
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#! @bash@/bin/bash
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echo @unchanged@
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@hello@/bin/hello --greeting @greeting@
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```
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the following derivation will make substitutions to `@bash@`, `@hello@`, and `@greeting@`:
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```nix
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{
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substituteAll,
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bash,
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hello,
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}:
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substituteAll {
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src = ./say-goodbye.sh;
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env = {
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inherit bash hello;
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greeting = "goodbye";
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};
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}
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```
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such that `$out` will result in something like the following:
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```
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#! /nix/store/s30jrpgav677fpc9yvkqsib70xfmx7xi-bash-5.2p26/bin/bash
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echo @unchanged@
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/nix/store/566f5isbvw014h7knmzmxa5l6hshx43k-hello-2.12.1/bin/hello --greeting goodbye
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```
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:::
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## `pkgs.substituteAllFiles` {#pkgs-substituteallfiles}
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`pkgs.substituteAllFiles` replaces `@varName@` with the value of the environment variable `varName`.
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It expects `src` to be a directory and requires a `files` argument that specifies which files will be subject to replacements; only these files will be placed in `$out`.
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As it also uses the `substituteAll` function, it is subject to the same limitations on environment variables as discussed in [pkgs.substituteAll](#pkgs-substituteall).
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:::{.example #ex-pkgs-substitute-all-files}
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# Usage of `pkgs.substituteAllFiles`
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If the current directory contains `{foo,bar,baz}.txt` and the following `default.nix`
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```nix
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{ substituteAllFiles }:
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substituteAllFiles {
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src = ./.;
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files = [
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"foo.txt"
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"bar.txt"
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];
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hello = "there";
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}
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```
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in the resulting derivation, every instance of `@hello@` will be replaced with `there` in `$out/foo.txt` and` `$out/bar.txt`; `baz.txt` will not be processed nor will it appear in `$out`.
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:::
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