doc: add documentation for pkgs.{substitute,substituteAll,substituteAllFiles}

Fixes https://github.com/NixOS/nixpkgs/issues/65252
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Nathan Henrie 2024-07-11 14:47:04 -06:00 committed by Valentin Gagarin
parent c9ec828978
commit f5f24cdb58
2 changed files with 103 additions and 0 deletions

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# Build Support {#sec-build-support}
## `pkgs.substitute` {#pkgs-substitute}
`pkgs.substitute` is a wrapper around [the `substitute` Bash function](#fun-substitute) in the standard environment.
It replaces strings in `src` as specified by the `substitutions` argument.
:::{.example #ex-pkgs-substitute}
# Usage of `pkgs.substitute`
In a build script, the line:
```bash
substitute $infile $outfile --replace-fail @foo@ ${foopkg}/bin/foo
```
is equivalent to:
```nix
{ substitute, foopkg }:
substitute {
src = ./sourcefile.txt;
substitutions = [
"--replace"
"@foo@"
"${foopkg}/bin/foo"
];
}
```
:::
## `pkgs.substituteAll` {#pkgs-substituteall}
`pkgs.substituteAll` substitutes all instances of `@varName@` (`@`s included) in file `src` with the value of the corresponding environment variable.
As this uses the [`substituteAll`] (#fun-substitute) function, its limitations regarding variable names that will or will not be replaced also apply here.
:::{.example #ex-pkgs-substituteAll}
# Usage of `pkgs.substituteAll`
If `say-goodbye.sh` contains the following:
```bash
#! @bash@/bin/bash
echo @unchanged@
@hello@/bin/hello --greeting @greeting@
```
the following derivation will make substitutions to `@bash@`, `@hello@`, and `@greeting@`:
```nix
{
substituteAll,
bash,
hello,
}:
substituteAll {
src = ./say-goodbye.sh;
env = {
inherit bash hello;
greeting = "goodbye";
};
}
```
such that `$out` will result in something like the following:
```
#! /nix/store/s30jrpgav677fpc9yvkqsib70xfmx7xi-bash-5.2p26/bin/bash
echo @unchanged@
/nix/store/566f5isbvw014h7knmzmxa5l6hshx43k-hello-2.12.1/bin/hello --greeting goodbye
```
:::
## `pkgs.substituteAllFiles` {#pkgs-substituteallfiles}
`pkgs.substituteAllFiles` replaces `@varName@` with the value of the environment variable `varName`.
It expects `src` to be a directory and requires a `files` argument that specifies which files will be subject to replacements; only these files will be placed in `$out`.
As it also uses the `substituteAll` function, it is subject to the same limitations on environment variables as discussed in [pkgs.substituteAll](#pkgs-substituteall).
:::{.example #ex-pkgs-substitute-all-files}
# Usage of `pkgs.substituteAllFiles`
If the current directory contains `{foo,bar,baz}.txt` and the following `default.nix`
```nix
{ substituteAllFiles }:
substituteAllFiles {
src = ./.;
files = [
"foo.txt"
"bar.txt"
];
hello = "there";
}
```
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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@ -27,4 +27,5 @@ urxvt.section.md
vcpkg.section.md
weechat.section.md
xorg.section.md
build-support.md
```