da31bd5673
Init patchRcPath hooks, which provides utilities to patch shell scripts to be sourced by users. Add test cases and documentation.
50 lines
2.2 KiB
Markdown
50 lines
2.2 KiB
Markdown
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# `patchRcPath` hooks {#sec-patchRcPathHooks}
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These hooks provide shell-specific utilities (with the same name as the hook) to patch shell scripts meant to be sourced by software users.
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The typical usage is to patch initialisation or [rc](https://unix.stackexchange.com/questions/3467/what-does-rc-in-bashrc-stand-for) scripts inside `$out/bin` or `$out/etc`.
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Such scripts, when being sourced, would insert the binary locations of certain commands into `PATH`, modify other environment variables or run a series of start-up commands.
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When shipped from the upstream, they sometimes use commands that might not be available in the environment they are getting sourced in.
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The compatible shells for each hook are:
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- `patchRcPathBash`: [Bash](https://www.gnu.org/software/bash/), [ksh](http://www.kornshell.org/), [zsh](https://www.zsh.org/) and other shells supporting the Bash-like parameter expansions.
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- `patchRcPathCsh`: Csh scripts, such as those targeting [tcsh](https://www.tcsh.org/).
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- `patchRcPathFish`: [Fish](https://fishshell.com/) scripts.
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- `patchRcPathPosix`: POSIX-conformant shells supporting the limited parameter expansions specified by the POSIX standard. Current implementation uses the parameter expansion `${foo-}` only.
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For each supported shell, it modifies the script with a `PATH` prefix that is later removed when the script ends.
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It allows nested patching, which guarantees that a patched script may source another patched script.
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Syntax to apply the utility to a script:
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```sh
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patchRcPath<shell> <file> <PATH-prefix>
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```
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Example usage:
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Given a package `foo` containing an init script `this-foo.fish` that depends on `coreutils`, `man` and `which`,
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patch the init script for users to source without having the above dependencies in their `PATH`:
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```nix
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{ lib, stdenv, patchRcPathFish}:
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stdenv.mkDerivation {
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# ...
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nativeBuildInputs = [
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patchRcPathFish
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];
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postFixup = ''
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patchRcPathFish $out/bin/this-foo.fish ${lib.makeBinPath [ coreutils man which ]}
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'';
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}
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```
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::: {.note}
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`patchRcPathCsh` and `patchRcPathPosix` implementation depends on `sed` to do the string processing.
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The others are in vanilla shell and have no third-party dependencies.
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:::
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