patchRcPath hooks

These hooks provide shell-specific utilities (with the same name as the hook) to patch shell scripts meant to be sourced by software users.

The typical usage is to patch initialisation or rc scripts inside $out/bin or $out/etc. 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. When shipped from the upstream, they sometimes use commands that might not be available in the environment they are getting sourced in.

The compatible shells for each hook are:

• patchRcPathBash: Bash, ksh, zsh and other shells supporting the Bash-like parameter expansions.
• patchRcPathCsh: Csh scripts, such as those targeting tcsh.
• patchRcPathFish: Fish scripts.
• patchRcPathPosix: POSIX-conformant shells supporting the limited parameter expansions specified by the POSIX standard. Current implementation uses the parameter expansion ${foo-} only.

For each supported shell, it modifies the script with a PATH prefix that is later removed when the script ends. It allows nested patching, which guarantees that a patched script may source another patched script.

Syntax to apply the utility to a script:

patchRcPath<shell> <file> <PATH-prefix>

Example usage:

Given a package foo containing an init script this-foo.fish that depends on coreutils, man and which, patch the init script for users to source without having the above dependencies in their PATH:

{ lib, stdenv, patchRcPathFish}:
stdenv.mkDerivation {

  # ...

  nativeBuildInputs = [
    patchRcPathFish
  ];

  postFixup = ''
    patchRcPathFish $out/bin/this-foo.fish ${lib.makeBinPath [ coreutils man which ]}
  '';
}