Thanks... I'm not super sure to make it work in my case though

    substituteInPlace src/python/CMakeLists.txt \
      --replace-fail "find_package(pybind11 ${PYBIND11_VER} QUIET)" "find_package(pybind11 QUIET)"

In reply to @emilazy:matrix.org
because bash will also try to expand it

In reply to @emilazy:matrix.org
that's not so bad

In reply to @emilazy:matrix.org
welcome to the worst string syntax in the universe!

In reply to @emilazy:matrix.org
just putting this here to scare you ''''\'''${a}''

let bashFoo = "\${foo}"; in ''
  echo "${bashFoo}"
'';

If it's a large enough block of text to justify it, you can always put it in a separate file and readFile it. If you also need to include a handful of nix vars/expressions in the string, you could map them to bash vars using lib.toShellVars:

{
  env = {
    foo = "bar";
    sum = 1 + 2;
    hello = lib.getExe pkgs.hello;
    PATH = lib.makeBinPath [
      pkgs.git
      pkgs.cowsay
    ];
  };

  text = ''
    ${lib.toShellVars env}
    export PATH

    ${builtins.readFile ./script.sh}
  '';
}

If it's a large enough block of text to justify it, you can always put it in a separate file and readFile it. If you also need to include a handful of nix vars/expressions in the string, you could map them to bash vars using lib.toShellVars:

rec {
  env = {
    foo = "bar";
    sum = 1 + 2;
    hello = lib.getExe pkgs.hello;
    PATH = lib.makeBinPath [
      pkgs.git
      pkgs.cowsay
    ];
  };

  text = ''
    ${lib.toShellVars env}
    export PATH

    ${builtins.readFile ./script.sh}
  '';
}