Shell Scripts
the package writeShellScript can be used to add shell scripts to nix expressions
someBuildHelper = { name, sha256 }:
stdenv.mkDerivation {
inherit name;
outputHashMode = "recursive";
outputHashAlgo = "sha256";
outputHash = sha256;
builder = writeShellScript "builder.sh" ''
echo "hi, my name is ''${0}" # escape bash variable
echo "hi, my hash is ${sha256}" # use nix variable
echo "hello world" >output.txt
'';
};
External builder.sh script
Longer bash scripts are usually stored as external script files, and called from Nix:
# default.nix
{
outputTxtPath = stdenv.mkDerivation rec {
name = "output.txt";
# disable unpackPhase etc
phases = "buildPhase";
builder = ./builder.sh;
nativeBuildInputs = [ coreutils jq ];
PATH = lib.makeBinPath nativeBuildInputs;
# only strings can be passed to builder
someString = "hello";
someNumber = builtins.toString 42;
someJson = builtins.toJSON { dst = "world"; };
};
}
# builder.sh
echo "$someString $(echo "$someJson" | jq -r '.dst') $someNumber" >$out
See also
runCommand + builder.sh
Instead of stdenv.mkDerivation, we can also use runCommand to call an external bash script:
# default.nix
{
outputTxtPath = runCommand "output.txt" {
nativeBuildInputs = [ coreutils jq ];
# only strings can be passed to builder
someString = "hello";
someNumber = builtins.toString 42;
someJson = builtins.toJSON { dst = "world"; };
} (builtins.readFile ./builder.sh);
}
Packaging
example:
# nix-build -E 'with import <nixpkgs> { }; callPackage ./default.nix { }'
{ stdenv
, lib
, fetchFromGitHub
, bash
, subversion
, makeWrapper
}:
stdenv.mkDerivation {
pname = "github-downloader";
version = "08049f6";
src = fetchFromGitHub {
# https://github.com/Decad/github-downloader
owner = "Decad";
repo = "github-downloader";
rev = "08049f6183e559a9a97b1d144c070a36118cca97";
sha256 = "073jkky5svrb7hmbx3ycgzpb37hdap7nd9i0id5b5yxlcnf7930r";
};
buildInputs = [ bash subversion ];
nativeBuildInputs = [ makeWrapper ];
installPhase = ''
mkdir -p $out/bin
cp github-downloader.sh $out/bin/github-downloader.sh
wrapProgram $out/bin/github-downloader.sh \
--prefix PATH : ${lib.makeBinPath [ bash subversion ]}
'';
};
wrapProgram will move the original script to .github-downloader.sh-wrapped
Command not found
for example, the script throws the error svn: command not found, because the dependency subversion is missing.
when a command is missing, you can use nix-locate to find the package name. for example, the stat command:
$ nix-locate bin/stat | grep 'bin/stat$'
coreutils.out 0 s /nix/store/vr96j3cxj75xsczl8pzrgsv1k57hcxyp-coreutils-8.31/bin/stat
Posix Shell
some environments (like OpenWRT, via busybox) offer only a "limited" shell (sh instead of bash).
on nixos, posix shells are provided by the packages dash and posh