Failed when `nix-build hello.nix` - nix

Question

I followed the steps on http://lethalman.blogspot.com/2014/08/nix-pill-8-generic-builders.html to build GNU Hello, and here is the files I used to build GNU hello 2.9:
$ wget -c http://ftp.gnu.org/gnu/hello/hello-2.9.tar.gz
hello.nix:
$ cat hello.nix
let
pkgs = import <nixpkgs> {};
mkDerivation = import ./autotools.nix pkgs;
in mkDerivation {
name = "hello";
src = ./hello-2.9.tar.gz;
}
autotools.nix:
$ cat autotools.nix
pkgs: attrs:
with pkgs;
let defaultAttrs = {
builder = "${bash}/bin/bash";
args = [ ./builder.sh ];
baseInputs = [ gnutar gzip gnumake gcc binutils coreutils gawk gnused gnugrep ];
buildInputs = [];
system = builtins.currentSystem;
};
in
derivation (defaultAttrs // attrs)
builder.sh:
$ cat builder.sh
set -e
unset PATH
for p in $buildInputs; do
export PATH=$p/bin${PATH:+:}$PATH
done
tar -xf $src
for d in *; do
if [ -d "$d" ]; then
cd "$d"
break
fi
done
./configure --prefix=$out
make
make install
Error messages:
$ nix-build hello.nix
these derivations will be built:
/nix/store/d84l57agx3rmw00lxs8gjlw8srmx1bh9-hello.drv
building '/nix/store/d84l57agx3rmw00lxs8gjlw8srmx1bh9-hello.drv'...
/nix/store/vv3xqdggviqqbvym25jf2pwv575y9j1r-builder.sh: line 7: tar: No such file or directory
builder for '/nix/store/d84l57agx3rmw00lxs8gjlw8srmx1bh9-hello.drv' failed with exit code 127
error: build of '/nix/store/d84l57agx3rmw00lxs8gjlw8srmx1bh9-hello.drv' failed
It seems there is gnutar in the autotools.nix but builder still complains tar: No such file or directory, why is this?

Answer 1

The problem is probably that gnutar is in the baseInputs list, while the buildInputs list you are building your PATH from is totally empty so nothing will be on your PATH. Try changing the for line in your shell script so that it uses the concatentation of both lists to build the path:
for p in $baseInputs $buildInputs; do
You can add echo $PATH to your builder script to debug issues like this.
That is what the blog post author was asking you to do in this sentence from the post:
Complete the new builder.sh by adding $baseInputs in the for loop together with $buildInputs.