nix/install: Don't rely on tar for decompression.

Older versions of tar didn't detect the compression type and thus tried
to extract an uncompressed archive and even older versions of tar didn't
even have the -j argument at all, so let's download, decompress and
unpack in one go.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

nix/install

@@ -4,16 +4,16 @@
 # downloading a binary distribution and running its installer script
 # (which in turn creates and populates /nix).
 
-tarball=nix-binary-tarball.tar.bz2
 unpack=nix-binary-tarball-unpack
 
-cleanup() {
-    rm -rf "$unpack" "$tarball"
+require_util() {
+    type "$1" > /dev/null 2>&1 || which "$1" > /dev/null 2>&1 ||
+        oops "you do not have \`$1' installed, which i need to $2"
 }
 
 oops() {
     echo "$0: $@" >&2
-    cleanup
+    rm -rf "$unpack"
     exit 1
 }
 
@@ -26,19 +26,16 @@ esac
 
 url="https://nixos.org/releases/nix/nix-1.7/nix-1.7-$system.tar.bz2"
 
-type curl > /dev/null 2>&1 || which curl > /dev/null 2>&1 ||
-    oops "you do not have \`curl' installed," \
-         "which I need to download the binary tarball"
+require_util curl "download the binary tarball"
+require_util bzcat "decompress the binary tarball"
+require_util tar "unpack the binary tarball"
 
-echo "downloading Nix binary tarball for $system from \`$url'..."
-curl -L -o "$tarball" "$url" || oops "failed to download \`$url'"
-
-echo "unpacking binary tarball..."
-mkdir "$unpack"
-tar xf "$tarball" -C "$unpack"
+echo "unpacking Nix binary tarball for $system from \`$url'..."
+mkdir "$unpack" || oops "failed to create \`$unpack' directory"
+curl -L "$url" | bzcat | tar x -C "$unpack" || oops "failed to unpack \`$url'"
 
 [ -e "$unpack"/*/install ] ||
     oops "installation script is missing from the binary tarball!"
 
 "$unpack"/*/install
-cleanup
+rm -rf "$unpack"