From ae8d4501b65ad6be7d83b3da60672c39e1b8ffcb Mon Sep 17 00:00:00 2001
From: Marc Weber <marco-oweber@gmx.de>
Date: Tue, 27 Apr 2010 18:44:23 +0000
Subject: [PATCH] adding maybeEnv. This will replace from-env.nix in nixos and
 will be reused in copySystemConfiguration

svn path=/nixpkgs/trunk/; revision=21353
---
 pkgs/lib/misc.nix | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/pkgs/lib/misc.nix b/pkgs/lib/misc.nix
index 2cfd15735a74..0a8c61d6c85c 100644
--- a/pkgs/lib/misc.nix
+++ b/pkgs/lib/misc.nix
@@ -9,6 +9,11 @@ with import ./strings.nix;
 
 rec {
 
+  # returns default if env var is not set
+  maybeEnv = name: default:
+    let value = builtins.getEnv name; in
+    if value == "" then default else value;
+
   defaultMergeArg = x : y: if builtins.isAttrs y then
     y
   else