* Implemented Eelco V.'s `nix-env -I' command to specify the default

  path of the Nix expression to be used with the import, upgrade, and
  query commands.  For instance,

  $ nix-env -I ~/nixpkgs/pkgs/system/i686-linux.nix

  $ nix-env --query --available   [aka -qa]
  sylpheed-0.9.7
  bison-1.875
  pango-1.2.5
  subversion-0.35.1
  ...

  $ nix-env -i sylpheed

  $ nix-env -u subversion

  There can be only one default at a time.

* If the path to a Nix expression is a symlink, follow the symlink
  prior to resolving relative path references in the expression.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 60b86b162..28e276a32 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -109,6 +109,20 @@ bool pathExists(const Path & path)
 }
 
 
+Path readLink(const Path & path)
+{
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting status of `%1%'") % path);
+    if (!S_ISLNK(st.st_mode))
+        throw Error(format("`%1%' is not a symlink") % path);
+    char buf[st.st_size];
+    if (readlink(path.c_str(), buf, st.st_size) != st.st_size)
+        throw SysError(format("reading symbolic link `%1%'") % path);
+    return string(buf, st.st_size);
+}
+
+
 Strings readDirectory(const Path & path)
 {
     Strings names;