diff --git a/ofborg/src/nixenv.rs b/ofborg/src/nixenv.rs
new file mode 100644
index 0000000..0a05f90
--- /dev/null
+++ b/ofborg/src/nixenv.rs
@@ -0,0 +1,95 @@
+/// Evaluates the expression like Hydra would, with regards to
+/// architecture support and recursed packages.
+use crate::nixstats::EvaluationStats;
+use crate::outpathdiff;
+use ofborg::nix;
+use serde_json;
+use std::fs;
+use std::fs::File;
+use std::io::BufReader;
+use std::io::Seek;
+use std::io::SeekFrom;
+use std::io::Write;
+use std::path::PathBuf;
+
+pub struct HydraNixEnv {
+    path: PathBuf,
+    nix: nix::Nix,
+    check_meta: bool,
+}
+
+impl HydraNixEnv {
+    pub fn new(nix: nix::Nix, path: PathBuf, check_meta: bool) -> HydraNixEnv {
+        HydraNixEnv {
+            nix,
+            path,
+            check_meta,
+        }
+    }
+
+    pub fn execute(&self) -> Result<(outpathdiff::PackageOutPaths, EvaluationStats), Error> {
+        self.place_nix()?;
+        let (status, stdout, mut stderr) = self.run_nix_env();
+        self.remove_nix()?;
+
+        if status {
+            Err(Error::Fd(stderr))
+        } else if let Ok(stats) = serde_json::from_reader(&mut stderr) {
+            let outpaths = outpathdiff::parse_lines(&mut BufReader::new(stdout));
+            Ok((outpaths, stats))
+        } else {
+            stderr
+                .seek(SeekFrom::Start(0))
+                .expect("Seeking to Start(0)");
+            Err(Error::Fd(stderr))
+        }
+    }
+
+    /// Put outpaths.nix in to the project root, which is what
+    /// emulates Hydra's behavior.
+    fn place_nix(&self) -> Result<(), std::io::Error> {
+        let mut file = File::create(self.outpath_nix_path())?;
+        file.write_all(include_bytes!("outpaths.nix"))?;
+
+        Ok(())
+    }
+
+    fn remove_nix(&self) -> Result<(), std::io::Error> {
+        fs::remove_file(self.outpath_nix_path())?;
+        Ok(())
+    }
+
+    fn outpath_nix_path(&self) -> PathBuf {
+        self.path.join(".gc-of-borg-outpaths.nix")
+    }
+
+    fn run_nix_env(&self) -> (bool, File, File) {
+        let check_meta = if self.check_meta { "true" } else { "false" };
+
+        let mut cmd = self.nix.safe_command(
+            &nix::Operation::QueryPackagesOutputs,
+            &self.path,
+            &[
+                "-f",
+                ".gc-of-borg-outpaths.nix",
+                "--arg",
+                "checkMeta",
+                check_meta,
+            ],
+            &[],
+        );
+        cmd.env("NIX_SHOW_STATS", "1");
+        self.nix.run_stderr_stdout(cmd)
+    }
+}
+
+pub enum Error {
+    Io(std::io::Error),
+    Fd(File),
+}
+
+impl From<std::io::Error> for Error {
+    fn from(e: std::io::Error) -> Error {
+        Error::Io(e)
+    }
+}