* A garbage collector for installed packages. nix-collect-garbage

  doesn't actually delete any packages, it just prints their
  descriptor hashes.  So we can do

    nix info $(nix-collect-garbage)

  to print out the ids of the packages that would be deleted, and

    nix delpkg $(nix-collect-garbage)

  to actually delete them.

1 files changed, 22 insertions, 0 deletions

diff --git a/scripts/nix-collect-garbage b/scripts/nix-collect-garbage
new file mode 100755
index 000000000000..adaba5b7c65b
--- /dev/null
+++ b/scripts/nix-collect-garbage
@@ -0,0 +1,22 @@
+#! /usr/bin/perl -w
+
+my $prefix = $ENV{"NIX"} || "/nix"; # !!! use prefix
+my $linkdir = "$prefix/var/nix/links";
+
+my %alive;
+
+open HASHES, "nix closure \$(cat $linkdir/*.hash) |";
+while (<HASHES>) {
+	chomp;
+	$alive{$_} = 1;
+}
+close HASHES;
+
+open HASHES, "nix listinst |";
+while (<HASHES>) {
+	chomp;
+	if (!$alive{$_}) {
+	    print "$_\n";
+	}
+}
+close HASHES;