Simple nixos module to enable configuration of freetds and setup the expected environment variables

nixos/modules/module-list.nix

@@ -58,6 +58,7 @@
   ./programs/ssmtp.nix
   ./programs/venus.nix
   ./programs/wvdial.nix
+  ./programs/freetds.nix
   ./programs/zsh/zsh.nix
   ./programs/screen.nix
   ./rename.nix

nixos/modules/programs/freetds.nix

@@ -0,0 +1,61 @@
+# Global configuration for freetds environment.
+
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.environment.freetds;
+
+in
+{
+  ###### interface
+
+  options = {
+
+    environment.freetds = mkOption {
+      type = types.attrsOf types.str;
+      default = {};
+      example = {
+        MYDATABASE = 
+          ''
+          host = 10.0.2.100
+          port = 1433
+          tds version = 7.2
+          '';
+      };
+      description = 
+        ''
+        Configure freetds database entries. Each attribute denotes
+        a section within freetds.conf, and the value (a string) is the config
+        content for that section. When at least one entry is configured
+        the global environment variables FREETDSCONF, FREETDS and SYBASE
+        will be configured to allow the programs that use freetds to find the
+        library and config.
+        '';
+
+    };
+
+  };
+
+  ###### implementation
+
+  config = mkIf (length (attrNames cfg) > 0) {
+
+    environment.variables.FREETDSCONF = "/etc/freetds.conf";
+    environment.variables.FREETDS = "/etc/freetds.conf";
+    environment.variables.SYBASE = "${pkgs.freetds}";
+
+    environment.etc."freetds.conf" = { text = 
+      (concatStrings (mapAttrsToList (name: value:
+        ''
+        [${name}]
+        ${value}
+        ''
+      ) cfg));
+    };
+
+  };
+
+}